WO2023008267A1 - Electrode for electrochemical element, and method of manufacturing electrode for electrochemical element - Google Patents

Electrode for electrochemical element, and method of manufacturing electrode for electrochemical element Download PDF

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Publication number
WO2023008267A1
WO2023008267A1 PCT/JP2022/028114 JP2022028114W WO2023008267A1 WO 2023008267 A1 WO2023008267 A1 WO 2023008267A1 JP 2022028114 W JP2022028114 W JP 2022028114W WO 2023008267 A1 WO2023008267 A1 WO 2023008267A1
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electrode
polymer
thermally expandable
positive electrode
particles
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PCT/JP2022/028114
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French (fr)
Japanese (ja)
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明彦 宮崎
麻貴 召田
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日本ゼオン株式会社
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Priority to CN202280050827.6A priority Critical patent/CN117693835A/en
Priority to JP2023538461A priority patent/JPWO2023008267A1/ja
Priority to KR1020247000785A priority patent/KR20240035448A/en
Publication of WO2023008267A1 publication Critical patent/WO2023008267A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to an electrode for an electrochemical device and a method for manufacturing an electrode for an electrochemical device.
  • Electrochemical devices such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvements in battery members such as electrodes have been studied for the purpose of further improving the performance of electrochemical devices.
  • electrodes used in electrochemical devices such as lithium ions usually include a current collector and an electrode mixture layer formed on the current collector. Then, this electrode mixture layer is formed by, for example, applying a slurry composition containing an electrode active material and a binder composition containing a binder onto a current collector and drying the applied slurry composition. It is formed.
  • An electrochemical element may experience thermal runaway due to the occurrence of an internal short circuit and a chain of various internal chemical reactions.
  • thermal runaway it has been conventional to blend thermally expandable particles encapsulating a substance capable of inhibiting a chemical reaction when the temperature inside the electrochemical element rises into an electrode for an electrochemical element. (See, for example, Patent Documents 1 to 3).
  • the electrodes for electrochemical devices are required to achieve both good heat generation suppressing performance and reduced IV resistance of the secondary battery.
  • the above conventional electrodes for electrochemical devices have room for improvement in terms of achieving both of these properties at a higher level.
  • an object of the present invention is to provide an electrode for an electrochemical device and a method for manufacturing the same, which can improve the heat generation suppression performance of the electrochemical device and reduce the IV resistance.
  • the inventor of the present invention conducted intensive studies with the aim of solving the above problems. Further, the present inventors have found that heat generation suppressing performance of an electrochemical element can be improved by using an electrode for an electrochemical element in which thermally expandable particles having an expansion start temperature within a predetermined temperature range are exposed on the surface of the electrode at a predetermined rate. The inventors have newly found that the IV resistance can be increased and the IV resistance can be reduced, thus completing the present invention.
  • an object of the present invention is to advantageously solve the above problems.
  • the electrode mixture layer includes at least an electrode active material and thermally expandable particles having an expansion start temperature of 400° C. or lower, and the exposed diameter present on the surface of the electrode mixture layer is equal to the electrode active material
  • the exposed particles A are thermally expandable particles having a volume average particle diameter D50 of 0.5 to 5.0 times the volume average particle diameter D50 of the substance
  • the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5. It is characterized by being 5% or more and 20% or less.
  • the expansion starting temperature of the thermally expandable particles, the volume average particle diameter D50 of the electrode active material, and the occupied area ratio of the exposed particles A can be measured by the methods described in the examples of the present specification.
  • the volume average particle diameter D50 of the thermally expandable particles is 0.3 times the volume average particle diameter D50 of the electrode active material. It is preferable that it is more than 5.0 times or less. If an electrode for an electrochemical device is used in which the volume average particle diameter D50 of the thermally expandable particles and the volume average particle diameter D50 of the electrode active material satisfy the above relationship, the heat generation suppression performance of the electrochemical device can be further enhanced, and IV The resistance can be further reduced.
  • the value of the volume average particle diameter D50 can be measured by the method described in the examples of this specification.
  • the number density of the exposed particles A on the surface of the electrode mixture layer is 10 particles/ mm2 or more and 300 particles/ mm 2 or less is preferred.
  • the electrode mixture layer further contains a binder, and the binder is a carboxylic acid It is preferably a polymer having at least one functional group selected from the group consisting of groups, hydroxyl groups, nitrile groups, amino groups, epoxy groups, oxazoline groups, sulfonic acid groups, ester groups and amide groups. If the electrode mixture layer further contains a predetermined binder, the adhesiveness of the electrode mixture layer can be enhanced.
  • An object of the present invention is to advantageously solve the above problems.
  • a method for manufacturing an electrode for an electrochemical device as described above wherein the slurry composition for electrode lower layer is applied onto a current collector and dried to form an electrode lower layer, and an electrode upper layer is formed on the electrode lower layer applying and drying a slurry composition for forming an electrode upper layer, wherein the electrode upper layer slurry composition and the electrode lower layer slurry composition each contain an electrode active material and thermally expandable particles.
  • the thermally expandable particle concentration of the electrode upper layer slurry composition is higher than the thermally expandable particle concentration of the electrode lower layer slurry composition.
  • an electrode for an electrochemical element and a method for manufacturing the same, which can improve the heat generation suppression performance of the electrochemical element and reduce the IV resistance.
  • the electrode for an electrochemical device of the present invention (hereinafter also simply referred to as “electrode”) can be used when manufacturing an electrochemical device.
  • the electrode for an electrochemical device of the present invention can be suitably used as a positive electrode for an electrochemical device, particularly a secondary battery.
  • An electrode for an electrochemical device of the present invention comprises a current collector and an electrode mixture layer.
  • the electrode mixture layer includes at least an electrode active material and thermally expandable particles having an expansion start temperature of 400 ° C. or less, and the exposed diameter present on the electrode mixture layer surface is
  • the exposed particles A are thermally expandable particles having a volume average particle diameter D50 of 0.5 to 5.0 times the volume average particle diameter D50 of the active material
  • the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5. It is characterized by being 5% or more and 20% or less.
  • the occupied area of the exposed particles A whose exposed diameter is within the predetermined range is equal to or greater than the predetermined lower limit, the volume of the thermally expandable particles embedded in the electrode mixture layer is reduced, and the electrode mixture layer The resistance can be reduced, and if the area occupied by the exposed particles A is equal to or less than a predetermined upper limit, the resistance between the electrode and a member adjacent to the electrode (e.g., separator) will not increase in a normal state. As a result, it is speculated that the IV resistance of the electrochemical device can be reduced.
  • ⁇ Current collector> a material having electrical conductivity and electrochemical durability is used.
  • a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used.
  • one type of the above materials may be used alone, or two or more types may be used in combination at an arbitrary ratio.
  • the electrode mixture layer provided in the electrode contains an electrode active material and thermally expandable particles having an expansion initiation temperature of 400° C. or less, and optionally contains a binder, a conductive material, and other additives. may be Further, the electrode mixture layer requires that the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5% or more and 20% or less. As a result, it is possible to improve the heat generation suppression performance of the obtained electrochemical device and to reduce the IV resistance. Furthermore, in the electrode mixture layer, it is preferable that the thermally expandable particles are unevenly distributed on the surface and in the region near the surface. If the thermally expandable particles are unevenly distributed on the surface and near the surface, the heat generation suppression performance of the resulting electrochemical device can be further enhanced and the IV resistance can be further reduced.
  • the exposed particles A refer to thermally expandable particles that exist on the surface of the electrode mixture layer and have an exposed diameter that is 0.5 to 5.0 times the volume average particle diameter D50 of the electrode active material.
  • Thermally expandable particles having an exposed diameter of 0.5 to 5.0 times the volume average particle diameter D50 of the electrode active material are defined as exposed particles, thereby obtaining thermally expandable particles having an appropriate exposed size. It is possible to quantify the existence ratio on the surface of the electrode mixture layer, and thereby to evaluate the existence mode of the thermally expandable particles that effectively contribute to the improvement of the heat generation suppression performance.
  • the number density of the exposed particles A on the surface of the electrode mixture layer is preferably 10/mm 2 or more, more preferably 20/mm 2 or more, and further preferably 40/mm 2 or more.
  • the number is preferably 300/mm 2 or less, more preferably 250/mm 2 or less, even more preferably 150/mm 2 or less, and 110/mm 2 or less. Especially preferred. If the number density of the exposed particles A on the surface of the electrode mixture layer is within the above range, the heat generation suppression performance of the resulting electrochemical device can be further enhanced, and the IV resistance can be further reduced.
  • the distance between the electrode and the member adjacent thereto is effectively increased when the thermally expandable particles expand. It is possible to effectively improve the heat generation suppression performance of the electrochemical device. Further, if the number density of the exposed particles A on the surface of the electrode mixture layer is equal to or less than the above upper limit value, the exposed thermally expandable particles are suppressed from increasing the internal resistance of the electrochemical element in normal times, and the electrochemical element can reduce the IV resistance of
  • the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer should be 0.5% or more, preferably 2.0% or more, and 20% or less. % or less, more preferably 5.0% or less. If the occupied area ratio of the exposed particles A is within the above range, the heat generation suppressing performance of the resulting electrochemical device can be enhanced and the IV resistance can be reduced.
  • the thermally expandable particles must have an expansion start temperature of 400° C. or less.
  • the expansion start temperature is preferably 300° C. or lower, preferably 130° C. or higher, more preferably 150° C. or higher, and even more preferably 170° C. or higher. If the expansion start temperature is equal to or higher than the above lower limit, expansion of the thermally expandable particles in the manufacturing process of the electrochemical device can be suppressed, and an increase in the IV resistance of the resulting electrochemical device can be suppressed. Further, if the expansion start temperature is equal to or lower than the above upper limit, it is possible to quickly suppress the internal temperature from rising when an abnormality occurs in the electrochemical element, thereby effectively suppressing the occurrence of thermal runaway.
  • the volume average particle diameter D50 of the thermally expandable particles is preferably 0.3 times or more, more preferably 0.5 times or more, of the volume average particle diameter D50 of the electrode active material. It is preferably 0 times or less, more preferably 3.0 times or less. If the particle size ratio between the thermally expandable particles and the electrode active material is equal to or greater than the above lower limit, the thermally expandable particles are suppressed from becoming resistance in the electrode mixture layer, and the heat generation suppression performance due to expansion is enhanced. can be done. Further, if the particle size ratio between the thermally expandable particles and the electrode active material is equal to or less than the above upper limit, the IV resistance and heat generation suppression performance of the electrochemical device can be enhanced.
  • the thermally expandable particles preferably have a volume average particle diameter D50 of 0.1 ⁇ m or more, more preferably 1 ⁇ m or more, even more preferably 5 ⁇ m or more, and preferably 100 ⁇ m or less. , is more preferably 80 ⁇ m or less, further preferably 50 ⁇ m or less, and particularly preferably 30 ⁇ m or less.
  • the volume average particle diameter D50 of the thermally expandable particles is at least the above lower limit, it is possible to suppress an increase in the internal resistance of the electrochemical device due to the thermally expandable particles acting as resistance. If the volume average particle diameter D50 of the thermally expandable particles is equal to or less than the above upper limit, the coatability of the obtained electrode slurry composition can be improved, and the heat generation suppression performance of the obtained electrochemical element can be enhanced. can.
  • the amount of the thermally expandable particles contained in the electrode is preferably 40% by mass or more, with the total content (based on mass) of the binder and the thermally expandable particles described later being 100 parts by mass. , more preferably 50 mass % or more, preferably 97 mass parts or less, and more preferably 93 mass parts or less.
  • the content of the thermally expandable particles is at least the above lower limit, the heat generation suppression performance of the resulting electrochemical device can be further enhanced. If the content of the thermally expandable particles is equal to or less than the above upper limit, the IV resistance of the resulting electrochemical device can be further reduced.
  • thermally expandable particles any thermally expandable particles can be used as long as the expansion start temperature is 400°C or less.
  • thermally expandable particles commercially available thermally expandable particles such as Matsumoto Microsphere (registered trademark) and Expancel (manufactured by Nippon Philite Co., Ltd.), and thermally expandable particles satisfying a specific structure described later can be used. .
  • Particles having a core-shell structure comprising a core and a shell covering the outer surface of the core are preferable as the thermally expandable particles.
  • the shell "covers the outer surface of the core” means that the shell is present on at least a portion of the outer surface of the core.
  • the shell may cover a portion of the outer surface of the core, or may cover the entire outer surface of the core.
  • the shell is not particularly limited as long as it contains at least two types of polymers, and includes one or more layers.
  • the layers constituting the shell may contain a plurality of types of polymers in one layer, or may contain two or more layers each of which is composed of one type of polymer.
  • the core of the thermally expandable particles is made of a gas generating substance that gasifies at 400°C or less.
  • gas-generating substance means a compound capable of generating a gas at a given temperature; “gasification” includes substances that undergo a phase change to gas.
  • the core may optionally contain additives such as urea. Gas generating substances that gasify at 400°C or less gasify when the internal temperature of the electrochemical element rises to a predetermined temperature (temperature of 400°C or less), increase the internal resistance, and initiate a chain of electrochemical reactions. By suppressing, the occurrence of thermal runaway can be suppressed.
  • the core may contain a trace amount of metal oxide when prepared according to the method for producing thermally expandable particles described later.
  • the gasification temperature of the gas generating substance must be 400° C. or lower, preferably 300° C. or lower, more preferably 150° C. or lower, preferably 10° C. or higher, and preferably 20° C. or higher. It is more preferable that the temperature is 26° C. or higher.
  • the gasification temperature is equal to or lower than the above upper limit, it is possible to suppress the internal temperature from rising when an abnormality occurs in the electrochemical element, and to effectively suppress the occurrence of thermal runaway. If the gasification temperature is equal to or higher than the above lower limit, the easiness of manufacturing the thermally expandable particles is enhanced.
  • Gas-generating substances include isopentane (gasification temperature: 28°C), isooctane, n-pentane, n-hexane, isohexane, 2,2-dimethylbutane (gasification temperature: 50°C), cyclohexane (gasification temperature: 81 ° C), hydrocarbon compounds such as heptane and petroleum ether, bicarbonate compounds such as sodium bicarbonate (gasification temperature: 150 ° C), guanidine compounds such as guanidine nitrate, nitroguanidine and aminoguanidine nitrate, azobis Azo compounds such as isobutyronitrile (gasification temperature: 108°C) and azodicarbonamide (gasification temperature: 200°C), melamine, ammeline, ammelide, melamine cyanurate (gasification temperature: 280°C), trihydrazine triazine triazine compounds such as (1,3,5-triazine-2,4,6(1H,
  • isopentane, 2,2-dimethylbutane, cyclohexane, azobisisobutyronitrile, and sodium hydrogen carbonate are preferable from the viewpoint of enhancing the heat generation suppression performance of the obtained electrochemical device.
  • the content of the core in the thermally expandable particles is preferably 0.1% by mass or more, more preferably 5% by mass or more, more preferably 90% by mass, based on the total mass of the thermally expandable particles being 100% by mass. or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less.
  • the content of the core in the thermally expandable particles is at least the above lower limit, the heat generation suppression performance of the resulting electrochemical device can be further enhanced.
  • the content of the core in the thermally expandable particles is equal to or less than the above upper limit, it is possible to prevent the thermally expandable particles from becoming brittle and collapsing during normal operation of the electrochemical device.
  • the content ratio of the core in the thermally expandable particles is the content ratio in the state where the core is enclosed in the shell.
  • the shell of the thermally expandable particles consists of at least two types of polymers.
  • the shell needs to have an electrolytic solution swelling degree of 500% by mass or less, preferably 350% by mass or less, and more preferably 300% by mass or less.
  • the electrolyte swelling degree of the shell is equal to or less than the above upper limit, the elution of the core into the electrolyte in the electrochemical element can be satisfactorily suppressed, and the heat generation suppressing performance of the electrochemical element can be enhanced.
  • the lower limit of the degree of swelling of the electrolyte in the shell is not particularly limited. From the viewpoint of reducing the internal resistance of the resulting electrochemical device, it is preferable that the electrolyte swelling degree of the shell is 120% by mass or more.
  • the degree of swelling of the electrolyte solution of at least two kinds of polymers constituting the shell is preferably 500% by mass or less, more preferably 350% by mass or less, and even more preferably 300% by mass or less. If the degree of swelling of the electrolyte solution of at least two types of polymers constituting the shell is equal to or lower than the above upper limits, the elution of the core into the electrolyte solution in the electrochemical element can be satisfactorily suppressed, and the heat generation of the electrochemical element can be suppressed. It can improve performance.
  • the degree of swelling of each of the at least two types of polymers constituting the shell may be 100% by mass, and from the viewpoint of reducing the internal resistance of the resulting electrochemical device, it should be 120% by mass or more. is preferred.
  • the degree of swelling of at least two kinds of polymers forming the shell can be measured by the method described in Examples.
  • the shell preferably has a degree of swelling with respect to N-methyl-2-pyrrolidone (hereinafter sometimes referred to as "NMP swelling degree") of 500% by mass or less, and preferably 350% by mass or less. More preferably, it is 300% by mass or less. If the NMP swelling degree of the shell is equal to or less than the above upper limit, when the electrode of the present invention is formed using a solution containing NMP as a solvent, the elution of the core into NMP in the electrode manufacturing process can be suppressed satisfactorily. , the heat generation suppression performance of the resulting electrochemical device can be enhanced.
  • the lower limit of the NMP swelling degree of the shell is not particularly limited, and is, for example, 100% by mass, and may not swell at all. The degree of NMP swelling of the shell can be measured by the method described in Examples below.
  • the degree of NMP swelling of at least two kinds of polymers constituting the shell is preferably 500% by mass or less, more preferably 350% by mass or less, and even more preferably 300% by mass or less. If the degree of NMP swelling of at least two kinds of polymers constituting the shell is equal to or less than the above upper limit, the binder composition of the present invention is used when preparing a positive electrode slurry composition for a secondary battery using NMP as a solvent. In this case, the elution of the core into the NMP in the slurry composition can be satisfactorily suppressed, and the heat generation suppression performance of the resulting electrochemical device can be enhanced.
  • the NMP swelling degree of each of the at least two types of polymers constituting the shell is not particularly limited, and may be 100% by mass. The degree of NMP swelling of at least two types of polymers constituting the shell can be measured by the method described in Examples.
  • At least two types of polymers constituting the shell must contain at least two types of polymers having a glass transition temperature difference of 10°C or more and 230°C or less. More specifically, the shell may contain only two types of polymers with different glass transition temperatures in the range of 10° C. or higher and 230° C. or lower, or in addition to these two types of polymers, other polymers ( For example, a polymer having a glass transition temperature difference of less than 10° C. or more than 230° C. with at least one of the above two types of polymers may be included. When the shell contains three or more types of polymers, the two types of polymers having the higher content (by mass) should satisfy the above relative relationship regarding the glass transition temperature.
  • the temperature difference between the two types of glass transition temperatures is preferably 60°C or higher, more preferably 90°C or higher, preferably 150°C or lower, and more preferably 120°C or lower. If the temperature difference is equal to or greater than the above lower limit, it is possible to prevent the shell from leaking out of the thermally expandable particles even when pressurized in the manufacturing process of the electrochemical device. Therefore, it is possible to obtain a high-density electrode by pressing the electrode mixture layer at a high pressure, and further improve the heat generation suppressing performance of the electrochemical device provided with such a high-density electrode. If the temperature difference is equal to or less than the above upper limit, the high-temperature storage characteristics of the electrochemical device can be enhanced.
  • the highest temperature among the glass transition temperatures of the polymer contained in the shell is higher than the gasification temperature of the gas generating substance forming the core. If the highest temperature among the glass transition temperatures of the polymer contained in the shell is higher than the gasification temperature of the gas-generating substance, the leakage of the gas-generating substance when pressurized during the production of the electrochemical device can be suppressed satisfactorily. It is possible to further improve the heat generation suppression performance of the resulting electrochemical device.
  • the difference between the highest glass transition temperature of the polymer contained in the shell and the gasification temperature of the gas generating substance is preferably 10°C or more, more preferably 45°C or more, and more preferably 60°C. It is more preferable that it is above. Although the upper limit of the difference is not particularly limited, it can be 200° C., for example.
  • one of the at least two types of polymers forming the shell has a glass transition temperature of 60°C or higher and the other has a glass transition temperature of less than 60°C.
  • the shell contains three or more types of polymers, it is preferable that the two types of polymers having the highest content (based on mass) be either one of such polymers.
  • the glass transition temperature of the polymer having a glass transition temperature of 60° C. or higher (hereinafter sometimes referred to as “polymer 1”) is preferably 80° C. or higher, preferably 180° C. or lower, and 150° C. It is more preferably 130° C. or less, more preferably 130° C. or less. If the glass transition temperature of polymer 1 is at least the above lower limit, the shell can be well protected even when pressure is applied in the manufacturing process of the electrochemical device, and gas is generated outside the thermally expandable particles. Outflow of substances can be well suppressed.
  • the glass transition temperature is equal to or lower than the above upper limit, the polymerization stability during polymerization of Polymer 1 can be enhanced, and the production efficiency of the electrode can be enhanced.
  • the solubility parameter (hereinafter sometimes referred to as SP value) of polymer 1 is preferably 23.0 MPa 1/2 or more, more preferably 24.0 MPa 1/2 or more. It is preferably 30.0 MPa 1/2 or less, more preferably 29.5 MPa 1/2 or less. More specifically, the SP value of Polymer 1 is preferably higher than the SP values of NMP and the electrolyte that can be used in manufacturing the electrochemical device. If the SP value of the polymer 1 is different from the SP values of the NMP and the electrolyte, the polymer 1 is less likely to swell and dissolve in the NMP and the electrolyte. The electrochemical element it contains operates normally and becomes effective when it generates heat.
  • the solubility parameter is the Hansen solubility parameter whose definition and calculation method are described in the following literature. Charles M. Hansen, "Hansen Solubility Parameters: A Users Handbook,” CRC Press, 2007.
  • Hansen Solubility Parameters in Practice HSPiP
  • the composition of polymer 1 is not particularly limited.
  • the polymer 1 for example, it is preferable to use a polymer containing a monomer unit having a nitrile group.
  • a polymer "containing a monomer unit” means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer”.
  • the content ratio of various monomer units in the polymer can be measured using a nuclear magnetic resonance (NMR) method such as 1 H-NMR.
  • NMR nuclear magnetic resonance
  • Examples of monomer units having a nitrile group include ⁇ , ⁇ -ethylenically unsaturated nitrile monomer units.
  • the monomer forming the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer unit is not limited as long as it is an ⁇ , ⁇ -ethylenically unsaturated compound having a nitrile group, and acrylonitrile; ⁇ -chloroacrylonitrile; - ⁇ -halogenoacrylonitrile such as bromoacrylonitrile; ⁇ -alkylacrylonitrile such as methacrylonitrile; and the like, with acrylonitrile and methacrylonitrile being preferred.
  • the ⁇ , ⁇ -ethylenically unsaturated nitrile monomer a plurality of these may be used in combination.
  • the content of the monomer unit having a nitrile group in Polymer 1 is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 85% by mass or more, based on 100% by mass of all repeating units contained in Polymer 1. More preferably, it is 98% by mass or less, and more preferably 97% by mass or less. If the content of the monomer unit having a nitrile group is at least the above lower limit, it is possible to suppress the degree of swelling of polymer 1 from increasing in the electrolyte solution. Moreover, if the content of the monomer unit having a nitrile group is equal to or less than the above upper limit, the polymerization stability of the polymer 1 can be enhanced.
  • the polymer containing a nitrile group-containing monomer unit may be a copolymer of a monomer forming a nitrile group-containing monomer unit and a copolymerizable monomer.
  • the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, and methyl vinylbenzoate.
  • vinylnaphthalene chloromethylstyrene, hydroxymethylstyrene, ⁇ -methylstyrene and other aromatic vinyl monomers; acrylamide, N-methylolacrylamide, acrylamido-2-methylpropanesulfonic acid and other amide monomers; ethylene, Olefins such as propylene; diene-based monomers such as butadiene and isoprene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; N-vinylpyrrolidone, vinylpyridine, vinylimide
  • butyl methacrylate such as n-butyl methacrylate and t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, heptyl methacrylate, octyl methacrylate such as 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, methacrylic acid alkyl ester such as stearyl methacrylate, and the like.
  • a plurality of these types may be used in combination as the copolymerizable monomer.
  • the polymer containing a monomer unit having a nitrile group as the polymer 1 may have a crosslinkable monomer unit.
  • crosslinkable monomers capable of forming crosslinkable monomer units include polyfunctional monomers having two or more polymerizable reactive groups.
  • polyfunctional monomers include divinyl compounds such as allyl methacrylate and divinylbenzene; di(meth)acrylic esters such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butylene glycol diacrylate.
  • (meth)acryl means acryl or methacryl.
  • the content of the crosslinkable monomer units in the polymer 1 is not particularly limited, for example, the total repeating units contained in the polymer 1 is 100% by mass, preferably 0.05% by mass or more, It is more preferably 0.5% by mass or more, more preferably 0.5% by mass or more, preferably 3.0% by mass or less, and more preferably 2.0% by mass or less. If the content of the crosslinkable monomer units in Polymer 1 is at least the above lower limit, it is possible to effectively suppress the outflow of the core from the thermally expandable particle by increasing the strength of the shell.
  • the thermal expansion is prevented from being inhibited due to an excessive increase in the crosslink density, and the thermally expandable particles expand at a desired temperature. becomes possible.
  • the glass transition temperature of the polymer having a glass transition temperature of less than 60°C (hereinafter sometimes referred to as "polymer 2") must be less than 60°C, preferably 40°C or less, and 25°C. It is more preferably -50°C or higher, more preferably -40°C or higher, and even more preferably -30°C or higher. If the glass transition temperature of the polymer 2 is equal to or lower than the above upper limit, the adhesion of the binder composition can be further enhanced, and the shell is thermally expandable even when pressurized in the manufacturing process of the electrochemical device. Leakage to the outside of the particles can be suppressed.
  • the heat generation suppression performance of the obtained electrochemical device can be further enhanced. Therefore, it is possible to obtain a high-density electrode by pressing the electrode mixture layer at a high pressure, and further improve the heat generation suppressing performance of the electrochemical device provided with such a high-density electrode.
  • the glass transition temperature of the polymer 2 is at least the above lower limit, the polymerization stability of the polymer 2 can be enhanced, and the productivity of the electrode can be enhanced.
  • the SP value of polymer 2 is preferably 16.0 MPa 1/2 or more, more preferably 18.0 MPa 1/2 or more, and preferably 24.0 MPa 1/2 or less. 0 MPa 1/2 or less is more preferable, and 21.0 MPa 1/2 or less is even more preferable. More specifically, the SP value of Polymer 2 is preferably lower than the SP values of NMP and the electrolyte that can be used in manufacturing the electrochemical device. If the SP value of the polymer 2 is different from the SP values of the NMP and the electrolyte, the polymer 2 is less likely to swell and dissolve in the NMP and the electrolyte, and as a result, the thermally expandable particles are formed. The electrochemical element it contains operates normally and becomes effective when it generates heat.
  • the composition of polymer 2 is not particularly limited.
  • Polymer 2 includes, for example, polymers containing aromatic vinyl monomer units.
  • aromatic vinyl monomer units include units formed using aromatic vinyl monomers listed as monomers that can be used in preparing polymer 1 . Among them, styrene is preferred.
  • the content of aromatic vinyl monomer units in polymer 2 is preferably 40% by mass or more, more preferably 50% by mass or more, based on 100% by mass of all repeating units contained in polymer 2. , is preferably 90% by mass or less, more preferably 80% by mass or less. When the content ratio of the aromatic vinyl monomer units in the polymer 2 is at least the above lower limit, it is possible to suppress an excessive increase in the degree of swelling of the polymer 2 in the electrolytic solution.
  • Polymer 2 may contain a (meth)acrylic acid ester monomer unit instead of or in addition to the aromatic vinyl monomer unit.
  • a (meth)acrylic acid ester monomer unit As the (meth)acrylic acid ester monomer that can be used to form such a (meth)acrylic acid ester monomer unit, various monomers listed as those that can be used in preparing the polymer 1 are mentioned. Among them, 2-ethylhexyl acrylate is preferred.
  • Polymer 2 may contain other monomeric units in addition to or in place of the aromatic vinyl monomeric units and (meth)acrylic acid ester monomeric units described above.
  • Examples of the monomer units include units formed using various monomers listed as monomers that can be used in preparing polymer 1 .
  • the polymer 2 contains a crosslinkable monomer unit.
  • Crosslinkable monomers that can be used to form the crosslinkable monomeric units in Polymer 2 include the various compounds listed above in connection with Polymer 1 .
  • allyl methacrylate is preferable as the monomer used to form the crosslinkable monomer units in the polymer 2.
  • the content ratio of the crosslinkable monomer units in the polymer 2 is not particularly limited, and is preferably 0.05% by mass or more based on 100% by mass of the total repeating units contained in the polymer 2. It is more preferably 0.1% by mass or more, further preferably 0.2% by mass or more, preferably 3.0% by mass or less, and more preferably 2.0% by mass or less. . If the content of the crosslinkable monomer units in the polymer 2 is at least the above lower limit, it is possible to effectively prevent the core from flowing out of the thermally expandable particles by increasing the strength of the shell. If the content of the crosslinkable monomer units in the polymer 2 is equal to or less than the above upper limit, the easiness of shell production can be enhanced.
  • the polymer 2 may contain a monomer containing a carbon-carbon double bond and an epoxy group (epoxy group-containing unsaturated monomer) separately from such a crosslinkable monomer.
  • crosslinkable monomer does not include monomers corresponding to epoxy group-containing unsaturated monomers.
  • epoxy group-containing unsaturated monomers include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; butadiene monoepoxide, chloroprene monoepoxide, monoepoxides of dienes or polyenes such as 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene; 3,4-epoxy-1 - alkenyl epoxides such as butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-he
  • the content of the epoxy group-containing unsaturated monomer in the polymer 2 is preferably 0.5% by mass or more, preferably 1.0% by mass or more, based on 100% by mass of the total repeating units contained in the polymer 2. more preferably 10.0% by mass or less, and more preferably 8.0% by mass or less. If the content of the epoxy group-containing unsaturated monomer in the polymer 2 is within such a range, the heat generation suppression performance of the electrochemical device can be further enhanced.
  • the composition of the shell is not particularly limited.
  • the shell can include the various monomeric units exemplified above as monomeric units that can be included in Polymer 1 and Polymer 2.
  • the content of aromatic vinyl monomer units in the shell is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 50% by mass or less, and 40% by mass. The following are more preferable.
  • the content of the nitrile group-containing monomer unit in the shell is preferably 20% by mass or more, more preferably 25% by mass or more, preferably 50% by mass or less, and 40% by mass. The following are more preferable.
  • the content of (meth)acrylate monomer units in the shell is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 50% by mass or less. % or less is more preferable. If the content of the aromatic vinyl monomer unit, the content of the nitrile group-containing monomer unit, and the content of the (meth)acrylic acid ester monomer unit in the shell are each independently within the above ranges. , the glass transition temperature of the shell, the degree of swelling of the electrolyte, and the degree of swelling of NMP can be appropriately controlled.
  • the content of the crosslinkable monomer unit in the shell is preferably 0.1% by mass or more, and 0.2% by mass or more, from the viewpoint of shell strength, electrolyte swelling degree, and NMP swelling degree. more preferably 3.0% by mass or less, more preferably 2.0% by mass or less.
  • the content of the epoxy group-containing unsaturated monomer unit in the shell is preferably 0.5% by mass or more, and 1.0% by mass or more, from the viewpoint of the degree of swelling of the electrolyte and the degree of swelling of NMP. is more preferably 10.0% by mass or less, and more preferably 8.0% by mass or less.
  • the structure of the thermally expandable particles is not particularly limited as long as it is a structure in which a core made of a gas-generating substance is covered with a shell containing polymer 1 and polymer 2.
  • the shell comprises a layer A made of the polymer 1 and a layer B made of the polymer 2.
  • the layer A made of the polymer 1 exists inside (the core side) the layer B made of the polymer 2.
  • the thermally expandable particles may have a conductive carbon material, which will be described later in the ⁇ Conductive material> section, on the surface thereof. In this case, the IV resistance of the electrochemical device can be further reduced.
  • the total area ratio ⁇ (%) of polymer 1 and the total area ratio ⁇ (%) of polymer 2 in the shell satisfy the relationship ⁇ . If the total area ratio of the polymers 1 and 2 contained in the shell satisfies the relationship ⁇ , the heat generation suppression performance of the resulting electrochemical device can be further enhanced.
  • the difference between the total area ratio ⁇ (%) of polymer 1 and the total area ratio ⁇ (%) of polymer 2 is preferably 1% or more, and 20% or more. is more preferable.
  • the thickness a of the layer A containing the polymer 1 and the thickness b of the layer B containing the polymer 2 satisfy the relation a ⁇ b. is preferably satisfied. If the thickness of each layer constituting the shell satisfies the relation of a ⁇ b, the heat generation suppression performance of the resulting electrochemical device can be further enhanced. If the thickness of the layer A containing the polymer 1 whose glass transition temperature is higher than that of the polymer 2 is thicker than the thickness of the layer B, the thermally expandable particles are less likely to expand when the shell is gasified. from the viewpoint of further increasing the thickness b of the layer B is preferably 1.2 times or more the thickness a of the layer A, more preferably 1.4 times or more.
  • Thermally expandable particles can be prepared, for example, by polymerizing a monomer composition containing the above monomers in a colloidal aqueous solution in which a gas generating substance is dispersed.
  • the proportion of each monomer in the monomer composition is generally the same as the proportion of each monomer unit in the thermally expandable particles.
  • the polymerization mode is not particularly limited, and any method such as a suspension polymerization method, an emulsion polymerization aggregation method, and a pulverization method can be used. Among them, the suspension polymerization method and the emulsion polymerization aggregation method are preferable, and the suspension polymerization method is more preferable.
  • the polymerization reaction any reaction such as radical polymerization and living radical polymerization can be used.
  • the monomer composition used for preparing the thermally expandable particles includes a chain transfer agent, a polymerization modifier, a polymerization reaction retarder, a reactive fluidizing agent, a filler, a flame retardant, an antioxidant, a coloring agent, and a coloring agent.
  • a chain transfer agent e.g., a chain transfer agent
  • a polymerization modifier e.g., a polymerization modifier
  • a polymerization reaction retarder e.g., a reactive fluidizing agent
  • a filler e.g., a filler, a flame retardant, an antioxidant, a coloring agent, and a coloring agent.
  • a coloring agent e.g., a coloring agent that can be included in any amount.
  • a metal hydroxide as a dispersion stabilizer is dispersed in water to prepare a colloidal dispersion containing the metal hydroxide. Then, a core-forming gas-generating substance and a shell-forming monomer composition 1 and/or monomer composition 2 are added to the colloidal dispersion. Further, a polymerization initiator is added to obtain a mixed liquid, and droplets are formed.
  • the method of forming the droplets is not particularly limited, and for example, the droplets can be formed by shearing and stirring the mixed liquid using a disperser such as an emulsifying disperser.
  • polymerization initiators examples include oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate and azobisisobutyronitrile.
  • oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate and azobisisobutyronitrile.
  • dispersion stabilizers for example, metal hydroxides such as magnesium hydroxide, sodium dodecylbenzenesulfonate, and the like can be used.
  • the water containing the formed droplets is heated to initiate polymerization. Then, when only one of the monomer composition 1 and the monomer composition 2 is blended in the droplets in the above step (2), at the stage when the polymerization conversion rate is sufficiently increased , 1/2 of the monomer composition not added in step (2) is added to continue the polymerization. As a result, thermally expandable particles having a predetermined structure are formed in water.
  • the reaction temperature for the polymerization is preferably 50°C or higher and 95°C or lower.
  • the duration of each polymerization reaction is preferably 1 hour or more and 10 hours or less, preferably 8 hours or less.
  • the amount ratio between the gas-generating substance and the monomer composition and 2 can be appropriately set so as to satisfy the preferred range of the "core content ratio in the thermally expandable particles" described above.
  • the amount ratio between the monomer compositions 1 and 2 is such that it satisfies the preferred ranges of the above-mentioned "area ratio of polymer 1 and polymer 2 in the shell” and "thickness ratio of layer A and layer B in the shell". can be set as appropriate.
  • the electrode preferably further contains a binder.
  • the binder is not particularly limited as long as it is a polymer capable of exhibiting binding ability in the electrode mixture layer, and any polymer can be used.
  • Preferred examples of the polymer used as the binder include polymers mainly containing aliphatic conjugated diene monomer units, hydrides thereof (diene-based polymers), and (meth)acrylic acid ester monomer units.
  • acrylic polymers, nitrile polymers, and fluoropolymers are more preferred.
  • the binder may be used singly or in combination of two or more at any ratio. Further, in the present specification, the phrase "mainly containing" a certain monomer unit in a polymer means "when the amount of all repeating units contained in the polymer is 100% by mass, the content of the monomer unit proportion exceeds 50% by mass”.
  • the binder does not contain the gas-generating substance described above and is selected from the group consisting of a carboxylic acid group, a hydroxyl group, a nitrile group, an amino group, an epoxy group, an oxazoline group, a sulfonic acid group, an ester group and an amide group. It is preferable that the polymer has at least one functional group (these functional groups may be collectively referred to as “specific functional group” hereinafter).
  • the polymer as the binder may have one type of the specific functional groups described above, or may have two or more types. By using a polymer having these specific functional groups as a binder, the IV resistance of the electrochemical device can be further reduced.
  • the polymer as the binder preferably has at least one selected from the group consisting of carboxylic acid groups, hydroxyl groups and nitrile groups. and a nitrile group, and more preferably both a carboxylic acid group and a nitrile group.
  • the method of introducing the above-described specific functional group into the polymer is not particularly limited.
  • a polymer may be prepared using a monomer having a specific functional group (specific functional group-containing monomer) to obtain a polymer containing a specific functional group-containing monomer unit, or any polymer may be modified to obtain a polymer into which the above-described specific functional group has been introduced, but the former is preferred.
  • the polymer as the binder includes carboxylic acid group-containing monomer units, hydroxyl group-containing monomer units, nitrile group-containing monomer units, amino group-containing monomer units, and epoxy group-containing monomer units.
  • an oxazoline group-containing monomer unit an oxazoline group-containing monomer unit, a sulfonic acid group-containing monomer unit, an ester group-containing monomer unit and an amide group-containing monomer unit.
  • units more preferably at least one of hydroxyl group-containing monomer units and nitrile group-containing monomer units, including at least one of carboxylic acid group-containing monomer units and nitrile group-containing monomer units is more preferred, and it is particularly preferred to contain both carboxylic acid group-containing monomer units and nitrile group-containing monomer units.
  • Carboxylic acid group-containing monomers capable of forming carboxylic acid group-containing monomer units include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, their derivatives, and the like.
  • Monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid and the like.
  • Monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, ⁇ -chloro- ⁇ -E-methoxyacrylic acid and the like.
  • Dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, and the like.
  • Dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoro maleate.
  • Examples include maleic acid monoesters such as alkyls.
  • Acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
  • an acid anhydride that produces a carboxylic acid group by hydrolysis can also be used. Among them, acrylic acid and methacrylic acid are preferable as the carboxylic acid group-containing monomer.
  • the carboxylic acid group-containing monomers may be used singly or in combination of two or more at any ratio.
  • hydroxyl group-containing monomers capable of forming hydroxyl group-containing monomer units include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-buten-1-ol, and 5-hexene-1-ol; 2-hydroxyethyl acid, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, itacon alkanol esters of ethylenically unsaturated carboxylic acids such as di- 2 -hydroxypropyl acid; , q is an integer of 2 to 4, R a represents a hydrogen atom or a methyl group) esters of polyalkylene glycol and (meth)acrylic acid; 2-hydroxyethyl-2′-(meth ) Acryloyloxyphthalate, 2-hydroxyethyl-2′
  • Vinyl ethers (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl Alkylene glycol mono(meth)allyl ethers such as -3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, (meth)allyl-6-hydroxyhexyl ether; diethylene glycol mono(meth)allyl ether, dipropylene glycol Polyoxyalkylene glycol mono(meth)allyl ethers such as mono(meth)allyl ether; glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, (meth)allyl-2- Mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycol
  • nitrile group-containing monomer unit examples include ⁇ , ⁇ -ethylenically unsaturated nitrile monomers. Specifically, those exemplified as ⁇ , ⁇ -ethylenically unsaturated compounds having a nitrile group that can be used to form polymer 1 can be used. In addition, these compounds may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
  • amino group-containing monomer unit examples include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, aminoethyl vinyl ether, and dimethylaminoethyl vinyl ether.
  • an amino group-containing monomer may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
  • epoxy group-containing monomer unit examples include various carbon-carbon double bonds listed as compounds that can be used to form crosslinkable monomer units in Polymer 2. and epoxy group-containing monomers. In addition, these monomers may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
  • oxazoline group-containing monomer unit examples include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2- oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc. are mentioned.
  • the oxazoline group-containing monomers may be used singly or in combination of two or more at any ratio.
  • sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, (meth)acrylic acid-2- ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid and the like.
  • the sulfonic acid group-containing monomers may be used singly or in combination of two or more at any ratio.
  • ester group-containing monomer unit As an ester group-containing monomer capable of forming an ester group-containing monomer unit, for example, a (meth)acrylic acid ester monomer can be used.
  • (meth)acrylate monomers include the various (meth)acrylate monomers listed as usable to form the (meth)acrylate monomer units in Polymer 2. is mentioned. In addition, these monomers may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios. Moreover, in the present invention, when a certain monomer has a specific functional group other than an ester group, the monomer is not included in the ester group-containing monomer.
  • amide group-containing monomer unit examples include acrylamide, methacrylamide, and vinylpyrrolidone.
  • the amide group-containing monomers may be used singly or in combination of two or more at any ratio.
  • the content ratio of the specific functional group-containing monomer unit in the polymer is the IV resistance of the electrochemical element. From the viewpoint of further reduction, the content is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more.
  • the upper limit of the content of the specific functional group-containing monomer unit in the polymer used as the binder is not particularly limited, and may be 100% by mass or less, for example, 99% by mass or less.
  • the polymer as the binder may contain repeating units (other repeating units) other than the specific functional group-containing monomer units described above.
  • Such other repeating units are not particularly limited, but when the polymer is a diene-based polymer, aliphatic conjugated diene-based monomer units may be mentioned.
  • Aliphatic conjugated diene-based monomers capable of forming aliphatic conjugated diene-based monomer units include, for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3- Pentadiene may be mentioned. These may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
  • the "aliphatic conjugated diene-based monomer unit” is obtained by further hydrogenating the monomer unit contained in the polymer obtained using the aliphatic conjugated diene-based monomer. Structural units (hydride units) are also included. Among the aliphatic conjugated diene-based monomers mentioned above, 1,3-butadiene and isoprene are preferred.
  • the aliphatic conjugated diene-based monomer unit is preferably a 1,3-butadiene unit, an isoprene unit, a 1,3-butadiene hydride unit, an isoprene hydride unit, a 1,3-butadiene hydride unit, More preferred are isoprene hydride units.
  • the unit content is preferably more than 50% by mass, more preferably 60% by mass or more, and preferably 90% by mass or less. It is preferably 70% by mass or less, more preferably 70% by mass or less.
  • a method for preparing the binder is not particularly limited.
  • a binder that is a polymer is produced, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent and optionally hydrogenating or modifying the monomer composition.
  • the content ratio of each monomer in the monomer composition can be determined according to the content ratio of desired monomer units in the polymer.
  • the polymerization mode is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used.
  • any reaction such as ionic polymerization, radical polymerization, living radical polymerization, various types of condensation polymerization, and addition polymerization can be used.
  • known emulsifiers and polymerization initiators can be used as necessary.
  • Hydrogenation and modification can also be carried out by known methods.
  • the ratio of the total content of the thermally expandable particles and the binder in the electrode mixture layer is preferably 1% by mass or more based on the total weight of the electrode mixture layer being 100% by mass. It is more preferably 5% by mass or more, preferably 10% by mass or less, and more preferably 5% by mass or less.
  • the electrode mixture layer may contain other components known as additives that can be blended in the electrode mixture layer of the electrochemical device.
  • Other components include, for example, wetting agents, leveling agents, electrolytic solution decomposition inhibitors, and the like.
  • An electrode active material is a material that transfers electrons in an electrode of an electrochemical device.
  • the electrochemical device is a lithium ion secondary battery
  • the present invention is not limited to the following example.
  • an electrode active material for a lithium ion secondary battery a material capable of intercalating and deintercalating lithium is usually used.
  • the electrode active material is preferably 90% by mass or more, more preferably 92% by mass or more, with the total mass of the electrode mixture layer being 100% by mass. , and preferably 99.5% by mass or less, more preferably 99% by mass or less.
  • the positive electrode active material for lithium ion secondary batteries is not particularly limited, and lithium-containing cobalt oxide (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), and lithium-containing nickel oxide.
  • LiNiO 2 Co—Ni—Mn lithium-containing composite oxide (Li(CoMnNi)O 2 ), Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, olivine type lithium iron phosphate (LiFePO 4 ), olivine type lithium manganese phosphate (LiMnPO 4 ), Li 2 MnO 3 —LiNiO 2 solid solution, Li 1+x Mn 2-x O 4 (0 ⁇ X ⁇ 2) known positive electrode active materials such as lithium-rich spinel compounds, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O 2 , LiNi 0.5 Mn 1.5 O 4 .
  • the amount and particle size of the positive electrode active material are not particularly limited, and may be the same as those of conventionally used positive electrode active materials.
  • Negative electrode active material examples of negative electrode active materials for lithium ion secondary batteries include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials in which these are combined.
  • the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton and capable of inserting lithium (also referred to as “doping”).
  • Examples of carbon-based negative electrode active materials include carbonaceous materials and graphite quality materials.
  • Examples of the carbonaceous material include graphitizable carbon and non-graphitizable carbon having a structure close to an amorphous structure represented by glassy carbon.
  • graphitizable carbon includes, for example, carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolytic vapor growth carbon fibers.
  • Examples of non-graphitic carbon include phenolic resin sintered material, polyacrylonitrile-based carbon fiber, pseudoisotropic carbon, and furfuryl alcohol resin sintered material (PFA).
  • graphite materials include natural graphite and artificial graphite.
  • artificial graphite for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB obtained by heat-treating MCMB at 2000 ° C. or higher, mesophase pitch-based carbon fiber at 2000 ° C.
  • Graphitized mesophase pitch-based carbon fibers heat-treated as described above may be used.
  • the metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of intercalating lithium in its structure, and the theoretical electric capacity per unit mass when lithium is intercalated is 500 mAh / g or more.
  • the metal-based active material for example, lithium metal, elemental metals capable of forming a lithium alloy (eg, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn , Sr, Zn, Ti, etc.) and alloys thereof, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like.
  • active materials containing silicon are preferable as the metal-based negative electrode active materials. This is because the use of the silicon-based negative electrode active material can increase the capacity of the lithium ion secondary battery.
  • Silicon-based negative electrode active materials include, for example, silicon (Si), alloys containing silicon, SiO, SiO x , and composites of Si-containing materials and conductive carbon obtained by coating or combining Si-containing materials with conductive carbon. etc.
  • the amount and particle size of the negative electrode active material are not particularly limited, and can be the same as those of conventionally used negative electrode active materials.
  • the conductive material is for ensuring electrical contact between the electrode active materials.
  • carbon black for example, acetylene black, Ketjenblack (registered trademark), furnace black, etc.
  • single-walled or multi-walled carbon nanotubes multi-walled carbon nanotubes include cup-stacked types
  • carbon Conductive carbon materials such as nanohorns, vapor-grown carbon fibers, milled carbon fibers obtained by pulverizing polymer fibers after firing, monolayer or multilayer graphene, and carbon nonwoven fabric sheets obtained by firing nonwoven fabrics made of polymer fibers; Metal fibers or foils can be used. These can be used individually by 1 type or in combination of 2 or more types.
  • a conductive carbon material is preferable as the conductive material in terms of excellent chemical stability.
  • the content of the conductive material in the electrode mixture layer is preferably 0.1% by mass or more and 3.0% by mass or less, with the total mass of the electrode mixture layer being 100% by mass. It is preferably 2.5% by mass or less, and more preferably 2.5% by mass or less. If the content of the conductive material is equal to or higher than the above lower limit, it is possible to sufficiently ensure electrode contact between the electrode active materials. On the other hand, if the content of the conductive material is equal to or less than the above upper limit, the density of the electrode mixture layer can be maintained satisfactorily, and the capacity of the electrochemical device can be sufficiently increased.
  • the electrode for an electrochemical device of the present invention can be produced by, for example, a step of preparing a slurry composition containing an electrode active material, thermally expandable particles, an optional binder, a conductive material, and other components (slurry composition preparation step), a step of applying the slurry composition on the current collector (application step), and a step of drying the slurry composition applied on the current collector to form an electrode mixture layer on the current collector. (Drying step).
  • ⁇ Slurry composition preparation step> It can be prepared by dissolving or dispersing each of the above components in a solvent such as an organic solvent.
  • a solvent such as an organic solvent.
  • the components may be added all at once, or may be added stepwise and mixed. Specifically, by mixing each of the above components and a solvent using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, film mix, etc. , a slurry composition can be prepared.
  • the method for applying the slurry composition onto the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the electrode mixture layer obtained by drying.
  • the method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used. A drying method by irradiation can be mentioned.
  • a drying method by irradiation can be mentioned.
  • By drying the slurry composition on the current collector in this way it is possible to form an electrode mixture layer on the current collector and obtain a secondary battery electrode comprising the current collector and the electrode mixture layer. can.
  • the drying step it is preferable to carry out drying at a low temperature followed by drying at a higher temperature with a stepwise increase in temperature. Specifically, for example, it is preferable to dry under low temperature conditions of 110° C. or less, preferably 95° C. or less, more preferably 90° C. or less, and then dry under temperature conditions of 140° C. or less, preferably 120° C. or less.
  • the electrode upper layer slurry composition and the electrode lower layer slurry composition each contain an electrode active material and thermally expandable particles, and the concentration of the thermally expandable particles in the electrode upper layer slurry composition is equal to that of the electrode. It is higher than the thermally expandable particle concentration of the lower layer slurry composition.
  • the frequency of the thermally expandable particles in the surface and the region near the surface of the electrode mixture layer is higher than that in the lower part of the electrode mixture layer, and the distribution mode can be effectively adjusted. can be created. If the thermally expandable particles are unevenly distributed on the surface and in the vicinity thereof in the electrode mixture layer, the heat generation suppressing performance of the electrochemical element can be enhanced and the IV resistance can be further reduced.
  • the electrode mixture layer may be pressurized using a mold press or a roll press.
  • the pressure treatment can improve the adhesion between the electrode mixture layer and the current collector.
  • An electrochemical device can be provided using the electrode for an electrochemical device of the present invention described above.
  • An electrochemical device comprising the electrode for an electrochemical device of the present invention is excellent in heat generation suppression performance.
  • Examples of the electrochemical device include a secondary battery using the electrode for an electrochemical device of the present invention as a positive electrode.
  • the secondary battery is a lithium ion secondary battery
  • the present invention is not limited to the following example.
  • the electrodes other than the electrochemical device electrodes described above that can be used in the electrochemical device are not particularly limited, and known electrodes that are used in the production of electrochemical devices can be used.
  • the electrodes other than the electrodes for the electrochemical device described above an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method can be used.
  • the separator is not particularly limited, and for example, those described in JP-A-2012-204303 can be used. Among these, polyolefin-based ( A microporous membrane made of resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.
  • an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used.
  • Lithium salts for example, are used as supporting electrolytes for lithium ion secondary batteries.
  • lithium salts include LiPF6 , LiAsF6 , LiBF4 , LiSbF6 , LiAlCl4 , LiClO4, CF3SO3Li , C4F9SO3Li , CF3COOLi , ( CF3CO ) 2NLi . , (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 )NLi and the like.
  • LiPF 6 , LiClO 4 and CF 3 SO 3 Li are preferable, and LiPF 6 is particularly preferable, because they are easily dissolved in a solvent and exhibit a high degree of dissociation.
  • one electrolyte may be used alone, or two or more electrolytes may be used in combination at an arbitrary ratio.
  • lithium ion conductivity tends to increase as a supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted depending on the type of supporting electrolyte.
  • the organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte.
  • Examples include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); esters such as ethyl propionate, propyl propionate, ⁇ -butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane , sulfur-containing compounds such as dimethylsulfoxide; and the like are preferably used. A mixture of these solvents may also be used.
  • the concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate, for example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. is more preferred. Further, known additives such as vinylene carbonate, fluoroethylene carbonate, ethyl methyl sulfone, etc. may be added to the electrolytic solution.
  • a secondary battery as an electrochemical element includes, for example, a positive electrode and a negative electrode, which are superimposed with a separator interposed therebetween, and, if necessary, are rolled or folded according to the shape of the battery, placed in a battery container, and placed in a battery container. It can be produced by injecting an electrolytic solution into the container and sealing it.
  • a fuse an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary.
  • the shape of the secondary battery may be, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, rectangular, or flat.
  • thermogravimetric analysis using a thermogravimetric analyzer (manufactured by Rigaku, "TG8110" is performed under a nitrogen atmosphere at a temperature increase rate of 10 ° C./min from 25 ° C. to 500 ° C. The temperature at which the measured mass became 95% of the mass at the start of measurement (25° C.) was taken as the gasification temperature of the gas generating substance.
  • EC ethylene carbonate
  • EP ethyl propionate
  • PP propyl propionate
  • a solution obtained by dissolving LiPF 6 at a concentration of 1M in a mixed solvent consisting of the following was used. Then, let A be the shell thickness before the immersion test and B be the shell thickness after the immersion test. ⁇ NMP swelling degree of shell> The test was carried out by replacing the electrolyte with NMP.
  • the electrolyte solution swelling degree of the polymer is calculated from the following formula and evaluated according to the following criteria.
  • a solution obtained by dissolving LiPF 6 at a concentration of 1M in a mixed solvent consisting of the following was used.
  • Degree of swelling (%) B/A x 100 (%)
  • NMP swelling degree of polymer 1 and polymer 2 Except for changing the electrolytic solution to NMP and changing the immersion temperature to 45 ° C., the same operation as the method for measuring the degree of swelling of the electrolytic solution described above was performed to measure the NMP swelling degree of polymer 1 and polymer 2. bottom.
  • ⁇ Expansion start temperature> The prepared thermally expandable particles were heated at a heating rate of 10° C./min using a heating stage (FTIR600 manufactured by Linkcom). The particle diameter of the thermally expandable particles during heating was observed with an optical microscope (manufactured by Keyence, VHX-900) to observe changes in diameter with respect to temperature.
  • the expansion start temperature was defined as the point at which the change in diameter was 1.3 times or more that before heating.
  • a cross-section polisher (IB-09020CP manufactured by JEOL Ltd.) was used to process the positive electrodes prepared in Examples and Comparative Examples for observation.
  • cross-sectional observation was performed with an FE-SEM (JSM-7800F manufactured by JEOL Ltd.). The observation magnification was 1000 times, the irradiation voltage was 10 kV, and the irradiation current was 5.0 ⁇ 10 ⁇ 8 A.
  • the diameter of each thermally expandable particle was defined as the diameter obtained by fitting the circumscribed circle to each thermally expandable particle. Next, based on the obtained diameter, the volume of the thermally expandable particles assuming a spherical shape was calculated.
  • the volume average particle diameter D50 of the thermally expandable particles in the observed cross section is the diameter of the particles whose cumulative volume exceeds 50% when the volume is accumulated from the small diameter side of each particle. and The above observation was carried out in five fields of view, and the average value of the obtained volume average particle diameters D50 was defined as the volume average particle diameter D50 of the thermally expandable particles. Similar measurements and calculations were performed for the positive electrode active material, and the volume average particle diameter D50 was obtained.
  • thermally expandable particles having an exposed diameter of 0.5 to 5.0 times the volume average particle diameter D50 of the positive electrode active material were defined as exposed particles A.
  • the lithium-ion secondary batteries as electrochemical devices produced in Examples and Comparative Examples were allowed to stand at a temperature of 25° C. for 5 hours after electrolyte injection.
  • the battery was charged to a cell voltage of 3.65 V by a constant current method at a temperature of 25° C. and 0.2 C, and then subjected to aging treatment at a temperature of 60° C. for 12 hours.
  • the battery was discharged to a cell voltage of 3.00 V by a constant current method at a temperature of 25° C. and 0.2 C.
  • CC-CV charging upper limit cell voltage 4.35V
  • CC discharge was performed to 3.00V by a 0.2C constant current method.
  • the DCR relative value of each example was calculated with the DCR of Example 1 set to 100, and evaluated according to the following criteria. A smaller RCR relative value indicates a smaller IV resistance of the lithium ion secondary battery.
  • CC-CV charging upper limit cell voltage 4.35V
  • CC discharge was performed to 3.00V by a 0.2C constant current method. This charge/discharge at 0.2C was repeated three times.
  • the battery was charged to 4.35 V (cutoff condition: 0.02 C) by a constant voltage constant current (CC-CV) method at a charging rate of 0.2 C.
  • CC-CV constant voltage constant current
  • monomer composition 2 34.1 parts of styrene as the aromatic vinyl monomer, 27.3 parts of 2-ethylhexyl acrylate as the (meth)acrylic acid ester monomer, and 4.7 parts of glycidyl methacrylate as the epoxy group-containing unsaturated monomer and 0.5 part of allyl methacrylate as a crosslinkable monomer were mixed to prepare a monomer composition 2.
  • a colloidal dispersion containing magnesium hydroxide containing the gas-generating substance and monomer composition 1 was placed in a 5 MPa pressure vessel equipped with a stirrer and reacted at 70° C. for 8 hours. The pressure during the reaction was 0.5 MPa. 2,2′-azobis[2-methyl-N-(2- Hydroxyethyl)-propionamide] (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) 0.1 part was added and reacted at 90°C for 5 hours. After continuing the polymerization reaction, the reaction is stopped by water cooling, and the core comprising the gas generating material is covered with a shell (including an inner layer made of polymer 1 and an outer layer made of polymer 2).
  • aqueous dispersion containing expandable particles was obtained. Furthermore, while stirring the aqueous dispersion containing the thermally expandable particles, sulfuric acid was added dropwise at room temperature (25° C.), and acid washing was performed until the pH became 6.5 or less. Subsequently, filtration separation was performed, and 500 parts of ion-exchanged water was added to the obtained solid content to re-slurry, and the water washing treatment (washing, filtration and dehydration) was repeated several times. Then, filtration separation was performed, and the obtained solid content was placed in a container of a dryer and dried at 35° C. for 48 hours to obtain dried thermally expandable particles. Attributes of the obtained thermally expandable particles were analyzed according to the above, and the gasification temperature of the core was 28° C., and the shell had the following attributes.
  • the autoclave was returned to the atmospheric pressure, and 25 mg of palladium acetate as a catalyst for hydrogenation reaction was dissolved in 60 mL of water containing nitric acid in an amount of 4 times the molar amount of Pd and added.
  • the contents of the autoclave were heated to 50° C. while the pressure was increased to 3 MPa with hydrogen gas, and the hydrogenation reaction (second stage hydrogenation reaction) was carried out for 6 hours. , to obtain an aqueous dispersion of the binder.
  • An appropriate amount of NMP was added to the obtained aqueous dispersion of the binder to obtain a mixture. Thereafter, vacuum distillation was carried out at 90° C. to remove water and excess NMP from the mixture to obtain an NMP solution of the binder (solid concentration: 8%).
  • ⁇ Preparation of binder composition 10 parts by mass of a binder in terms of solid content and 90 parts by mass of thermally expandable particles are mixed, and NMP is added to adjust the solid content concentration to 30%, thereby forming a binder composition. prepared.
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,600 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
  • the positive electrode lower layer slurry composition was applied onto a 20 ⁇ m-thick aluminum foil as a current collector with a comma coater in an amount of 10 ⁇ 0.5 mg/cm 2 . Furthermore, the positive electrode lower layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C.
  • the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20 ⁇ 0.5 mg/cm 2 . Furthermore, the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min.
  • the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25 ⁇ 3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 .
  • a positive electrode was obtained.
  • the exposed area ratio of the thermally expandable particles, the volume average particle size D50 of the positive electrode active material, and the volume average particle size D50 of the thermally expandable particles were measured, and the particle sizes of the thermally expandable particles and the positive electrode active material were determined. A ratio was calculated. Table 2 shows the results.
  • a planetary mixer was charged with 48.75 parts of artificial graphite (theoretical capacity of 360 mAh/g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity of 360 mAh/g), and carboxymethyl cellulose as a thickener. 1 part was put in for a minute. Further, the mixture was diluted with ion-exchanged water to a solid content concentration of 60%, and then kneaded for 60 minutes at a rotational speed of 45 rpm. Thereafter, 1.5 parts of the binder composition for a negative electrode obtained above was added in terms of solid content, and kneaded at a rotation speed of 40 rpm for 40 minutes.
  • a negative electrode slurry composition was prepared.
  • the negative electrode slurry composition was applied to the surface of a copper foil having a thickness of 15 ⁇ m as a current collector with a comma coater in an amount of 11 ⁇ 0.5 mg/cm 2 .
  • the copper foil coated with the negative electrode slurry composition was conveyed at a speed of 400 mm/min in an oven at a temperature of 80° C. for 2 minutes and further in an oven at a temperature of 110° C. for 2 minutes.
  • the negative electrode slurry composition on the foil was dried to obtain a negative electrode raw roll in which a negative electrode mixture layer was formed on a current collector.
  • the negative electrode mixture layer side of the negative electrode raw fabric thus prepared was roll-pressed under the conditions of a linear pressure of 11 t (tons) under an environment of a temperature of 25 ⁇ 3° C., and the density of the negative electrode mixture layer was 1.60 g/cm 3 .
  • a negative electrode was obtained.
  • EC ethylene carbonate
  • EP ethyl propionate
  • PP propyl propionate
  • Example 2 The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
  • ⁇ Preparation of slurry composition for positive electrode mixture layer> In a planetary mixer, 94.0 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 2.0 parts of the binder composition equivalent to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ⁇ 3 ° C.
  • a positive electrode slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 2,200 mPa ⁇ s, and a solid content concentration of 66% using a Brookfield viscometer at 60 rpm (rotor M4).
  • the positive electrode slurry composition was applied onto a 20 ⁇ m thick aluminum foil as a current collector with a comma coater so that the coating amount was 20 ⁇ 0.5 mg/cm 2 .
  • the positive electrode slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 110° C. for 2 minutes and then in an oven at a temperature of 120° C.
  • a positive electrode raw roll having a positive electrode mixture layer formed on a current collector was obtained.
  • the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25 ⁇ 3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 .
  • a positive electrode was obtained.
  • Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
  • Example 3 The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
  • ⁇ Preparation of positive electrode lower layer slurry composition> In a planetary mixer, 93.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 2.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ⁇ 3 ° C.
  • a positive electrode lower layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,600 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,400 mPa ⁇ s, and a solid content concentration of 68% using a Brookfield viscometer at 60 rpm (rotor M4).
  • the positive electrode lower layer slurry composition obtained above was applied onto a 20 ⁇ m thick aluminum foil as a current collector with a comma coater so that the coating amount was 10 ⁇ 0.5 mg/cm 2 .
  • the positive electrode lower layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C.
  • the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20 ⁇ 0.5 mg/cm 2 . Furthermore, the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min.
  • a positive electrode blank in which a positive electrode mixture layer was formed on a current collector.
  • the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25 ⁇ 3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 .
  • a positive electrode was obtained.
  • Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
  • Example 4 The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
  • ⁇ Preparation of positive electrode lower layer slurry composition> In a planetary mixer, 95.5 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 0.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ⁇ 3 ° C.
  • a positive electrode lower layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,600 mPa ⁇ s, and a solid content concentration of 68% using a Brookfield viscometer at 60 rpm (rotor M4).
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,400 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
  • the positive electrode lower layer slurry composition obtained above was applied onto a 20 ⁇ m thick aluminum foil as a current collector with a comma coater so that the coating amount was 10 ⁇ 0.5 mg/cm 2 .
  • the positive electrode lower layer slurry composition on the aluminum foil was transported in an oven at a temperature of 90°C for 2 minutes and further in an oven at a temperature of 120°C for 2 minutes. It was dried to obtain a positive electrode raw fabric (lower layer) in which a positive electrode mixture layer (lower layer) was formed on the current collector.
  • the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20 ⁇ 0.5 mg/cm 2 .
  • the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C.
  • Example 5 The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
  • ⁇ Preparation of positive electrode lower layer slurry composition> In a planetary mixer, 95.8 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 0.2 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ⁇ 3 ° C.
  • a positive electrode lower layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,800 mPa ⁇ s, and a solid content concentration of 67% using a Brookfield viscometer at 60 rpm (rotor M4).
  • the positive electrode lower layer slurry composition obtained above was applied onto a 20 ⁇ m thick aluminum foil as a current collector with a comma coater so that the coating amount was 10 ⁇ 0.5 mg/cm 2 . Further, at a speed of 0.5 m/min, the positive electrode lower layer slurry composition on the aluminum foil was transported in an oven at a temperature of 90°C for 2 minutes and further in an oven at a temperature of 120°C for 2 minutes.
  • the positive electrode raw fabric (lower layer) in which a positive electrode mixture layer (lower layer) was formed on the current collector.
  • the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20 ⁇ 0.5 mg/cm 2 .
  • the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode blank in which a positive electrode mixture layer was formed on a current collector.
  • the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25 ⁇ 3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 .
  • a positive electrode was obtained.
  • Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
  • Example 6 The procedure of Example 1 was repeated except that lithium cobaltate having a different volume average particle diameter D50 (25 ⁇ m) was used as the positive electrode active material, and the following operations were carried out during the production of the positive electrode.
  • ⁇ Preparation of positive electrode lower layer slurry composition> In a planetary mixer, 94.5 parts of lithium cobalt oxide (volume average particle diameter D50: 25 ⁇ m) as a positive electrode active material, and carbon black (manufactured by Denka, trade name “Li-100”) as a conductive material equivalent to the solid content.
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,600 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4). Table 2 shows the results.
  • Example 7 Commercially available thermally expandable particles (F260D, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) were used as the thermally expandable particles, and lithium cobaltate having a different volume average particle diameter D50 (7 ⁇ m) was used as the positive electrode active material. The procedure was the same as in Example 1, except that the following operations were performed. ⁇ Preparation of positive electrode lower layer slurry composition> In a planetary mixer, 94.5 parts of lithium cobalt oxide (volume average particle diameter D50: 7 ⁇ m) as a positive electrode active material, and carbon black (manufactured by Denka, trade name “Li-100”) as a conductive material equivalent to the solid content.
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,400 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4). Table 2 shows the results.
  • the drying conditions for manufacturing the positive electrode are that the drying condition is 0.5 m / min, and the first drying is conveyed in an oven at a temperature of 90 ° C. for 2 minutes and further in an oven at a temperature of 120 ° C. for 2 minutes.
  • Various operations, evaluations and measurements were performed in the same manner as in Example 2, except that the temperature was changed to slightly lower conditions. Table 2 shows the results.
  • Example 2 Various operations, evaluations and measurements were performed in the same manner as in Example 2 except that the solid content concentration was 68% (viscosity was 3700 mPa ⁇ s) when preparing the positive electrode mixture layer slurry composition. Table 2 shows the results.
  • Example 3 The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode. Table 2 shows the results.
  • ⁇ Preparation of positive electrode lower layer slurry composition> 92.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 3.5 parts of the binder composition equivalent to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ⁇ 3 ° C.
  • a positive electrode lower layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,400 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,600 mPa ⁇ s, and a solid content concentration of 68% using a Brookfield viscometer at 60 rpm (rotor M4).
  • Example 4 The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode. Table 2 shows the results.
  • ⁇ Preparation of positive electrode lower layer slurry composition> In a planetary mixer, 96.0 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) was added and mixed, NMP was gradually added, and the mixture was stirred and mixed at a temperature of 25 ⁇ 3 ° C. and a rotation speed of 60 rpm.
  • a positive electrode lower layer slurry composition was obtained at a temperature of ⁇ 3° C., a viscosity of 3,500 mPa ⁇ s, and a solid content concentration of 67%.
  • ⁇ Preparation of positive electrode upper layer slurry composition> In a planetary mixer, 92.0 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 4.0 parts equivalent to the solid content of the binder composition are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ⁇ 3 ° C.
  • a positive electrode upper layer slurry composition was obtained at 25 ⁇ 3° C., a viscosity of 3,600 mPa ⁇ s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
  • D50 particle size indicates the volume average particle size D50
  • HNBR indicates hydrogenated nitrile rubber
  • an electrode for an electrochemical element and a method for manufacturing the same, which can improve the heat generation suppression performance of the electrochemical element and reduce the IV resistance.

Abstract

This electrode for an electrochemical element is provided with a current collector and a predetermined electrode mixture layer. The electrode mixture layer contains at least an electrode active material and thermally expandable particles having an expansion start temperature of 400 °C or less. When the exposed particles A are thermally expandable particles that are present on the surface of the electrode mixture layer and have an exposure diameter that is 0.5-5.0 times the volume average particle diameter D50 of the electrode active material, the occupied area percentage of the exposed particles A on the surface of the electrode mixture layer is 0.5-20%.

Description

電気化学素子用電極及び電気化学素子用電極の製造方法ELECTROCHEMICAL DEVICE ELECTRODE AND METHOD FOR MANUFACTURING ELECTROCHEMICAL DEVICE ELECTRODE
　本発明は、電気化学素子用電極及び電気化学素子用電極の製造方法に関するものである。 The present invention relates to an electrode for an electrochemical device and a method for manufacturing an electrode for an electrochemical device.
　リチウムイオン二次電池などの電気化学素子は、小型で軽量、かつエネルギー密度が高く、更に繰り返し充放電が可能という特性があり、幅広い用途に使用されている。そのため、近年では、電気化学素子の更なる高性能化を目的として、電極などの電池部材の改良が検討されている。 Electrochemical devices such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvements in battery members such as electrodes have been studied for the purpose of further improving the performance of electrochemical devices.
　ここで、リチウムイオンなどの電気化学素子に用いられる電極は、通常、集電体と、集電体上に形成された電極合材層とを備えている。そして、この電極合材層は、例えば、電極活物質と、結着材を含むバインダー組成物などとを含むスラリー組成物を集電体上に塗布し、塗布したスラリー組成物を乾燥させることにより形成される。 Here, electrodes used in electrochemical devices such as lithium ions usually include a current collector and an electrode mixture layer formed on the current collector. Then, this electrode mixture layer is formed by, for example, applying a slurry composition containing an electrode active material and a binder composition containing a binder onto a current collector and drying the applied slurry composition. It is formed.
　電気化学素子は、内部短絡の発生、及び内部における各種の化学反応の連鎖などに起因して、熱暴走を生じる虞がある。かかる熱暴走の発生を抑制するために、従来から、電気化学素子内部の温度上昇時に化学反応を阻害することが可能な物質を内包した熱膨張性粒子を電気化学素子用電極に配合することが行われてきた（例えば、特許文献１～３参照）。 An electrochemical element may experience thermal runaway due to the occurrence of an internal short circuit and a chain of various internal chemical reactions. In order to suppress the occurrence of such thermal runaway, it has been conventional to blend thermally expandable particles encapsulating a substance capable of inhibiting a chemical reaction when the temperature inside the electrochemical element rises into an electrode for an electrochemical element. (See, for example, Patent Documents 1 to 3).
国際公開第２０１５／１３３４２３号WO2015/133423 国際公開第２０１９／１８９８６５号WO2019/189865 特開２００３－０３１２０８号公報Japanese Patent Application Laid-Open No. 2003-031208
　ここで、電気化学素子用電極には、得られる二次電池に良好な発熱抑制性能を付与することと、二次電池のＩＶ抵抗を低減することとを両立することが求められている。しかし、上記従来の電気化学素子用電極には、これらの性質を一層高いレベルで両立するという点で改善の余地があった。 Here, the electrodes for electrochemical devices are required to achieve both good heat generation suppressing performance and reduced IV resistance of the secondary battery. However, the above conventional electrodes for electrochemical devices have room for improvement in terms of achieving both of these properties at a higher level.
　そこで、本発明は、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができる、電気化学素子用電極及びその製造方法を提供することを目的とする。 Therefore, an object of the present invention is to provide an electrode for an electrochemical device and a method for manufacturing the same, which can improve the heat generation suppression performance of the electrochemical device and reduce the IV resistance.
　本発明者は、上記課題を解決することを目的として鋭意検討を行った。そして、本発明者は、膨張開始温度が所定の温度範囲である熱膨張性粒子が、電極表面に所定割合で露出してなる電気化学素子用電極を用いれば、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができることを新たに見出し、本発明を完成させた。 The inventor of the present invention conducted intensive studies with the aim of solving the above problems. Further, the present inventors have found that heat generation suppressing performance of an electrochemical element can be improved by using an electrode for an electrochemical element in which thermally expandable particles having an expansion start temperature within a predetermined temperature range are exposed on the surface of the electrode at a predetermined rate. The inventors have newly found that the IV resistance can be increased and the IV resistance can be reduced, thus completing the present invention.
　即ち、この発明は、上記課題を有利に解決することを目的とするものであり、〔１〕本発明の電気化学素子用電極は、集電体及び電極合材層を備える電気化学素子用電極であって、前記電極合材層が、少なくとも、電極活物質と膨張開始温度が４００℃以下である熱膨張性粒子とを含み、前記電極合材層表面に存在する、露出径が前記電極活物質の体積平均粒子径Ｄ５０の０．５倍以上５．０倍以下である熱膨張性粒子を露出粒子Ａとした場合に、前記電極合材層表面における露出粒子Ａの占有面積率が０．５％以上２０％以下であることを特徴とする。かかる特徴を有する電気化学素子用電極を用いれば、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができる。
　なお、熱膨張性粒子の膨張開始温度、電極活物質の体積平均粒子径Ｄ５０、及び露出粒子Ａの占有面積率は、本明細書の実施例に記載の方法により測定することができる。 That is, an object of the present invention is to advantageously solve the above problems. wherein the electrode mixture layer includes at least an electrode active material and thermally expandable particles having an expansion start temperature of 400° C. or lower, and the exposed diameter present on the surface of the electrode mixture layer is equal to the electrode active material When the exposed particles A are thermally expandable particles having a volume average particle diameter D50 of 0.5 to 5.0 times the volume average particle diameter D50 of the substance, the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5. It is characterized by being 5% or more and 20% or less. By using an electrode for an electrochemical device having such characteristics, the heat generation suppression performance of the electrochemical device can be enhanced and the IV resistance can be reduced.
The expansion starting temperature of the thermally expandable particles, the volume average particle diameter D50 of the electrode active material, and the occupied area ratio of the exposed particles A can be measured by the methods described in the examples of the present specification.
　ここで、〔２〕上記〔１〕にかかる本発明の電気化学素子用電極において、前記熱膨張性粒子の体積平均粒子径Ｄ５０が、前記電極活物質の体積平均粒子径Ｄ５０の０．３倍以上５．０倍以下であることが好ましい。熱膨張性粒子の体積平均粒子径Ｄ５０と電極活物質の体積平均粒子径Ｄ５０とが、上記関係を満たす、電気化学素子用電極を用いれば、電気化学素子の発熱抑制性能を一層高めるとともに、ＩＶ抵抗を一層低減することができる。
　なお、体積平均粒子径Ｄ５０の値は、本明細書の実施例に記載の方法により測定することができる。 Here, [2] In the electrochemical device electrode of the present invention according to [1] above, the volume average particle diameter D50 of the thermally expandable particles is 0.3 times the volume average particle diameter D50 of the electrode active material. It is preferable that it is more than 5.0 times or less. If an electrode for an electrochemical device is used in which the volume average particle diameter D50 of the thermally expandable particles and the volume average particle diameter D50 of the electrode active material satisfy the above relationship, the heat generation suppression performance of the electrochemical device can be further enhanced, and IV The resistance can be further reduced.
In addition, the value of the volume average particle diameter D50 can be measured by the method described in the examples of this specification.
　また、〔３〕上記〔１〕又は〔２〕に記載した本発明の電気化学素子用電極は、前記電極合材層表面における前記露出粒子Ａの個数密度が１０個／ｍｍ２以上３００個／ｍｍ２以下であることが好ましい。電極表面における露出粒子Ａの個数密度が上記範囲内である電気化学素子用電極を用いれば、電気化学素子の発熱抑制性能を一層高めるとともに、ＩＶ抵抗を一層低減することができる。
　なお、電極表面における露出粒子Ａの個数密度は、本明細書の実施例に記載の方法により測定することができる。 [3] In the electrode for an electrochemical element of the present invention described in [1] or [2] above, the number density of the exposed particles A on the surface of the electrode mixture layer is 10 particles/ mm2 or more and 300 particles/ mm 2 or less is preferred. By using an electrochemical device electrode in which the number density of the exposed particles A on the electrode surface is within the above range, the heat generation suppressing performance of the electrochemical device can be further enhanced and the IV resistance can be further reduced.
The number density of the exposed particles A on the electrode surface can be measured by the method described in the examples of the present specification.
　さらに、〔４〕上記〔１〕～〔３〕の何れかに記載した本発明の電気化学素子用電極において、前記電極合材層が結着材をさらに含み、前記結着材は、カルボン酸基、ヒドロキシル基、ニトリル基、アミノ基、エポキシ基、オキサゾリン基、スルホン酸基、エステル基及びアミド基からなる群から選択される少なくとも１種の官能基を有するポリマーであることが好ましい。電極合材層が、所定の結着材を更に含んでいれば、電極合材層の接着性を高めることができる。 [4] In the electrode for an electrochemical device according to any one of [1] to [3] above, the electrode mixture layer further contains a binder, and the binder is a carboxylic acid It is preferably a polymer having at least one functional group selected from the group consisting of groups, hydroxyl groups, nitrile groups, amino groups, epoxy groups, oxazoline groups, sulfonic acid groups, ester groups and amide groups. If the electrode mixture layer further contains a predetermined binder, the adhesiveness of the electrode mixture layer can be enhanced.
　そして、〔５〕この発明は、上記課題を有利に解決することを目的とするものであり、上記〔１〕～〔４〕の何れかに記載した本発明の電気化学素子電極の製造方法は、上述した電気化学素子用電極の製造方法であって、集電体上に、電極下層用スラリー組成物を塗布及び乾燥して、電極下層を形成する工程と、前記電極下層上に、電極上層用スラリー組成物を塗布及び乾燥して、電極上層を形成する工程とを含み、前記電極上層用スラリー組成物及び前記電極下層用スラリー組成物は、それぞれ、電極活物質及び熱膨張性粒子を含有してなり、前記電極上層用スラリー組成物の熱膨張性粒子濃度が前記電極下層用スラリー組成物の熱膨張性粒子濃度よりも高いことを特徴とする。かかる製造方法によれば、上述した本発明の電気化学素子用電極を効率的に製造することができる。 [5] An object of the present invention is to advantageously solve the above problems. A method for manufacturing an electrode for an electrochemical device as described above, wherein the slurry composition for electrode lower layer is applied onto a current collector and dried to form an electrode lower layer, and an electrode upper layer is formed on the electrode lower layer applying and drying a slurry composition for forming an electrode upper layer, wherein the electrode upper layer slurry composition and the electrode lower layer slurry composition each contain an electrode active material and thermally expandable particles. The thermally expandable particle concentration of the electrode upper layer slurry composition is higher than the thermally expandable particle concentration of the electrode lower layer slurry composition. According to such a production method, the above-described electrode for an electrochemical device of the present invention can be efficiently produced.
　本発明によれば、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができる、電気化学素子用電極及びその製造方法を提供することができる。 According to the present invention, it is possible to provide an electrode for an electrochemical element and a method for manufacturing the same, which can improve the heat generation suppression performance of the electrochemical element and reduce the IV resistance.
　以下、本発明の実施形態について詳細に説明する。
　ここで、本発明の電気化学素子用電極（以下、単に「電極」ともいう。）は、電気化学素子を製造する際に用いることができる。本発明の電気化学素子用電極は、電気化学素子、特には二次電池の正極として好適に用いることができる。 Hereinafter, embodiments of the present invention will be described in detail.
Here, the electrode for an electrochemical device of the present invention (hereinafter also simply referred to as "electrode") can be used when manufacturing an electrochemical device. The electrode for an electrochemical device of the present invention can be suitably used as a positive electrode for an electrochemical device, particularly a secondary battery.
（電気化学素子用電極）
　本発明の電気化学素子用電極は、集電体及び電極合材層を備える。具体的には、電極は、電極合材層は、少なくとも、電極活物質と膨張開始温度が４００℃以下である熱膨張性粒子とを含み、電極合材層表面に存在する、露出径が電極活物質の体積平均粒子径Ｄ５０の０．５倍以上５．０倍以下である熱膨張性粒子を露出粒子Ａとした場合に、電極合材層表面における露出粒子Ａの占有面積率が０．５％以上２０％以下であることを特徴とする。膨張開始温度が所定の温度範囲である熱膨張性粒子が、電極表面に所定割合で露出してなる電気化学素子用電極を用いれば、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができる。その理由は明らかではないが、以下の通りであると推察される。 (electrode for electrochemical device)
An electrode for an electrochemical device of the present invention comprises a current collector and an electrode mixture layer. Specifically, in the electrode, the electrode mixture layer includes at least an electrode active material and thermally expandable particles having an expansion start temperature of 400 ° C. or less, and the exposed diameter present on the electrode mixture layer surface is When the exposed particles A are thermally expandable particles having a volume average particle diameter D50 of 0.5 to 5.0 times the volume average particle diameter D50 of the active material, the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5. It is characterized by being 5% or more and 20% or less. By using an electrode for an electrochemical element in which thermally expandable particles having an expansion start temperature within a predetermined temperature range are exposed at a predetermined ratio on the electrode surface, the heat generation suppression performance of the electrochemical element is enhanced and the IV resistance is reduced. can do. Although the reason is not clear, it is presumed to be as follows.
　電極合材層表面に、露出径が所定の範囲内である露出粒子Ａが所定範囲の占有面積率で存在することにより、熱膨張性粒子の膨張開始温度以上に素子内温度が上昇した異常時において、電極と当該電極に隣接する部材（例えば、セパレータ）との間隔を効果的に離すことができるため、異常時における短絡を抑制され、これにより電気化学素子の発熱抑制性能を高めることができると推察される。また、露出径が所定の範囲内である露出粒子Ａの占有面積が所定の下限値以上であれば、電極合材層内に埋没する熱膨張性粒子の体積が少なくなり、電極合材層における抵抗を低減することができるとともに、露出粒子Ａの占有面積が所定の上限値以下であれば、電極と当該電極に隣接する部材（例えば、セパレータ）との間における抵抗が平常状態において高まらないようにすることができ、その結果、電気化学素子のＩＶ抵抗を低減することができると推察される。 When the temperature inside the element rises above the expansion start temperature of the thermally expandable particles due to the existence of the exposed particles A whose exposed diameter is within the predetermined range on the surface of the electrode mixture layer and the occupied area ratio is within the predetermined range. In , since the distance between the electrode and the member adjacent to the electrode (e.g., separator) can be effectively separated, short circuiting in the event of an abnormality is suppressed, thereby improving the heat generation suppression performance of the electrochemical element. It is speculated that Further, when the occupied area of the exposed particles A whose exposed diameter is within the predetermined range is equal to or greater than the predetermined lower limit, the volume of the thermally expandable particles embedded in the electrode mixture layer is reduced, and the electrode mixture layer The resistance can be reduced, and if the area occupied by the exposed particles A is equal to or less than a predetermined upper limit, the resistance between the electrode and a member adjacent to the electrode (e.g., separator) will not increase in a normal state. As a result, it is speculated that the IV resistance of the electrochemical device can be reduced.
＜集電体＞
　集電体としては、電気導電性を有し、かつ、電気化学的に耐久性のある材料が用いられる。具体的には、集電体としては、例えば、鉄、銅、アルミニウム、ニッケル、ステンレス鋼、チタン、タンタル、金、白金などからなる集電体を用い得る。なお、前記の材料は、１種類を単独で用いてもよく、２種類以上を任意の比率で組み合わせて用いてもよい。 <Current collector>
As the current collector, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. In addition, one type of the above materials may be used alone, or two or more types may be used in combination at an arbitrary ratio.
＜電極合材層＞
　電極に備えられる電極合材層は、電極活物質と、膨張開始温度が４００℃以下である熱膨張性粒子とを含み、任意で、結着材、導電材、及びその他の添加剤を含有していてもよい。そして、電極合材層は、電極合材層表面における露出粒子Ａの占有面積率が０．５％以上２０％以下であることを必要とする。これにより、得られる電気化学素子の発熱抑制性能を高めるとともにＩＶ抵抗を低減することができる。さらに、電極合材層において、表面及び表面付近の領域に熱膨張性粒子が偏在することが好ましい。熱膨張性粒子が表面及び表面付近に偏在していれば、得られる電気化学素子の発熱抑制性能を一層高めるとともにＩＶ抵抗を一層低減することができる。 <Electrode mixture layer>
The electrode mixture layer provided in the electrode contains an electrode active material and thermally expandable particles having an expansion initiation temperature of 400° C. or less, and optionally contains a binder, a conductive material, and other additives. may be Further, the electrode mixture layer requires that the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5% or more and 20% or less. As a result, it is possible to improve the heat generation suppression performance of the obtained electrochemical device and to reduce the IV resistance. Furthermore, in the electrode mixture layer, it is preferable that the thermally expandable particles are unevenly distributed on the surface and in the region near the surface. If the thermally expandable particles are unevenly distributed on the surface and near the surface, the heat generation suppression performance of the resulting electrochemical device can be further enhanced and the IV resistance can be further reduced.
＜＜電極合材層表面における露出粒子Ａの占有面積率＞＞
　まず、露出粒子Ａとは、電極合材層表面に存在する、露出径が電極活物質の体積平均粒子径Ｄ５０の０．５倍以上５．０倍以下である熱膨張性粒子を指す。露出径が、電極活物質の体積平均粒子径Ｄ５０の０．５倍以上５．０倍以下である熱膨張性粒子を露出粒子として定義することで、適度な露出サイズを有する熱膨張性粒子の電極合材層表面における存在割合を定量することができ、これにより、発熱抑制性能向上に効果的に寄与する熱膨張性粒子の存在態様を評価することができる。 <<Occupied Area Ratio of Exposed Particles A on Surface of Electrode Mixture Layer>>
First, the exposed particles A refer to thermally expandable particles that exist on the surface of the electrode mixture layer and have an exposed diameter that is 0.5 to 5.0 times the volume average particle diameter D50 of the electrode active material. Thermally expandable particles having an exposed diameter of 0.5 to 5.0 times the volume average particle diameter D50 of the electrode active material are defined as exposed particles, thereby obtaining thermally expandable particles having an appropriate exposed size. It is possible to quantify the existence ratio on the surface of the electrode mixture layer, and thereby to evaluate the existence mode of the thermally expandable particles that effectively contribute to the improvement of the heat generation suppression performance.
＜＜電極合材層表面における露出粒子Ａの個数密度＞＞
　電極合材層表面における露出粒子Ａの個数密度は、１０個／ｍｍ２以上であることが好ましく、２０個／ｍｍ２以上であることがより好ましく、４０個／ｍｍ２以上であることがさらに好ましく、３００個／ｍｍ２以下であることが好ましく、２５０個／ｍｍ２以下であることがより好ましく、１５０個／ｍｍ２以下であることがさらに好ましく、１１０個／ｍｍ２以下であることが特に好ましい。電極合材層表面における露出粒子Ａの個数密度が上記範囲内であれば、得られる電気化学素子の発熱抑制性能を一層高めることができるとともに、ＩＶ抵抗を一層低減することができる。特に、電極合材層表面における露出粒子Ａの個数密度が上記下限値以上である場合には、熱膨張性粒子の膨張時に、電極とそれに隣接する部材との間の距離を効果的に離すことができ、電気化学素子の発熱抑制性能を効果的に高めることができる。また、電極合材層表面における露出粒子Ａの個数密度が上記上限値以下であれば、平常時に、露出した熱膨張性粒子が電気化学素子の内部抵抗を高めることを抑制して、電気化学素子のＩＶ抵抗を低減することができる。 <<Number Density of Exposed Particles A on Surface of Electrode Mixture Layer>>
The number density of the exposed particles A on the surface of the electrode mixture layer is preferably 10/mm 2 or more, more preferably 20/mm 2 or more, and further preferably 40/mm 2 or more. The number is preferably 300/mm 2 or less, more preferably 250/mm 2 or less, even more preferably 150/mm 2 or less, and 110/mm 2 or less. Especially preferred. If the number density of the exposed particles A on the surface of the electrode mixture layer is within the above range, the heat generation suppression performance of the resulting electrochemical device can be further enhanced, and the IV resistance can be further reduced. In particular, when the number density of the exposed particles A on the surface of the electrode mixture layer is equal to or higher than the above lower limit, the distance between the electrode and the member adjacent thereto is effectively increased when the thermally expandable particles expand. It is possible to effectively improve the heat generation suppression performance of the electrochemical device. Further, if the number density of the exposed particles A on the surface of the electrode mixture layer is equal to or less than the above upper limit value, the exposed thermally expandable particles are suppressed from increasing the internal resistance of the electrochemical element in normal times, and the electrochemical element can reduce the IV resistance of
　ここで、電極合材層表面における露出粒子Ａの占有面積率は、０．５％以上である必要があり、２．０％以上であることが好ましく、２０％以下である必要があり、１０％以下であることが好ましく、５．０％以下であることがより好ましい。露出粒子Ａの占有面積率が上記範囲内であれば、得られる電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができる。 Here, the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer should be 0.5% or more, preferably 2.0% or more, and 20% or less. % or less, more preferably 5.0% or less. If the occupied area ratio of the exposed particles A is within the above range, the heat generation suppressing performance of the resulting electrochemical device can be enhanced and the IV resistance can be reduced.
＜＜熱膨張性粒子＞＞
　熱膨張性粒子は、膨張開始温度が４００℃以下である必要がある。膨張開始温度は、３００℃以下であることが好ましく、１３０℃以上であることが好ましく、１５０℃以上であることがより好ましく、１７０℃以上であることがさらに好ましい。膨張開始温度が上記下限値以上であれば、電気化学素子の製造工程において熱膨張性粒子が膨張することを抑制して、得られる電気化学素子のＩＶ抵抗が高まることを抑制することができる。また、膨張開始温度が上記上限値以下であれば、電気化学素子に異常が発生した際に内部温度が上昇することを迅速に抑制し、熱暴走の発生を効果的に抑制することができる。 <<Thermal expandable particles>>
The thermally expandable particles must have an expansion start temperature of 400° C. or less. The expansion start temperature is preferably 300° C. or lower, preferably 130° C. or higher, more preferably 150° C. or higher, and even more preferably 170° C. or higher. If the expansion start temperature is equal to or higher than the above lower limit, expansion of the thermally expandable particles in the manufacturing process of the electrochemical device can be suppressed, and an increase in the IV resistance of the resulting electrochemical device can be suppressed. Further, if the expansion start temperature is equal to or lower than the above upper limit, it is possible to quickly suppress the internal temperature from rising when an abnormality occurs in the electrochemical element, thereby effectively suppressing the occurrence of thermal runaway.
　また、熱膨張性粒子は、体積平均粒子径Ｄ５０が、電極活物質の体積平均粒子径Ｄ５０の０．３倍以上であることが好ましく、０．５倍以上であることがより好ましく、５．０倍以下であることが好ましく、３．０倍以下であることがより好ましい。熱膨張性粒子と電極活物質との粒子径比が上記下限値以上であれば、熱膨張性粒子が電極合材層中において抵抗となることを抑制するとともに、膨張による発熱抑制性能を高めることができる。また、熱膨張性粒子と電極活物質との粒子径比が上記上限値以下であれば、電気化学素子のＩＶ抵抗及び発熱抑制性能を高めることができる。 The volume average particle diameter D50 of the thermally expandable particles is preferably 0.3 times or more, more preferably 0.5 times or more, of the volume average particle diameter D50 of the electrode active material. It is preferably 0 times or less, more preferably 3.0 times or less. If the particle size ratio between the thermally expandable particles and the electrode active material is equal to or greater than the above lower limit, the thermally expandable particles are suppressed from becoming resistance in the electrode mixture layer, and the heat generation suppression performance due to expansion is enhanced. can be done. Further, if the particle size ratio between the thermally expandable particles and the electrode active material is equal to or less than the above upper limit, the IV resistance and heat generation suppression performance of the electrochemical device can be enhanced.
　さらにまた、熱膨張性粒子は、体積平均粒子径Ｄ５０が０．１μｍ以上であることが好ましく、１μｍ以上であることがより好ましく、５μｍ以上であることがさらに好ましく、１００μｍ以下であることが好ましく、８０μｍ以下であることがより好ましく、５０μｍ以下であることがさらに好ましく、３０μｍ以下であることが特に好ましい。熱膨張性粒子の体積平均粒子径Ｄ５０が上記下限値以上であれば、熱膨張性粒子が抵抗となり電気化学素子の内部抵抗が増大することを抑制することができる。熱膨張性粒子の体積平均粒子径Ｄ５０が上記上限値以下であれば、得られる電極用スラリー組成物の塗工性を高めることができるとともに、得られる電気化学素子の発熱抑制性能を高めることができる。 Furthermore, the thermally expandable particles preferably have a volume average particle diameter D50 of 0.1 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, and preferably 100 μm or less. , is more preferably 80 μm or less, further preferably 50 μm or less, and particularly preferably 30 μm or less. When the volume average particle diameter D50 of the thermally expandable particles is at least the above lower limit, it is possible to suppress an increase in the internal resistance of the electrochemical device due to the thermally expandable particles acting as resistance. If the volume average particle diameter D50 of the thermally expandable particles is equal to or less than the above upper limit, the coatability of the obtained electrode slurry composition can be improved, and the heat generation suppression performance of the obtained electrochemical element can be enhanced. can.
　ここで、電極に含有される熱膨張性粒子の量は、後述する結着材と熱膨張性粒子との合計含有量（質量基準）を１００質量部として、４０質量％以上であることが好ましく、５０質量％以上であることがより好ましく、９７質量部以下であることが好ましく、９３質量部以下であることがより好ましい。熱膨張性粒子の含有量が上記下限値以上であれば、得られる電気化学素子の発熱抑制性能を一層高めることができる。熱膨張性粒子の含有量が上記上限値以下であれば、得られる電気化学素子のＩＶ抵抗を一層低減することができる。 Here, the amount of the thermally expandable particles contained in the electrode is preferably 40% by mass or more, with the total content (based on mass) of the binder and the thermally expandable particles described later being 100 parts by mass. , more preferably 50 mass % or more, preferably 97 mass parts or less, and more preferably 93 mass parts or less. When the content of the thermally expandable particles is at least the above lower limit, the heat generation suppression performance of the resulting electrochemical device can be further enhanced. If the content of the thermally expandable particles is equal to or less than the above upper limit, the IV resistance of the resulting electrochemical device can be further reduced.
　ここで、熱膨張性粒子としては、膨張開始温度が４００℃以下である限りにおいて、あらゆる熱膨張性粒子を用いることができる。例えば、熱膨張性粒子としては、マツモトマイクロスフェアー（登録商標）、Ｅｘｐａｎｃｅｌ（日本フィライト社製）などの市販の熱膨張性粒子や、後述する特定構造を満たす熱膨張性粒子を用いることができる。 Here, as the thermally expandable particles, any thermally expandable particles can be used as long as the expansion start temperature is 400°C or less. For example, as the thermally expandable particles, commercially available thermally expandable particles such as Matsumoto Microsphere (registered trademark) and Expancel (manufactured by Nippon Philite Co., Ltd.), and thermally expandable particles satisfying a specific structure described later can be used. .
　熱膨張性粒子としては、コアと、コアの外表面を覆うシェルとを備えるコアシェル構造を有する粒子が好ましい。本明細書において、シェルが「コアの外表面を覆う」とは、コアの外表面の少なくとも一部の上にシェルが存在していることを意味する。シェルはコアの外表面の一部を覆っていてもよいし、コアの外表面の全部を覆っていてもよい。また、シェルは、少なくとも二種類のポリマーを含む限りにおいて特に限定されることなく、一層又は複数層を含む。シェルを構成する層は、一層中に複数種のポリマーを含有していてもよいし、一層が一種のポリマーよりなり、かかる層を二層以上含んでいてもよい。 Particles having a core-shell structure comprising a core and a shell covering the outer surface of the core are preferable as the thermally expandable particles. As used herein, the shell "covers the outer surface of the core" means that the shell is present on at least a portion of the outer surface of the core. The shell may cover a portion of the outer surface of the core, or may cover the entire outer surface of the core. Also, the shell is not particularly limited as long as it contains at least two types of polymers, and includes one or more layers. The layers constituting the shell may contain a plurality of types of polymers in one layer, or may contain two or more layers each of which is composed of one type of polymer.
　熱膨張性粒子のコアは、４００℃以下でガス化するガス発生物質よりなる。本明細書にて、「ガス発生物質」とは所定の温度となるとガスを発生可能な化合物を意味し；「ガス化する」とはガスに相変化する物質を含む。コアは、任意で尿素などの添加剤を含有していてもよい。４００℃以下でガス化するガス発生物質は、電気化学素子の内部温度が所定の温度（４００℃以下の温度）に上昇した際にガス化し、内部における抵抗を増大させ、電気化学反応の連鎖を抑制することにより、熱暴走の発生を抑制することができる。さらにコアは、後述する熱膨張性粒子の製造方法に従って調製した場合には、微量の金属酸化物を含有することがある。 The core of the thermally expandable particles is made of a gas generating substance that gasifies at 400°C or less. As used herein, "gas-generating substance" means a compound capable of generating a gas at a given temperature; "gasification" includes substances that undergo a phase change to gas. The core may optionally contain additives such as urea. Gas generating substances that gasify at 400°C or less gasify when the internal temperature of the electrochemical element rises to a predetermined temperature (temperature of 400°C or less), increase the internal resistance, and initiate a chain of electrochemical reactions. By suppressing, the occurrence of thermal runaway can be suppressed. Furthermore, the core may contain a trace amount of metal oxide when prepared according to the method for producing thermally expandable particles described later.
　ガス発生物質のガス化温度は、４００℃以下である必要があり、３００℃以下であることが好ましく、１５０℃以下であることがより好ましく、１０℃以上であることが好ましく、２０℃以上であることがより好ましく、２６℃以上であることが更に好ましい。ガス化温度が上記上限値以下であれば、電気化学素子に異常が発生した際に内部温度が上昇することを抑制し、熱暴走の発生を効果的に抑制することができる。ガス化温度が上記下限値以上であれば、熱膨張性粒子の製造容易性が高まる。 The gasification temperature of the gas generating substance must be 400° C. or lower, preferably 300° C. or lower, more preferably 150° C. or lower, preferably 10° C. or higher, and preferably 20° C. or higher. It is more preferable that the temperature is 26° C. or higher. When the gasification temperature is equal to or lower than the above upper limit, it is possible to suppress the internal temperature from rising when an abnormality occurs in the electrochemical element, and to effectively suppress the occurrence of thermal runaway. If the gasification temperature is equal to or higher than the above lower limit, the easiness of manufacturing the thermally expandable particles is enhanced.
　ガス発生物質としては、イソペンタン（ガス化温度：２８℃）、イソオクタン、ｎ－ペンタン、ｎ－ヘキサン、イソヘキサン、２，２－ジメチルブタン（ガス化温度：５０℃）、シクロヘキサン（ガス化温度：８１℃）、へプタン、及び石油エーテルなどの炭化水素化合物、炭酸水素ナトリウム（ガス化温度：１５０℃）などの炭酸水素塩化合物、硝酸グアニジン、ニトログアニジン、及びアミノグアニジン硝酸塩などのグアニジン化合物、アゾビスイソブチロニトリル（ガス化温度：１０８℃）及びアゾジカルボンアミド（ガス化温度：２００℃）などのアゾ化合物、メラミン、アンメリン、アンメリド、メラミンシアヌレート（ガス化温度：２８０℃）、トリヒドラジントリアジン（１，３，５－トリアジン－２，４，６（１Ｈ，３Ｈ，５Ｈ）－トリオントリヒドラゾン）などのトリアジン化合物、ｐ，ｐ’－オキシビスベンゼンスルホニルヒドラジド（ガス化温度：１６０℃）及びｐ－トルエンスルホニルヒドラジドなどのヒドラジド化合物、ヒドラゾジカルボンアミド、及びｐ－トルエンスルホニルセミカルバジドなどのヒドラゾ化合物、ジニトロソペンタメチレンテトラミン及びトリメチレントリニトロアミンなどニトロアミン化合物、５－アミノテトラゾール及び５－フェニルテトラゾールなどのテトラゾール化合物、５，５’－ビテトラゾールジアンモニウム及びビテトラゾールピペラジンなどのビテトラゾール化合物が挙げられる。これらは一種を単独で、又は複数種を併用して用いることができる。中でも、得られる電気化学素子の発熱抑制性能を高める観点からは、イソペンタン、２，２－ジメチルブタン、シクロヘキサン、アゾビスイソブチロニトリル、及び炭酸水素ナトリウムが好ましい。 Gas-generating substances include isopentane (gasification temperature: 28°C), isooctane, n-pentane, n-hexane, isohexane, 2,2-dimethylbutane (gasification temperature: 50°C), cyclohexane (gasification temperature: 81 ° C), hydrocarbon compounds such as heptane and petroleum ether, bicarbonate compounds such as sodium bicarbonate (gasification temperature: 150 ° C), guanidine compounds such as guanidine nitrate, nitroguanidine and aminoguanidine nitrate, azobis Azo compounds such as isobutyronitrile (gasification temperature: 108°C) and azodicarbonamide (gasification temperature: 200°C), melamine, ammeline, ammelide, melamine cyanurate (gasification temperature: 280°C), trihydrazine triazine triazine compounds such as (1,3,5-triazine-2,4,6(1H,3H,5H)-trione trihydrazone), p,p'-oxybisbenzenesulfonyl hydrazide (gasification temperature: 160° C.) and hydrazide compounds such as p-toluenesulfonylhydrazide, hydrazodicarbonamides and hydrazo compounds such as p-toluenesulfonyl semicarbazide, nitroamine compounds such as dinitrosopentamethylenetetramine and trimethylenetrinitroamine, 5-aminotetrazole and 5-phenyltetrazole and tetrazole compounds such as 5,5'-bitetrazolediammonium and bitetrazolepiperazine. These can be used individually by 1 type or in combination of multiple types. Among them, isopentane, 2,2-dimethylbutane, cyclohexane, azobisisobutyronitrile, and sodium hydrogen carbonate are preferable from the viewpoint of enhancing the heat generation suppression performance of the obtained electrochemical device.
　熱膨張性粒子におけるコアの含有割合は、熱膨張性粒子の全質量を１００質量％として、０．１質量％以上であることが好ましく、５質量％以上であることがより好ましく、９０質量％以下であることが好ましく、５０質量％以下であることがより好ましく、３０質量％以下であることがさらに好ましい。熱膨張性粒子におけるコアの含有割合が上記下限値以上であれば、得られる電気化学素子の発熱抑制性能を一層高めることができる。また、熱膨張性粒子におけるコアの含有割合が上記上限値以下であれば、熱膨張性粒子がもろくなり電気化学素子が通常動作している最中に崩壊することを抑制することができる。なお、「熱膨張性粒子におけるコアの含有割合」とは、コアがシェルに内包された状態における含有割合である。 The content of the core in the thermally expandable particles is preferably 0.1% by mass or more, more preferably 5% by mass or more, more preferably 90% by mass, based on the total mass of the thermally expandable particles being 100% by mass. or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less. When the content of the core in the thermally expandable particles is at least the above lower limit, the heat generation suppression performance of the resulting electrochemical device can be further enhanced. Moreover, if the content of the core in the thermally expandable particles is equal to or less than the above upper limit, it is possible to prevent the thermally expandable particles from becoming brittle and collapsing during normal operation of the electrochemical device. In addition, "the content ratio of the core in the thermally expandable particles" is the content ratio in the state where the core is enclosed in the shell.
　熱膨張性粒子のシェルは、少なくとも二種類のポリマーよりなる。シェルは、電解液膨潤度が５００質量％以下であることを必要とし、３５０質量％以下であることが好ましく、３００質量％以下であることがより好ましい。シェルの電解液膨潤度が上記上限値以下であれば、電気化学素子内においてコアが電解液中に溶出することを良好に抑制し、電気化学素子の発熱抑制性能を高めることができる。なお、シェルの電解液膨潤度の下限値は特に限定されず、例えば、１００質量％であり、まったく膨潤しなくてもよい。得られる電気化学素子の内部抵抗を低減する観点からは、シェルの電解液膨潤度が１２０質量％以上であることが好ましい。 The shell of the thermally expandable particles consists of at least two types of polymers. The shell needs to have an electrolytic solution swelling degree of 500% by mass or less, preferably 350% by mass or less, and more preferably 300% by mass or less. When the electrolyte swelling degree of the shell is equal to or less than the above upper limit, the elution of the core into the electrolyte in the electrochemical element can be satisfactorily suppressed, and the heat generation suppressing performance of the electrochemical element can be enhanced. The lower limit of the degree of swelling of the electrolyte in the shell is not particularly limited. From the viewpoint of reducing the internal resistance of the resulting electrochemical device, it is preferable that the electrolyte swelling degree of the shell is 120% by mass or more.
　さらに、シェルを構成する少なくとも二種類のポリマーの電解液膨潤度がそれぞれ５００質量％以下であることが好ましく、３５０質量％以下であることがより好ましく、３００質量％以下であることがさらに好ましい。シェルを構成する少なくとも二種類のポリマーの電解液膨潤度がそれぞれ上記上限値以下であれば、電気化学素子内においてコアが電解液中に溶出することを良好に抑制し、電気化学素子の発熱抑制性能を高めることができる。また、シェルを構成する少なくとも二種類のポリマーの各電解液膨潤度は、１００質量％であってもよく、得られる電気化学素子の内部抵抗を低減する観点からは、１２０質量％以上であることが好ましい。
　なお、シェルを構成する少なくとも二種類のポリマーの電解液膨潤度は、実施例に記載の方法により測定することができる。 Further, the degree of swelling of the electrolyte solution of at least two kinds of polymers constituting the shell is preferably 500% by mass or less, more preferably 350% by mass or less, and even more preferably 300% by mass or less. If the degree of swelling of the electrolyte solution of at least two types of polymers constituting the shell is equal to or lower than the above upper limits, the elution of the core into the electrolyte solution in the electrochemical element can be satisfactorily suppressed, and the heat generation of the electrochemical element can be suppressed. It can improve performance. Further, the degree of swelling of each of the at least two types of polymers constituting the shell may be 100% by mass, and from the viewpoint of reducing the internal resistance of the resulting electrochemical device, it should be 120% by mass or more. is preferred.
The degree of swelling of at least two kinds of polymers forming the shell can be measured by the method described in Examples.
　さらに、シェルは、Ｎ－メチル－２－ピロリドンに対する膨潤度（以下、「ＮＭＰ膨潤度」と称することがある。）が、５００質量％以下であることが好ましく、３５０質量％以下であることがより好ましく、３００質量％以下であることがさらに好ましい。シェルのＮＭＰ膨潤度が上記上限値以下であれば、ＮＭＰを溶媒とする溶液を用いて本発明の電極を形成した場合において、電極製造工程においてコアがＮＭＰ中に溶出することを良好に抑制し、得られる電気化学素子の発熱抑制性能を高めることができる。シェルのＮＭＰ膨潤度の下限値は特に限定されず、例えば、１００質量％であり、まったく膨潤しなくてもよい。
　なお、シェルのＮＭＰ膨潤度は、後述する実施例に記載の方法により測定することができる。 Further, the shell preferably has a degree of swelling with respect to N-methyl-2-pyrrolidone (hereinafter sometimes referred to as "NMP swelling degree") of 500% by mass or less, and preferably 350% by mass or less. More preferably, it is 300% by mass or less. If the NMP swelling degree of the shell is equal to or less than the above upper limit, when the electrode of the present invention is formed using a solution containing NMP as a solvent, the elution of the core into NMP in the electrode manufacturing process can be suppressed satisfactorily. , the heat generation suppression performance of the resulting electrochemical device can be enhanced. The lower limit of the NMP swelling degree of the shell is not particularly limited, and is, for example, 100% by mass, and may not swell at all.
The degree of NMP swelling of the shell can be measured by the method described in Examples below.
　さらに、シェルを構成する少なくとも二種類のポリマーのＮＭＰ膨潤度がそれぞれ５００質量％以下であることが好ましく、３５０質量％以下であることがより好ましく、３００質量％以下であることがさらに好ましい。シェルを構成する少なくとも二種類のポリマーのＮＭＰ膨潤度がそれぞれ上記上限値以下であれば、ＮＭＰを溶媒とする二次電池の正極用スラリー組成物を調製する際に本発明のバインダー組成物を用いた場合において、スラリー組成物中においてコアがＮＭＰ中に溶出することを良好に抑制し、得られる電気化学素子の発熱抑制性能を高めることができる。また、シェルを構成する少なくとも二種類のポリマーの各ＮＭＰ膨潤度は特に限定されず、１００質量％であってもよい。
　なお、シェルを構成する少なくとも二種類のポリマーのＮＭＰ膨潤度は、実施例に記載の方法により測定することができる。 Furthermore, the degree of NMP swelling of at least two kinds of polymers constituting the shell is preferably 500% by mass or less, more preferably 350% by mass or less, and even more preferably 300% by mass or less. If the degree of NMP swelling of at least two kinds of polymers constituting the shell is equal to or less than the above upper limit, the binder composition of the present invention is used when preparing a positive electrode slurry composition for a secondary battery using NMP as a solvent. In this case, the elution of the core into the NMP in the slurry composition can be satisfactorily suppressed, and the heat generation suppression performance of the resulting electrochemical device can be enhanced. Moreover, the NMP swelling degree of each of the at least two types of polymers constituting the shell is not particularly limited, and may be 100% by mass.
The degree of NMP swelling of at least two types of polymers constituting the shell can be measured by the method described in Examples.
　シェルを構成する少なくとも二種類のポリマーは、ガラス転移温度差が１０℃以上２３０℃以下である少なくとも二種類のポリマーを含むことを必要とする。より具体的には、シェルは、ガラス転移温度が１０℃以上２３０℃以下の範囲で相異なる二種類のポリマーのみを含んでいてもよいし、これら二種類のポリマーに加えて、その他のポリマー（例えば、上記二種類のポリマーのうちの少なくとも一方とのガラス転移温度の差分が、１０℃未満であるか２３０℃超であるポリマー）を含有していてもよい。シェルが三種類以上のポリマーを含有する場合には、含有量（質量基準）の多い二種類のポリマーが、ガラス転移温度に関する上記相対関係を満たせばよい。 At least two types of polymers constituting the shell must contain at least two types of polymers having a glass transition temperature difference of 10°C or more and 230°C or less. More specifically, the shell may contain only two types of polymers with different glass transition temperatures in the range of 10° C. or higher and 230° C. or lower, or in addition to these two types of polymers, other polymers ( For example, a polymer having a glass transition temperature difference of less than 10° C. or more than 230° C. with at least one of the above two types of polymers may be included. When the shell contains three or more types of polymers, the two types of polymers having the higher content (by mass) should satisfy the above relative relationship regarding the glass transition temperature.
　上記二種類のガラス転移温度の温度差は、６０℃以上であることが好ましく、９０℃以上であることがより好ましく、１５０℃以下であることが好ましく、１２０℃以下であることがより好ましい。温度差が上記下限値以上であれば、電気化学素子の製造工程において加圧された場合であってもシェルが熱膨張性粒子の外に漏出することを抑制することができる。よって、特に電極合材層を高圧でプレスして高密度電極を得て、かかる高密度電極を備える電気化学素子の発熱抑制性能を一層高めることができる。温度差が上記上限値以下であれば、電気化学素子の高温保存特性を高めることができる。 The temperature difference between the two types of glass transition temperatures is preferably 60°C or higher, more preferably 90°C or higher, preferably 150°C or lower, and more preferably 120°C or lower. If the temperature difference is equal to or greater than the above lower limit, it is possible to prevent the shell from leaking out of the thermally expandable particles even when pressurized in the manufacturing process of the electrochemical device. Therefore, it is possible to obtain a high-density electrode by pressing the electrode mixture layer at a high pressure, and further improve the heat generation suppressing performance of the electrochemical device provided with such a high-density electrode. If the temperature difference is equal to or less than the above upper limit, the high-temperature storage characteristics of the electrochemical device can be enhanced.
　さらに、シェルに含まれるポリマーのガラス転移温度のうち、最高温度が、コアを形成するガス発生物質のガス化温度よりも高いことが好ましい。シェルに含まれるポリマーのガラス転移温度のうち最高温度が、ガス発生物質のガス化温度よりも高ければ、電気化学素子の製造時に加圧された際にガス発生物質が漏出することを良好に抑制することができ、得られる電気化学素子の発熱抑制性能を一層高めることができる。ここで、シェルに含まれるポリマーのガラス転移温度のうち最高温度とガス発生物質のガス化温度との差は、１０℃以上であることが好ましく、４５℃以上であることがより好ましく、６０℃以上であることがさらに好ましい。なお、かかる差の上限は特に限定されないが、例えば、２００℃でありうる。 Furthermore, it is preferable that the highest temperature among the glass transition temperatures of the polymer contained in the shell is higher than the gasification temperature of the gas generating substance forming the core. If the highest temperature among the glass transition temperatures of the polymer contained in the shell is higher than the gasification temperature of the gas-generating substance, the leakage of the gas-generating substance when pressurized during the production of the electrochemical device can be suppressed satisfactorily. It is possible to further improve the heat generation suppression performance of the resulting electrochemical device. Here, the difference between the highest glass transition temperature of the polymer contained in the shell and the gasification temperature of the gas generating substance is preferably 10°C or more, more preferably 45°C or more, and more preferably 60°C. It is more preferable that it is above. Although the upper limit of the difference is not particularly limited, it can be 200° C., for example.
　好ましくは、シェルを構成する少なくとも二種類のポリマーのうちの一方のガラス転移温度が６０℃以上であり、他方のガラス転移温度が６０℃未満である。そして、シェルが三種類以上のポリマーを含有する場合には、含有量（質量基準）の多い二種類のポリマーが、かかるポリマーのうちのいずれかであることが好ましい。 Preferably, one of the at least two types of polymers forming the shell has a glass transition temperature of 60°C or higher and the other has a glass transition temperature of less than 60°C. Then, when the shell contains three or more types of polymers, it is preferable that the two types of polymers having the highest content (based on mass) be either one of such polymers.
［ガラス転移温度が６０℃以上であるポリマー（ポリマー１）］
　ガラス転移温度が６０℃以上であるポリマー（以下、「ポリマー１」と称することがある。）のガラス転移温度は、８０℃以上であることが好ましく、１８０℃以下であることが好ましく、１５０℃以下であることがより好ましく、１３０℃以下であることがさらに好ましい。ポリマー１のガラス転移温度が上記下限値以上であれば、電気化学素子の製造工程において加圧された場合であっても、シェルを良好保護することができ、熱膨張性粒子の外にガス発生物質が流出することを良好に抑制することができる。したがって、特に電極合材層を高圧でプレスすることが可能になり、高密度電極効率的に製造することができるようになる。ガラス転移温度が上記上限値以下であれば、ポリマー１の重合時の重合安定性を高めることができ、電極の製造効率を高めることができる。 [Polymer having a glass transition temperature of 60° C. or higher (polymer 1)]
The glass transition temperature of the polymer having a glass transition temperature of 60° C. or higher (hereinafter sometimes referred to as “polymer 1”) is preferably 80° C. or higher, preferably 180° C. or lower, and 150° C. It is more preferably 130° C. or less, more preferably 130° C. or less. If the glass transition temperature of polymer 1 is at least the above lower limit, the shell can be well protected even when pressure is applied in the manufacturing process of the electrochemical device, and gas is generated outside the thermally expandable particles. Outflow of substances can be well suppressed. Therefore, it becomes possible to press the electrode mixture layer at a high pressure, and to efficiently manufacture a high-density electrode. If the glass transition temperature is equal to or lower than the above upper limit, the polymerization stability during polymerization of Polymer 1 can be enhanced, and the production efficiency of the electrode can be enhanced.
　さらに、ポリマー１は、溶解度パラメータ（Solubility Parameter；以下、ＳＰ値と称することがある。）が、２３．０ＭＰａ1/2以上であることが好ましく、２４．０ＭＰａ1/2以上であることがより好ましく、３０．０ＭＰａ1/2以下であることが好ましく、２９．５ＭＰａ1/2以下であることがより好ましい。より具体的には、ポリマー１のＳＰ値は、電気化学素子を製造する際に使用し得る、ＮＭＰ及び電解液のＳＰ値よりも高いことが好ましい。ポリマー１のＳＰ値がＮＭＰ及び電解液のＳＰ値とは離れた値となるようにすれば、ポリマー１がＮＭＰ及び電解液に対して膨潤及び溶出しにくくなり、この結果、熱膨張性粒子を含む電気化学素子が通常作動し、発熱時に効果を発揮できるようになる。 Furthermore, the solubility parameter (hereinafter sometimes referred to as SP value) of polymer 1 is preferably 23.0 MPa 1/2 or more, more preferably 24.0 MPa 1/2 or more. It is preferably 30.0 MPa 1/2 or less, more preferably 29.5 MPa 1/2 or less. More specifically, the SP value of Polymer 1 is preferably higher than the SP values of NMP and the electrolyte that can be used in manufacturing the electrochemical device. If the SP value of the polymer 1 is different from the SP values of the NMP and the electrolyte, the polymer 1 is less likely to swell and dissolve in the NMP and the electrolyte. The electrochemical element it contains operates normally and becomes effective when it generates heat.
　なお、溶解度パラメータは、下記の文献に定義及び計算方法が記載されているハンセン溶解度パラメータである。
　Ｃｈａｒｌｅｓ　Ｍ．　Ｈａｎｓｅｎ著、「Ｈａｎｓｅｎ　Ｓｏｌｕｂｉｌｉｔｙ　Ｐａｒａｍｅｔｅｒｓ：　Ａ　Ｕｓｅｒｓ　Ｈａｎｄｂｏｏｋ」、ＣＲＣプレス、２００７年。 The solubility parameter is the Hansen solubility parameter whose definition and calculation method are described in the following literature.
Charles M. Hansen, "Hansen Solubility Parameters: A Users Handbook," CRC Press, 2007.
　また、ハンセン溶解度パラメータの文献値が未知の物質については、コンピュータソフトウェア（Ｈａｎｓｅｎ　Ｓｏｌｕｂｉｌｉｔｙ　Ｐａｒａｍｅｔｅｒｓ　ｉｎ　Ｐｒａｃｔｉｃｅ（ＨＳＰｉＰ））を用いることによって、その化学構造から簡便にハンセン溶解度パラメータを推算することができる。 In addition, for substances for which the literature value of the Hansen solubility parameter is unknown, the Hansen solubility parameter can be easily estimated from the chemical structure by using computer software (Hansen Solubility Parameters in Practice (HSPiP)).
　ここで、ポリマー１の組成は、特に限定されない。ポリマー１としては、例えば、ニトリル基を有する単量体単位を含むポリマーを用いることが好ましい。本明細書においてポリマーが「単量体単位を含む」とは、「その単量体を用いて得たポリマー中に単量体由来の繰り返し単位が含まれている」ことを意味する。また、本発明において、ポリマー中の各種単量体単位の含有割合は、１Ｈ－ＮＭＲなどの核磁気共鳴（ＮＭＲ）法を用いて測定することができる。 Here, the composition of polymer 1 is not particularly limited. As the polymer 1, for example, it is preferable to use a polymer containing a monomer unit having a nitrile group. In the present specification, a polymer "containing a monomer unit" means that "a polymer obtained using the monomer contains a repeating unit derived from the monomer". In addition, in the present invention, the content ratio of various monomer units in the polymer can be measured using a nuclear magnetic resonance (NMR) method such as 1 H-NMR.
　ニトリル基を有する単量体単位としては、α，β－エチレン性不飽和ニトリル単量体単位等が挙げられる。α，β－エチレン性不飽和ニトリル単量体単位を形成する単量体としては、ニトリル基を有するα，β－エチレン性不飽和化合物であれば限定されず、アクリロニトリル；α－クロロアクリロニトリル、α－ブロモアクリロニトリルなどのα－ハロゲノアクリロニトリル；メタクリロニトリルなどのα－アルキルアクリロニトリル；などが挙げられ、アクリロニトリル及びメタクリロニトリルが好ましい。α，β－エチレン性不飽和ニトリル単量体として、これらの複数種を併用してもよい。 Examples of monomer units having a nitrile group include α,β-ethylenically unsaturated nitrile monomer units. The monomer forming the α,β-ethylenically unsaturated nitrile monomer unit is not limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and acrylonitrile; α-chloroacrylonitrile; -α-halogenoacrylonitrile such as bromoacrylonitrile; α-alkylacrylonitrile such as methacrylonitrile; and the like, with acrylonitrile and methacrylonitrile being preferred. As the α,β-ethylenically unsaturated nitrile monomer, a plurality of these may be used in combination.
　ポリマー１におけるニトリル基を有する単量体単位の含有割合は、ポリマー１に含まれる全繰り返し単位を１００質量％として、７０質量％以上が好ましく、８０質量％以上がより好ましく、８５質量％以上がさらに好ましく、９８質量％以下が好ましく、９７質量％以下がより好ましい。ニトリル基を有する単量体単位の含有割合が上記下限値以上であれば、ポリマー１の電解液膨潤度が高くなることを抑制することができる。また、ニトリル基を有する単量体単位の含有割合が上記上限値以下であれば、ポリマー１の重合安定性を高めることができる。 The content of the monomer unit having a nitrile group in Polymer 1 is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 85% by mass or more, based on 100% by mass of all repeating units contained in Polymer 1. More preferably, it is 98% by mass or less, and more preferably 97% by mass or less. If the content of the monomer unit having a nitrile group is at least the above lower limit, it is possible to suppress the degree of swelling of polymer 1 from increasing in the electrolyte solution. Moreover, if the content of the monomer unit having a nitrile group is equal to or less than the above upper limit, the polymerization stability of the polymer 1 can be enhanced.
　ニトリル基を有する単量体単位を含むポリマーは、ニトリル基を有する単量体単位を形成する単量体と共重合可能な単量体とのコポリマーであってもよい。前記共重合可能な単量体としては、アクリル酸、メタクリル酸、イタコン酸、フマル酸などの不飽和カルボン酸類；スチレン、クロロスチレン、ビニルトルエン、ｔ－ブチルスチレン、ビニル安息香酸、ビニル安息香酸メチル、ビニルナフタレン、クロロメチルスチレン、ヒドロキシメチルスチレン、α－メチルスチレン等の芳香族ビニル単量体；アクリルアミド、Ｎ－メチロールアクリルアミド、アクリルアミド－２－メチルプロパンスルホン酸などのアミド系単量体；エチレン、プロピレン等のオレフィン類；ブタジエン、イソプレン等のジエン系単量体；塩化ビニル、塩化ビニリデン等のハロゲン原子含有単量体；酢酸ビニル、プロピオン酸ビニル、酪酸ビニル、安息香酸ビニル等のビニルエステル類；メチルビニルエーテル、エチルビニルエーテル、ブチルビニルエーテル等のビニルエーテル類；メチルビニルケトン、エチルビニルケトン、ブチルビニルケトン、ヘキシルビニルケトン、イソプロペニルビニルケトン等のビニルケトン類；Ｎ－ビニルピロリドン、ビニルピリジン、ビニルイミダゾール等の複素環含有ビニル化合物；メチルアクリレート、エチルアクリレート、ｎ－プロピルアクリレート、イソプロピルアクリレート、ｎ－ブチルアクリレート及びｔ－ブチルアクリレートなどのブチルアクリレート、ペンチルアクリレート、ヘキシルアクリレート、シクロへキシルアクリレート、イソボリニルアクリレート、ヘプチルアクリレート、２－エチルヘキシルアクリレートなどのオクチルアクリレート、ノニルアクリレート、デシルアクリレート、ラウリルアクリレート、ｎ－テトラデシルアクリレート、ステアリルアクリレート等のアクリル酸アルキルエステル；並びにメチルメタクリレート、エチルメタクリレート、ｎ－プロピルメタクリレート、イソプロピルメタクリレート、ｎ－ブチルメタクリレート及びｔ－ブチルメタクリレートなどのブチルメタクリレート、ペンチルメタクリレート、ヘキシルメタクリレート、シクロへキシルメタクリレート、イソボルニルメタクリレート、ヘプチルメタクリレート、２－エチルヘキシルメタクリレートなどのオクチルメタクリレート、ノニルメタクリレート、デシルメタクリレート、ラウリルメタクリレート、ｎ－テトラデシルメタクリレート、ステアリルメタクリレート等のメタクリル酸アルキルエステルなどが挙げられる。前記共重合可能な単量体として、これらの複数種を併用してもよい。 The polymer containing a nitrile group-containing monomer unit may be a copolymer of a monomer forming a nitrile group-containing monomer unit and a copolymerizable monomer. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, and methyl vinylbenzoate. , vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene and other aromatic vinyl monomers; acrylamide, N-methylolacrylamide, acrylamido-2-methylpropanesulfonic acid and other amide monomers; ethylene, Olefins such as propylene; diene-based monomers such as butadiene and isoprene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; N-vinylpyrrolidone, vinylpyridine, vinylimidazole and the like Heterocycle-containing vinyl compounds; butyl acrylate such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate and t-butyl acrylate, pentyl acrylate, hexyl acrylate, cyclohexyl acrylate, isoborinyl acrylate, octyl acrylate such as heptyl acrylate, 2-ethylhexyl acrylate, acrylic acid alkyl esters such as nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate. butyl methacrylate such as n-butyl methacrylate and t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, heptyl methacrylate, octyl methacrylate such as 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, methacrylic acid alkyl ester such as stearyl methacrylate, and the like. A plurality of these types may be used in combination as the copolymerizable monomer.
　さらに、ポリマー１としてのニトリル基を有する単量体単位を含むポリマーは、架橋性単量体単位を有していてもよい。架橋性単量体単位を形成し得る架橋性単量体としては、例えば、当該単量体に２個以上の重合反応性基を有する多官能単量体を挙げることができる。多官能単量体としては、例えば、アリルメタクリレート、ジビニルベンゼン等のジビニル化合物；ジエチレングリコールジメタクリレート、エチレングリコールジメタクリレート、ジエチレングリコールジアクリレート、１，３－ブチレングリコールジアクリレート等のジ（メタ）アクリル酸エステル化合物；トリメチロールプロパントリメタクリレート、トリメチロールプロパントリアクリレート等のトリ（メタ）アクリル酸エステル化合物；などが挙げられる。中でも、エチレングリコールジメタクリレートが好ましい。なお、これらの架橋性単量体は、１種類を単独で用いてもよく、２種類以上を任意の比率で組み合わせて用いてもよい。なお、本明細書において（メタ）アクリルとはアクリル又はメタクリルを意味する。 Furthermore, the polymer containing a monomer unit having a nitrile group as the polymer 1 may have a crosslinkable monomer unit. Examples of crosslinkable monomers capable of forming crosslinkable monomer units include polyfunctional monomers having two or more polymerizable reactive groups. Examples of polyfunctional monomers include divinyl compounds such as allyl methacrylate and divinylbenzene; di(meth)acrylic esters such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butylene glycol diacrylate. compounds; tri(meth)acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; Among them, ethylene glycol dimethacrylate is preferred. In addition, these crosslinkable monomers may be used singly, or two or more of them may be used in combination at an arbitrary ratio. In this specification, (meth)acryl means acryl or methacryl.
　ポリマー１における架橋性単量体単位の含有割合は、特に限定されることなく、例えばポリマー１に含有される全繰り返し単位を１００質量％として、０．０５質量％以上であることが好ましく、０．１質量％以上であることがより好ましく、０．５質量％以上であることがさらに好ましく、３．０質量％以下であることが好ましく、２．０質量％以下であることがより好ましい。ポリマー１における架橋性単量体単位の含有割合が上記下限値以上であれば、シェルの強度を高めることによりコアが熱膨張性粒子の外に流出することを効果的に抑制することができる。ポリマー１における架橋性単量体単位の含有割合が上記上限値以下であれば、架橋密度が過度に高まり熱膨張を阻害することを抑制して、熱膨張性粒子が所望の温度において膨張することが可能となる。 The content of the crosslinkable monomer units in the polymer 1 is not particularly limited, for example, the total repeating units contained in the polymer 1 is 100% by mass, preferably 0.05% by mass or more, It is more preferably 0.5% by mass or more, more preferably 0.5% by mass or more, preferably 3.0% by mass or less, and more preferably 2.0% by mass or less. If the content of the crosslinkable monomer units in Polymer 1 is at least the above lower limit, it is possible to effectively suppress the outflow of the core from the thermally expandable particle by increasing the strength of the shell. If the content of the crosslinkable monomer units in the polymer 1 is equal to or less than the above upper limit value, the thermal expansion is prevented from being inhibited due to an excessive increase in the crosslink density, and the thermally expandable particles expand at a desired temperature. becomes possible.
［ガラス転移温度が６０℃未満であるポリマー（ポリマー２）］
　ガラス転移温度が６０℃未満であるポリマー（以下、「ポリマー２」と称することがある。）のガラス転移温度は、６０℃未満である必要があり、４０℃以下であることが好ましく、２５℃以下であることがより好ましく、－５０℃以上であることが好ましく、－４０℃以上であることがより好ましく、－３０℃以上であることがさらに好ましい。ポリマー２のガラス転移温度が上記上限値以下であれば、バインダー組成物の接着性を一層高めることができるとともに、電気化学素子の製造工程において加圧された場合であってもシェルが熱膨張性粒子の外に漏出することを抑制することができる。その結果、得られる電気化学素子の発熱抑制性能を一層高めることができる。よって、特に電極合材層を高圧でプレスして高密度電極を得て、かかる高密度電極を備える電気化学素子の発熱抑制性能を一層高めることができる。ポリマー２のガラス転移温度が上記下限値以上であれば、ポリマー２の重合安定性を高めることができ、電極の生産性を高めることができる。 [Polymer having a glass transition temperature of less than 60°C (polymer 2)]
The glass transition temperature of the polymer having a glass transition temperature of less than 60°C (hereinafter sometimes referred to as "polymer 2") must be less than 60°C, preferably 40°C or less, and 25°C. It is more preferably -50°C or higher, more preferably -40°C or higher, and even more preferably -30°C or higher. If the glass transition temperature of the polymer 2 is equal to or lower than the above upper limit, the adhesion of the binder composition can be further enhanced, and the shell is thermally expandable even when pressurized in the manufacturing process of the electrochemical device. Leakage to the outside of the particles can be suppressed. As a result, the heat generation suppression performance of the obtained electrochemical device can be further enhanced. Therefore, it is possible to obtain a high-density electrode by pressing the electrode mixture layer at a high pressure, and further improve the heat generation suppressing performance of the electrochemical device provided with such a high-density electrode. When the glass transition temperature of the polymer 2 is at least the above lower limit, the polymerization stability of the polymer 2 can be enhanced, and the productivity of the electrode can be enhanced.
　さらに、ポリマー２は、ＳＰ値が１６．０ＭＰａ1/2以上であることが好ましく、１８．０ＭＰａ1/2以上であることがより好ましく、２４．０ＭＰａ1/2以下であることが好ましく、２３．０ＭＰａ1/2以下であることがより好ましく、２１．０ＭＰａ1/2以下であることがさらに好ましい。より具体的には、ポリマー２のＳＰ値は、電気化学素子を製造する際に使用し得る、ＮＭＰ及び電解液のＳＰ値よりも低いことが好ましい。ポリマー２のＳＰ値がＮＭＰ及び電解液のＳＰ値とは離れた値となるようにすれば、ポリマー２がＮＭＰ及び電解液に対して膨潤及び溶出しにくくなり、この結果、熱膨張性粒子を含む電気化学素子が通常作動し、発熱時に効果を発揮できるようになる。 Furthermore, the SP value of polymer 2 is preferably 16.0 MPa 1/2 or more, more preferably 18.0 MPa 1/2 or more, and preferably 24.0 MPa 1/2 or less. 0 MPa 1/2 or less is more preferable, and 21.0 MPa 1/2 or less is even more preferable. More specifically, the SP value of Polymer 2 is preferably lower than the SP values of NMP and the electrolyte that can be used in manufacturing the electrochemical device. If the SP value of the polymer 2 is different from the SP values of the NMP and the electrolyte, the polymer 2 is less likely to swell and dissolve in the NMP and the electrolyte, and as a result, the thermally expandable particles are formed. The electrochemical element it contains operates normally and becomes effective when it generates heat.
　ここで、ポリマー２の組成は、特に限定されない。ポリマー２としては、例えば、芳香族ビニル単量体単位を含むポリマーが挙げられる。芳香族ビニル単量体単位としては、ポリマー１を調製する際に用いることができる単量体として列挙した芳香族ビニル単量体を用いて形成した単位を挙げることができる。中でも、スチレンが好ましい。ポリマー２における芳香族ビニル単量体単位の含有割合は、ポリマー２に含有される全繰り返し単位を１００質量％として、４０質量％以上であることが好ましく、５０質量％以上であることがより好ましく、９０質量％以下であることが好ましく、８０質量％以下であることがより好ましい。ポリマー２における芳香族ビニル単量体単位の含有割合が上記下限値以上であれば、ポリマー２の電解液膨潤度が過剰に高まることを抑制することができる。 Here, the composition of polymer 2 is not particularly limited. Polymer 2 includes, for example, polymers containing aromatic vinyl monomer units. Examples of aromatic vinyl monomer units include units formed using aromatic vinyl monomers listed as monomers that can be used in preparing polymer 1 . Among them, styrene is preferred. The content of aromatic vinyl monomer units in polymer 2 is preferably 40% by mass or more, more preferably 50% by mass or more, based on 100% by mass of all repeating units contained in polymer 2. , is preferably 90% by mass or less, more preferably 80% by mass or less. When the content ratio of the aromatic vinyl monomer units in the polymer 2 is at least the above lower limit, it is possible to suppress an excessive increase in the degree of swelling of the polymer 2 in the electrolytic solution.
　ポリマー２は、芳香族ビニル単量体単位に代えて、或いはこれに加えて、（メタ）アクリル酸エステル単量単位を含有していてもよい。かかる（メタ）アクリル酸エステル単量単位を形成するために用いることができる（メタ）アクリル酸エステル単量体としては、ポリマー１を調製する際に使用されうるものとして列挙した各種の単量体が挙げられる。中でも、２－エチルヘキシルアクリレートが好ましい。 Polymer 2 may contain a (meth)acrylic acid ester monomer unit instead of or in addition to the aromatic vinyl monomer unit. As the (meth)acrylic acid ester monomer that can be used to form such a (meth)acrylic acid ester monomer unit, various monomers listed as those that can be used in preparing the polymer 1 are mentioned. Among them, 2-ethylhexyl acrylate is preferred.
　さらに、ポリマー２は上記した芳香族ビニル単量体単位及び（メタ）アクリル酸エステル単量単位に加えて、又はこれらに代えて、その他の単量体単位を含有していてもよい、かかる単量体単位としては、ポリマー１を調製する際に用いることができる単量体として列挙した各種の単量体を用いて形成した単位を挙げることができる。 Further, Polymer 2 may contain other monomeric units in addition to or in place of the aromatic vinyl monomeric units and (meth)acrylic acid ester monomeric units described above. Examples of the monomer units include units formed using various monomers listed as monomers that can be used in preparing polymer 1 .
　中でも、ポリマー２が架橋性単量体単位を含有することが好ましい。ポリマー２における架橋性単量体単位を形成するために用いることができる架橋性単量体としては、ポリマー１と関連して上記に列挙した各種の化合物を挙げることができる。 Above all, it is preferable that the polymer 2 contains a crosslinkable monomer unit. Crosslinkable monomers that can be used to form the crosslinkable monomeric units in Polymer 2 include the various compounds listed above in connection with Polymer 1 .
　中でも、ポリマー２における架橋性単量体単位を形成するために用いる単量体としては、アリルメタクリレートが好ましい。そして、ポリマー２における架橋性単量体単位の含有割合は、特に限定されることなく、ポリマー２に含有される全繰り返し単位を１００質量％として、０．０５質量％以上であることが好ましく、０．１質量％以上であることがより好ましく、０．２質量％以上であることがさらに好ましく、３．０質量％以下であることが好ましく、２．０質量％以下であることがより好ましい。ポリマー２における架橋性単量体単位の含有割合が上記下限値以上であれば、シェルの強度を高めることによりコアが熱膨張性粒子の外に流出することを効果的に抑制することができる。ポリマー２における架橋性単量体単位の含有割合が上記上限値以下であれば、シェルの製造容易性を高めることができる。 Among them, allyl methacrylate is preferable as the monomer used to form the crosslinkable monomer units in the polymer 2. The content ratio of the crosslinkable monomer units in the polymer 2 is not particularly limited, and is preferably 0.05% by mass or more based on 100% by mass of the total repeating units contained in the polymer 2. It is more preferably 0.1% by mass or more, further preferably 0.2% by mass or more, preferably 3.0% by mass or less, and more preferably 2.0% by mass or less. . If the content of the crosslinkable monomer units in the polymer 2 is at least the above lower limit, it is possible to effectively prevent the core from flowing out of the thermally expandable particles by increasing the strength of the shell. If the content of the crosslinkable monomer units in the polymer 2 is equal to or less than the above upper limit, the easiness of shell production can be enhanced.
　さらに、ポリマー２は、かかる架橋性単量体とは別途に、炭素－炭素二重結合及びエポキシ基を含有する単量体（エポキシ基含有不飽和単量体）を含んでいてもよい。本明細書において、「架橋性単量体」には、エポキシ基含有不飽和単量体に相当する単量体は含まないものとする。 Furthermore, the polymer 2 may contain a monomer containing a carbon-carbon double bond and an epoxy group (epoxy group-containing unsaturated monomer) separately from such a crosslinkable monomer. As used herein, the term "crosslinkable monomer" does not include monomers corresponding to epoxy group-containing unsaturated monomers.
　ここで、エポキシ基含有不飽和単量体としては、例えば、ビニルグリシジルエーテル、アリルグリシジルエーテル、ブテニルグリシジルエーテル、ｏ－アリルフェニルグリシジルエーテルなどの不飽和グリシジルエーテル；ブタジエンモノエポキシド、クロロプレンモノエポキシド、４，５－エポキシ－２－ペンテン、３，４－エポキシ－１－ビニルシクロヘキセン、１，２－エポキシ－５，９－シクロドデカジエンなどのジエン又はポリエンのモノエポキシド；３，４－エポキシ－１－ブテン、１，２－エポキシ－５－ヘキセン、１，２－エポキシ－９－デセンなどのアルケニルエポキシド；グリシジルアクリレート、グリシジルメタクリレート、グリシジルクロトネート、グリシジル－４－ヘプテノエート、グリシジルソルベート、グリシジルリノレート、グリシジル－４－メチル－３－ペンテノエート、３－シクロヘキセンカルボン酸のグリシジルエステル、４－メチル－３－シクロヘキセンカルボン酸のグリシジルエステルなどの、不飽和カルボン酸のグリシジルエステル類；が挙げられる。なお、これらは、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 Examples of epoxy group-containing unsaturated monomers include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; butadiene monoepoxide, chloroprene monoepoxide, monoepoxides of dienes or polyenes such as 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene; 3,4-epoxy-1 - alkenyl epoxides such as butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linolate , glycidyl-4-methyl-3-pentenoate, glycidyl esters of 3-cyclohexenecarboxylic acid, glycidyl esters of 4-methyl-3-cyclohexenecarboxylic acid, and other unsaturated carboxylic acid esters; In addition, these may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
　ポリマー２におけるエポキシ基含有不飽和単量体の含有割合は、ポリマー２に含有される全繰り返し単位を１００質量％として、０．５質量％以上であることが好ましく、１．０質量％以上であることがより好ましく、１０．０質量％以下であることが好ましく、８．０質量％以下であることがより好ましい 。ポリマー２におけるエポキシ基含有不飽和単量体の含有割合がかかる範囲内であれば、電気化学素子の発熱抑制性能を一層高めることができる。 The content of the epoxy group-containing unsaturated monomer in the polymer 2 is preferably 0.5% by mass or more, preferably 1.0% by mass or more, based on 100% by mass of the total repeating units contained in the polymer 2. more preferably 10.0% by mass or less, and more preferably 8.0% by mass or less. If the content of the epoxy group-containing unsaturated monomer in the polymer 2 is within such a range, the heat generation suppression performance of the electrochemical device can be further enhanced.
［シェルの組成］
　シェルの組成は特に限定されない。例えば、シェルは、ポリマー１及びポリマー２に含まれうる単量体単位として上記に例示列挙した各種の単量体単位を含むことができる。中でも、シェルにおける芳香族ビニル単量体単位の含有割合が、２０質量％以上であることが好ましく、３０質量％以上であることがより好ましく、５０質量％以下であることが好ましく、４０質量％以下であることがより好ましい。また、シェルにおけるニトリル基含有単量体単位の含有割合が、２０質量％以上であることが好ましく、２５質量％以上であることがより好ましく、５０質量％以下であることが好ましく、４０質量％以下であることがより好ましい。さらに、シェルにおける（メタ）アクリル酸エステル単量単位の含有割合が、２０質量％以上であることが好ましく、３０質量％以上であることがより好ましく、５０質量％以下であることが好ましく、４０質量％以下であることがより好ましい。シェルにおける芳香族ビニル単量体単位の含有割合、ニトリル基含有単量体単位の含有割合、及び、（メタ）アクリル酸エステル単量体単位の含有割合がそれぞれ独立して上記範囲内であれば、シェルのガラス転移温度、電解液膨潤度、及びＮＭＰ膨潤度を適切に制御することが可能となる。さらに、シェルにおける架橋性単量体単位の含有割合が、シェル強度、電解液膨潤度、及びＮＭＰ膨潤度の観点から、０．１質量％以上であることが好ましく、０．２質量％以上であることがより好ましく、３．０質量％以下であることが好ましく、２．０質量％以下であることがより好ましい。そして、シェルにおけるエポキシ基含有不飽和単量体単位の含有割合が、電解液膨潤度及びＮＭＰ膨潤度の観点から、０．５質量％以上であることが好ましく、１．０質量％以上であることがより好ましく、１０．０質量％以下であることが好ましく、８．０質量％以下であることがより好ましい。これらの含有割合は、すべてシェルを構成する全ポリマーに含まれる繰り返し単位の合計を１００質量％としたときの割合である。 [Shell composition]
The composition of the shell is not particularly limited. For example, the shell can include the various monomeric units exemplified above as monomeric units that can be included in Polymer 1 and Polymer 2. Among them, the content of aromatic vinyl monomer units in the shell is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 50% by mass or less, and 40% by mass. The following are more preferable. In addition, the content of the nitrile group-containing monomer unit in the shell is preferably 20% by mass or more, more preferably 25% by mass or more, preferably 50% by mass or less, and 40% by mass. The following are more preferable. Furthermore, the content of (meth)acrylate monomer units in the shell is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 50% by mass or less. % or less is more preferable. If the content of the aromatic vinyl monomer unit, the content of the nitrile group-containing monomer unit, and the content of the (meth)acrylic acid ester monomer unit in the shell are each independently within the above ranges. , the glass transition temperature of the shell, the degree of swelling of the electrolyte, and the degree of swelling of NMP can be appropriately controlled. Furthermore, the content of the crosslinkable monomer unit in the shell is preferably 0.1% by mass or more, and 0.2% by mass or more, from the viewpoint of shell strength, electrolyte swelling degree, and NMP swelling degree. more preferably 3.0% by mass or less, more preferably 2.0% by mass or less. Then, the content of the epoxy group-containing unsaturated monomer unit in the shell is preferably 0.5% by mass or more, and 1.0% by mass or more, from the viewpoint of the degree of swelling of the electrolyte and the degree of swelling of NMP. is more preferably 10.0% by mass or less, and more preferably 8.0% by mass or less. These content ratios are ratios when the total of repeating units contained in all the polymers constituting the shell is taken as 100% by mass.
　熱膨張性粒子の構造は、ガス発生物質よりなるコアを、ポリマー１及びポリマー２を含むシェルが被覆してなる構造である限りにおいて特に限定されない。得られる電気化学素子の発熱抑制性能を効果的に高める観点からは、シェルがポリマー１よりなる層Ａ及びポリマー２よりなる層Ｂを備えることが好ましい。さらに、バインダー組成物の接着性を高める観点からは、ポリマー１よりなる層Ａがポリマー２よりなる層Ｂよりも内側（コア側）に存在することが好ましい。また、熱膨張性粒子は、その表面に＜導電材＞の項目にて後述する導電性炭素材料を有していてもよい。この場合、電気化学素子のＩＶ抵抗を一層低減することができる。 The structure of the thermally expandable particles is not particularly limited as long as it is a structure in which a core made of a gas-generating substance is covered with a shell containing polymer 1 and polymer 2. From the viewpoint of effectively improving the heat generation suppressing performance of the obtained electrochemical device, it is preferable that the shell comprises a layer A made of the polymer 1 and a layer B made of the polymer 2. Furthermore, from the viewpoint of enhancing the adhesiveness of the binder composition, it is preferable that the layer A made of the polymer 1 exists inside (the core side) the layer B made of the polymer 2. Moreover, the thermally expandable particles may have a conductive carbon material, which will be described later in the <Conductive material> section, on the surface thereof. In this case, the IV resistance of the electrochemical device can be further reduced.
　シェルにおけるポリマー１の合計面積率α（％）と、ポリマー２の合計面積率β（％）とが、α≦βの関係を満たすことが好ましい。シェルに含まれる各ポリマー１，２の合計面積率がα≦βの関係を満たしていれば、得られる電気化学素子の発熱抑制性能を一層高めることができる。ここで、かかる効果を一層高める観点から、ポリマー１の合計面積率α（％）と、ポリマー２の合計面積率β（％）との差分が、１％以上であることが好ましく、２０％以上であることがより好ましい。 It is preferable that the total area ratio α (%) of polymer 1 and the total area ratio β (%) of polymer 2 in the shell satisfy the relationship α≦β. If the total area ratio of the polymers 1 and 2 contained in the shell satisfies the relationship α≦β, the heat generation suppression performance of the resulting electrochemical device can be further enhanced. Here, from the viewpoint of further enhancing such effects, the difference between the total area ratio α (%) of polymer 1 and the total area ratio β (%) of polymer 2 is preferably 1% or more, and 20% or more. is more preferable.
　ポリマー１及びポリマー２が、それぞれ層Ａ及び層Ｂを形成してなるシェルにおいては、ポリマー１を含む層Ａの厚みａと、ポリマー２を含む層Ｂの厚みｂとが、ａ≦ｂの関係を満たすことが好ましい。シェルを構成する各層の厚みがａ≦ｂの関係を満たしていれば、得られる電気化学素子の発熱抑制性能を一層高めることができる。ガラス転移温度がポリマー２よりも高いポリマー１を含む層Ａの厚みが層Ｂの厚みより厚ければ、シェルがガス化した際に熱膨張性粒子が膨張しにくくなるため、ここで、かかる効果を一層高める観点から、層Ｂの厚みｂが、層Ａの厚みａの１．２倍以上であることが好ましく、１．４倍以上であることがより好ましい。 In the shell in which the layers A and B are formed by the polymer 1 and the polymer 2, respectively, the thickness a of the layer A containing the polymer 1 and the thickness b of the layer B containing the polymer 2 satisfy the relation a≦b. is preferably satisfied. If the thickness of each layer constituting the shell satisfies the relation of a≦b, the heat generation suppression performance of the resulting electrochemical device can be further enhanced. If the thickness of the layer A containing the polymer 1 whose glass transition temperature is higher than that of the polymer 2 is thicker than the thickness of the layer B, the thermally expandable particles are less likely to expand when the shell is gasified. from the viewpoint of further increasing the thickness b of the layer B is preferably 1.2 times or more the thickness a of the layer A, more preferably 1.4 times or more.
［熱膨張性粒子の製造方法］
　熱膨張性粒子は、例えば、ガス発生物質を分散させてなるコロイド水溶液中において上述した単量体を含む単量体組成物を重合することにより調製することができる。ここで、単量体組成物中の各単量体の割合は、通常、熱膨張性粒子中の各単量体単位の割合と同様とする。 [Method for producing thermally expandable particles]
Thermally expandable particles can be prepared, for example, by polymerizing a monomer composition containing the above monomers in a colloidal aqueous solution in which a gas generating substance is dispersed. Here, the proportion of each monomer in the monomer composition is generally the same as the proportion of each monomer unit in the thermally expandable particles.
　そして、重合様式は、特に限定されず、例えば、懸濁重合法、乳化重合凝集法、粉砕法などのいずれの方法も用いることができる。中でも、懸濁重合法及び乳化重合凝集法が好ましく、懸濁重合法がより好ましい。また、重合反応としては、ラジカル重合、リビングラジカル重合などいずれの反応も用いることができる。 The polymerization mode is not particularly limited, and any method such as a suspension polymerization method, an emulsion polymerization aggregation method, and a pulverization method can be used. Among them, the suspension polymerization method and the emulsion polymerization aggregation method are preferable, and the suspension polymerization method is more preferable. As the polymerization reaction, any reaction such as radical polymerization and living radical polymerization can be used.
　また、熱膨張性粒子を調製する際に用いる単量体組成物には、連鎖移動剤、重合調整剤、重合反応遅延剤、反応性流動化剤、充填剤、難燃剤、老化防止剤、着色料などのその他の配合剤を任意の配合量で配合することができる。 In addition, the monomer composition used for preparing the thermally expandable particles includes a chain transfer agent, a polymerization modifier, a polymerization reaction retarder, a reactive fluidizing agent, a filler, a flame retardant, an antioxidant, a coloring agent, and a coloring agent. Other compounding agents such as ingredients can be included in any amount.
　ここで、一例として、懸濁重合法による熱膨張性粒子の調製方法について説明する。 Here, as an example, a method for preparing thermally expandable particles by suspension polymerization will be described.
－懸濁重合法による熱膨張性粒子の調製
（１）単量体組成物の調製
　はじめに、シェルを構成するポリマー１及びポリマー２の組成にそれぞれ対応する組成の単量体組成物１及び単量体組成物２をそれぞれ準備する。この際、ポリマー１及びポリマー２の組成に合わせて、各種の単量体を配合し、さらに、必要に応じて添加されるその他の配合剤を混合する。 -Preparation of Thermally Expandable Particles by Suspension Polymerization (1) Preparation of Monomer Composition First, monomer composition 1 and monomers having compositions corresponding to the compositions of polymer 1 and polymer 2 constituting the shell, respectively A body composition 2 is prepared respectively. At this time, various monomers are blended in accordance with the compositions of Polymer 1 and Polymer 2, and other blending agents are added as necessary.
（２）液滴の形成
　次に、水中に分散安定剤としての金属水酸化物を分散させて、金属水酸化物を含むコロイド分散液を調製する。そして、かかるコロイド分散液中にコアを形成し得るガス発生物質及びシェルを形成し得る単量体組成物１及び単量体組成物２のうちの双方又はいずれか一方を添加する。さらに、重合開始剤を添加して混合液を得てから、液滴を形成する。ここで、液滴を形成する方法は特に限定されず、例えば、混合液を乳化分散機などの分散機を用いて剪断撹拌することにより形成することができる。また、重合開始剤としては、例えば、ｔ－ブチルパーオキシ－２－エチルヘキサノエート、アゾビスイソブチロニトリルなどの油溶性重合開始剤が挙げられる。さらに、分散安定剤としては、例えば、水酸化マグネシウムなどの金属水酸化物及びドデシルベンゼンスルホン酸ナトリウムなどを用いることができる。 (2) Formation of droplets Next, a metal hydroxide as a dispersion stabilizer is dispersed in water to prepare a colloidal dispersion containing the metal hydroxide. Then, a core-forming gas-generating substance and a shell-forming monomer composition 1 and/or monomer composition 2 are added to the colloidal dispersion. Further, a polymerization initiator is added to obtain a mixed liquid, and droplets are formed. Here, the method of forming the droplets is not particularly limited, and for example, the droplets can be formed by shearing and stirring the mixed liquid using a disperser such as an emulsifying disperser. Examples of polymerization initiators include oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate and azobisisobutyronitrile. Furthermore, as dispersion stabilizers, for example, metal hydroxides such as magnesium hydroxide, sodium dodecylbenzenesulfonate, and the like can be used.
（３）重合
　そして、液滴を形成後、当該形成された液滴を含む水を昇温して重合を開始する。そして、上記工程（２）で単量体組成物１及び単量体組成物２のうちのいずれか一方のみを液滴に配合していた場合には、重合転化率が十分に高まった段階で、工程（２）で添加しなかった方の単量体組成物１／２を添加して重合を継続する。その結果、水中に所定の構造を有する熱膨張性粒子が形成される。その際、重合の反応温度は、好ましくは５０℃以上９５℃以下である。また、各重合反応の継続時間は、好ましくは１時間以上１０時間以下であり、好ましくは８時間以下である。 (3) Polymerization After forming the droplets, the water containing the formed droplets is heated to initiate polymerization. Then, when only one of the monomer composition 1 and the monomer composition 2 is blended in the droplets in the above step (2), at the stage when the polymerization conversion rate is sufficiently increased , 1/2 of the monomer composition not added in step (2) is added to continue the polymerization. As a result, thermally expandable particles having a predetermined structure are formed in water. At that time, the reaction temperature for the polymerization is preferably 50°C or higher and 95°C or lower. The duration of each polymerization reaction is preferably 1 hour or more and 10 hours or less, preferably 8 hours or less.
（４）洗浄、濾過、脱水及び乾燥工程
　重合終了後、熱膨張性粒子を含む水を、常法に従い、洗浄、濾過、及び乾燥を行うことで、所定の構造を有する熱膨張性粒子を得ることができる。 (4) Washing, Filtration, Dehydration and Drying Steps After completion of the polymerization, the water containing the heat-expandable particles is washed, filtered and dried in accordance with conventional methods to obtain heat-expandable particles having a predetermined structure. be able to.
　なお、ガス発生物質と、単量体組成物及び２との量比は、上述した「熱膨張性粒子におけるコアの含有割合」の好適範囲を満たすように、適宜設定することができる。また、単量体組成物１及び２間の量比は、上述した、「シェルにおけるポリマー１及びポリマー２の面積比率」及び「シェルにおける層Ａ及び層Ｂの厚み比」の好適範囲を満たすように、適宜設定することができる。 The amount ratio between the gas-generating substance and the monomer composition and 2 can be appropriately set so as to satisfy the preferred range of the "core content ratio in the thermally expandable particles" described above. In addition, the amount ratio between the monomer compositions 1 and 2 is such that it satisfies the preferred ranges of the above-mentioned "area ratio of polymer 1 and polymer 2 in the shell" and "thickness ratio of layer A and layer B in the shell". can be set as appropriate.
＜＜結着材＞＞
　電極は、結着材をさらに含むことが好ましい。結着材としては、電極合材層中において結着能を発揮し得るポリマーであれば特に限定されず、任意のポリマーを用いることができる。そして結着材として用いられるポリマーの好適な例としては、脂肪族共役ジエン単量体単位を主として含むポリマー及びその水素化物（ジエン系ポリマー）、（メタ）アクリル酸エステル単量体単位を主として含む重合体（アクリル系ポリマー）、（メタ）アクリロニトリルを主として含むポリマー（ニトリル系ポリマー）、フッ素含有単量体単位を主として含むポリマー（フッ素系ポリマー）、ビニルアルコール単量体単位を主として含むポリマー（ビニルアルコール系ポリマー）が挙げられる。これらの中でも、アクリル系ポリマー、ニトリル系ポリマー、及びフッ素系ポリマーがより好ましい。
　なお、結着材は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。また、本明細書において、ポリマーがある単量体単位を「主として含む」とは、「重合体に含有される全繰り返し単位の量を１００質量％とした場合に、当該単量体単位の含有割合が５０質量％を超える」ことを意味する。 <<Binder>>
The electrode preferably further contains a binder. The binder is not particularly limited as long as it is a polymer capable of exhibiting binding ability in the electrode mixture layer, and any polymer can be used. Preferred examples of the polymer used as the binder include polymers mainly containing aliphatic conjugated diene monomer units, hydrides thereof (diene-based polymers), and (meth)acrylic acid ester monomer units. Polymer (acrylic polymer), polymer mainly containing (meth)acrylonitrile (nitrile polymer), polymer mainly containing fluorine-containing monomer unit (fluoropolymer), polymer mainly containing vinyl alcohol monomer unit (vinyl alcohol-based polymer). Among these, acrylic polymers, nitrile polymers, and fluoropolymers are more preferred.
The binder may be used singly or in combination of two or more at any ratio. Further, in the present specification, the phrase "mainly containing" a certain monomer unit in a polymer means "when the amount of all repeating units contained in the polymer is 100% by mass, the content of the monomer unit proportion exceeds 50% by mass".
　また結着剤は、上述ガス発生物質を非含有であるとともに、カルボン酸基、ヒドロキシル基、ニトリル基、アミノ基、エポキシ基、オキサゾリン基、スルホン酸基、エステル基及びアミド基からなる群から選択される少なくとも１種の官能基（以下、これらの官能基を纏めて「特定官能基」と称する場合がある。）を有するポリマーであることが好ましい。結着材としてのポリマーは、上述した特定官能基を１種有していてもよく、２種以上有していてもよい。
　これらの特定官能基を有するポリマーを結着材として用いれば、電気化学素子のＩＶ抵抗を一層低下させることができる。そして、電気化学素子のＩＶ抵抗を低下させる観点から、結着材としてのポリマーは、カルボン酸基、ヒドロキシル基及びニトリル基からなる群から選択される少なくとも１種を有することが好ましく、カルボン酸基とニトリル基の少なくとも一方を有することがより好ましく、カルボン酸基及びニトリル基の双方を有することが更に好ましい。 The binder does not contain the gas-generating substance described above and is selected from the group consisting of a carboxylic acid group, a hydroxyl group, a nitrile group, an amino group, an epoxy group, an oxazoline group, a sulfonic acid group, an ester group and an amide group. It is preferable that the polymer has at least one functional group (these functional groups may be collectively referred to as “specific functional group” hereinafter). The polymer as the binder may have one type of the specific functional groups described above, or may have two or more types.
By using a polymer having these specific functional groups as a binder, the IV resistance of the electrochemical device can be further reduced. From the viewpoint of reducing the IV resistance of the electrochemical device, the polymer as the binder preferably has at least one selected from the group consisting of carboxylic acid groups, hydroxyl groups and nitrile groups. and a nitrile group, and more preferably both a carboxylic acid group and a nitrile group.
　ここで、ポリマーに上述した特定官能基を導入する方法は特に限定されない。例えば、上述した特定官能基を有する単量体（特定官能基含有単量体）を用いてポリマーを調製し、特定官能基含有単量体単位を含むポリマーを得てもよいし、任意のポリマーを変性することにより、上述した特定官能基が導入されたポリマーを得てもよいが、前者が好ましい。すなわち、結着材としてのポリマーは、カルボン酸基含有単量体単位、ヒドロキシル基含有単量体単位、ニトリル基含有単量体単位、アミノ基含有単量体単位、エポキシ基含有単量体単位、オキサゾリン基含有単量体単位、スルホン酸基含有単量体単位、エステル基含有単量体単位及びアミド基含有単量体単位の少なくともいずれかを含むことが好ましく、カルボン酸基含有単量体単位、ヒドロキシル基含有単量体単位及びニトリル基含有単量体単位の少なくともいずれかを含むことがより好ましく、カルボン酸基含有単量体単位とニトリル基含有単量体単位の少なくとも一方を含むことが更に好ましく、カルボン酸基含有単量体単位とニトリル基含有単量体単位の双方を含むことが特に好ましい。 Here, the method of introducing the above-described specific functional group into the polymer is not particularly limited. For example, a polymer may be prepared using a monomer having a specific functional group (specific functional group-containing monomer) to obtain a polymer containing a specific functional group-containing monomer unit, or any polymer may be modified to obtain a polymer into which the above-described specific functional group has been introduced, but the former is preferred. That is, the polymer as the binder includes carboxylic acid group-containing monomer units, hydroxyl group-containing monomer units, nitrile group-containing monomer units, amino group-containing monomer units, and epoxy group-containing monomer units. , an oxazoline group-containing monomer unit, a sulfonic acid group-containing monomer unit, an ester group-containing monomer unit and an amide group-containing monomer unit. units, more preferably at least one of hydroxyl group-containing monomer units and nitrile group-containing monomer units, including at least one of carboxylic acid group-containing monomer units and nitrile group-containing monomer units is more preferred, and it is particularly preferred to contain both carboxylic acid group-containing monomer units and nitrile group-containing monomer units.
［カルボン酸基含有単量体単位］
　カルボン酸基含有単量体単位を形成し得るカルボン酸基含有単量体としては、モノカルボン酸及びその誘導体や、ジカルボン酸及びその酸無水物並びにそれらの誘導体などが挙げられる。
　モノカルボン酸としては、アクリル酸、メタクリル酸、クロトン酸などが挙げられる。
　モノカルボン酸誘導体としては、２－エチルアクリル酸、イソクロトン酸、α－アセトキシアクリル酸、β－ｔｒａｎｓ－アリールオキシアクリル酸、α－クロロ－β－Ｅ－メトキシアクリル酸などが挙げられる。
　ジカルボン酸としては、マレイン酸、フマル酸、イタコン酸などが挙げられる。
　ジカルボン酸誘導体としては、メチルマレイン酸、ジメチルマレイン酸、フェニルマレイン酸、クロロマレイン酸、ジクロロマレイン酸、フルオロマレイン酸や、マレイン酸ノニル、マレイン酸デシル、マレイン酸ドデシル、マレイン酸オクタデシル、マレイン酸フルオロアルキルなどのマレイン酸モノエステルが挙げられる。
　ジカルボン酸の酸無水物としては、無水マレイン酸、アクリル酸無水物、メチル無水マレイン酸、ジメチル無水マレイン酸などが挙げられる。
　また、カルボン酸基含有単量体としては、加水分解によりカルボン酸基を生成する酸無水物も使用できる。中でも、カルボン酸基含有単量体としては、アクリル酸及びメタクリル酸が好ましい。なお、カルボン酸基含有単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Carboxylic acid group-containing monomer unit]
Carboxylic acid group-containing monomers capable of forming carboxylic acid group-containing monomer units include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, their derivatives, and the like.
Monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid and the like.
Monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid and the like.
Dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, and the like.
Dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoro maleate. Examples include maleic acid monoesters such as alkyls.
Acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
As the carboxylic acid group-containing monomer, an acid anhydride that produces a carboxylic acid group by hydrolysis can also be used. Among them, acrylic acid and methacrylic acid are preferable as the carboxylic acid group-containing monomer. The carboxylic acid group-containing monomers may be used singly or in combination of two or more at any ratio.
［ヒドロキシル基含有単量体単位］
　ヒドロキシル基含有単量体単位を形成し得るヒドロキシル基含有単量体としては、（メタ）アリルアルコール、３－ブテン－１－オール、５－ヘキセン－１－オールなどのエチレン性不飽和アルコール；アクリル酸－２－ヒドロキシエチル、アクリル酸－２－ヒドロキシプロピル、メタクリル酸－２－ヒドロキシエチル、メタクリル酸－２－ヒドロキシプロピル、マレイン酸ジ－２－ヒドロキシエチル、マレイン酸ジ－４－ヒドロキシブチル、イタコン酸ジ－２－ヒドロキシプロピルなどのエチレン性不飽和カルボン酸のアルカノールエステル類；一般式：ＣＨ２＝ＣＲａ－ＣＯＯ－（ＣｑＨ２ｑＯ）ｐ－Ｈ（式中、ｐは２～９の整数、ｑは２～４の整数、Ｒａは水素原子又はメチル基を表す）で表されるポリアルキレングリコールと（メタ）アクリル酸とのエステル類；２－ヒドロキシエチル－２’－（メタ）アクリロイルオキシフタレート、２－ヒドロキシエチル－２’－（メタ）アクリロイルオキシサクシネートなどのジカルボン酸のジヒドロキシエステルのモノ（メタ）アクリル酸エステル類；２－ヒドロキシエチルビニルエーテル、２－ヒドロキシプロピルビニルエーテルなどのビニルエーテル類；（メタ）アリル－２－ヒドロキシエチルエーテル、（メタ）アリル－２－ヒドロキシプロピルエーテル、（メタ）アリル－３－ヒドロキシプロピルエーテル、（メタ）アリル－２－ヒドロキシブチルエーテル、（メタ）アリル－３－ヒドロキシブチルエーテル、（メタ）アリル－４－ヒドロキシブチルエーテル、（メタ）アリル－６－ヒドロキシヘキシルエーテルなどのアルキレングリコールのモノ（メタ）アリルエーテル類；ジエチレングリコールモノ（メタ）アリルエーテル、ジプロピレングリコールモノ（メタ）アリルエーテルなどのポリオキシアルキレングリコールモノ（メタ）アリルエーテル類；グリセリンモノ（メタ）アリルエーテル、（メタ）アリル－２－クロロ－３－ヒドロキシプロピルエーテル、（メタ）アリル－２－ヒドロキシ－３－クロロプロピルエーテルなどの、（ポリ）アルキレングリコールのハロゲン及びヒドロキシ置換体のモノ（メタ）アリルエーテル；オイゲノール、イソオイゲノールなどの多価フェノールのモノ（メタ）アリルエーテル及びそのハロゲン置換体；（メタ）アリル－２－ヒドロキシエチルチオエーテル、（メタ）アリル－２－ヒドロキシプロピルチオエーテルなどのアルキレングリコールの（メタ）アリルチオエーテル類；Ｎ－ヒドロキシメチルアクリルアミド（Ｎ－メチロールアクリルアミド）、Ｎ－ヒドロキシメチルメタクリルアミド、Ｎ－ヒドロキシエチルアクリルアミド、Ｎ－ヒドロキシエチルメタクリルアミドなどのヒドロキシル基を有するアミド類などが挙げられる。なお、ヒドロキシル基含有単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。
　なお、本明細書において「（メタ）アクリロイル」とは、アクリロイル及び／又はメタクリロイルを意味する。 [Hydroxyl Group-Containing Monomer Unit]
Examples of hydroxyl group-containing monomers capable of forming hydroxyl group-containing monomer units include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-buten-1-ol, and 5-hexene-1-ol; 2-hydroxyethyl acid, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, itacon alkanol esters of ethylenically unsaturated carboxylic acids such as di- 2 -hydroxypropyl acid; , q is an integer of 2 to 4, R a represents a hydrogen atom or a methyl group) esters of polyalkylene glycol and (meth)acrylic acid; 2-hydroxyethyl-2′-(meth ) Acryloyloxyphthalate, 2-hydroxyethyl-2′-(meth)acryloyloxysuccinate, and other dihydroxy esters of dicarboxylic acid mono (meth) acrylic acid esters; 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, etc. Vinyl ethers; (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl Alkylene glycol mono(meth)allyl ethers such as -3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, (meth)allyl-6-hydroxyhexyl ether; diethylene glycol mono(meth)allyl ether, dipropylene glycol Polyoxyalkylene glycol mono(meth)allyl ethers such as mono(meth)allyl ether; glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, (meth)allyl-2- Mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols such as hydroxy-3-chloropropyl ether; Mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol, and halogen-substituted products thereof ; (meth) allyl-2-hydroxyethyl thioether, (meth) allyl-2-hydroxy (meth)allyl thioethers of alkylene glycol such as propylthioether; hydroxyl groups such as N-hydroxymethylacrylamide (N-methylolacrylamide), N-hydroxymethylmethacrylamide, N-hydroxyethylacrylamide, N-hydroxyethylmethacrylamide and the like having amides. The hydroxyl group-containing monomers may be used singly or in combination of two or more at any ratio.
In addition, in this specification, "(meth)acryloyl" means acryloyl and/or methacryloyl.
［ニトリル基含有単量体単位］
　ニトリル基含有単量体単位を形成し得るニトリル基含有単量体としては、α，β－エチレン性不飽和ニトリル単量体が挙げられる。具体的には、ポリマー１を形成するために用いることができるニトリル基を有するα，β－エチレン性不飽和化合物として例示列挙したものを用いることができる。なお、これらの化合物は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Nitrile group-containing monomer unit]
Examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, those exemplified as α,β-ethylenically unsaturated compounds having a nitrile group that can be used to form polymer 1 can be used. In addition, these compounds may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
［アミノ基含有単量体単位］
　アミノ基含有単量体単位を形成し得るアミノ基含有単量体としては、ジメチルアミノエチル（メタ）アクリレート、ジエチルアミノエチル（メタ）アクリレート、アミノエチルビニルエーテル、ジメチルアミノエチルビニルエーテルなどが挙げられる。なお、アミノ基含有単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Amino group-containing monomer unit]
Examples of amino group-containing monomers capable of forming amino group-containing monomer units include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, aminoethyl vinyl ether, and dimethylaminoethyl vinyl ether. In addition, an amino group-containing monomer may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
［エポキシ基含有単量体単位］
　エポキシ基含有単量体単位を形成し得るエポキシ基含有単量体としては、ポリマー２における架橋性単量体単位を形成するために用いることができる化合物として列挙した各種の炭素－炭素二重結合及びエポキシ基を含有する単量体が挙げられる。なお、これらの単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Epoxy group-containing monomer unit]
Examples of epoxy group-containing monomers capable of forming epoxy group-containing monomer units include various carbon-carbon double bonds listed as compounds that can be used to form crosslinkable monomer units in Polymer 2. and epoxy group-containing monomers. In addition, these monomers may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
［オキサゾリン基含有単量体単位］
　オキサゾリン基含有単量体単位を形成し得るオキサゾリン基含有単量体としては、２－ビニル－２－オキサゾリン、２－ビニル－４－メチル－２－オキサゾリン、２－ビニル－５－メチル－２－オキサゾリン、２－イソプロペニル－２－オキサゾリン、２－イソプロペニル－４－メチル－２－オキサゾリン、２－イソプロペニル－５－メチル－２－オキサゾリン、２－イソプロペニル－５－エチル－２－オキサゾリンなどが挙げられる。なお、オキサゾリン基含有単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Oxazoline group-containing monomer unit]
Examples of oxazoline group-containing monomers capable of forming oxazoline group-containing monomer units include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2- oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc. are mentioned. The oxazoline group-containing monomers may be used singly or in combination of two or more at any ratio.
［スルホン酸基含有単量体単位］
　スルホン酸基含有単量体単位を形成し得るスルホン酸基含有単量体としては、ビニルスルホン酸、メチルビニルスルホン酸、（メタ）アリルスルホン酸、スチレンスルホン酸、（メタ）アクリル酸－２－スルホン酸エチル、２－アクリルアミド－２－メチルプロパンスルホン酸、３－アリロキシ－２－ヒドロキシプロパンスルホン酸などが挙げられる。なお、スルホン酸基含有単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Sulfonic Acid Group-Containing Monomer Unit]
Examples of sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, (meth)acrylic acid-2- ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid and the like. The sulfonic acid group-containing monomers may be used singly or in combination of two or more at any ratio.
［エステル基含有単量体単位］
　エステル基含有単量体単位を形成し得るエステル基含有単量体としては、例えば、（メタ）アクリル酸エステル単量体を用いることができる。（メタ）アクリル酸エステル単量体の例としては、ポリマー２における（メタ）アクリル酸エステル単量単位を形成するために用いることができるものとして列挙した各種の（メタ）アクリル酸エステル単量体が挙げられる。なお、これらの単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。
　また、本発明において、ある単量体が、エステル基以外の特定官能基を有する場合、その単量体は、エステル基含有単量体には含まれないものとする。 [Ester group-containing monomer unit]
As an ester group-containing monomer capable of forming an ester group-containing monomer unit, for example, a (meth)acrylic acid ester monomer can be used. Examples of (meth)acrylate monomers include the various (meth)acrylate monomers listed as usable to form the (meth)acrylate monomer units in Polymer 2. is mentioned. In addition, these monomers may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
Moreover, in the present invention, when a certain monomer has a specific functional group other than an ester group, the monomer is not included in the ester group-containing monomer.
［アミド基含有単量体単位］
　アミド基含有単量体単位を形成し得るアミド基含有単量体としては、アクリルアミド、メタクリルアミド、ビニルピロリドンなどが挙げられる。なお、アミド基含有単量体は、１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。 [Amido group-containing monomer unit]
Examples of amide group-containing monomers capable of forming amide group-containing monomer units include acrylamide, methacrylamide, and vinylpyrrolidone. The amide group-containing monomers may be used singly or in combination of two or more at any ratio.
　ここで、結着材としてのポリマーに含有される全繰り返し単位の量を１００質量％とした場合の、ポリマー中の特定官能基含有単量体単位の含有割合は、電気化学素子のＩＶ抵抗を一層低下させる観点から、１０質量％以上であることが好ましく、２０質量％以上であることがより好ましく、３０質量％以上であることが更に好ましい。なお、結着材としてのポリマー中の特定官能基含有単量体単位の含有割合の上限は特に限定されず、１００質量％以下であり、例えば９９質量％以下とすることができる。 Here, when the amount of all repeating units contained in the polymer as a binder is 100% by mass, the content ratio of the specific functional group-containing monomer unit in the polymer is the IV resistance of the electrochemical element. From the viewpoint of further reduction, the content is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. The upper limit of the content of the specific functional group-containing monomer unit in the polymer used as the binder is not particularly limited, and may be 100% by mass or less, for example, 99% by mass or less.
［その他の繰り返し単位］
　結着材としてのポリマーは、上述した特定官能基含有単量体単位以外の繰り返し単位（その他の繰り返し単位）を含んでいてもよい。このようなその他の繰り返し単位としては、特に限定されないが、ポリマーがジエン系ポリマーである場合は、脂肪族共役ジエン系単量体単位が挙げられる。
　脂肪族共役ジエン系単量体単位を形成し得る脂肪族共役ジエン系単量体としては、例えば、１，３－ブタジエン、イソプレン、２，３－ジメチル－１，３－ブタジエン、１，３－ペンタジエンが挙げられる。これらは１種を単独で用いてもよく、２種以上を任意の比率で組み合わせて用いてもよい。
　なお、本発明において、「脂肪族共役ジエン系単量体単位」には、脂肪族共役ジエン系単量体を用いて得たポリマーに含まれる単量体単位に、更に水素添加することで得られる構造単位（水素化物単位）も含まれるものとする。
　そして上述した脂肪族共役ジエン系単量体の中でも、１，３－ブタジエン、イソプレンが好ましい。換言すると、脂肪族共役ジエン系単量体単位としては、１，３－ブタジエン単位、イソプレン単位、１，３－ブタジエン水素化物単位、イソプレン水素化物単位が好ましく、１，３－ブタジエン水素化物単位、イソプレン水素化物単位がより好ましい。 [Other repeating units]
The polymer as the binder may contain repeating units (other repeating units) other than the specific functional group-containing monomer units described above. Such other repeating units are not particularly limited, but when the polymer is a diene-based polymer, aliphatic conjugated diene-based monomer units may be mentioned.
Aliphatic conjugated diene-based monomers capable of forming aliphatic conjugated diene-based monomer units include, for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3- Pentadiene may be mentioned. These may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.
In the present invention, the "aliphatic conjugated diene-based monomer unit" is obtained by further hydrogenating the monomer unit contained in the polymer obtained using the aliphatic conjugated diene-based monomer. Structural units (hydride units) are also included.
Among the aliphatic conjugated diene-based monomers mentioned above, 1,3-butadiene and isoprene are preferred. In other words, the aliphatic conjugated diene-based monomer unit is preferably a 1,3-butadiene unit, an isoprene unit, a 1,3-butadiene hydride unit, an isoprene hydride unit, a 1,3-butadiene hydride unit, More preferred are isoprene hydride units.
　ここで、結着材としてのポリマーが脂肪族共役ジエン系単量体単位を含む場合、ポリマーに含有される全繰り返し単位の量を１００質量％とした場合の、ポリマー中のジエン系単量体単位の含有割合は、電気化学素子のＩＶ抵抗を低下させる観点から、５０質量％超であることが好ましく、６０質量％以上であることがより好ましく、９０質量％以下であることが好ましく、８０質量％以下であることが好ましく、７０質量％以下であることが更に好ましい。 Here, when the polymer as the binder contains an aliphatic conjugated diene-based monomer unit, the amount of the diene-based monomer in the polymer when the amount of all repeating units contained in the polymer is 100% by mass From the viewpoint of reducing the IV resistance of the electrochemical device, the unit content is preferably more than 50% by mass, more preferably 60% by mass or more, and preferably 90% by mass or less. It is preferably 70% by mass or less, more preferably 70% by mass or less.
［結着材の調製方法］
　結着材の調製方法は特に限定されない。ポリマーである結着材は、例えば、１種又は２種以上の単量体を含む単量体組成物を水系溶媒中で重合し、任意に水素化や変性を行うことにより製造される。なお、単量体組成物中の各単量体の含有割合は、ポリマー中の所望の単量体単位の含有割合に準じて定めることができる。
　なお、重合様式は、特に制限なく、溶液重合法、懸濁重合法、塊状重合法、乳化重合法などのいずれの方法も用いることができる。また、重合反応としては、イオン重合、ラジカル重合、リビングラジカル重合、各種縮合重合、付加重合などいずれの反応も用いることができる。そして、重合に際しては、必要に応じて既知の乳化剤や重合開始剤を使用することができる。また、水素化及び変性は、既知の方法により行うことができる。 [Method for preparing binder]
A method for preparing the binder is not particularly limited. A binder that is a polymer is produced, for example, by polymerizing a monomer composition containing one or more monomers in an aqueous solvent and optionally hydrogenating or modifying the monomer composition. The content ratio of each monomer in the monomer composition can be determined according to the content ratio of desired monomer units in the polymer.
The polymerization mode is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. Moreover, as the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, living radical polymerization, various types of condensation polymerization, and addition polymerization can be used. In the polymerization, known emulsifiers and polymerization initiators can be used as necessary. Hydrogenation and modification can also be carried out by known methods.
＜＜電極合材層中における熱膨張性粒子及び結着材の合計含有量の比率＞＞
　なお、電極合材層中における、熱膨張性粒子及び結着材の合計含有量の比率は、電極合材層の全質量を１００質量％として、１質量％以上であることが好ましく、１．５質量％以上であることがより好ましく、また、１０質量％以下であることが好ましく、５質量％以下であることがより好ましい。 <<Ratio of Total Content of Thermally Expandable Particles and Binder in Electrode Mixture Layer>>
In addition, the ratio of the total content of the thermally expandable particles and the binder in the electrode mixture layer is preferably 1% by mass or more based on the total weight of the electrode mixture layer being 100% by mass. It is more preferably 5% by mass or more, preferably 10% by mass or less, and more preferably 5% by mass or less.
［その他の成分］
　電極合材層は、電気化学素子の電極合材層に配合されうる添加剤として公知であるその他の成分を含んでいてもよい。その他の成分としては、例えば、濡れ剤、レベリング剤、電解液分解抑制剤などが挙げられる。 [Other ingredients]
The electrode mixture layer may contain other components known as additives that can be blended in the electrode mixture layer of the electrochemical device. Other components include, for example, wetting agents, leveling agents, electrolytic solution decomposition inhibitors, and the like.
　＜＜電極活物質＞＞
　電極活物質は、電気化学素子の電極において電子の受け渡しをする物質である。なお、以下では、一例として電気化学素子がリチウムイオン二次電池である場合について説明するが、本発明は以下の一例に限定されるものではない。そして、リチウムイオン二次電池用の電極活物質としては、通常は、リチウムを吸蔵及び放出し得る物質を用いる。なお、電池容量が実用範囲となることから、電極活物質は、電極合材層の全質量を１００質量％として、９０質量％以上であることが好ましく、９２質量％以上であることがより好ましく、また、９９．５質量％以下であることが好ましく、９９質量％以下であることがより好ましい。 <<Electrode active material>>
An electrode active material is a material that transfers electrons in an electrode of an electrochemical device. In addition, although the case where the electrochemical device is a lithium ion secondary battery will be described below as an example, the present invention is not limited to the following example. As an electrode active material for a lithium ion secondary battery, a material capable of intercalating and deintercalating lithium is usually used. In addition, since the battery capacity is within the practical range, the electrode active material is preferably 90% by mass or more, more preferably 92% by mass or more, with the total mass of the electrode mixture layer being 100% by mass. , and preferably 99.5% by mass or less, more preferably 99% by mass or less.
［正極活物質］
　具体的には、リチウムイオン二次電池用の正極活物質としては、特に限定されることなく、リチウム含有コバルト酸化物（ＬｉＣｏＯ2）、マンガン酸リチウム（ＬｉＭｎ2Ｏ4）、リチウム含有ニッケル酸化物（ＬｉＮｉＯ2）、Ｃｏ－Ｎｉ－Ｍｎのリチウム含有複合酸化物（Ｌｉ（ＣｏＭｎＮｉ）Ｏ2）、Ｎｉ－Ｍｎ－Ａｌのリチウム含有複合酸化物、Ｎｉ－Ｃｏ－Ａｌのリチウム含有複合酸化物、オリビン型リン酸鉄リチウム（ＬｉＦｅＰＯ4）、オリビン型リン酸マンガンリチウム（ＬｉＭｎＰＯ4）、Ｌｉ2ＭｎＯ3－ＬｉＮｉＯ2系固溶体、Ｌｉ1+xＭｎ2-xＯ4（０＜Ｘ＜２）で表されるリチウム過剰のスピネル化合物、Ｌｉ［Ｎｉ0.17Ｌｉ０．２Ｃｏ0.07Ｍｎ0.56］Ｏ2、ＬｉＮｉ0.5Ｍｎ1.5Ｏ4等の既知の正極活物質が挙げられる。
　なお、正極活物質の配合量や粒子径は、特に限定されることなく、従来使用されている正極活物質と同様とすることができる。 [Positive electrode active material]
Specifically, the positive electrode active material for lithium ion secondary batteries is not particularly limited, and lithium-containing cobalt oxide (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), and lithium-containing nickel oxide. (LiNiO 2 ), Co—Ni—Mn lithium-containing composite oxide (Li(CoMnNi)O 2 ), Ni—Mn—Al lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, olivine type lithium iron phosphate (LiFePO 4 ), olivine type lithium manganese phosphate (LiMnPO 4 ), Li 2 MnO 3 —LiNiO 2 solid solution, Li 1+x Mn 2-x O 4 (0<X<2) known positive electrode active materials such as lithium-rich spinel compounds, Li[Ni 0.17 Li 0.2 Co 0.07 Mn 0.56 ]O 2 , LiNi 0.5 Mn 1.5 O 4 .
The amount and particle size of the positive electrode active material are not particularly limited, and may be the same as those of conventionally used positive electrode active materials.
［負極活物質］
　また、リチウムイオン二次電池用の負極活物質としては、例えば、炭素系負極活物質、金属系負極活物質、及びこれらを組み合わせた負極活物質などが挙げられる。 [Negative electrode active material]
Examples of negative electrode active materials for lithium ion secondary batteries include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials in which these are combined.
　ここで、炭素系負極活物質とは、リチウムを挿入（「ドープ」ともいう。）可能な、炭素を主骨格とする活物質をいい、炭素系負極活物質としては、例えば炭素質材料と黒鉛質材料とが挙げられる。 Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton and capable of inserting lithium (also referred to as “doping”). Examples of carbon-based negative electrode active materials include carbonaceous materials and graphite quality materials.
　そして、炭素質材料としては、例えば、易黒鉛性炭素や、ガラス状炭素に代表される非晶質構造に近い構造を持つ難黒鉛性炭素などが挙げられる。
　ここで、易黒鉛性炭素としては、例えば、石油又は石炭から得られるタールピッチを原料とした炭素材料が挙げられる。具体例を挙げると、コークス、メソカーボンマイクロビーズ（ＭＣＭＢ）、メソフェーズピッチ系炭素繊維、熱分解気相成長炭素繊維などが挙げられる。
　また、難黒鉛性炭素としては、例えば、フェノール樹脂焼成体、ポリアクリロニトリル系炭素繊維、擬等方性炭素、フルフリルアルコール樹脂焼成体（ＰＦＡ）などが挙げられる。 Examples of the carbonaceous material include graphitizable carbon and non-graphitizable carbon having a structure close to an amorphous structure represented by glassy carbon.
Here, graphitizable carbon includes, for example, carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolytic vapor growth carbon fibers.
Examples of non-graphitic carbon include phenolic resin sintered material, polyacrylonitrile-based carbon fiber, pseudoisotropic carbon, and furfuryl alcohol resin sintered material (PFA).
　更に、黒鉛質材料としては、例えば、天然黒鉛、人造黒鉛などが挙げられる。
　ここで、人造黒鉛としては、例えば、易黒鉛性炭素を含んだ炭素を主に２８００℃以上で熱処理した人造黒鉛、ＭＣＭＢを２０００℃以上で熱処理した黒鉛化ＭＣＭＢ、メソフェーズピッチ系炭素繊維を２０００℃以上で熱処理した黒鉛化メソフェーズピッチ系炭素繊維などが挙げられる。 Furthermore, examples of graphite materials include natural graphite and artificial graphite.
Here, as artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB obtained by heat-treating MCMB at 2000 ° C. or higher, mesophase pitch-based carbon fiber at 2000 ° C. Graphitized mesophase pitch-based carbon fibers heat-treated as described above may be used.
　また、金属系負極活物質とは、金属を含む活物質であり、通常は、リチウムの挿入が可能な元素を構造に含み、リチウムが挿入された場合の単位質量当たりの理論電気容量が５００ｍＡｈ／ｇ以上である活物質をいう。金属系活物質としては、例えば、リチウム金属、リチウム合金を形成し得る単体金属（例えば、Ａｇ、Ａｌ、Ｂａ、Ｂｉ、Ｃｕ、Ｇａ、Ｇｅ、Ｉｎ、Ｎｉ、Ｐ、Ｐｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｓｒ、Ｚｎ、Ｔｉなど）及びその合金、並びに、それらの酸化物、硫化物、窒化物、ケイ化物、炭化物、燐化物などが用いられる。これらの中でも、金属系負極活物質としては、ケイ素を含む活物質（シリコン系負極活物質）が好ましい。シリコン系負極活物質を用いることにより、リチウムイオン二次電池を高容量化することができるからである。 In addition, the metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of intercalating lithium in its structure, and the theoretical electric capacity per unit mass when lithium is intercalated is 500 mAh / g or more. As the metal-based active material, for example, lithium metal, elemental metals capable of forming a lithium alloy (eg, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn , Sr, Zn, Ti, etc.) and alloys thereof, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like. Among these, active materials containing silicon (silicon-based negative electrode active materials) are preferable as the metal-based negative electrode active materials. This is because the use of the silicon-based negative electrode active material can increase the capacity of the lithium ion secondary battery.
　シリコン系負極活物質としては、例えば、ケイ素（Ｓｉ）、ケイ素を含む合金、ＳｉＯ、ＳｉＯｘ、Ｓｉ含有材料を導電性カーボンで被覆又は複合化してなるＳｉ含有材料と導電性カーボンとの複合化物などが挙げられる。
　なお、負極活物質の配合量や粒径は、特に限定されることなく、従来使用されている負極活物質と同様とすることができる。 Silicon-based negative electrode active materials include, for example, silicon (Si), alloys containing silicon, SiO, SiO x , and composites of Si-containing materials and conductive carbon obtained by coating or combining Si-containing materials with conductive carbon. etc.
The amount and particle size of the negative electrode active material are not particularly limited, and can be the same as those of conventionally used negative electrode active materials.
＜導電材＞
　導電材は、電極活物質同士の電気的接触を確保するためのものである。そして、導電材としては、カーボンブラック（例えば、アセチレンブラック、ケッチェンブラック（登録商標）、ファーネスブラックなど）、単層又は多層のカーボンナノチューブ（多層カーボンナノチューブにはカップスタック型が含まれる）、カーボンナノホーン、気相成長炭素繊維、ポリマー繊維を焼成後に粉砕して得られるミルドカーボン繊維、単層又は多層グラフェン、ポリマー繊維からなる不織布を焼成して得られるカーボン不織布シートなどの導電性炭素材料；各種金属のファイバー又は箔などを用いることができる。
　これらは１種類を単独で、又は、２種類以上を組み合わせて用いることができる。また、上述した中でも、化学的安定性に優れるという点で、導電材としては導電性炭素材料が好ましい。 <Conductive material>
The conductive material is for ensuring electrical contact between the electrode active materials. As the conductive material, carbon black (for example, acetylene black, Ketjenblack (registered trademark), furnace black, etc.), single-walled or multi-walled carbon nanotubes (multi-walled carbon nanotubes include cup-stacked types), carbon Conductive carbon materials such as nanohorns, vapor-grown carbon fibers, milled carbon fibers obtained by pulverizing polymer fibers after firing, monolayer or multilayer graphene, and carbon nonwoven fabric sheets obtained by firing nonwoven fabrics made of polymer fibers; Metal fibers or foils can be used.
These can be used individually by 1 type or in combination of 2 or more types. Among the materials described above, a conductive carbon material is preferable as the conductive material in terms of excellent chemical stability.
　そして、電極合材層中の導電材の含有割合は、電極合材層の全質量を１００質量％として、０．１質量％以上であることが好ましく、３．０質量％以下であることが好ましく、２．５質量％以下であることがより好ましい。導電材の含有割合が上記下限値以上であれば、電極活物質同士の電極接触を十分に確保することができる。一方、導電材の含有割合が上記上限値以下であれば、電極合剤層の密度を良好に維持して、電気化学素子を十分に高容量化することができる。 The content of the conductive material in the electrode mixture layer is preferably 0.1% by mass or more and 3.0% by mass or less, with the total mass of the electrode mixture layer being 100% by mass. It is preferably 2.5% by mass or less, and more preferably 2.5% by mass or less. If the content of the conductive material is equal to or higher than the above lower limit, it is possible to sufficiently ensure electrode contact between the electrode active materials. On the other hand, if the content of the conductive material is equal to or less than the above upper limit, the density of the electrode mixture layer can be maintained satisfactorily, and the capacity of the electrochemical device can be sufficiently increased.
（電気化学素子電極の製造方法）
　本発明の電気化学素子用電極は、例えば、電極活物質及び熱膨張性粒子、並びに、任意の結着材、導電材、及びその他成分などを含むスラリー組成物を調製する工程（スラリー組成物調製工程）と、集電体上にスラリー組成物を塗布する工程（塗布工程）と、集電体上に塗布されたスラリー組成物を乾燥して集電体上に電極合材層を形成する工程（乾燥工程）とを経て製造される。 (Manufacturing method of electrochemical element electrode)
The electrode for an electrochemical device of the present invention can be produced by, for example, a step of preparing a slurry composition containing an electrode active material, thermally expandable particles, an optional binder, a conductive material, and other components (slurry composition preparation step), a step of applying the slurry composition on the current collector (application step), and a step of drying the slurry composition applied on the current collector to form an electrode mixture layer on the current collector. (Drying step).
＜スラリー組成物調製工程＞
　上記各成分を有機溶媒などの溶媒中に溶解又は分散させることにより調製することができる。混合順序としては、成分を一括投入してもよいし、段階的に投入し混合してもよい。具体的には、ボールミル、サンドミル、ビーズミル、顔料分散機、らい潰機、超音波分散機、ホモジナイザー、プラネタリーミキサー、フィルミックスなどの混合機を用いて上記各成分と溶媒とを混合することにより、スラリー組成物を調製することができる。 <Slurry composition preparation step>
It can be prepared by dissolving or dispersing each of the above components in a solvent such as an organic solvent. As for the order of mixing, the components may be added all at once, or may be added stepwise and mixed. Specifically, by mixing each of the above components and a solvent using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, film mix, etc. , a slurry composition can be prepared.
＜塗布工程＞
　上記スラリー組成物を集電体上に塗布する方法としては、特に限定されず公知の方法を用いることができる。具体的には、塗布方法としては、ドクターブレード法、ディップ法、リバースロール法、ダイレクトロール法、グラビア法、エクストルージョン法、ハケ塗り法などを用いることができる。この際、スラリー組成物を集電体の片面だけに塗布してもよいし、両面に塗布してもよい。塗布後乾燥前の集電体上のスラリー膜の厚みは、乾燥して得られる電極合材層の厚みに応じて適宜に設定し得る。 <Coating process>
The method for applying the slurry composition onto the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the electrode mixture layer obtained by drying.
＜乾燥工程＞
　集電体上のスラリー組成物を乾燥する方法としては、特に限定されず公知の方法を用いることができ、例えば温風、熱風、低湿風による乾燥法、真空乾燥法、赤外線や電子線などの照射による乾燥法が挙げられる。このように集電体上のスラリー組成物を乾燥することで、集電体上に電極合材層を形成し、集電体と電極合材層とを備える二次電池用電極を得ることができる。乾燥工程では、低温での乾燥についで、より高い温度での乾燥を実施する段階的な昇温を伴う乾燥を実施することが好ましい。具体的には、例えば１１０℃以下、好ましくは９５℃以下、より好ましくは９０℃以下の低温条件で乾燥したのちに、１４０℃以下、好ましくは１２０℃以下の温度条件で乾燥することが好ましい。 <Drying process>
The method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used. A drying method by irradiation can be mentioned. By drying the slurry composition on the current collector in this way, it is possible to form an electrode mixture layer on the current collector and obtain a secondary battery electrode comprising the current collector and the electrode mixture layer. can. In the drying step, it is preferable to carry out drying at a low temperature followed by drying at a higher temperature with a stepwise increase in temperature. Specifically, for example, it is preferable to dry under low temperature conditions of 110° C. or less, preferably 95° C. or less, more preferably 90° C. or less, and then dry under temperature conditions of 140° C. or less, preferably 120° C. or less.
　さらに、本発明の電気化学素子用電極を効率的に製造するための一つの手段として、上述した塗布工程及び乾燥工程において、下記工程を実施することが好ましい。すなわち、集電体上に、電極下層用スラリー組成物を塗布及び乾燥して、電極下層を形成する工程と、電極下層上に、電極上層用スラリー組成物を塗布及び乾燥して、電極上層を形成する工程を実施する。ここで、電極上層用スラリー組成物及び前記電極下層用スラリー組成物は、それぞれ、電極活物質及び熱膨張性粒子を含有してなり、電極上層用スラリー組成物の熱膨張性粒子濃度が前記電極下層用スラリー組成物の熱膨張性粒子濃度よりも高い。電極の製造工程においてこのような工程を実施することで、電極合材層の表面及び表面付近の領域における熱膨張性粒子の頻度が、電極合材層下部よりも高い、分布態様を効率的に創出することができる。電極合材層中において熱膨張性粒子が表面及びその近傍に偏在していれば、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を一層低減することができる。 Furthermore, as one means for efficiently producing the electrode for an electrochemical device of the present invention, it is preferable to carry out the following steps in the coating step and drying step described above. That is, a step of applying and drying the electrode lower layer slurry composition on the current collector to form the electrode lower layer, and applying and drying the electrode upper layer slurry composition on the electrode lower layer to form the electrode upper layer. A forming step is performed. Here, the electrode upper layer slurry composition and the electrode lower layer slurry composition each contain an electrode active material and thermally expandable particles, and the concentration of the thermally expandable particles in the electrode upper layer slurry composition is equal to that of the electrode. It is higher than the thermally expandable particle concentration of the lower layer slurry composition. By carrying out such a step in the manufacturing process of the electrode, the frequency of the thermally expandable particles in the surface and the region near the surface of the electrode mixture layer is higher than that in the lower part of the electrode mixture layer, and the distribution mode can be effectively adjusted. can be created. If the thermally expandable particles are unevenly distributed on the surface and in the vicinity thereof in the electrode mixture layer, the heat generation suppressing performance of the electrochemical element can be enhanced and the IV resistance can be further reduced.
　なお、乾燥工程の後、金型プレス又はロールプレスなどを用い、電極合材層に加圧処理を施してもよい。加圧処理により、電極合材層と集電体との密着性を向上させることができる。 After the drying process, the electrode mixture layer may be pressurized using a mold press or a roll press. The pressure treatment can improve the adhesion between the electrode mixture layer and the current collector.
（電気化学素子）
　上述した本発明の電気化学素子用電極を用いて電気化学素子を提供することができる。そして、本発明の電気化学素子用電極を備える電気化学素子は、発熱抑制性能に優れている。
　電気化学素子としては、本発明の電気化学素子用電極を正極として用いた二次電池が挙げられる。また、以下では、一例として二次電池がリチウムイオン二次電池である場合について説明するが、本発明は下記の一例に限定されるものではない。 (Electrochemical device)
An electrochemical device can be provided using the electrode for an electrochemical device of the present invention described above. An electrochemical device comprising the electrode for an electrochemical device of the present invention is excellent in heat generation suppression performance.
Examples of the electrochemical device include a secondary battery using the electrode for an electrochemical device of the present invention as a positive electrode. Moreover, although the case where the secondary battery is a lithium ion secondary battery will be described below as an example, the present invention is not limited to the following example.
＜電極＞
　ここで、電気化学素子に使用し得る、上述した電気化学素子用電極以外の電極としては、特に限定されることなく、電気化学素子の製造に用いられる既知の電極を用いることができる。具体的には、上述した電気化学素子用電極以外の電極としては、既知の製造方法を用いて集電体上に電極合材層を形成してなる電極を用いることができる。 <Electrode>
Here, the electrodes other than the electrochemical device electrodes described above that can be used in the electrochemical device are not particularly limited, and known electrodes that are used in the production of electrochemical devices can be used. Specifically, as the electrodes other than the electrodes for the electrochemical device described above, an electrode obtained by forming an electrode mixture layer on a current collector using a known manufacturing method can be used.
＜セパレータ＞
　セパレータとしては、特に限定されることなく、例えば特開２０１２－２０４３０３号公報に記載のものを用いることができる。これらの中でも、セパレータ全体の膜厚を薄くすることができ、これにより、二次電池内の電極活物質の比率を高くして体積あたりの容量を高くすることができるという点より、ポリオレフィン系（ポリエチレン、ポリプロピレン、ポリブテン、ポリ塩化ビニル）の樹脂からなる微多孔膜が好ましい。 <Separator>
The separator is not particularly limited, and for example, those described in JP-A-2012-204303 can be used. Among these, polyolefin-based ( A microporous membrane made of resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.
＜電解液＞
　電解液としては、通常、有機溶媒に支持電解質を溶解した有機電解液が用いられる。リチウムイオン二次電池の支持電解質としては、例えば、リチウム塩が用いられる。リチウム塩としては、例えば、ＬｉＰＦ6、ＬｉＡｓＦ6、ＬｉＢＦ4、ＬｉＳｂＦ6、ＬｉＡｌＣｌ4、ＬｉＣｌＯ4、ＣＦ3ＳＯ3Ｌｉ、Ｃ4Ｆ9ＳＯ3Ｌｉ、ＣＦ3ＣＯＯＬｉ、（ＣＦ3ＣＯ）2ＮＬｉ、（ＣＦ3ＳＯ2）2ＮＬｉ、（Ｃ2Ｆ5ＳＯ2）ＮＬｉなどが挙げられる。中でも、溶媒に溶けやすく高い解離度を示すので、ＬｉＰＦ6、ＬｉＣｌＯ4、ＣＦ3ＳＯ3Ｌｉが好ましく、ＬｉＰＦ6が特に好ましい。なお、電解質は１種類を単独で用いてもよく、２種類以上を任意の比率で組み合わせて用いてもよい。通常は、解離度の高い支持電解質を用いるほどリチウムイオン伝導度が高くなる傾向があるので、支持電解質の種類によりリチウムイオン伝導度を調節することができる。 <Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. Lithium salts, for example, are used as supporting electrolytes for lithium ion secondary batteries. Examples of lithium salts include LiPF6 , LiAsF6 , LiBF4 , LiSbF6 , LiAlCl4 , LiClO4, CF3SO3Li , C4F9SO3Li , CF3COOLi , ( CF3CO ) 2NLi . , (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 )NLi and the like. Among them, LiPF 6 , LiClO 4 and CF 3 SO 3 Li are preferable, and LiPF 6 is particularly preferable, because they are easily dissolved in a solvent and exhibit a high degree of dissociation. In addition, one electrolyte may be used alone, or two or more electrolytes may be used in combination at an arbitrary ratio. Generally, lithium ion conductivity tends to increase as a supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted depending on the type of supporting electrolyte.
　電解液に使用する有機溶媒としては、支持電解質を溶解できるものであれば特に限定されないが、例えば、ジメチルカーボネート（ＤＭＣ）、エチレンカーボネート（ＥＣ）、ジエチルカーボネート（ＤＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、メチルエチルカーボネート（ＥＭＣ）等のカーボネート類；プロピオン酸エチル、プロピオン酸プロピル、γ－ブチロラクトン、ギ酸メチル等のエステル類；１，２－ジメトキシエタン、テトラヒドロフラン等のエーテル類；スルホラン、ジメチルスルホキシド等の含硫黄化合物類；などが好適に用いられる。またこれらの溶媒の混合液を用いてもよい。中でも、誘電率が高く、安定な電位領域が広いのでカーボネート類を用いることが好ましく、電気化学的安定性を高める観点からはエステル類を用いることが好ましく、これれらの混合物を用いることがより好ましい。
　なお、電解液中の電解質の濃度は適宜調整することができ、例えば０．５～１５質量％することが好ましく、２～１３質量％とすることがより好ましく、５～１０質量％とすることが更に好ましい。また、電解液には、既知の添加剤、例えばビニレンカーボネート、フルオロエチレンカーボネート、エチルメチルスルホンなどを添加してもよい。 The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); esters such as ethyl propionate, propyl propionate, γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane , sulfur-containing compounds such as dimethylsulfoxide; and the like are preferably used. A mixture of these solvents may also be used. Among them, it is preferable to use carbonates because of their high dielectric constant and wide stable potential region, and it is preferable to use esters from the viewpoint of enhancing electrochemical stability, and more preferably to use mixtures thereof. preferable.
The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate, for example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. is more preferred. Further, known additives such as vinylene carbonate, fluoroethylene carbonate, ethyl methyl sulfone, etc. may be added to the electrolytic solution.
＜二次電池の製造方法＞
　電気化学素子としての二次電池は、例えば、正極と、負極とを、セパレータを介して重ね合わせ、これを必要に応じて電池形状に応じて巻く、折るなどして電池容器に入れ、電池容器に電解液を注入して封口することにより製造することができる。二次電池の内部の圧力上昇、過充放電等の発生を防止するために、必要に応じて、ヒューズ、ＰＴＣ素子等の過電流防止素子、エキスパンドメタル、リード板などを設けてもよい。二次電池の形状は、例えば、コイン型、ボタン型、シート型、円筒型、角形、扁平型など、何れであってもよい。 <Method for manufacturing secondary battery>
A secondary battery as an electrochemical element includes, for example, a positive electrode and a negative electrode, which are superimposed with a separator interposed therebetween, and, if necessary, are rolled or folded according to the shape of the battery, placed in a battery container, and placed in a battery container. It can be produced by injecting an electrolytic solution into the container and sealing it. In order to prevent an increase in internal pressure of the secondary battery and the occurrence of overcharge/discharge, etc., a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, rectangular, or flat.
　以下、本発明について実施例に基づき具体的に説明するが、本発明はこれら実施例に限定されるものではない。なお、以下の説明において、量を表す「％」及び「部」は、特に断らない限り、質量基準である。
　また、複数種類の単量体を共重合して製造されるポリマーにおいて、ある単量体を重合して形成される単量体単位の前記ポリマーにおける割合は、別に断らない限り、通常は、そのポリマーの重合に用いる全単量体に占める当該ある単量体の比率（仕込み比）と一致する。
　そして、実施例及び比較例において、各種測定及び評価は、それぞれ以下に従って実施した。 EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified.
In addition, in a polymer produced by copolymerizing a plurality of types of monomers, the proportion of monomer units formed by polymerizing a certain monomer in the polymer is usually the same unless otherwise specified. It corresponds to the ratio (feeding ratio) of the certain monomer to the total monomers used for polymer polymerization.
In Examples and Comparative Examples, various measurements and evaluations were carried out according to the following.
＜コアのガス化温度＞
　実施例、比較例でコアを形成するために用いるガス発生物質を準備し、熱抽出ＧＣ－ＭＳ（フロンティアラボ社製、ＰＹ－２０２０ＩＤ)にて、２５℃から３５０℃まで昇温速度１０℃／分で昇温させることでコア成分を検出した。かかる定性分析により検出したコア成分単体を準備し、熱重量分析装置（Ｒｉｇａｋｕ製、「ＴＧ８１１０」）を用いた熱重量分析において、窒素雰囲気下、２５℃から５００℃まで昇温速度１０℃／分で昇温させながら質量を測定し、測定される質量が測定開始時（２５℃）質量の９５％となった温度を、ガス発生物質のガス化温度とした。 <Gasification temperature of core>
A gas-generating substance used to form the core in Examples and Comparative Examples was prepared, and heated from 25°C to 350°C at a rate of 10°C/ The core component was detected by raising the temperature in minutes. A single core component detected by such qualitative analysis is prepared, and a thermogravimetric analysis using a thermogravimetric analyzer (manufactured by Rigaku, "TG8110") is performed under a nitrogen atmosphere at a temperature increase rate of 10 ° C./min from 25 ° C. to 500 ° C. The temperature at which the measured mass became 95% of the mass at the start of measurement (25° C.) was taken as the gasification temperature of the gas generating substance.
＜シェルの電解液膨潤度＞
　実施例、比較例で製造した熱膨張性粒子を、温度６０℃の電解液中に浸漬し、前後のシェルの厚みを光学顕微鏡（キーエンス製、ＶＨＸ－９００）にて観察した。観察は１０粒子をランダムで抽出して行い平均厚みを算出した。浸漬試験前後のシェル厚みから、下式によってシェルの膨張倍率を算出した。
　なお、電解液としては、エチレンカーボネート（ＥＣ）とプロピオン酸エチル（ＥＰ）とプロピオン酸プロピル（ＰＰ）とをＥＣ:ＥＰ:ＰＰ＝３：５：２（２０℃での容積比）で混合してなる混合溶媒にＬｉＰＦ６を１Ｍの濃度で溶解させた溶液を用いた。
　そして、浸漬試験前のシェル厚みをＡとし、浸漬試験後のシェル厚みをＢとして、下式に従って
　電解液膨潤度（％）＝Ｂ／Ａ×１００（％）
＜シェルのＮＭＰ膨潤度＞
　上記の電解液をＮＭＰにおきかえて試験を実施した。 <Swelling degree of electrolytic solution of shell>
The thermally expandable particles produced in Examples and Comparative Examples were immersed in an electrolytic solution at a temperature of 60° C., and the thickness of the shell before and after was observed with an optical microscope (Keyence VHX-900). Observation was performed by randomly extracting 10 particles, and the average thickness was calculated. From the shell thicknesses before and after the immersion test, the expansion ratio of the shell was calculated by the following formula.
As the electrolytic solution, ethylene carbonate (EC), ethyl propionate (EP), and propyl propionate (PP) were mixed at EC:EP:PP=3:5:2 (volume ratio at 20° C.). A solution obtained by dissolving LiPF 6 at a concentration of 1M in a mixed solvent consisting of the following was used.
Then, let A be the shell thickness before the immersion test and B be the shell thickness after the immersion test.
<NMP swelling degree of shell>
The test was carried out by replacing the electrolyte with NMP.
＜ポリマー１及びポリマー２の電解液膨潤度＞
　実施例及び比較例で調製した単量体組成物１及び単量体組成物２と同じ組成の単量体組成物を、それぞれ、熱膨張性粒子の調製時における重合条件（添加剤なども含む）と同じ条件で重合して、測定試料となるポリマーを含む水分散液をそれぞれ調製した。
　上記のように調製したポリマーを含む水分散液をポリテトラフルオロエチレン製シートにキャストし、乾燥してキャストフィルムを得た。このキャストフィルム４ｃｍ２を切り取って質量（浸漬前質量Ａ）を測定し、その後、温度６０℃の電解液中に浸漬した。浸漬したフィルムを７２時間後に引き上げ、タオルペーパーで拭きとってすぐに質量（浸漬後質量Ｂ）を測定した。ポリマーの電解液膨潤度を下記の式より算出し、以下の基準で評価する。なお、電解液としては、エチレンカーボネート（ＥＣ）とプロピオン酸エチル（ＥＰ）とプロピオン酸プロピル（ＰＰ）とをＥＣ:ＥＰ:ＰＰ＝３：５：２（２０℃での容積比）で混合してなる混合溶媒にＬｉＰＦ６を１Ｍの濃度で溶解させた溶液を用いた。
　膨潤度（％）＝Ｂ／Ａ×１００（％） <Electrolytic solution swelling degree of polymer 1 and polymer 2>
A monomer composition having the same composition as the monomer composition 1 and the monomer composition 2 prepared in Examples and Comparative Examples was prepared under the polymerization conditions (including additives etc.) at the time of preparing the thermally expandable particles. ) to prepare an aqueous dispersion containing a polymer to be a measurement sample.
An aqueous dispersion containing the polymer prepared as described above was cast onto a polytetrafluoroethylene sheet and dried to obtain a cast film. A 4 cm 2 piece of this cast film was cut to measure the mass (mass A before immersion), and then immersed in an electrolytic solution at a temperature of 60°C. After 72 hours, the immersed film was pulled up, wiped off with towel paper, and immediately weighed (mass B after immersion). The electrolyte solution swelling degree of the polymer is calculated from the following formula and evaluated according to the following criteria. As the electrolytic solution, ethylene carbonate (EC), ethyl propionate (EP), and propyl propionate (PP) were mixed at EC:EP:PP=3:5:2 (volume ratio at 20° C.). A solution obtained by dissolving LiPF 6 at a concentration of 1M in a mixed solvent consisting of the following was used.
Degree of swelling (%) = B/A x 100 (%)
＜ポリマー１及びポリマー２のＮＭＰ膨潤度＞
　電解液をＮＭＰに変更し、且つ、浸漬温度を４５℃に変更した以外は、上述した電解液膨潤度の測定方法と同様の操作を実施して、ポリマー１及びポリマー２のＮＭＰ膨潤度を測定した。 <NMP swelling degree of polymer 1 and polymer 2>
Except for changing the electrolytic solution to NMP and changing the immersion temperature to 45 ° C., the same operation as the method for measuring the degree of swelling of the electrolytic solution described above was performed to measure the NMP swelling degree of polymer 1 and polymer 2. bottom.
＜熱膨張性粒子の構造、層厚み、及びポリマー１及び２のガラス転移温度＞
　得られた粒子をエポキシ系包埋樹脂に包埋し、ミクロトームで切削することで断面出しを実施した。原子間力顕微鏡（ＡＦＭ）のコンタクトモードで得られたＡＦＭ像よりシェルが二層構成を有することを確認し、さらに各層の厚みを測定した。またｎａｎｏＴＡ（ナノサーマルアナリシス）により各層のガラス転移温度をそれぞれ３点測定し、その平均値を各層のガラス転移温度とした。さらに各層の厚み、及び各層のガラス転移温度を測定した。 <Structure of Thermally Expandable Particles, Layer Thickness, and Glass Transition Temperature of Polymers 1 and 2>
The resulting particles were embedded in an epoxy-based embedding resin and cut with a microtome to obtain a cross-section. From an AFM image obtained in contact mode with an atomic force microscope (AFM), it was confirmed that the shell had a two-layer structure, and the thickness of each layer was measured. The glass transition temperature of each layer was measured at three points by nanoTA (nano thermal analysis), and the average value was taken as the glass transition temperature of each layer. Furthermore, the thickness of each layer and the glass transition temperature of each layer were measured.
＜シェルにおけるポリマー１及びポリマー２の面積比率＞
　ＡＦＭのコンタクトモードで得られたＡＦＭ像において、測定対象とする熱膨張性粒子（ランダムに１０個を選定）の粒子径を測定した。粒子径は、対象とする熱膨張性粒子を包含する外接円の粒子径とした。かかる粒子径をa、シェルを構成する、コアに近い側の層の厚みをｂ、コアの直径をｃとし、測定対象とする各熱膨張性粒子につき５点測定した。その平均値をそれぞれＡ，Ｂ，Ｃとした。
　これらの値Ａ，Ｂ，Ｃを用いて、シェルにおけるポリマー１及びポリマー２の面積比率をそれぞれ算出した。
　ポリマー１の面積比率＝{（B＋C/2）２－（C/2）２}/｛（A/2）２－（C/2）２｝×100
　ポリマー２の面積比率＝{（A/2）２－（B＋C/2）２}/｛（A/2）２－（C/2）２｝×100
　上記を任意の１０粒子に対して同様に算出し、ポリマー１及びポリマー２の面積比率の平均値を得た。 <Area Ratio of Polymer 1 and Polymer 2 in Shell>
In the AFM image obtained in the contact mode of AFM, the particle diameter of the thermally expandable particles (10 particles were randomly selected) to be measured was measured. The particle size was the particle size of the circumscribed circle containing the target thermally expandable particles. The particle diameter was a, the thickness of the layer close to the core constituting the shell was b, and the diameter of the core was c. The average values were designated as A, B, and C, respectively.
Using these values A, B, and C, the area ratios of polymer 1 and polymer 2 in the shell were calculated.
Area ratio of polymer 1 = {(B + C/2) 2 - (C/2) 2 }/{(A/2) 2 - (C/2) 2 } x 100
Area ratio of polymer 2 = {(A/2) 2 - (B + C/2) 2 }/{(A/2) 2 - (C/2) 2 } x 100
The above calculation was performed for 10 arbitrary particles in the same manner to obtain the average value of the area ratios of polymer 1 and polymer 2.
＜ＳＰ値＞
　コンピュータソフトウェア（Ｈａｎｓｅｎ　Ｓｏｌｕｂｉｌｉｔｙ　Ｐａｒａｍｅｔｅｒｓ　ｉｎ　Ｐｒａｃｔｉｃｅ（ＨＳＰｉＰ））を用いて、ポリマー１及びポリマー２の溶解度パラメータを算出した。 <SP value>
Solubility parameters of polymer 1 and polymer 2 were calculated using computer software (Hansen Solubility Parameters in Practice (HSPiP)).
＜膨張開始温度＞
　調製した熱膨張性粒子を、加熱ステージ（リンカム社製ＦＴＩＲ６００）を用いて１０℃／分の昇温速度にて加熱した。加熱中の熱膨張性粒子の粒子径を、光学顕微鏡（キーエンス製、ＶＨＸ－９００）にて観察し、温度に対する直径変化を観察した。直径の変化が加熱前の１.３倍以上になる点を膨張開始温度と定義した。 <Expansion start temperature>
The prepared thermally expandable particles were heated at a heating rate of 10° C./min using a heating stage (FTIR600 manufactured by Linkcom). The particle diameter of the thermally expandable particles during heating was observed with an optical microscope (manufactured by Keyence, VHX-900) to observe changes in diameter with respect to temperature. The expansion start temperature was defined as the point at which the change in diameter was 1.3 times or more that before heating.
＜体積平均粒子径＞
　実施例、比較例で作製した正極にクロスセクションポリッシャ（日本電子製ＩＢ－０９０２０ＣＰ）をもちいて観察断面出し加工をおこなった。次に、ＦＥ－ＳＥＭ（日本電子株式会社製ＪＳＭ－７８００Ｆ）にて断面観察をおこなった。観察倍率は１０００倍、照射電圧は１０ｋＶ、照射電流は５．０×１０－８Ａの条件にておこなった。得られた断面像において、各熱膨張性粒子に対して外接円フィッティングをすることにより得られた直径を各熱膨張性粒子の直径と定義した。次に、得られた直径をもとに、球状を仮定した場合の熱膨張性粒子の体積を算出した。熱膨張性粒子に対して、各粒子の直径が小さい側から体積を累積していった場合の累計体積が５０％を超過する粒子の直径を観察断面における熱膨張性粒子の体積平均粒子径Ｄ５０とした。以上の観察を５視野にて実施し、得られた体積平均粒子径Ｄ５０の平均値を、熱膨張性粒子の体積平均粒子径Ｄ５０と定義した。正極活物質についても同様の測定及び計算を実施し、体積平均粒子径Ｄ５０を得た。 <Volume average particle size>
A cross-section polisher (IB-09020CP manufactured by JEOL Ltd.) was used to process the positive electrodes prepared in Examples and Comparative Examples for observation. Next, cross-sectional observation was performed with an FE-SEM (JSM-7800F manufactured by JEOL Ltd.). The observation magnification was 1000 times, the irradiation voltage was 10 kV, and the irradiation current was 5.0×10 −8 A. In the obtained cross-sectional image, the diameter of each thermally expandable particle was defined as the diameter obtained by fitting the circumscribed circle to each thermally expandable particle. Next, based on the obtained diameter, the volume of the thermally expandable particles assuming a spherical shape was calculated. For the thermally expandable particles, the volume average particle diameter D50 of the thermally expandable particles in the observed cross section is the diameter of the particles whose cumulative volume exceeds 50% when the volume is accumulated from the small diameter side of each particle. and The above observation was carried out in five fields of view, and the average value of the obtained volume average particle diameters D50 was defined as the volume average particle diameter D50 of the thermally expandable particles. Similar measurements and calculations were performed for the positive electrode active material, and the volume average particle diameter D50 was obtained.
＜熱膨張性粒子及び正極活物質の粒子径比＞
　上述のようにして測定した正極活物質の体積平均粒子径Ｄ５０、及び、熱膨張性粒子の体積平均粒子径Ｄ５０を用い、下記式に従って、粒子径比率（倍）を算出した。
　粒子径比率（倍）＝熱膨張性粒子の体積平均粒子径Ｄ５０／正極活物質の体積平均粒子径Ｄ５０ <Particle Size Ratio of Thermally Expandable Particles and Positive Electrode Active Material>
Using the volume average particle diameter D50 of the positive electrode active material and the volume average particle diameter D50 of the thermally expandable particles measured as described above, the particle diameter ratio (times) was calculated according to the following formula.
Particle diameter ratio (times) = Volume average particle diameter D50 of thermally expandable particles/Volume average particle diameter D50 of positive electrode active material
＜熱膨張性粒子の電極合材層表面露出径＞
　実施例、比較例で作製した正極の電極合材層表面にクロスセクションポリッシャ（日本電子製ＩＢ－０９０２０ＣＰ）を用いて、観察断面出し加工をおこなった。次に、ＦＥ－ＳＥＭ（日本電子株式会社製ＪＳＭ－７８００Ｆ）にて断面観察をおこなった。観察倍率は５００倍、照射電圧は１０ｋＶ、照射電流は５．０×１０－８Ａとして、断面観察し電極合材層の表面像を得た。得られた表面像において、各熱膨張性粒子に対して、外接円フィッティングし、その直径を熱膨張性粒子の露出径と定義した。そして、露出径が正極活物質の体積平均粒子径Ｄ５０の０．５倍以上５．０倍以下である熱膨張性粒子を、露出粒子Ａと定義した。 <Exposure diameter of the electrode mixture layer surface of the thermally expandable particles>
Using a cross-section polisher (IB-09020CP manufactured by JEOL Ltd.), the surface of the electrode mixture layer of the positive electrode produced in Examples and Comparative Examples was subjected to observation cross-section processing. Next, cross-sectional observation was performed with an FE-SEM (JSM-7800F manufactured by JEOL Ltd.). A surface image of the electrode mixture layer was obtained by cross-sectional observation at an observation magnification of 500 times, an irradiation voltage of 10 kV, and an irradiation current of 5.0×10 −8 A. In the obtained surface image, circumscribed circle fitting was applied to each thermally expandable particle, and the diameter thereof was defined as the exposed diameter of the thermally expandable particle. Thermally expandable particles having an exposed diameter of 0.5 to 5.0 times the volume average particle diameter D50 of the positive electrode active material were defined as exposed particles A.
＜熱膨張性粒子の電極合材層表面における露出面積率＞
　上記で得られた表面像において、露出粒子Ａの面積を合計し、下記式に従って、電極合材層表面における露出粒子Ａの占有面積率を算出した。
　露出粒子Ａの占有面積率(％)＝（露出粒子Ａの合計面積／表面像の面積）×１００
　上記の計算を５視野の像について行い、その平均値を露出粒子Ａの占有面積率とした。 <Exposed Area Ratio of Thermally Expandable Particles on Surface of Electrode Mixture Layer>
In the surface image obtained above, the areas of the exposed particles A were totaled, and the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer was calculated according to the following formula.
Occupied area ratio (%) of exposed particles A = (total area of exposed particles A/area of surface image) x 100
The above calculation was performed for the images of the five fields of view, and the average value was taken as the occupied area ratio of the exposed particles A.
＜露出粒子Ａの個数密度＞
　上記で得られた表面像において、露出粒子Ａの個数を算出し、下記式に従って、露出粒子Ａの個数密度を算出した。
　露出粒子Ａの個数密度(個/ｍｍ２)＝露出粒子Ａの個数(個)/表面像の面積(ｍｍ２)
　上記の計算を５視野の像について行い、その平均値を露出粒子Ａの個数密度とした。 <Number Density of Exposed Particles A>
In the surface image obtained above, the number of exposed particles A was calculated, and the number density of the exposed particles A was calculated according to the following formula.
Number density of exposed particles A (particles/mm 2 )=number of exposed particles A (particles)/surface image area (mm 2 )
The above calculation was performed for the images of the five fields of view, and the average value was taken as the number density of the exposed particles A.
＜ＩＶ抵抗測定＞
　実施例、比較例で製造した電気化学素子としてのリチウムイオン二次電池を、電解液注液後、温度２５℃で５時間静置した。次に、温度２５℃、０．２Ｃの定電流法にて、セル電圧３．６５Ｖまで充電し、その後、温度６０℃で１２時間エージング処理を行った。そして、温度２５℃、０．２Ｃの定電流法にて、セル電圧３．００Ｖまで放電した。その後、０．２Ｃの定電流法にて、ＣＣ－ＣＶ充電（上限セル電圧４．３５Ｖ）を行い、０．２Ｃの定電流法にて３．００ＶまでＣＣ放電した。この０．２Ｃにおける充放電を３回繰り返し実施した。その後、２５℃の環境下で、０．２Ｃで充電深度（ＳＯＣ；State of Charge）５０％となるように充電の操作を行い。６００秒静置した。６００秒目の電圧をＶ０とした。その後、０．５Ｃ（=Ｉ０．５）の定電流法にて１０秒間放電し、１０秒目の電圧をＶ0.5とした。その後、０．２Ｃの定電流法にて直前の放電電気量を充電した。次に、１．０Ｃ（=Ｉ１．０）の定電流法にて１０秒間放電し、１０秒目の電圧をＶ1.0とした。その後０．２Ｃの定電流法にて直前の放電電気量を充電した。次に１．５Ｃ（=Ｉ１．５）の定電流法にて１０秒間放電し、１０秒目の電圧をＶ1.5とした。(Ｉ0.5,Ｖ0.5),(Ｉ1.0,Ｖ1.0),(Ｉ1.5,Ｖ1.5)をＸＹグラフにプロットし,下記の式にて回帰直線の傾きｂを求め、ＤＣＲ（直流抵抗）とした。
Figure JPOXMLDOC01-appb-M000001
 　実施例１のＤＣＲを１００とした時の各実施例のＤＣＲ相対値を計算し、以下の基準により評価した。ＲＣＲ相対値が小さいほど、リチウムイオン二次電池のＩＶ抵抗が小さいことを示す。
　Ａ:ＤＣＲ相対値が１０３以下
　Ｂ:ＤＣＲ相対値が１０３超１０５以下
　Ｃ:ＤＣＲ相対値が１０５超１１０以下
　Ｄ:ＤＣＲ相対値が１１０超 <IV resistance measurement>
The lithium-ion secondary batteries as electrochemical devices produced in Examples and Comparative Examples were allowed to stand at a temperature of 25° C. for 5 hours after electrolyte injection. Next, the battery was charged to a cell voltage of 3.65 V by a constant current method at a temperature of 25° C. and 0.2 C, and then subjected to aging treatment at a temperature of 60° C. for 12 hours. Then, the battery was discharged to a cell voltage of 3.00 V by a constant current method at a temperature of 25° C. and 0.2 C. After that, CC-CV charging (upper limit cell voltage 4.35V) was performed by a 0.2C constant current method, and CC discharge was performed to 3.00V by a 0.2C constant current method. This charge/discharge at 0.2C was repeated three times. After that, in an environment of 25° C., charging was performed so that the state of charge (SOC) was 50% at 0.2C. It was left still for 600 seconds. The voltage at 600 seconds was taken as V0. After that, the battery was discharged for 10 seconds by a constant current method of 0.5 C (=I 0.5 ), and the voltage at 10 seconds was taken as V 0.5 . After that, the battery was charged by the constant current method at 0.2C to the amount of electricity just discharged. Next, discharge was performed for 10 seconds by a constant current method of 1.0 C (=I 1.0 ), and the voltage at 10 seconds was defined as V 1.0 . After that, the battery was charged by the constant current method at 0.2C to the amount of electricity just discharged. Next, discharge was performed for 10 seconds by a constant current method of 1.5 C (=I 1.5 ), and the voltage at 10 seconds was defined as V 1.5 . (I 0.5 , V 0.5 ), (I 1.0 , V 1.0 ), (I 1.5 , V 1.5 ) are plotted on an XY graph, and the slope b of the regression line is obtained by the following formula and used as DCR (direct current resistance) .
Figure JPOXMLDOC01-appb-M000001
 The DCR relative value of each example was calculated with the DCR of Example 1 set to 100, and evaluated according to the following criteria. A smaller RCR relative value indicates a smaller IV resistance of the lithium ion secondary battery.
A: DCR relative value is 103 or less B: DCR relative value is over 103 and 105 or less C: DCR relative value is over 105 and 110 or less D: DCR relative value is over 110
＜内部短絡時の発熱抑制（強制内部短絡試験）＞
　実施例、比較例で製造した電気化学素子としてのリチウムイオン二次電池を、電解液注液後、温度２５℃で５時間静置した。次に、温度２５℃、０．２Ｃの定電流法にて、セル電圧３．６５Ｖまで充電し、その後、温度６０℃で１２時間エージング処理を行った。そして、温度２５℃、０．２Ｃの定電流法にて、セル電圧３．００Ｖまで放電した。その後、０．２Ｃの定電流法にて、ＣＣ－ＣＶ充電（上限セル電圧４．３５Ｖ）を行い、０．２Ｃの定電流法にて３．００ＶまでＣＣ放電した。この０．２Ｃにおける充放電を３回繰り返し実施した。その後、２５℃の雰囲気下で、０．２Ｃの充電レートにて定電圧定電流（ＣＣ－ＣＶ）方式で４．３５Ｖ（カットオフ条件：０．０２Ｃ）まで充電した。その後、リチウムイオン二次電池の中央付近に、直径３ｍｍ、長さ１０ｃｍの鉄製の釘を５ｍ／分の速度で貫通させることにより、強制的に短絡させた。この強制的な短絡を、同一の操作でそれぞれ作製した５つのリチウムイオン二次電池（試験体）について行い、破裂も発火も生じない試験体の数により、下記の基準で評価した。破壊も発火も生じない試験体の数が多いほど、リチウムイオン二次電池が内部短絡時の発熱抑制性能に優れることを示す。
　Ａ：破裂も発火も生じない試験体の数が４個又は５個
　Ｂ：破裂も発火も生じない試験体の数が３個
　Ｃ：破裂も発火も生じない試験体の数が２個
　Ｄ：破裂も発火も生じない試験体の数が１個又は０個 <Heat suppression during internal short circuit (forced internal short circuit test)>
The lithium-ion secondary batteries as electrochemical devices produced in Examples and Comparative Examples were allowed to stand at a temperature of 25° C. for 5 hours after electrolyte injection. Next, it was charged to a cell voltage of 3.65 V by a constant current method at a temperature of 25° C. and 0.2 C, and then subjected to aging treatment at a temperature of 60° C. for 12 hours. Then, the battery was discharged to a cell voltage of 3.00 V by a constant current method at a temperature of 25° C. and 0.2 C. After that, CC-CV charging (upper limit cell voltage 4.35V) was performed by a 0.2C constant current method, and CC discharge was performed to 3.00V by a 0.2C constant current method. This charge/discharge at 0.2C was repeated three times. After that, in an atmosphere of 25° C., the battery was charged to 4.35 V (cutoff condition: 0.02 C) by a constant voltage constant current (CC-CV) method at a charging rate of 0.2 C. After that, an iron nail having a diameter of 3 mm and a length of 10 cm was penetrated near the center of the lithium ion secondary battery at a speed of 5 m/min to forcibly short-circuit the battery. This forced short-circuiting was performed on 5 lithium-ion secondary batteries (test specimens) each produced by the same operation, and the number of specimens in which neither explosion nor ignition occurred was evaluated according to the following criteria. The greater the number of test specimens in which neither destruction nor ignition occurred, the more excellent the heat generation suppression performance of the lithium ion secondary battery during internal short circuit.
A: 4 or 5 specimens that neither rupture nor ignite B: 3 specimens that neither rupture nor ignite C: 2 specimens that neither rupture nor ignite D: The number of test specimens that neither rupture nor fire occurs is 1 or 0
（実施例１）
＜熱膨張性粒子の調製＞
［単量体組成物１の調製］
　ニトリル基を有する単量体としてのアクリロニトリル６０.０部及びメタアクリロニトリル５．５部、芳香族ビニル単量体としてのスチレン０．４部、（メタ）アクリル酸エステルのブチルアクリレート０．６部、並びに、架橋性単量体としてのエチレングリコールジメタクリレート（共栄社化学株式会社「ライトエステルＥＧ」）０．２部を混合し、単量体組成物１を調製した。
［単量体組成物２の調製］
　芳香族ビニル単量体としてのスチレン３４．１部、（メタ）アクリル酸エステル単量体としての２－エチルヘキシルアクリレート２７．３部、エポキシ基含有不飽和単量体としてのグリシジルメタクリレート４．７部、架橋性単量体としてのアリルメタクリレート０．５部を混合し、単量体組成物２を調製した。
［コロイド分散液の調製］
　イオン交換水２００部に塩化マグネシウム８．０部を溶解してなる水溶液に、イオン交換水５０部に水酸化ナトリウム５．６部を溶解してなる水溶液を撹拌下で徐々に添加して、金属水酸化物としての水酸化マグネシウムを含むコロイド分散液を調製した。
［懸濁重合法］
　懸濁重合法により熱膨張性粒子を調製した。具体的には、上記水酸化マグネシウムを含むコロイド分散液に、ガス発生物質としてのイソペンタンを１５．０部、上述のようにして得た単量体組成物１を投入し、更に撹拌した後、重合開始剤としてのｔ－ブチルパーオキシ－２－エチルヘキサノエート（日油社製、「パーブチルＯ」）２．０部を添加して混合液を得た。得られた混合液を、インライン型乳化分散機（大平洋機工社製、「キャビトロン」）を用いて１５，０００ｒｐｍの回転数で１分間高剪断撹拌して、水酸化マグネシウムを含むコロイド分散液中に、ガス発生物質と単量体組成物１とを含む分散液を得た。なお、撹拌温度は５～１０℃で管理した。
　上記ガス発生物質と単量体組成物１とを含む、水酸化マグネシウムを含むコロイド分散液を、撹拌機を備えた５ＭＰａ耐圧容器に仕込み、７０℃にて８時間反応させた。反応時の圧力は０．５ＭＰａで行った。
　こうして得られた重合体を含んだ水分散体に、単量体組成物２及びイオン交換水１０部に溶解した重合開始剤である２，２’－アゾビス〔２－メチル－Ｎ－（２－ヒドロキシエチル）－プロピオンアミド〕（和光純薬社製、商品名：ＶＡ－０８６、水溶性開始剤）０．１部を添加し、９０℃で５時間反応させた。重合反応を継続した後、水冷して反応を停止し、ガス発生物質を含んでなるコアが、シェル（ポリマー１よりなる内側層及びポリマー２よりなる外側層を含む）により被覆されてなる、熱膨張性粒子を含む水分散体を得た。
　更に、上記熱膨張性粒子を含む水分散体を撹拌しながら、室温（２５℃）下で硫酸を滴下し、ｐＨが６．５以下となるまで酸洗浄を行った。次いで、濾過分離を行い、得られた固形分にイオン交換水５００部を加えて再スラリー化させて、水洗浄処理（洗浄、濾過及び脱水）を数回繰り返し行った。それから、濾過分離を行い、得られた固形分を乾燥器の容器内に入れ、３５℃で４８時間乾燥を行い、乾燥した熱膨張性粒子を得た。
　得られた熱膨張性粒子について、上記に従って属性を分析したところ、コアのガス化温度は２８℃であり、シェルは下記の属性を有していた。 (Example 1)
<Preparation of thermally expandable particles>
[Preparation of monomer composition 1]
60.0 parts of acrylonitrile and 5.5 parts of methacrylonitrile as monomers having a nitrile group, 0.4 parts of styrene as aromatic vinyl monomers, 0.6 parts of butyl acrylate of (meth)acrylic acid ester, In addition, 0.2 parts of ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd. "Light Ester EG") as a crosslinkable monomer was mixed to prepare a monomer composition 1.
[Preparation of monomer composition 2]
34.1 parts of styrene as the aromatic vinyl monomer, 27.3 parts of 2-ethylhexyl acrylate as the (meth)acrylic acid ester monomer, and 4.7 parts of glycidyl methacrylate as the epoxy group-containing unsaturated monomer and 0.5 part of allyl methacrylate as a crosslinkable monomer were mixed to prepare a monomer composition 2.
[Preparation of colloidal dispersion]
An aqueous solution prepared by dissolving 5.6 parts of sodium hydroxide in 50 parts of ion-exchanged water was gradually added to an aqueous solution prepared by dissolving 8.0 parts of magnesium chloride in 200 parts of ion-exchanged water while stirring to obtain a metal. A colloidal dispersion was prepared containing magnesium hydroxide as the hydroxide.
[Suspension polymerization method]
Thermally expandable particles were prepared by a suspension polymerization method. Specifically, 15.0 parts of isopentane as a gas-generating substance and monomer composition 1 obtained as described above are added to the colloidal dispersion containing magnesium hydroxide, and the mixture is further stirred. 2.0 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, "PERBUTYL O") was added as a polymerization initiator to obtain a mixture. The resulting mixed solution is stirred with high shear for 1 minute at a rotation speed of 15,000 rpm using an in-line emulsifying disperser (manufactured by Taihei Kiko Co., Ltd., "Cavitron") to obtain a colloidal dispersion containing magnesium hydroxide. Then, a dispersion containing the gas generating substance and the monomer composition 1 was obtained. The stirring temperature was controlled at 5-10°C.
A colloidal dispersion containing magnesium hydroxide containing the gas-generating substance and monomer composition 1 was placed in a 5 MPa pressure vessel equipped with a stirrer and reacted at 70° C. for 8 hours. The pressure during the reaction was 0.5 MPa.
2,2′-azobis[2-methyl-N-(2- Hydroxyethyl)-propionamide] (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) 0.1 part was added and reacted at 90°C for 5 hours. After continuing the polymerization reaction, the reaction is stopped by water cooling, and the core comprising the gas generating material is covered with a shell (including an inner layer made of polymer 1 and an outer layer made of polymer 2). An aqueous dispersion containing expandable particles was obtained.
Furthermore, while stirring the aqueous dispersion containing the thermally expandable particles, sulfuric acid was added dropwise at room temperature (25° C.), and acid washing was performed until the pH became 6.5 or less. Subsequently, filtration separation was performed, and 500 parts of ion-exchanged water was added to the obtained solid content to re-slurry, and the water washing treatment (washing, filtration and dehydration) was repeated several times. Then, filtration separation was performed, and the obtained solid content was placed in a container of a dryer and dried at 35° C. for 48 hours to obtain dried thermally expandable particles.
Attributes of the obtained thermally expandable particles were analyzed according to the above, and the gasification temperature of the core was 28° C., and the shell had the following attributes.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
＜結着材の調製＞
　撹拌機付きのオートクレーブに、イオン交換水２４０部、アルキルベンゼンスルホン酸ナトリウム２．５部、ニトリル基含有単量体としてのアクリロニトリル３０部、カルボン酸基含有単量体としてのメタクリル酸５部、連鎖移動剤としてのｔ－ドデシルメルカプタン０．２５部をこの順で入れ、ボトル内部を窒素置換した。その後、脂肪族共役ジエン単量体としての１，３－ブタジエン６５部を圧入し、過硫酸アンモニウム０．２５部を添加して、反応温度４０℃で重合反応させた。そして、アクリロニトリル、メタクリル酸及び１，３－ブタジエンを含む重合体を得た。重合転化率は８５％であった。
　得られた重合体に対して水を用いて全固形分濃度を１２％に調整した４００ｍＬ（全固形分４８ｇ）の溶液を、容積１Ｌの撹拌機付きオートクレーブに投入し、窒素ガスを１０分間流して溶液中の溶存酸素を除去した後、水素添加反応用触媒としての酢酸パラジウム７５ｍｇを、Ｐｄに対して４倍モルの硝酸を添加したイオン交換水１８０ｍＬに溶解して、添加した。系内を水素ガスで２回置換した後、３ＭＰａまで水素ガスで加圧した状態でオートクレーブの内容物を５０℃に加温し、６時間水素添加反応（第一段階の水素添加反応）を行った。
　次いで、オートクレーブを大気圧にまで戻し、更に水素添加反応用触媒として、酢酸パラジウム２５ｍｇを、Ｐｄに対して４倍モルの硝酸を添加した水６０ｍＬに溶解して、添加した。系内を水素ガスで２回置換した後、３ＭＰａまで水素ガスで加圧した状態でオートクレーブの内容物を５０℃に加温し、６時間水素添加反応（第二段階の水素添加反応）を行い、結着材の水分散液を得た。得られた結着材の水分散液に、ＮＭＰを適量添加して混合物を得た。その後、９０℃にて減圧蒸留を実施して混合物から水及び過剰なＮＭＰを除去し、結着材のＮＭＰ溶液（固形分濃度：８％）を得た。 <Preparation of binder>
An autoclave equipped with a stirrer was charged with 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 30 parts of acrylonitrile as a nitrile group-containing monomer, 5 parts of methacrylic acid as a carboxylic acid group-containing monomer, and chain transfer. 0.25 part of t-dodecyl mercaptan as an agent was added in this order, and the inside of the bottle was replaced with nitrogen. After that, 65 parts of 1,3-butadiene as an aliphatic conjugated diene monomer was injected under pressure, 0.25 part of ammonium persulfate was added, and polymerization was carried out at a reaction temperature of 40°C. A polymer containing acrylonitrile, methacrylic acid and 1,3-butadiene was obtained. The polymerization conversion rate was 85%.
A solution of 400 mL (total solid content of 48 g) adjusted to a total solid content concentration of 12% using water for the obtained polymer was put into an autoclave with a volume of 1 L and equipped with a stirrer, and nitrogen gas was flowed for 10 minutes. After removing oxygen dissolved in the solution with a rag, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 mL of ion-exchanged water containing nitric acid in an amount of 4 times the molar amount of Pd, and added. After replacing the inside of the system with hydrogen gas twice, the contents of the autoclave were heated to 50° C. while the pressure was increased to 3 MPa with hydrogen gas, and the hydrogenation reaction (first stage hydrogenation reaction) was performed for 6 hours. rice field.
Then, the autoclave was returned to the atmospheric pressure, and 25 mg of palladium acetate as a catalyst for hydrogenation reaction was dissolved in 60 mL of water containing nitric acid in an amount of 4 times the molar amount of Pd and added. After replacing the inside of the system with hydrogen gas twice, the contents of the autoclave were heated to 50° C. while the pressure was increased to 3 MPa with hydrogen gas, and the hydrogenation reaction (second stage hydrogenation reaction) was carried out for 6 hours. , to obtain an aqueous dispersion of the binder. An appropriate amount of NMP was added to the obtained aqueous dispersion of the binder to obtain a mixture. Thereafter, vacuum distillation was carried out at 90° C. to remove water and excess NMP from the mixture to obtain an NMP solution of the binder (solid concentration: 8%).
＜バインダー組成物の調製＞
　結着材を固形分換算で１０質量部と、熱膨張性粒子を９０質量部とを混合し、ＮＭＰを加えて、固形分濃度が３０％となるように調整することで、バインダー組成物を調製した。 <Preparation of binder composition>
10 parts by mass of a binder in terms of solid content and 90 parts by mass of thermally expandable particles are mixed, and NMP is added to adjust the solid content concentration to 30%, thereby forming a binder composition. prepared.
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウム（体積平均粒子径Ｄ５０：１２μｍ）を９４．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で１．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，５００ｍＰａ・ｓ、固形分濃度を６８％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９３．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で２．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６９％として、正極上層用スラリー組成物を得た。
＜正極の製造＞
　正極下層用スラリー組成物を、コンマコーターで、集電体である厚さ２０μｍのアルミニウム箔の上に、塗布量が１０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極下層用スラリー組成物を乾燥させ、集電体上に正極合材層（下層）が形成された正極原反（下層）を得た。次いで、上記で得られた正極上層用スラリー組成物を、コンマコーターで、正極原反（下層）上に、下層＋上層の塗布量が２０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極上層用スラリー組成物を乾燥させ、集電体上に正極合材層が形成された正極原反を得た。その後、作製した正極原反の正極合材層側を温度２５±３℃の環境下、荷重１４ｔ（トン）の条件でロールプレスし、正極合材層の密度が３．８０ｇ／ｃｍ３である正極を得た。得られた正極について、熱膨張性粒子の露出面積率、正極活物質の体積平均粒子径Ｄ５０、熱膨張性粒子の体積平均粒子径Ｄ５０を測定し、熱膨張性粒子及び正極活物質の粒子径比を算出した。結果を表２に示す。 <Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 94.5 parts of lithium cobalt oxide (volume average particle diameter D50: 12 μm) as a positive electrode active material, and carbon black (manufactured by Denka, trade name “Li-100”) as a conductive material equivalent to the solid content. 2.0 parts of PVDF (Solef 5130), 2.0 parts of PVDF (Solef 5130), and 1.5 parts of the binder composition equivalent to the solid content were added and mixed, and NMP was gradually added, and the temperature was 25 ± 3 ° C., rotating Stir and mix at several 60 rpm, Brookfield viscometer, 60 rpm (rotor M4) at 25 ± 3 ° C., viscosity of 3,500 mPa s, solid content concentration of 68%, slurry composition for positive electrode lower layer Obtained.
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 93.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 2.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,600 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
<Production of positive electrode>
The positive electrode lower layer slurry composition was applied onto a 20 μm-thick aluminum foil as a current collector with a comma coater in an amount of 10±0.5 mg/cm 2 . Furthermore, the positive electrode lower layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode raw sheet (lower layer) in which a positive electrode mixture layer (lower layer) was formed on the current collector. Next, the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20±0.5 mg/cm 2 . Furthermore, the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode blank in which a positive electrode mixture layer was formed on a current collector. After that, the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25±3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 . A positive electrode was obtained. For the obtained positive electrode, the exposed area ratio of the thermally expandable particles, the volume average particle size D50 of the positive electrode active material, and the volume average particle size D50 of the thermally expandable particles were measured, and the particle sizes of the thermally expandable particles and the positive electrode active material were determined. A ratio was calculated. Table 2 shows the results.
＜負極の製造＞
　撹拌機付き５ＭＰａ耐圧容器に、芳香族ビニル単量体としてのスチレン６３部、脂肪族共役ジエン系単量体としての１，３－ブタジエン３４部、カルボン酸基含有単量体としてのイタコン酸２部、ヒドロキシル基含有単量体としてのアクリル酸－２－ヒドロキシエチル１部、分子量調整剤としてのｔ－ドデシルメルカプタン０．３部、乳化剤としてのドデシルベンゼンスルホン酸ナトリウム５部、溶媒としてのイオン交換水１５０部、及び、重合開始剤としての過硫酸カリウム１部を投入し、十分に撹拌した後、温度５５℃に加温して重合を開始した。単量体消費量が９５．０％になった時点で冷却し、反応を停止した。こうして得られた重合体を含んだ水分散体に、５％水酸化ナトリウム水溶液を添加して、ｐＨを８に調整した。その後、加熱減圧蒸留によって未反応単量体の除去を行った。さらにその後、温度３０℃以下まで冷却することにより、負極用結着材を含む水分散液（負極用結着材組成物）を得た。
　プラネタリーミキサーに、負極活物質としての人造黒鉛（理論容量３６０ｍＡｈ／ｇ）を４８．７５部、天然黒鉛（理論容量３６０ｍＡｈ／ｇ）を４８．７５部、そして増粘剤としてのカルボキシメチルセルロースを固形分相当で１部投入した。さらに、イオン交換水にて固形分濃度が６０％となるように希釈し、その後、回転速度４５ｒｐｍで６０分間混練した。その後、上述で得られた負極用結着材組成物を固形分相当で１．５部投入し、回転速度４０ｒｐｍで４０分間混練した。そして、粘度が３０００±５００ｍＰａ・ｓ（Ｂ型粘度計、２５℃、６０ｒｐｍで測定）となるようにイオン交換水を加えることにより、負極用スラリー組成物を調製した。
　上記負極用スラリー組成物を、コンマコーターで、集電体である厚さ１５μｍの銅箔の表面に、塗付量が１１±０．５ｍｇ／ｃｍ２となるように塗布した。その後、負極用スラリー組成物が塗布された銅箔を、４００ｍｍ／分の速度で、温度８０℃のオーブン内を２分間、さらに温度１１０℃のオーブン内を２分間かけて搬送することにより、銅箔上の負極用スラリー組成物を乾燥させ、集電体上に負極合材層が形成された負極原反を得た。その後、作製した負極原反の負極合材層側を温度２５±３℃の環境下、線圧１１ｔ（トン）の条件でロールプレスし、負極合材層の密度が１．６０ｇ／ｃｍ３の負極を得た。 <Production of negative electrode>
In a 5 MPa pressure vessel equipped with a stirrer, 63 parts of styrene as an aromatic vinyl monomer, 34 parts of 1,3-butadiene as an aliphatic conjugated diene-based monomer, and 2 itaconic acid as a carboxylic acid group-containing monomer 1 part of 2-hydroxyethyl acrylate as a hydroxyl group-containing monomer, 0.3 parts of t-dodecylmercaptan as a molecular weight modifier, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, ion exchange as a solvent 150 parts of water and 1 part of potassium persulfate as a polymerization initiator were added, and after sufficiently stirring, the mixture was heated to 55° C. to initiate polymerization. When the monomer consumption reached 95.0%, the reaction was stopped by cooling. A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the polymer thus obtained to adjust the pH to 8. Thereafter, unreacted monomers were removed by heating under reduced pressure distillation. After that, by cooling to a temperature of 30° C. or lower, an aqueous dispersion containing the binder for negative electrode (binder composition for negative electrode) was obtained.
A planetary mixer was charged with 48.75 parts of artificial graphite (theoretical capacity of 360 mAh/g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity of 360 mAh/g), and carboxymethyl cellulose as a thickener. 1 part was put in for a minute. Further, the mixture was diluted with ion-exchanged water to a solid content concentration of 60%, and then kneaded for 60 minutes at a rotational speed of 45 rpm. Thereafter, 1.5 parts of the binder composition for a negative electrode obtained above was added in terms of solid content, and kneaded at a rotation speed of 40 rpm for 40 minutes. Then, ion-exchanged water was added so that the viscosity was 3000±500 mPa·s (measured with a Brookfield viscometer at 25° C. and 60 rpm) to prepare a negative electrode slurry composition.
The negative electrode slurry composition was applied to the surface of a copper foil having a thickness of 15 μm as a current collector with a comma coater in an amount of 11±0.5 mg/cm 2 . After that, the copper foil coated with the negative electrode slurry composition was conveyed at a speed of 400 mm/min in an oven at a temperature of 80° C. for 2 minutes and further in an oven at a temperature of 110° C. for 2 minutes. The negative electrode slurry composition on the foil was dried to obtain a negative electrode raw roll in which a negative electrode mixture layer was formed on a current collector. After that, the negative electrode mixture layer side of the negative electrode raw fabric thus prepared was roll-pressed under the conditions of a linear pressure of 11 t (tons) under an environment of a temperature of 25±3° C., and the density of the negative electrode mixture layer was 1.60 g/cm 3 . A negative electrode was obtained.
＜セパレータの準備＞
　単層のポリプロピレン製セパレータ（セルガード製、商品名「＃２５００」）を準備した。 <Preparation of separator>
A single-layer polypropylene separator (manufactured by Celgard, trade name “#2500”) was prepared.
＜リチウムイオン二次電池の作製＞
　上記の負極及び正極、セパレータを用いて、積層ラミネートセル（初期設計放電容量３Ａｈ相当）を作製し、アルミ包材内に配置して、６０℃、１０時間の条件にて真空乾燥をおこなった。その後、電解液としてエチレンカーボネート（ＥＣ）とプロピオン酸エチル（ＥＰ）とプロピオン酸プロピル（ＰＰ）とをＥＣ:ＥＰ:ＰＰ＝３：５：２（２０℃での容積比）で混合してなる混合溶媒にＬｉＰＦ６を１Ｍの濃度で溶解させ、添加剤：ビニレンカーボネート２体積％（溶媒比）で配合した溶液を充填した。さらに、アルミ包材の開口を密封するために、温度１５０℃のヒートシールをしてアルミ包材を閉口し、リチウムイオン二次電池を製造した。得られたリチウムイオン電池について、ＩＶ抵抗及び内部短絡時の発熱抑制性能を評価した。結果を表２に示す。 <Production of lithium ion secondary battery>
A laminated laminate cell (equivalent to an initial design discharge capacity of 3 Ah) was produced using the above negative electrode, positive electrode, and separator, placed in an aluminum packaging material, and vacuum-dried at 60° C. for 10 hours. After that, ethylene carbonate (EC), ethyl propionate (EP), and propyl propionate (PP) are mixed as an electrolytic solution at EC:EP:PP=3:5:2 (volume ratio at 20° C.). LiPF 6 was dissolved in a mixed solvent at a concentration of 1 M, and a solution containing 2 vol % (solvent ratio) of vinylene carbonate as an additive was filled. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing was performed at a temperature of 150° C. to close the aluminum packaging material, thereby manufacturing a lithium ion secondary battery. The obtained lithium ion battery was evaluated for IV resistance and heat generation suppression performance during an internal short circuit. Table 2 shows the results.
（実施例２）
　正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。
＜正極合材層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９４．０部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で２．０部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を２,２００ｍＰａ・ｓ、固形分濃度を６６％として、正極用スラリー組成物を得た。
＜正極の製造＞
　上記正極用スラリー組成物を、コンマコーターで、集電体である厚さ２０μｍのアルミニウム箔の上に、塗布量が２０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度１１０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極用スラリー組成物を乾燥させ（乾燥条件）、集電体上に正極合材層が形成された正極原反を得た。その後、作製した正極原反の正極合材層側を温度２５±３℃の環境下、荷重１４ｔ（トン）の条件でロールプレスし、正極合材層の密度が３．８０ｇ／ｃｍ３である正極を得た。得られた正極について、実施例１と同様にして各種評価及び測定を実施した。結果を表２に示す。 (Example 2)
The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
<Preparation of slurry composition for positive electrode mixture layer>
In a planetary mixer, 94.0 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 2.0 parts of the binder composition equivalent to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode slurry composition was obtained at 25±3° C., a viscosity of 2,200 mPa·s, and a solid content concentration of 66% using a Brookfield viscometer at 60 rpm (rotor M4).
<Production of positive electrode>
The positive electrode slurry composition was applied onto a 20 μm thick aluminum foil as a current collector with a comma coater so that the coating amount was 20±0.5 mg/cm 2 . Furthermore, the positive electrode slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 110° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m / min. (dry conditions), a positive electrode raw roll having a positive electrode mixture layer formed on a current collector was obtained. After that, the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25±3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 . A positive electrode was obtained. Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
（実施例３）
　正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９３．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で２．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６９％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９４．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で１．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，４００ｍＰａ・ｓ、固形分濃度を６８％として、正極上層用スラリー組成物を得た。
＜正極の製造＞
　上記で得た正極下層用スラリー組成物を、コンマコーターで、集電体である厚さ２０μｍのアルミニウム箔の上に、塗布量が１０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極下層用スラリー組成物を乾燥させ、集電体上に正極合材層（下層）が形成された正極原反（下層）を得た。次いで、上記で得た正極上層用スラリー組成物を、コンマコーターで、正極原反（下層）上に、下層＋上層の塗布量が２０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極上層用スラリー組成物を乾燥させ、集電体上に正極合材層が形成された正極原反を得た。その後、作製した正極原反の正極合材層側を温度２５±３℃の環境下、荷重１４ｔ（トン）の条件でロールプレスし、正極合材層の密度が３．８０ｇ／ｃｍ３である正極を得た。得られた正極について、実施例１と同様にして各種評価及び測定を実施した。結果を表２に示す。 (Example 3)
The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 93.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 2.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode lower layer slurry composition was obtained at 25±3° C., a viscosity of 3,600 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 94.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 1.5 parts of the binder composition equivalent to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,400 mPa·s, and a solid content concentration of 68% using a Brookfield viscometer at 60 rpm (rotor M4).
<Production of positive electrode>
The positive electrode lower layer slurry composition obtained above was applied onto a 20 μm thick aluminum foil as a current collector with a comma coater so that the coating amount was 10±0.5 mg/cm 2 . Furthermore, the positive electrode lower layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode raw sheet (lower layer) in which a positive electrode mixture layer (lower layer) was formed on the current collector. Next, the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20±0.5 mg/cm 2 . Furthermore, the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode blank in which a positive electrode mixture layer was formed on a current collector. After that, the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25±3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 . A positive electrode was obtained. Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
（実施例４）
　正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９５．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で０．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６８％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９２．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で３．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，４００ｍＰａ・ｓ、固形分濃度を６９％として、正極上層用スラリー組成物を得た。
＜正極の製造＞
　上記で得た正極下層用スラリー組成物を、コンマコーターで、集電体である厚さ２０μｍのアルミニウム箔の上に、塗布量が１０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極用下層用スラリー組成物を乾燥させ、集電体上に正極合材層（下層）が形成された正極原反（下層）を得た。次いで、上記で得た正極上層用スラリー組成物を、コンマコーターで、正極原反（下層）上に、下層＋上層の塗布量が２０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極上層用スラリー組成物を乾燥させ、集電体上に正極合材層が形成された正極原反を得た。その後、作製した正極原反の正極合材層側を温度２５±３℃の環境下、荷重１４ｔ（トン）の条件でロールプレスし、正極合材層の密度が３．８０ｇ／ｃｍ３である正極を得た。得られた正極について、実施例１と同様にして各種評価及び測定を実施した。結果を表２に示す。 (Example 4)
The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 95.5 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 0.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode lower layer slurry composition was obtained at 25±3° C., a viscosity of 3,600 mPa·s, and a solid content concentration of 68% using a Brookfield viscometer at 60 rpm (rotor M4).
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 92.5 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 3.5 parts of the binder composition equivalent to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,400 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
<Production of positive electrode>
The positive electrode lower layer slurry composition obtained above was applied onto a 20 μm thick aluminum foil as a current collector with a comma coater so that the coating amount was 10±0.5 mg/cm 2 . Further, at a speed of 0.5 m/min, the positive electrode lower layer slurry composition on the aluminum foil was transported in an oven at a temperature of 90°C for 2 minutes and further in an oven at a temperature of 120°C for 2 minutes. It was dried to obtain a positive electrode raw fabric (lower layer) in which a positive electrode mixture layer (lower layer) was formed on the current collector. Next, the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20±0.5 mg/cm 2 . Furthermore, the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode blank in which a positive electrode mixture layer was formed on a current collector. After that, the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25±3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 . A positive electrode was obtained. Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
（実施例５）
　正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９５．８部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で０．２部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，８００ｍＰａ・ｓ、固形分濃度を６７％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９２．２部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で３．８部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，５００ｍＰａ・ｓ、固形分濃度を６９％として、正極上層用スラリー組成物を得た。
＜正極の製造＞
　上記で得た正極下層用スラリー組成物を、コンマコーターで、集電体である厚さ２０μｍのアルミニウム箔の上に、塗布量が１０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極用下層用スラリー組成物を乾燥させ、集電体上に正極合材層（下層）が形成された正極原反（下層）を得た。次いで、上記で得た正極上層用スラリー組成物を、コンマコーターで、正極原反（下層）上に、下層＋上層の塗布量が２０±０．５ｍｇ／ｃｍ２となるように塗布した。更に、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送することにより、アルミニウム箔上の正極上層用スラリー組成物を乾燥させ、集電体上に正極合材層が形成された正極原反を得た。その後、作製した正極原反の正極合材層側を温度２５±３℃の環境下、荷重１４ｔ（トン）の条件でロールプレスし、正極合材層の密度が３．８０ｇ／ｃｍ３である正極を得た。得られた正極について、実施例１と同様にして各種評価及び測定を実施した。結果を表２に示す。 (Example 5)
The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 95.8 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 0.2 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode lower layer slurry composition was obtained at 25±3° C., a viscosity of 3,800 mPa·s, and a solid content concentration of 67% using a Brookfield viscometer at 60 rpm (rotor M4).
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 92.2 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 3.8 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, Brookfield viscometer, 60 rpm (rotor M4), 25±3° C., viscosity of 3,500 mPa·s, solid content concentration of 69%, to obtain a positive electrode upper layer slurry composition.
<Production of positive electrode>
The positive electrode lower layer slurry composition obtained above was applied onto a 20 μm thick aluminum foil as a current collector with a comma coater so that the coating amount was 10±0.5 mg/cm 2 . Further, at a speed of 0.5 m/min, the positive electrode lower layer slurry composition on the aluminum foil was transported in an oven at a temperature of 90°C for 2 minutes and further in an oven at a temperature of 120°C for 2 minutes. It was dried to obtain a positive electrode raw fabric (lower layer) in which a positive electrode mixture layer (lower layer) was formed on the current collector. Next, the positive electrode upper layer slurry composition obtained above was applied onto the positive electrode material (lower layer) using a comma coater so that the coating amount of the lower layer + upper layer was 20±0.5 mg/cm 2 . Furthermore, the positive electrode upper layer slurry composition on the aluminum foil is dried by conveying it in an oven at a temperature of 90° C. for 2 minutes and then in an oven at a temperature of 120° C. for 2 minutes at a speed of 0.5 m/min. to obtain a positive electrode blank in which a positive electrode mixture layer was formed on a current collector. After that, the positive electrode material layer side of the positive electrode raw material prepared is roll-pressed under the condition of a load of 14 tons (tons) under an environment of a temperature of 25±3° C., and the density of the positive electrode material layer is 3.80 g/cm 3 . A positive electrode was obtained. Various evaluations and measurements were carried out in the same manner as in Example 1 for the obtained positive electrode. Table 2 shows the results.
（実施例６）
　正極活物質として、体積平均粒子径Ｄ５０が異なる（２５μｍ）コバルト酸リチウムを用いて、正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウム（体積平均粒子径Ｄ５０：２５μｍ）を９４．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で１．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６９％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９３．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で２．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６９％として、正極上層用スラリー組成物を得た。結果を表２に示す。 (Example 6)
The procedure of Example 1 was repeated except that lithium cobaltate having a different volume average particle diameter D50 (25 μm) was used as the positive electrode active material, and the following operations were carried out during the production of the positive electrode.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 94.5 parts of lithium cobalt oxide (volume average particle diameter D50: 25 μm) as a positive electrode active material, and carbon black (manufactured by Denka, trade name “Li-100”) as a conductive material equivalent to the solid content. 2.0 parts of PVDF (Solef 5130), 2.0 parts of PVDF (Solef 5130), and 1.5 parts of the binder composition equivalent to the solid content were added and mixed, and NMP was gradually added, and the temperature was 25 ± 3 ° C., rotating Stir and mix at several 60 rpm, Brookfield viscometer, 60 rpm (rotor M4) at 25 ± 3 ° C., viscosity of 3,600 mPa s, solid content concentration of 69%, slurry composition for positive electrode lower layer Obtained.
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 93.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 2.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,600 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4). Table 2 shows the results.
（実施例７）
　熱膨張性粒子として、市販の熱膨張性粒子（松本油脂製薬社製、Ｆ２６０Ｄ）を用いて、正極活物質として体積平均粒子径Ｄ５０が異なる（７μｍ）コバルト酸リチウムを用いて、正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウム（体積平均粒子径Ｄ５０：７μｍ）を９４．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、松本油脂製薬社製、Ｆ２６０Ｄを固形分相当で１．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，２００ｍＰａ・ｓ、固形分濃度を６８％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９３．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、松本油脂製薬社製、Ｆ２６０Ｄを固形分相当で２．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，４００ｍＰａ・ｓ、固形分濃度を６９％として、正極上層用スラリー組成物を得た。結果を表２に示す。 (Example 7)
Commercially available thermally expandable particles (F260D, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) were used as the thermally expandable particles, and lithium cobaltate having a different volume average particle diameter D50 (7 μm) was used as the positive electrode active material. The procedure was the same as in Example 1, except that the following operations were performed.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 94.5 parts of lithium cobalt oxide (volume average particle diameter D50: 7 μm) as a positive electrode active material, and carbon black (manufactured by Denka, trade name “Li-100”) as a conductive material equivalent to the solid content. 2.0 parts of PVDF (Solef 5130), 2.0 parts of PVDF (Solef 5130), 1.5 parts of F260D manufactured by Matsumoto Yushi Seiyaku Co., Ltd. were added and mixed, and NMP was gradually added, and the temperature was 25 ± 3. ° C., the number of revolutions 60 rpm, 25 ± 3 ° C. with a Brookfield viscometer, 60 rpm (rotor M4), viscosity 3,200 mPa s, solid content concentration 68%, slurry for positive electrode lower layer A composition was obtained.
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 93.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ), and 2.5 parts of F260D manufactured by Matsumoto Yushi Seiyaku Co., Ltd., equivalent to the solid content, are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm. Then, a positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,400 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4). Table 2 shows the results.
（比較例１）
　正極を製造する際の乾燥条件を、０．５ｍ／分の速度で、温度９０℃のオーブン内を２分間、さらに温度１２０℃のオーブン内を２分間かけて搬送する、という、一段目の乾燥温度がやや低い条件に変更した以外は、実施例２と同様の各種操作、評価及び測定を実施した。結果を表２に示す。 (Comparative example 1)
The drying conditions for manufacturing the positive electrode are that the drying condition is 0.5 m / min, and the first drying is conveyed in an oven at a temperature of 90 ° C. for 2 minutes and further in an oven at a temperature of 120 ° C. for 2 minutes. Various operations, evaluations and measurements were performed in the same manner as in Example 2, except that the temperature was changed to slightly lower conditions. Table 2 shows the results.
（比較例２）
　正極合材層スラリー組成物の調製時に、固形分濃度を６８％とした（粘度を３７００ｍＰａ・ｓ）以外は実施例２と同様の各種操作、評価及び測定を実施した。結果を表２に示す。 (Comparative example 2)
Various operations, evaluations and measurements were performed in the same manner as in Example 2 except that the solid content concentration was 68% (viscosity was 3700 mPa·s) when preparing the positive electrode mixture layer slurry composition. Table 2 shows the results.
（比較例３）
　正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。結果を表２に示す。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９２．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で３．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，４００ｍＰａ・ｓ、固形分濃度を６９％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９５．５部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で０．５部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６８％として、正極上層用スラリー組成物を得た。 (Comparative Example 3)
The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode. Table 2 shows the results.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 92.5 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 3.5 parts of the binder composition equivalent to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode lower layer slurry composition was obtained at 25±3° C., a viscosity of 3,400 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 95.5 parts of lithium cobalt oxide as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 0.5 parts of the binder composition corresponding to the solid content are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,600 mPa·s, and a solid content concentration of 68% using a Brookfield viscometer at 60 rpm (rotor M4).
（比較例４）
　正極の作成時に下記の操作を実施した以外は、実施例１と同様にした。結果を表２に示す。
＜正極下層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９６．０部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，５００ｍＰａ・ｓ、固形分濃度を６７％として、正極下層用スラリー組成物を得た。
＜正極上層用スラリー組成物の調製＞
　プラネタリーミキサーに、正極活物質としてのコバルト酸リチウムを９２．０部、導電材としてのカーボンブラック（デンカ製、商品名「Ｌｉ－１００」）を固形分相当で２．０部、ＰＶＤＦ（Ｓｏｌｅｆ５１３０）を２．０部、上記バインダー組成物を固形分相当で４．０部投入して混合し、更にＮＭＰを徐々に加えて、温度２５±３℃、回転数６０ｒｐｍにて撹拌混合して、Ｂ型粘度計、６０ｒｐｍ（ローターＭ４）にて、２５±３℃、粘度を３，６００ｍＰａ・ｓ、固形分濃度を６９％として、正極上層用スラリー組成物を得た。 (Comparative Example 4)
The procedure was the same as in Example 1, except that the following operations were performed during the production of the positive electrode. Table 2 shows the results.
<Preparation of positive electrode lower layer slurry composition>
In a planetary mixer, 96.0 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) was added and mixed, NMP was gradually added, and the mixture was stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm. A positive electrode lower layer slurry composition was obtained at a temperature of ±3° C., a viscosity of 3,500 mPa·s, and a solid content concentration of 67%.
<Preparation of positive electrode upper layer slurry composition>
In a planetary mixer, 92.0 parts of lithium cobaltate as a positive electrode active material, 2.0 parts of carbon black (manufactured by Denka, trade name "Li-100") as a conductive material in terms of solid content, PVDF (Solef 5130 ) and 4.0 parts equivalent to the solid content of the binder composition are added and mixed, NMP is gradually added, and the mixture is stirred and mixed at a temperature of 25 ± 3 ° C. and a rotation speed of 60 rpm, A positive electrode upper layer slurry composition was obtained at 25±3° C., a viscosity of 3,600 mPa·s, and a solid content concentration of 69% using a Brookfield viscometer at 60 rpm (rotor M4).
　なお、表２において、
　「Ｄ５０粒径」とは、体積平均粒子径Ｄ５０を示し、「ＨＮＢＲ」は水素化ニトリルゴムを示す。 In addition, in Table 2,
"D50 particle size" indicates the volume average particle size D50, and "HNBR" indicates hydrogenated nitrile rubber.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表２より、膨張開始温度が４００℃以下である熱膨張性粒子が所定の割合で表面に露出してなる構造を有する電極合材層を用いた実施例１～７では、発熱抑制性能とＩＶ抵抗の低さがバランスされた、電気化学素子を提供することができたことが分かる。一方、熱膨張性粒子の露出の少ない比較例１～３、露出の過剰な比較例４では、これらの属性を共に高めることができなかったことが分かる。 From Table 2, in Examples 1 to 7 using an electrode mixture layer having a structure in which thermally expandable particles having an expansion start temperature of 400 ° C. or less are exposed to the surface at a predetermined ratio, heat generation suppression performance and IV It can be seen that an electrochemical device with well-balanced low resistance could be provided. On the other hand, in Comparative Examples 1 to 3 in which the thermally expansive particles were less exposed and Comparative Example 4 in which the thermally expandable particles were excessively exposed, these attributes could not be improved.
　本発明によれば、電気化学素子の発熱抑制性能を高めるとともに、ＩＶ抵抗を低減することができる、電気化学素子用電極及びその製造方法を提供することができる。 According to the present invention, it is possible to provide an electrode for an electrochemical element and a method for manufacturing the same, which can improve the heat generation suppression performance of the electrochemical element and reduce the IV resistance.

Claims (5)

  1. 　集電体及び電極合材層を備える電気化学素子用電極であって、
    　前記電極合材層が、少なくとも、電極活物質と膨張開始温度が４００℃以下である熱膨張性粒子とを含み、
    　前記電極合材層表面に存在する、露出径が前記電極活物質の体積平均粒子径Ｄ５０の０．５倍以上５．０倍以下である熱膨張性粒子を露出粒子Ａとした場合に、前記電極合材層表面における露出粒子Ａの占有面積率が０．５％以上２０％以下である、電気化学素子用電極。     An electrode for an electrochemical device comprising a current collector and an electrode mixture layer,
    The electrode mixture layer contains at least an electrode active material and thermally expandable particles having an expansion start temperature of 400° C. or less,
    When the exposed particles A are thermally expandable particles having an exposed diameter of 0.5 to 5.0 times the volume average particle diameter D50 of the electrode active material, which are present on the surface of the electrode mixture layer, An electrode for an electrochemical device, wherein the occupied area ratio of the exposed particles A on the surface of the electrode mixture layer is 0.5% or more and 20% or less.
  2. 　前記熱膨張性粒子の体積平均粒子径Ｄ５０が、前記電極活物質の体積平均粒子径Ｄ５０の０．３倍以上５．０倍以下である、請求項１に記載の電気化学素子用電極。 2. The electrode for an electrochemical device according to claim 1, wherein the volume average particle diameter D50 of the thermally expandable particles is 0.3 to 5.0 times the volume average particle diameter D50 of the electrode active material.
  3. 　前記電極合材層表面における前記露出粒子Ａの個数密度が１０個／ｍｍ２以上３００個／ｍｍ２以下である、請求項１に記載の電気化学素子用電極。 The electrode for an electrochemical device according to claim 1, wherein the number density of the exposed particles A on the surface of the electrode mixture layer is 10 particles/ mm2 or more and 300 particles/ mm2 or less.
  4. 　前記電極合材層が、結着材をさらに含み、前記結着材は、
    　カルボン酸基、ヒドロキシル基、ニトリル基、アミノ基、エポキシ基、オキサゾリン基、スルホン酸基、エステル基及びアミド基からなる群から選択される少なくとも１種の官能基を有するポリマーである、請求項１に記載の電気化学素子用電極。     The electrode mixture layer further includes a binder, and the binder is
    Claim 1, wherein the polymer has at least one functional group selected from the group consisting of carboxylic acid groups, hydroxyl groups, nitrile groups, amino groups, epoxy groups, oxazoline groups, sulfonic acid groups, ester groups and amide groups. The electrode for an electrochemical device according to .
  5. 　請求項１～４のいずれかに記載の電気化学組成用電極の製造方法であって、
    　集電体上に、電極下層用スラリー組成物を塗布及び乾燥して、電極下層を形成する工程と、
    　前記電極下層上に、電極上層用スラリー組成物を塗布及び乾燥して、電極上層を形成する工程とを含み、
    　前記電極上層用スラリー組成物及び前記電極下層用スラリー組成物は、それぞれ、電極活物質及び熱膨張性粒子を含有してなり、前記電極上層用スラリー組成物の熱膨張性粒子濃度が前記電極下層用スラリー組成物の熱膨張性粒子濃度よりも高い、
    　電気化学素子用電極の製造方法。     A method for producing an electrochemical composition electrode according to any one of claims 1 to 4,
    A step of applying and drying an electrode lower layer slurry composition on a current collector to form an electrode lower layer;
    applying and drying a slurry composition for an electrode upper layer on the electrode lower layer to form an electrode upper layer;
    The electrode upper layer slurry composition and the electrode lower layer slurry composition each contain an electrode active material and thermally expandable particles, and the concentration of the thermally expandable particles in the electrode upper layer slurry composition is equal to that of the electrode lower layer. higher than the thermally expandable particle concentration of the slurry composition for
    A method for manufacturing an electrode for an electrochemical device.
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