WO2014083950A1 - Lithium ion secondary battery and method for manufacturing same - Google Patents

Lithium ion secondary battery and method for manufacturing same Download PDF

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Publication number
WO2014083950A1
WO2014083950A1 PCT/JP2013/077877 JP2013077877W WO2014083950A1 WO 2014083950 A1 WO2014083950 A1 WO 2014083950A1 JP 2013077877 W JP2013077877 W JP 2013077877W WO 2014083950 A1 WO2014083950 A1 WO 2014083950A1
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Prior art keywords
binder
electrode film
current collector
collector foil
secondary battery
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PCT/JP2013/077877
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French (fr)
Japanese (ja)
Inventor
千恵美 窪田
昌作 石原
菊池　廣
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株式会社日立製作所
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Publication of WO2014083950A1 publication Critical patent/WO2014083950A1/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
    • H01M4/13—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
    • 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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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 a lithium ion secondary battery and a manufacturing method thereof.
  • Patent Document 1 Japanese Patent No. 3482443
  • pastes having different binder concentrations are laminated in two portions.
  • patent 39539911 gazette patent document 2.
  • This publication states that “a method for producing a coating sheet coated with at least an active material, a binder and a solvent, wherein the coating film is at a temperature below the boiling point of the solvent contained in the coating.
  • Lithium ion secondary batteries have the advantages described above, and are therefore widely used in portable electronic devices such as digital cameras, notebook personal computers, and mobile phones.
  • lithium ion secondary batteries capable of realizing high capacity, high output, and high energy density as electric vehicle batteries and power storage batteries.
  • development of an electric vehicle that uses a motor as a power source and a hybrid vehicle that uses both an engine (internal combustion engine) and a motor as a power source are in progress.
  • Lithium ion secondary batteries have attracted attention as power sources for such electric vehicles and hybrid vehicles.
  • the importance in applications such as photovoltaic power generation and power storage for effective use of nighttime power has been increasing, and higher capacities have been demanded.
  • the solid members constituting the battery are an electrode film, a current collector foil, and a separator, but as the electrode film becomes thicker, the volume ratio of the electrode film to the current collector foil and the separator increases, and the electrode film volume occupies the battery volume. In other words, the battery capacity can be increased by increasing the active material ratio.
  • the electrode film of a lithium secondary battery is applied to a metal foil, which is a current collector, an electrode slurry prepared by kneading an active material capable of releasing and occluding lithium ions by charging / discharging and a conductive additive powder with a binder or solvent. After the electrodes and film are formed, the solvent is dried.
  • a metal foil which is a current collector
  • an electrode slurry prepared by kneading an active material capable of releasing and occluding lithium ions by charging / discharging and a conductive additive powder with a binder or solvent After the electrodes and film are formed, the solvent is dried.
  • it is difficult to increase the capacity by increasing the thickness of the electrode film for the following reasons.
  • the binder in the electrode film is distributed in the thickness direction of the electrode film and becomes non-uniform, and the electrode film surface side (on the current collector foil side) is compared with the electrode film current collector foil side.
  • the amount of binder increases, and the degree of non-uniform distribution becomes more prominent as the thick electrode film becomes thicker.
  • FIG. 2 when the electrode film thickness is 100 ⁇ m, the binder amount on the electrode film surface side is about twice that on the current collector foil side, and when the electrode film thickness is 300 ⁇ m, as shown in FIG. When the electrode film thickness is about 500 ⁇ m, it is about 4 times.
  • the decrease in the binder amount on the current collector foil side causes a decrease in the adhesion strength between the electrode film and the current collector foil, and the electrode film tends to be peeled off or cracked during winding or processing (cutting or winding) operations.
  • Patent Document 1 discloses that a slurry containing a binder at a high concentration is applied to the collector foil in order to increase the binder concentration on the collector foil side, and then a slurry of a low-concentration binder is formed thereon. Techniques for applying the are described. Such a method of increasing the binder concentration is not desirable for a lithium ion secondary battery in which a high capacity is required because the ratio of the active material in the electrode is reduced. Furthermore, in the manufacturing method in which the coating and drying are performed a plurality of times, an expensive manufacturing facility including a plurality of coating units and a drying unit is required. Alternatively, after the first coating / drying operation is performed and the electrode film is wound up, the coating / drying needs to be performed again, resulting in a significant reduction in productivity.
  • Patent Document 2 proposes a method in which the drying process is divided into a plurality of processes having different coating temperatures. Since this method includes a drying step at a low temperature, the drying rate of the electrode cannot be increased and the productivity is lowered. Furthermore, it is not easy to make the binder concentration distribution uniform by drying by evaporation of the solvent from the surface of the coating film.
  • the present invention suppresses the non-uniform distribution of the binder concentration in the electrode film, and has high adhesion to the current collector foil without increasing the binder concentration, and high capacity lithium ions. It is an object of the present invention to provide a secondary battery and a manufacturing method thereof.
  • the present application includes a plurality of means for solving the above-described problems.
  • a current collector foil as a current collector and a binder that adheres to the current collector film on the surface of the current collector foil are included.
  • the electrode film layer is a layer in which the concentration of the binder on the side of the current collector foil is higher than the concentration of the binder on the side opposite to the current collector foil.
  • the lithium ion secondary battery characterized by including. "
  • the binder concentration distribution in the electrode film is suppressed to be non-uniform, the adhesive force with the current collector foil is high without increasing the binder concentration, and a high-capacity lithium ion secondary battery and A manufacturing method thereof can be provided.
  • FIG. 1 It is a figure which shows the electrode film structure of embodiment of this invention. It is a figure which shows the concentration to the electrode film surface side of the binder after the conventional electrode film drying. It is a figure showing the electrode film formation process in the conventional method. It is a figure which shows the binder density
  • FIG. 1 It is a figure which shows the electrode film structure of embodiment of this invention. It is a figure which shows the concentration to the electrode film surface side of the binder after the conventional electrode film drying. It is a figure showing the electrode film formation process in the conventional method. It is a figure which shows the binder density
  • the lithium ion secondary battery in the present embodiment is wound or laminated via a separator that prevents contact between the positive electrode plate and the negative electrode plate.
  • the electrolytic solution is injected into the outer container.
  • the positive electrode plate and the negative electrode plate are formed by laminating a plurality of electrode film layers 5 on a current collector foil 4 that is a metal foil as a current collector to form an electrode film 6.
  • the electrode film layer 5 is an electrode slurry prepared by kneading an active material 1 capable of releasing and occluding lithium ions by charging and discharging, a conductive material 2, a binder 3 for bonding the current collector foil 4 and the electrode film 6 together with a solvent. It is formed by solidifying and drying.
  • an electrode slurry containing the active material 1, the binder 2, the conductive material 4, and the first solvent is applied on the base film.
  • the binder is precipitated and solidified by bringing the second solvent containing the solidified material of the binder 2 into contact with the electrode slurry.
  • the base film is peeled off to obtain a solidified electrode film wetted with the second solvent.
  • Arbitrary number (a plurality) of this solidified electrode film is laminated on the current collector foil 4, pressure-bonded by hot pressing or the like, and the remaining second solvent is dried to remove the liquid component, thereby the laminated electrode film 6.
  • each of the positive electrode plate and the negative electrode plate is formed.
  • a separator made of a porous insulating material that allows lithium ions to pass through is sandwiched between the positive electrode plate and the negative electrode plate while preventing contact between the positive electrode plate and the negative electrode plate, and the positive electrode plate, the separator, and the negative electrode plate are wound.
  • the electrode winding body which consists of the wound positive electrode plate, separator, and negative electrode plate can be formed.
  • electrolyte solution is inject
  • a lithium ion secondary battery can be manufactured by cap-sealing an exterior container.
  • the decrease in the adhesion of the electrode film is eliminated.
  • the decrease in the adhesion between the current collector foil 6 and the electrode film 5 causes the binder distribution in the electrode film 5 to become non-uniform during the drying process, and the binder concentration on the current collector foil 6 side is lower than the binder concentration on the protective film 8 side. This is what happens.
  • the binder distribution in the electrode film 6 is changed to the current collector foil 4. Since it can suppress that it becomes non-uniform
  • FIGS. A conventional method for forming an electrode film will be described with reference to FIGS. Conventionally, an electrode film slurry was applied to the surface of the current collector foil 4 and introduced into a drying chamber as it was to be dried.
  • the solvent in the electrode film 6 evaporates and dries.
  • the electrode film 6 is applied to the surface of the current collector foil 4, Evaporates from the surface of the electrode film 6.
  • the solvent on the side of the current collector foil 4 moves to the surface of the electrode film 6 and evaporates.
  • the binder 3 dissolved in the solvent moves together with the solvent toward the surface of the electrode film 6 in the direction of the arrow in FIG.
  • the moved solvent evaporates as the solvent 7 evaporated from the surface, but the dissolved binder 3 is deposited with the evaporation of the solvent and remains.
  • the binder 3 is concentrated on the surface side of the electrode film 6 as shown in FIG. 2, and the binder concentration part 8 is formed.
  • the method of solidifying the binder 3 of this embodiment is to bring the binder 3 into contact with the surface of the electrode film layer 5 containing the first solvent of this embodiment by contacting the second solvent containing the solidifying material of this embodiment. What is necessary is just to deposit. Therefore, a method of passing the coating film held on the surface of the current collector foil 4 through the liquid tank storing the second solvent, a method of spraying the second solvent on the coating film held on the surface of the current collector foil 4, A method of supplying the second solvent while flowing down is included, but is not limited thereto.
  • the binder distribution is basically the same as the binder distribution of the electrode slurry when the solidification is instantaneous, that is, the binder 3 is an electrode film. 6 has a uniform distribution.
  • the second solvent penetrates from the surface of the coated electrode film, and the binder 3 dissolved in the first solvent is precipitated by the second solvent. That is, the deposition of the binder 3 proceeds from the surface to the current collector foil 4 side, and the amount of the binder 3 on the current collector foil 4 side increases. Contrary to the conventional binder 3 on the surface side, the binder distribution increases on the current collector foil 4 side, so that the electrode film 6 having good adhesion to the current collector foil 4 is obtained.
  • the thickness of one electrode film layer 5 is preferably 10 to 200 ⁇ m, more preferably 20 to 150 ⁇ m, and more preferably 50 to 100 ⁇ m.
  • the lower limit of the contact time required for solidification generally requires time for the first solvent and the second solvent to diffuse and replace each other in the coating film, but the thickness of the electrode film layer 5 is If it is 1 mm or less, the contact time is preferably from 1 to 100 seconds, more preferably from 2 seconds to 50 seconds, and even more preferably from 5 seconds to 20 seconds.
  • a uniaxial press, a biaxial press, a roll press, an isostatic press, or the like can be used as a method for pressure-bonding the electrode film layer 5 onto the current collector foil 4.
  • a hot press that presses at a temperature near the softening point of the binder 3 at the time of pressure bonding. Further, by pressing at a temperature equal to or higher than the boiling point of the second solvent, drying can be performed simultaneously with the pressure bonding.
  • the electrode film layer 5 is wet with the second solvent and has high plasticity and high processing performance, it is pressed and dried after processing such as electrode punching to produce an electrode plate for a lithium ion secondary battery. be able to.
  • the method for drying the electrode film 6 is not limited to general hot air drying.
  • a heating method that irradiates electromagnetic waves such as infrared rays, far-infrared rays, or visible light may be used, or a dielectric heating method that uses a high-frequency electric field, or an induction heating method that uses a change in magnetic flux may be used.
  • a contact heating method using a heating roll or a hot plate incorporating a heater can also be used.
  • various application methods such as an extrusion coater, a reverse roller, a doctor blade, an applicator and the like can be employed.
  • the positive electrode active material used for the positive electrode is lithium cobaltate, a spinel-structure lithium-containing composite oxide containing manganese, or a composite containing nickel, cobalt, and manganese.
  • an oxide or an olivine type compound represented by olivine type iron phosphate is used, it is not limited thereto. Since the lithium-containing composite oxide having a spinel structure containing manganese is excellent in thermal stability, for example, a highly safe battery can be configured.
  • the positive electrode active material only a lithium-containing composite oxide having a spinel structure containing manganese may be used, but another positive electrode active material may be used in combination.
  • Examples of such other positive electrode active materials include olivine type compounds represented by Li1 + xMO2 ( ⁇ 0.1 ⁇ x ⁇ 0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, etc.) Is mentioned.
  • Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO2 and LiNi1-xCox-yAlyO2 (0.1 ⁇ x ⁇ 0.3, 0.01 ⁇ y ⁇ 0.2), and at least Co.
  • An oxide containing Ni and Mn (LiMn1 / 3Ni1 / 3Co1 / 3O2, LiMn5 / 12Ni5 / 12Co1 / 6O2, LiNi3 / 5Mn1 / 5Co1 / 5O2, etc.) can be used.
  • examples of the negative electrode active material used for the negative electrode include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; and easy graphite such as coke obtained by firing a pitch.
  • Carbonaceous materials carbon materials such as non-graphitizable carbonaceous materials such as amorphous carbon obtained by low-temperature firing of furfuryl alcohol resin (PFA), polyparaphenylene (PPP) and phenol resin .
  • lithium or a lithium-containing compound can also be used as the negative electrode active material.
  • the lithium-containing compound include a lithium alloy such as Li—Al, and an alloy containing an element that can be alloyed with lithium such as Si and Sn.
  • oxide-based materials such as Sn oxide and Si oxide can also be used.
  • the conductive material 2 is usually used as an electron conduction aid to be contained in the positive electrode film.
  • carbon materials such as carbon black, acetylene black, ketjen black, graphite, carbon fiber, and carbon nanotube are preferable.
  • acetylene black or ketjen black is particularly preferable from the viewpoint of the amount of addition and conductivity, and the manufacturability of the positive electrode mixture slurry for coating.
  • Such a conductive material 2 can be contained in the negative electrode film, and may be preferable.
  • the binder used in this embodiment liquid for example, a polyvinylidene fluoride polymer (a polymer of a fluorine-containing monomer group containing 80% by mass or more of vinylidene fluoride as a main component monomer), a rubber polymer, or the like is preferably used. It is done. Two or more of the above polymers may be used in combination. Further, the binder 3 of the present invention is preferably provided in the form of a solution dissolved in a solvent.
  • Examples of the fluorine-containing monomer group for synthesizing the polyvinylidene fluoride-based polymer include vinylidene fluoride; a mixture of vinylidene fluoride and another monomer, and a monomer mixture containing 80% by mass or more of vinylidene fluoride; Can be mentioned.
  • Examples of other monomers include vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, and fluoroalkyl vinyl ether.
  • Examples of the rubber-based polymer include styrene butadiene rubber (SBR), ethylene propylene diene rubber, and fluorine rubber.
  • SBR styrene butadiene rubber
  • ethylene propylene diene rubber examples include fluorine rubber.
  • the binder 3 of this embodiment may be added separately from the component having the performance as a solidifying material for solidifying the electrode film 6, or the binder 3 itself may have a function as a solidifying material.
  • the binder 3 is preferably the polymer material having the property of binding the active material 1 and the conductive material 2, but is not necessarily dissolved in the solvent 2.
  • the solution is not necessarily in the form of a solution, and may be in the form of an emulsion in which the polymer material is dispersed in the liquid.
  • the content of the binder 3 in the electrode film 6 is 0.1% by mass or more, more preferably 0.3% by mass or more and 10% by mass or less, more preferably 5% based on the electrode film 6 after drying. It is desirable that it is less than mass%. If the content of the binder 3 is too small, not only is the solidification in the solidification step of the present embodiment insufficient, but the mechanical strength of the electrode film 6 after drying is insufficient, and the electrode film peels from the current collector foil. There's a problem. Moreover, when there is too much content of the binder 3, there exists a possibility that the amount of active materials in the electrode film 6 may reduce, and battery capacity may become low.
  • the solvent 2 of the present embodiment is appropriately selected from the first solvent containing the binder 3 and the electrode film layer 5 and the second solvent containing the solidifying material 4. Moreover, the solvent 2 should be selected from the solubility of the solidifying material of this embodiment or the component of the binder 3 that also serves as the solidifying material, and the mutual solubility of the solvent.
  • an aprotic polar solvent represented by N-methylpyrrolidone, dimethyl sulfoxide, propylene carbonate, dimethylformamide, ⁇ -butyrolactone, or a mixture thereof can be selected.
  • a protic solvent typified by water, ethanol, isopropyl alcohol, acetic acid or the like, or a mixed solution thereof can be selected, but is not limited to the examples given here.
  • aliphatic saturated hydrocarbons, aliphatic amines, esters, ethers, various halogen-based solvents, and the like can be selected as the second solvent.
  • the selection of the solvent 2 in this embodiment depends on the selection of the solidifying component used for the electrode film and the combination of the two kinds of solvents 2 corresponding to the selection.
  • the current collector foil 4 used in the present embodiment is representatively shown, and is not limited to a sheet-like foil.
  • the substrate include pure aluminum, copper, stainless steel, titanium, and the like.
  • a metal, an alloy conductive material, or a net, a punched metal, a foam metal, a foil processed into a plate shape, or the like is used.
  • As the thickness of the conductive substrate for example, 5 to 30 ⁇ m, more preferably 8 to 16 ⁇ m is selected.
  • the lithium ion secondary battery that can be provided by the present embodiment can be manufactured in the same manner as a conventional secondary battery except that it includes a positive electrode and a negative electrode manufactured by the above-described method.
  • a positive electrode and a negative electrode manufactured by the above-described method There is no particular limitation on the structure and size of the battery container or the structure of the electrode body having positive and negative electrodes as main components.
  • the present embodiment it is possible to suppress the non-uniform concentration of the binder 2 in the electrode film 6 and to manufacture a lithium ion secondary battery having the electrode film 6 with high adhesion and high capacity. it can.
  • preferred examples of the present embodiment will be described based on experimental results.
  • a lithium transition metal composite oxide lithium manganese cobalt nickel composite oxide powder was used as an active material.
  • 9 parts by weight of graphite powder and 2 parts by weight of carbon black as a conductive material were mixed to prepare a positive electrode mixture.
  • NMP N-methyl-2-pyrrolidone
  • PVDF polyvinylidene fluoride
  • Solution dispersed in NMP to form a slurry.
  • the slurry for the positive electrode film prepared above is applied to the surface of the polypropylene base film using a die coater. Subsequently, the coated positive electrode film is immersed in pure water for 5 seconds to solidify the binder, and then the base film is peeled off to form a solidified positive electrode film. Five layers were laminated so that the side of the solidified positive electrode film that was in contact with the base film was on the current collector foil side, and pressure bonding was performed using a 120-degree hot roll press. Thereafter, the remaining liquid component was dried at 120 ° C. in a warm air drying furnace at a temperature rising rate of 3 ° / second to form a laminated positive electrode plate.
  • the binder distribution of the produced laminated positive electrode plate was composed of a plurality of layers, and the amount of the binder on the current collector foil side in each layer was increased as compared with the vicinity of the surface.
  • the amount of binder on the current collector foil side of each layer was 5.2%, and the surface side was 4.2%, which was 24% more.
  • a lithium transition metal composite oxide lithium manganese cobalt nickel composite oxide powder was used as an active material.
  • 9 parts by weight of graphite powder and 2 parts by weight of carbon black as a conductive material were mixed to prepare a positive electrode mixture.
  • NMP N-methyl-2-pyrrolidone
  • PVDF polyvinylidene fluoride
  • Solution dispersed in NMP to form a slurry.
  • the slurry for the positive electrode film prepared above is applied to the surface of the polypropylene base film using a die coater.
  • the coated positive electrode film is immersed in pure water for 5 seconds to solidify the binder, and then the base film is peeled off to form a solidified positive electrode film.
  • Five layers were laminated so that the side (back surface) and the surface side (front surface) that were in contact with the base film of the solidified positive electrode film were alternated, and pressure bonding was performed using a 120-degree hot roll press.
  • the layer closest to the current collector foil was laminated so that the back surface was on the current collector foil side.
  • the remaining liquid component was dried at 120 ° C. in a warm air drying furnace at a temperature rising rate of 3 ° / second to form a laminated positive electrode plate.
  • the binder distribution of the produced laminated positive electrode plate was composed of a plurality of layers, and the amount of the binder on the side of the current collector foil in the layer closest to the current collector foil was increased as compared with the vicinity of the surface.
  • a layer having a larger amount of binder on the front side than that on the current collector foil side and a layer having a smaller amount of binder on the front side than that on the current collector foil side were alternately present.
  • the difference in the binder concentration between the surface side and the current collector foil side was 24%.
  • the slurry for the positive electrode film of Example 1 is applied to the surface of the current collector foil formed of aluminum using a die coater. Subsequently, the coated positive electrode film was dried at 120 ° C. at a temperature rising rate of 3 ° C./second in a warm air drying furnace to form a positive electrode film having a thickness of 500 ⁇ m.
  • the binder distribution of the produced positive electrode film is such that the amount of the binder on the side of the current collector foil is smaller than that near the surface, and the amount of the binder on the side of the current collector foil of the positive electrode film is 2.2. %, And the surface side was 6.5%, 66% less.
  • the binder concentration on the base film side increases.
  • the electrode film layers were laminated so that the binder concentration on the current collector foil side was higher than the binder concentration on the surface side.

Abstract

The purpose of the present invention is to provide: a lithium ion secondary battery having high capacity, wherein a binder concentration distribution in an electrode film is prevented from being uneven and high adhesion to a collector foil is achieved without increasing the binder concentration; and a method for manufacturing the lithium ion secondary battery. A lithium ion secondary battery which is characterized by comprising: a collector foil that serves as a collector; and an electrode film that is obtained by laminating a plurality of electrode film layers on the surface of the collector foil, said electrode film layers containing a binder that adheres to the collector foil. This lithium ion secondary battery is also characterized in that the electrode film layers include a layer in which the binder concentration on the collector foil side is higher than the binder concentration on the opposite side.

Description

リチウムイオン二次電池及びその製造方法Lithium ion secondary battery and manufacturing method thereof
　本発明は、リチウムイオン二次電池及びその製造方法に関する。 The present invention relates to a lithium ion secondary battery and a manufacturing method thereof.
　本技術分野の背景技術として、特許第３４８２４４３号公報（特許文献１）がある。この公報には、「非水電解質二次電池用電極が集電体にバインダを含んだ電極合剤層が形成されているものであって、電極合剤層内のバインダ濃度を集電体近くにおいて濃くなるようにする。このために、バインダ濃度が異なるペーストを２回に分けて積層する」と記載されている。また、特許３９５３９１１公報（特許文献２）がある。この公報には、「少なくとも活物質材料、結着剤および溶媒を含有する塗料が塗布された塗膜シートの製造方法であって、前記塗料に含まれる前記溶媒の沸点未満の温度で前記塗膜シートを加熱する第１の工程と、前記塗膜内における前記結着剤の分布が均一化された状態を保つように、前記溶媒の沸点未満の前記温度より低い温度で前記塗膜シートを加熱する第２の工程と、前記塗膜シートを、前記溶媒の沸点未満の前記温度以上の温度で加熱する第３の工程とを備え、前記第３の工程を通して、前記塗膜シートは前記第２の工程によって前記塗膜内における前記結着剤の分布が均一化された状態が保たれている、塗膜シートの製造方法」と記載されている。 As a background art in this technical field, there is Japanese Patent No. 3482443 (Patent Document 1). In this publication, “the electrode mixture layer in which the electrode for the nonaqueous electrolyte secondary battery includes a binder in the current collector is formed, and the binder concentration in the electrode mixture layer is set near the current collector. In order to achieve this, pastes having different binder concentrations are laminated in two portions. ” Moreover, there exists patent 39539911 gazette (patent document 2). This publication states that “a method for producing a coating sheet coated with at least an active material, a binder and a solvent, wherein the coating film is at a temperature below the boiling point of the solvent contained in the coating. Heating the coating sheet at a temperature lower than the temperature below the boiling point of the solvent so as to maintain a uniform state of the first step of heating the sheet and the distribution of the binder in the coating film. A second step of heating and a third step of heating the coating sheet at a temperature equal to or higher than the temperature lower than the boiling point of the solvent. Through the third step, the coating sheet is the second step. It is described as “a method for producing a coating film sheet in which a state in which the distribution of the binder in the coating film is made uniform by the process is maintained” is described.
特許第３４８２４４３号公報Japanese Patent No. 3482443 特許第３９５３９１１号公報Japanese Patent No. 3953911
　携帯電子機器の発達に伴い、これらの携帯電子機器の電力供給源として、繰り返し充電が可能な小型二次電池が使用されている。中でも、エネルギー密度が高く、サイクルライフが長いとともに、自己放電性が低く、かつ、作動電圧が高いリチウムイオン二次電池が注目されている。リチウムイオン二次電池は、上述した利点を有するため、デジタルカメラ、ノート型パーソナルコンピュータ、携帯電話機などの携帯電子機器に多用されている。 With the development of portable electronic devices, small secondary batteries that can be repeatedly charged are used as power supply sources for these portable electronic devices. Among these, lithium ion secondary batteries that have high energy density, long cycle life, low self-discharge property, and high operating voltage are attracting attention. Lithium ion secondary batteries have the advantages described above, and are therefore widely used in portable electronic devices such as digital cameras, notebook personal computers, and mobile phones.
　さらに、近年では、電気自動車用電池や電力貯蔵用電池として、高容量、高出力、かつ、高エネルギー密度を実現できる大型のリチウムイオン二次電池の研究開発が進められている。特に、自動車産業においては、環境問題に対応するため、動力源としてモータを使用する電気自動車や、動力源としてエンジン（内燃機関）とモータとの両方を使用するハイブリッド車の開発が進められている。このような電気自動車やハイブリッド車の電源としてもリチウムイオン二次電池が注目されている。同様に、太陽光発電や夜間電力を有効利用するための電力貯蔵などの用途での重要性が増してきており、さらなる高容量化が求められるようになっている。 Furthermore, in recent years, research and development of large-sized lithium ion secondary batteries capable of realizing high capacity, high output, and high energy density as electric vehicle batteries and power storage batteries have been promoted. In particular, in the automobile industry, in order to cope with environmental problems, development of an electric vehicle that uses a motor as a power source and a hybrid vehicle that uses both an engine (internal combustion engine) and a motor as a power source are in progress. . Lithium ion secondary batteries have attracted attention as power sources for such electric vehicles and hybrid vehicles. Similarly, the importance in applications such as photovoltaic power generation and power storage for effective use of nighttime power has been increasing, and higher capacities have been demanded.
　リチウム二次電池の高容量化を達成するためには電池の電極膜の厚膜化が必要である。すなわち、電池を構成する固体部材は電極膜、集電箔およびセパレータであるが、電極膜を厚くすればするほど集電箔およびセパレータに対する電極膜体積割合が大きくなり、電池体積に占める電極膜体積、すなわち活物質割合が大きくなることで電池の高容量化が達成される。 In order to achieve higher capacity of lithium secondary batteries, it is necessary to increase the thickness of the battery electrode film. That is, the solid members constituting the battery are an electrode film, a current collector foil, and a separator, but as the electrode film becomes thicker, the volume ratio of the electrode film to the current collector foil and the separator increases, and the electrode film volume occupies the battery volume. In other words, the battery capacity can be increased by increasing the active material ratio.
　リチウム二次電池の電極膜は、充放電によりリチウムイオンの放出・吸蔵が可能な活物質と導電助剤の粉末を、バインダや溶剤などと混練した電極スラリを集電体である金属箔に塗布して電極と膜を形成後、溶剤を乾燥させることで製造されている。しかしながら、従来の製造方法では、以下の理由によって電極膜の厚膜化による高容量化は困難な状況である。 The electrode film of a lithium secondary battery is applied to a metal foil, which is a current collector, an electrode slurry prepared by kneading an active material capable of releasing and occluding lithium ions by charging / discharging and a conductive additive powder with a binder or solvent. After the electrodes and film are formed, the solvent is dried. However, in the conventional manufacturing method, it is difficult to increase the capacity by increasing the thickness of the electrode film for the following reasons.
　すなわち従来の電極膜作製工程においては、電極膜内のバインダが電極膜の厚さ方向で分布が発生し不均一となり、電極膜集電箔側と比較し電極膜表面側（集電箔側の反対側）ではバインダが多くなり、また不均一分布の程度は厚電極膜を厚くすればするほどより顕著になる。バインダの不均一度の概略は図２に示すように、電極膜厚が１００μｍの場合、電極膜表面側のバインダ量は集電箔側の約２倍、また電極膜厚を３００μｍとした場合では約３倍、電極膜厚を５００μｍとした場合では約４倍となる。集電箔側のバインダ量の減少は、電極膜と集電箔との密着強度の低下を引き起こし、電極膜の巻取りや加工（切断、捲回）作業中に剥離やひび割れを起こしやすくなる。 That is, in the conventional electrode film manufacturing process, the binder in the electrode film is distributed in the thickness direction of the electrode film and becomes non-uniform, and the electrode film surface side (on the current collector foil side) is compared with the electrode film current collector foil side. On the other side, the amount of binder increases, and the degree of non-uniform distribution becomes more prominent as the thick electrode film becomes thicker. As shown in FIG. 2, when the electrode film thickness is 100 μm, the binder amount on the electrode film surface side is about twice that on the current collector foil side, and when the electrode film thickness is 300 μm, as shown in FIG. When the electrode film thickness is about 500 μm, it is about 4 times. The decrease in the binder amount on the current collector foil side causes a decrease in the adhesion strength between the electrode film and the current collector foil, and the electrode film tends to be peeled off or cracked during winding or processing (cutting or winding) operations.
　上記の問題を解決するために、特許文献１には集電箔側のバインダ濃度を高めるために、バインダを高濃度に含有したスラリを集電箔に塗布後、その上に低濃度バインダのスラリを塗布する技術が記載されている。このようなバインダ濃度を増やす方法では、電極内活物質の割合が低減するため、高容量が要求されているリチウムイオン二次電池には望ましくない。さらに、複数回の塗布、乾燥する製造方法では、複数の塗布部および乾燥部を備えた高価な製造設備が必要となる。もしくは、一回目の塗布・乾燥作業を行い電極膜の巻き取りを行った後に再び塗布・乾燥を行う必要があり生産性が著しく低下する。 In order to solve the above problem, Patent Document 1 discloses that a slurry containing a binder at a high concentration is applied to the collector foil in order to increase the binder concentration on the collector foil side, and then a slurry of a low-concentration binder is formed thereon. Techniques for applying the are described. Such a method of increasing the binder concentration is not desirable for a lithium ion secondary battery in which a high capacity is required because the ratio of the active material in the electrode is reduced. Furthermore, in the manufacturing method in which the coating and drying are performed a plurality of times, an expensive manufacturing facility including a plurality of coating units and a drying unit is required. Alternatively, after the first coating / drying operation is performed and the electrode film is wound up, the coating / drying needs to be performed again, resulting in a significant reduction in productivity.
　また、特許文献２には乾燥工程を塗布温度の異なる複数工程に分けて行う方法が提案されている。この方法は低温での乾燥工程が含まれるため、電極の乾燥速度を速めることができず生産性が低下する。さらに、塗布膜の表面からの溶媒蒸発による乾燥では、バインダの濃度分布を均一化することは容易ではない。 Further, Patent Document 2 proposes a method in which the drying process is divided into a plurality of processes having different coating temperatures. Since this method includes a drying step at a low temperature, the drying rate of the electrode cannot be increased and the productivity is lowered. Furthermore, it is not easy to make the binder concentration distribution uniform by drying by evaporation of the solvent from the surface of the coating film.
　上記問題点に鑑み、本発明は、電極膜内でバインダの濃度分布が不均一になるのを抑制し、バインダ濃度を増加させることなく集電箔との密着力が高く、高容量なリチウムイオン二次電池およびその製造方法を提供することを目的とする。 In view of the above problems, the present invention suppresses the non-uniform distribution of the binder concentration in the electrode film, and has high adhesion to the current collector foil without increasing the binder concentration, and high capacity lithium ions. It is an object of the present invention to provide a secondary battery and a manufacturing method thereof.
　上記課題を解決するために、例えば特許請求の範囲に記載の構成を採用する。本願は上記課題を解決する手段を複数含んでいるが、その一例を挙げるならば、「集電体としての集電箔と、前記集電箔の表面に前記集電膜に接着するバインダが含まれる電極膜層が複数層積層された電極膜とを有し、前記電極膜層は、前記集電箔側の前記バインダの濃度が前記集電箔の反対側の前記バインダの濃度よりも高い層を含むことを特徴とするリチウムイオン二次電池。」を特徴とする。 In order to solve the above problems, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above-described problems. To give an example of such means, a current collector foil as a current collector and a binder that adheres to the current collector film on the surface of the current collector foil are included. The electrode film layer is a layer in which the concentration of the binder on the side of the current collector foil is higher than the concentration of the binder on the side opposite to the current collector foil. The lithium ion secondary battery characterized by including. "
　本発明によれば、電極膜内でバインダの濃度分布が不均一になるのを抑制し、バインダ濃度を増加させることなく集電箔との密着力が高く、高容量なリチウムイオン二次電池およびその製造方法を提供することができる。 According to the present invention, the binder concentration distribution in the electrode film is suppressed to be non-uniform, the adhesive force with the current collector foil is high without increasing the binder concentration, and a high-capacity lithium ion secondary battery and A manufacturing method thereof can be provided.
本発明実施形態の電極膜構造を示す図である。It is a figure which shows the electrode film structure of embodiment of this invention. 従来の電極膜乾燥後のバインダの電極膜表面側への濃縮を示す図である。It is a figure which shows the concentration to the electrode film surface side of the binder after the conventional electrode film drying. 従来法における電極膜形成過程を表す図である。It is a figure showing the electrode film formation process in the conventional method. 従来の電極膜厚さ方向のバインダ濃度を示す図である。It is a figure which shows the binder density | concentration of the conventional electrode film thickness direction. 実施例１における電極膜厚さ方向のバインダ分布を示す図である。It is a figure which shows the binder distribution of the electrode film thickness direction in Example 1. FIG. 実施例２における電極膜厚さ方向のバインダ分布を示す図である。It is a figure which shows the binder distribution of the electrode film thickness direction in Example 2. FIG.
　以下、本発明の実施形態について詳細に説明する。 Hereinafter, embodiments of the present invention will be described in detail.
　本実施形態におけるリチウムイオン二次電池の構成について、図１を用いて説明する。 The configuration of the lithium ion secondary battery in the present embodiment will be described with reference to FIG.
　本実施形態におけるリチウムイオン二次電池は、正極板と負極板の接触を防止するセパレータを介して捲回または積層されている。この捲回体または積層体を電池外装容器に収納した後、外装容器内に電解液が注入されている。正極板、負極板は、図１に示すとおり、集電体としての金属箔である集電箔４上に電極膜層５を複数枚積層させ、電極膜６を形成している。電極膜層５は、充放電によりリチウムイオンの放出・吸蔵が可能な活物質１と導電材２、集電箔４と電極膜６とを接着するバインダ３を溶剤と共に混練して作製した電極スラリを固化・乾燥することにより形成される。 The lithium ion secondary battery in the present embodiment is wound or laminated via a separator that prevents contact between the positive electrode plate and the negative electrode plate. After the wound body or the laminated body is stored in the battery outer container, the electrolytic solution is injected into the outer container. As shown in FIG. 1, the positive electrode plate and the negative electrode plate are formed by laminating a plurality of electrode film layers 5 on a current collector foil 4 that is a metal foil as a current collector to form an electrode film 6. The electrode film layer 5 is an electrode slurry prepared by kneading an active material 1 capable of releasing and occluding lithium ions by charging and discharging, a conductive material 2, a binder 3 for bonding the current collector foil 4 and the electrode film 6 together with a solvent. It is formed by solidifying and drying.
　本実施形態におけるリチウムイオン二次電池の製造工程の概略について説明する。まず、活物質１、バインダ２、導電材４、第１の溶剤を含む電極スラリを、基材フィルム上に塗布する。塗布後直ちにバインダ２の固化材を含む第２の溶剤を電極スラリに接触させることでバインダを析出固化させる。その後，基材フィルムを剥離し、第二の溶剤で湿潤した固化電極膜を得る。この固化電極膜を集電箔４上に任意の枚数（複数枚）積層し、熱間プレス等で圧着し、残存した第２の溶剤を乾燥して液体成分を除去することで積層電極膜６を形成する。これらの工程によって、正極板と負極板のそれぞれを形成する。続いて、正極板と負極板の間に正極板と負極板との接触を防止しつつ、リチウムイオンを通過させる多孔質の絶縁材料からなるセパレータを挟み、正極板とセパレータと負極板を捲回する。これにより、捲回した正極板とセパレータと負極板からなる電極捲回体を形成することができる。次に、この電極捲回体を電池の外装容器に挿入して固定した後、外装容器の内部に電解液を注入する。そして、外装容器をキャップ封止することにより、リチウムイオン二次電池を製造することができる。この方法を用いることで、電極膜の密着性の低下は解消される。集電箔６と電極膜５との密着性の低下は電極膜５内のバインダ分布が乾燥工程中に不均一となり、集電箔６側のバインダ濃度が保護膜８側のバインダ濃度よりも低くなるため発生するものである。本実施形態では、塗布された電極スラリを固化し、その固化電極膜（電極膜層５）を複数積層して圧着する工程を追加したことにより、電極膜６内のバインダ分布が集電箔４側とその反対側（表面側）で不均一になるのを抑制することができるため、集電箔４との密着性が高くなる。 The outline of the manufacturing process of the lithium ion secondary battery in the present embodiment will be described. First, an electrode slurry containing the active material 1, the binder 2, the conductive material 4, and the first solvent is applied on the base film. Immediately after application, the binder is precipitated and solidified by bringing the second solvent containing the solidified material of the binder 2 into contact with the electrode slurry. Thereafter, the base film is peeled off to obtain a solidified electrode film wetted with the second solvent. Arbitrary number (a plurality) of this solidified electrode film is laminated on the current collector foil 4, pressure-bonded by hot pressing or the like, and the remaining second solvent is dried to remove the liquid component, thereby the laminated electrode film 6. Form. By these steps, each of the positive electrode plate and the negative electrode plate is formed. Subsequently, a separator made of a porous insulating material that allows lithium ions to pass through is sandwiched between the positive electrode plate and the negative electrode plate while preventing contact between the positive electrode plate and the negative electrode plate, and the positive electrode plate, the separator, and the negative electrode plate are wound. Thereby, the electrode winding body which consists of the wound positive electrode plate, separator, and negative electrode plate can be formed. Next, after inserting and fixing this electrode winding body in the exterior container of a battery, electrolyte solution is inject | poured inside the exterior container. And a lithium ion secondary battery can be manufactured by cap-sealing an exterior container. By using this method, the decrease in the adhesion of the electrode film is eliminated. The decrease in the adhesion between the current collector foil 6 and the electrode film 5 causes the binder distribution in the electrode film 5 to become non-uniform during the drying process, and the binder concentration on the current collector foil 6 side is lower than the binder concentration on the protective film 8 side. This is what happens. In the present embodiment, by adding a step of solidifying the applied electrode slurry, laminating a plurality of the solidified electrode films (electrode film layer 5) and press-bonding them, the binder distribution in the electrode film 6 is changed to the current collector foil 4. Since it can suppress that it becomes non-uniform | heterogenous on the side and the opposite side (surface side), adhesiveness with the current collector foil 4 becomes high.
　従来の電極膜の形成方法について図３、４を用いて説明する。従来は、集電箔４の表面に電極膜スラリを塗布し、そのまま乾燥室に導入して乾燥していた。 A conventional method for forming an electrode film will be described with reference to FIGS. Conventionally, an electrode film slurry was applied to the surface of the current collector foil 4 and introduced into a drying chamber as it was to be dried.
　すなわち、図３に示すように電極膜６の乾燥工程において電極膜６内の溶剤が蒸発することで乾燥してゆくが、電極膜６は集電箔４の表面に塗布されているため、溶剤は電極膜６の表面から蒸発してゆく。乾燥が進行するに伴い、集電箔４側の溶剤は電極膜６の表面に移動し、蒸発する。 That is, as shown in FIG. 3, in the drying process of the electrode film 6, the solvent in the electrode film 6 evaporates and dries. However, since the electrode film 6 is applied to the surface of the current collector foil 4, Evaporates from the surface of the electrode film 6. As the drying proceeds, the solvent on the side of the current collector foil 4 moves to the surface of the electrode film 6 and evaporates.
　溶剤の蒸発に伴い、溶剤に溶解しているバインダ３は、溶剤と共に図３の矢印の向きに電極膜６の表面に向けて移動する。移動した溶剤は表面から気化した溶剤７として蒸発してゆくが、溶解していたバインダ３は溶剤の蒸発と共に析出し、残存する。このメカニズムによってバインダ３は図２に示すように電極膜６の表面側に濃縮され、バインダ濃縮部８が形成される。 As the solvent evaporates, the binder 3 dissolved in the solvent moves together with the solvent toward the surface of the electrode film 6 in the direction of the arrow in FIG. The moved solvent evaporates as the solvent 7 evaporated from the surface, but the dissolved binder 3 is deposited with the evaporation of the solvent and remains. By this mechanism, the binder 3 is concentrated on the surface side of the electrode film 6 as shown in FIG. 2, and the binder concentration part 8 is formed.
　本実施形態のバインダ３を固化させる方法は、本実施形態の第１の溶剤を含む電極膜層５表面に本実施形態の固化材が含まれた第２の溶剤を接触させることでバインダ３を析出させるものであればよい。従って、第２の溶剤を溜めた液槽内を集電箔４表面に保持した塗布膜を通過させる方式や、集電箔４表面に保持した塗布膜に第２の溶剤をスプレーで吹きかける方式や、第２の溶剤を流下しながら供給する方式などが含まれるが、これらに限定されるものではない。 The method of solidifying the binder 3 of this embodiment is to bring the binder 3 into contact with the surface of the electrode film layer 5 containing the first solvent of this embodiment by contacting the second solvent containing the solidifying material of this embodiment. What is necessary is just to deposit. Therefore, a method of passing the coating film held on the surface of the current collector foil 4 through the liquid tank storing the second solvent, a method of spraying the second solvent on the coating film held on the surface of the current collector foil 4, A method of supplying the second solvent while flowing down is included, but is not limited thereto.
　本実施形態では、第１の溶剤中に溶解しているバインダ３の析出による固化であるので、固化が瞬時の場合バインダ分布は基本的に電極スラリのバインダ分布と同様、すなわちバインダ３は電極膜６中で均一分布となる。一方、実際のバインダ３の固化は塗布電極膜の表面から第二の溶剤が浸透し、第１の溶剤中に溶解しているバインダ３が第二の溶剤により析出する。すなわちバインダ３の析出は表面から集電箔４側へと進み、集電箔４側のほうのバインダ３の量が多くなる。このバインダ分布は従来の表面側のバインダ３が多いのとは逆に集電箔４側のバインダ３が多くなるため、集電箔４との密着性が良好な電極膜６が得られる。 In the present embodiment, since the solidification is caused by precipitation of the binder 3 dissolved in the first solvent, the binder distribution is basically the same as the binder distribution of the electrode slurry when the solidification is instantaneous, that is, the binder 3 is an electrode film. 6 has a uniform distribution. On the other hand, in actual solidification of the binder 3, the second solvent penetrates from the surface of the coated electrode film, and the binder 3 dissolved in the first solvent is precipitated by the second solvent. That is, the deposition of the binder 3 proceeds from the surface to the current collector foil 4 side, and the amount of the binder 3 on the current collector foil 4 side increases. Contrary to the conventional binder 3 on the surface side, the binder distribution increases on the current collector foil 4 side, so that the electrode film 6 having good adhesion to the current collector foil 4 is obtained.
　しかしながら、電極膜６の厚みが厚くなると表面側のバインダ３が減少し、活物質の脱落がおこる可能性がある。そこで本実施形態では電極膜層５を複数枚重ねることで、より均一性の高い厚膜電極を得ることが可能となった。電極膜層５一層の厚みは１０～２００μｍが好ましく、より好ましくは２０～１５０μｍ、より好ましくは５０～１００μｍの程度となる。 However, when the thickness of the electrode film 6 is increased, the binder 3 on the surface side is reduced, and the active material may fall off. Therefore, in this embodiment, it is possible to obtain a thick film electrode with higher uniformity by stacking a plurality of electrode film layers 5. The thickness of one electrode film layer 5 is preferably 10 to 200 μm, more preferably 20 to 150 μm, and more preferably 50 to 100 μm.
　また、固化に必要な接触時間の下限としては、概して、塗布膜内を第１の溶剤と第２の溶剤が相互拡散して置換する時間が必要であるが、電極膜層５の厚さが1ｍｍ以下であれば、接触時間は１から１００秒が好ましく、より好ましくは２秒から５０秒、さらに好ましくは５秒から２０秒の程度となる。 The lower limit of the contact time required for solidification generally requires time for the first solvent and the second solvent to diffuse and replace each other in the coating film, but the thickness of the electrode film layer 5 is If it is 1 mm or less, the contact time is preferably from 1 to 100 seconds, more preferably from 2 seconds to 50 seconds, and even more preferably from 5 seconds to 20 seconds.
　電極膜層５を集電箔４上に圧着する方法としては、一軸プレス、二軸プレス、ロールプレス、静水圧プレスなどを用いることができる。集電箔４との密着性の観点から、圧着時にはバインダ３の軟化点付近の温度でプレスする熱間プレスを用いることが好ましい。また、第二の溶剤の沸点以上の温度でプレスすることにより、圧着と同時に乾燥を行うこともできる。 As a method for pressure-bonding the electrode film layer 5 onto the current collector foil 4, a uniaxial press, a biaxial press, a roll press, an isostatic press, or the like can be used. From the viewpoint of adhesion to the current collector foil 4, it is preferable to use a hot press that presses at a temperature near the softening point of the binder 3 at the time of pressure bonding. Further, by pressing at a temperature equal to or higher than the boiling point of the second solvent, drying can be performed simultaneously with the pressure bonding.
　さらに電極膜層５は第２の溶媒で湿潤しており、可塑性が高く加工性能が高いため、電極打抜きなどの加工を行った後に圧着、乾燥を行いリチウムイオン二次電池の電極板を製造することができる。 Furthermore, since the electrode film layer 5 is wet with the second solvent and has high plasticity and high processing performance, it is pressed and dried after processing such as electrode punching to produce an electrode plate for a lithium ion secondary battery. be able to.
　本実施形態のバインダ３固化後の乾燥に伴うバインダ３の移動は起こらない。従って、電極膜６を乾燥させる方法は一般的な温風乾燥に限定されるものではない。赤外線あるいは遠赤外線もしくは可視光といった電磁波を照射する加熱方式であってもよく、あるいは高周波電場による誘電加熱方式であってもよく、あるいは磁束の変化を利用する誘導加熱方式を用いることも可能である。さらにはヒーターを組み込んだ加熱ロールやホットプレートを利用する接触加熱方式も用いることができる。 The movement of the binder 3 accompanying the drying after the binder 3 is solidified in this embodiment does not occur. Therefore, the method for drying the electrode film 6 is not limited to general hot air drying. A heating method that irradiates electromagnetic waves such as infrared rays, far-infrared rays, or visible light may be used, or a dielectric heating method that uses a high-frequency electric field, or an induction heating method that uses a change in magnetic flux may be used. . Furthermore, a contact heating method using a heating roll or a hot plate incorporating a heater can also be used.
　また、本実施形態の電極膜スラリを塗布する方法として、例えば、押出しコーター、リバースローラー、ドクターブレード、アプリケーターなどをはじめ、各種塗布方法を採用することができる。 In addition, as a method for applying the electrode film slurry of the present embodiment, various application methods such as an extrusion coater, a reverse roller, a doctor blade, an applicator and the like can be employed.
　本実施形態で用いる活物質１のうち、正極に用いられる正極活物質としては、コバルト酸リチウムや、マンガンを含有するスピネル構造のリチウム含有複合酸化物、もしくはニッケル、コバルト、マンガンを含んでなる複合酸化物、あるいはオリビン型リン酸鉄に代表されるオリビン型化合物などを使用するが、これらに限定されるわけではない。マンガンを含有するスピネル構造のリチウム含有複合酸化物は熱的安定性に優れているため、例えば、安全性の高い電池を構成することができる。また正極活物質には、マンガンを含有するスピネル構造のリチウム含有複合酸化物のみを用いてもよいが、他の正極活物質を併用してもよい。このような他の正極活物質としては、例えば、Li１＋ｘＭＯ２(－０．１＜ｘ＜０．１、Ｍ：Ｃｏ、Ｎｉ、Ｍｎ、Ａｌ、Ｍｇ、Ｚｒ、Ｔｉなど)で表わされるオリビン型化合物などが挙げられる。また層状構造のリチウム含有遷移金属酸化物の具体例としては、ＬｉＣｏＯ２やＬｉＮｉ１－ｘＣｏｘ－ｙＡｌｙＯ２(０．１≦ｘ≦０．３、０．０１≦ｙ≦０．２)などの他、少なくともＣｏ、ＮｉおよびＭｎを含む酸化物(ＬｉＭｎ１／３Ｎｉ１／３Ｃｏ１／３Ｏ２、ＬｉＭｎ５／１２Ｎｉ５／１２Ｃｏ１／６Ｏ２、ＬｉＮｉ３／５Ｍｎ１／５Ｃｏ１／５Ｏ２など)などを用いることができる。 Among the active materials 1 used in the present embodiment, the positive electrode active material used for the positive electrode is lithium cobaltate, a spinel-structure lithium-containing composite oxide containing manganese, or a composite containing nickel, cobalt, and manganese. Although an oxide or an olivine type compound represented by olivine type iron phosphate is used, it is not limited thereto. Since the lithium-containing composite oxide having a spinel structure containing manganese is excellent in thermal stability, for example, a highly safe battery can be configured. As the positive electrode active material, only a lithium-containing composite oxide having a spinel structure containing manganese may be used, but another positive electrode active material may be used in combination. Examples of such other positive electrode active materials include olivine type compounds represented by Li1 + xMO2 (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, etc.) Is mentioned. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO2 and LiNi1-xCox-yAlyO2 (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0.2), and at least Co. An oxide containing Ni and Mn (LiMn1 / 3Ni1 / 3Co1 / 3O2, LiMn5 / 12Ni5 / 12Co1 / 6O2, LiNi3 / 5Mn1 / 5Co1 / 5O2, etc.) can be used.
　また、活物質１のうち、負極に用いられる負極活物質としては、例えば、天然黒鉛(鱗片状黒鉛)、人造黒鉛、膨張黒鉛などの黒鉛材料；ピッチを焼成して得られるコークスなどの易黒鉛化性炭素質材料；フルフリルアルコール樹脂(ＰＦＡ)やポリパラフェニレン(ＰＰＰ)およびフェノール樹脂を低温焼成して得られる非晶質炭素などの難黒鉛化性炭素質材料などの炭素材料が挙げられる。また、炭素材料の他に、リチウムやリチウム含有化合物も負極活物質として用いることができる。リチウム含有化合物としては、Ｌｉ－Ａｌなどのリチウム合金や、Ｓｉ、Ｓｎなどのリチウムとの合金化が可能な元素を含む合金が挙げられる。更にＳｎ酸化物やＳｉ酸化物などの酸化物系材料も用いることも可能である。 Among the active materials 1, examples of the negative electrode active material used for the negative electrode include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; and easy graphite such as coke obtained by firing a pitch. Carbonaceous materials; carbon materials such as non-graphitizable carbonaceous materials such as amorphous carbon obtained by low-temperature firing of furfuryl alcohol resin (PFA), polyparaphenylene (PPP) and phenol resin . In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include a lithium alloy such as Li—Al, and an alloy containing an element that can be alloyed with lithium such as Si and Sn. Furthermore, oxide-based materials such as Sn oxide and Si oxide can also be used.
　導電材２としては、通常、正極電極膜に含有させる電子伝導助剤として用いるもので、例えば、カーボンブラック、アセチレンブラック、ケッチェンブラック、グラファイト、カーボンファイバー、カーボンナノチューブなどの炭素材料が好ましい。上記の炭素材料の中でも、添加量と導電性の効果、および塗布用正極合剤スラリの製造性の点から、アセチレンブラックまたはケッチェンブラックが特に好ましい。かかる導電材２は負極電極膜に含有させることも可能であり、好ましい場合もある。 The conductive material 2 is usually used as an electron conduction aid to be contained in the positive electrode film. For example, carbon materials such as carbon black, acetylene black, ketjen black, graphite, carbon fiber, and carbon nanotube are preferable. Among the above carbon materials, acetylene black or ketjen black is particularly preferable from the viewpoint of the amount of addition and conductivity, and the manufacturability of the positive electrode mixture slurry for coating. Such a conductive material 2 can be contained in the negative electrode film, and may be preferable.
　本実施液体に用いるバインダとしては、例えば、ポリビニリデンフルオライド系ポリマー（主成分モノマーであるビニリデンフルオライドを８０質量％以上含有する含フッ素モノマー群の重合体）、ゴム系ポリマーなどが好適に用いられる。上記ポリマーは、２種以上を併用してもよい。また、本発明のバインダ３は、溶媒に溶解した溶液の形態で供されるものが好ましい。 As the binder used in this embodiment liquid, for example, a polyvinylidene fluoride polymer (a polymer of a fluorine-containing monomer group containing 80% by mass or more of vinylidene fluoride as a main component monomer), a rubber polymer, or the like is preferably used. It is done. Two or more of the above polymers may be used in combination. Further, the binder 3 of the present invention is preferably provided in the form of a solution dissolved in a solvent.
　上記ポリビニリデンフルオライド系ポリマーを合成するための含フッ素モノマー群としては、ビニリデンフルオライド；ビニリデンフルオライドと他のモノマーとの混合物で、ビニリデンフルオライドを８０質量％以上含有するモノマー混合物；などが挙げられる。 Examples of the fluorine-containing monomer group for synthesizing the polyvinylidene fluoride-based polymer include vinylidene fluoride; a mixture of vinylidene fluoride and another monomer, and a monomer mixture containing 80% by mass or more of vinylidene fluoride; Can be mentioned.
　他のモノマーとしては、例えば、ビニルフルオライド、トリフルオロエチレン、トリフルオロクロロエチレン、テトラフルオロエチレン、ヘキサフルオロプロピレン、フルオロアルキルビニルエーテルなどが挙げられる。 Examples of other monomers include vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, and fluoroalkyl vinyl ether.
　上記のゴム系ポリマーとしては、例えば、スチレンブタジエンゴム（ＳＢＲ）、エチレンプロピレンジエンゴム、フッ素ゴムなどが挙げられる。 Examples of the rubber-based polymer include styrene butadiene rubber (SBR), ethylene propylene diene rubber, and fluorine rubber.
　また、本実施形態のバインダ３は、電極膜６を固化させる固化材としての性能を有する成分と別個に加えてもよいし、バインダ３自体が固化材としての機能を有していてもよい。バインダ３を固化材としての性能を有する成分と別個に加える場合、バインダ３は活物質１および導電材２を結着する性質をもつ上記ポリマー材料が好適に使用されるが、必ずしも溶剤２に溶解した溶液の形態である必要はなく、液中にポリマー材料を分散させたエマルジョンの形態であってもよい。 Further, the binder 3 of this embodiment may be added separately from the component having the performance as a solidifying material for solidifying the electrode film 6, or the binder 3 itself may have a function as a solidifying material. When the binder 3 is added separately from the component having the performance as a solidifying material, the binder 3 is preferably the polymer material having the property of binding the active material 1 and the conductive material 2, but is not necessarily dissolved in the solvent 2. The solution is not necessarily in the form of a solution, and may be in the form of an emulsion in which the polymer material is dispersed in the liquid.
　電極膜６中におけるバインダ３の含有量は、乾燥後の電極膜６を基準として０．1質量％以上、より好ましくは０．３質量％以上であって、１０質量％以下、より好ましくは５質量％以下であることが望ましい。バインダ３の含有量が少なすぎると、本実施形態の固化工程における固化が不十分となるばかりでなく、乾燥後の電極膜６の機械的強度が不足し、電極膜が集電箔から剥離する問題がある。また、バインダ３の含有量が多すぎると、電極膜６中の活物質量が減少して、電池容量が低くなるおそれがある。 The content of the binder 3 in the electrode film 6 is 0.1% by mass or more, more preferably 0.3% by mass or more and 10% by mass or less, more preferably 5% based on the electrode film 6 after drying. It is desirable that it is less than mass%. If the content of the binder 3 is too small, not only is the solidification in the solidification step of the present embodiment insufficient, but the mechanical strength of the electrode film 6 after drying is insufficient, and the electrode film peels from the current collector foil. There's a problem. Moreover, when there is too much content of the binder 3, there exists a possibility that the amount of active materials in the electrode film 6 may reduce, and battery capacity may become low.
　本実施形態の溶剤２はバインダ３と電極膜層５の材料が含まれる第１の溶剤と固化材４が含まれる第２の溶剤を適切に選択して使うことが重要である。また、溶剤２は本実施形態の固化材もしくは固化材を兼用するバインダ３の成分の溶解性、溶剤相互の溶解性から選択されるべきである。第１の溶剤としてＮ－メチルピロリドン、ジメチルスルホキシド、プロピレンカーボネート、ジメチルホルムアミド、γ－ブチロラクトンなどに代表される非プロトン性極性溶剤もしくはこれらの混合液を選択できる。また、第２の溶剤として水、エタノール、イソプロピルアルコール、酢酸などに代表されるプロトン性溶剤もしくはこれらの混合液を選択できるが、ここにあげた例に限定されるわけではない。場合によっては第２の溶剤として脂肪族飽和炭化水素、脂肪族アミン類、エステル類、エーテル類、ハロゲン系各種溶剤などの選択も可能である。さらに、場合によっては第１の溶剤と第２の溶剤を交換する選択も可能である。かかる本実施形態の溶剤２の選択は電極膜に用いる固化成分の選択とそれに合致した２種の溶剤２の組み合わせに依存するのである。 It is important that the solvent 2 of the present embodiment is appropriately selected from the first solvent containing the binder 3 and the electrode film layer 5 and the second solvent containing the solidifying material 4. Moreover, the solvent 2 should be selected from the solubility of the solidifying material of this embodiment or the component of the binder 3 that also serves as the solidifying material, and the mutual solubility of the solvent. As the first solvent, an aprotic polar solvent represented by N-methylpyrrolidone, dimethyl sulfoxide, propylene carbonate, dimethylformamide, γ-butyrolactone, or a mixture thereof can be selected. As the second solvent, a protic solvent typified by water, ethanol, isopropyl alcohol, acetic acid or the like, or a mixed solution thereof can be selected, but is not limited to the examples given here. In some cases, aliphatic saturated hydrocarbons, aliphatic amines, esters, ethers, various halogen-based solvents, and the like can be selected as the second solvent. Further, in some cases, it is possible to select to exchange the first solvent and the second solvent. The selection of the solvent 2 in this embodiment depends on the selection of the solidifying component used for the electrode film and the combination of the two kinds of solvents 2 corresponding to the selection.
　また本実施形態で用いる集電箔４は代表的に示したものであり、シート状の箔に限定されることはなく、その基体としては、例えば、アルミニウム、銅、ステンレス鋼、チタンなどの純金属もしくは合金性導電材料を用いて、その形状として、網、パンチドメタル、フォームメタルや、板状に加工した箔などが用いられる。導電性基体の厚みとしては、例えば、5から３０μｍ、より好ましくは８から１６μｍが選択される。 The current collector foil 4 used in the present embodiment is representatively shown, and is not limited to a sheet-like foil. Examples of the substrate include pure aluminum, copper, stainless steel, titanium, and the like. A metal, an alloy conductive material, or a net, a punched metal, a foam metal, a foil processed into a plate shape, or the like is used. As the thickness of the conductive substrate, for example, 5 to 30 μm, more preferably 8 to 16 μm is selected.
　本実施形態により提供され得るリチウムイオン二次電池は、上述した方法で製造される正極及び負極を含むこと以外は従来の二次電池と同様にして製造することができる。電池の該容器の構造やサイズ、あるいは正負極を主構成要素とする電極体の構造等について、特に制限はない。 The lithium ion secondary battery that can be provided by the present embodiment can be manufactured in the same manner as a conventional secondary battery except that it includes a positive electrode and a negative electrode manufactured by the above-described method. There is no particular limitation on the structure and size of the battery container or the structure of the electrode body having positive and negative electrodes as main components.
　以上、本実施形態によれば電極膜６内でバインダ２の濃度が不均一になるのを抑制し、密着性の高く、高容量な電極膜６を有するリチウムイオン二次電池を製造することができる。以下本実施形態の好適な実施例について、実験結果に基づいて説明する。 As described above, according to the present embodiment, it is possible to suppress the non-uniform concentration of the binder 2 in the electrode film 6 and to manufacture a lithium ion secondary battery having the electrode film 6 with high adhesion and high capacity. it can. Hereinafter, preferred examples of the present embodiment will be described based on experimental results.
　ここでは、１００μｍの固化正極膜の向き（剥離面を裏とする）を同じ向きに集電箔４側のバインダ３の濃度が表面側のバインダ３の濃度よりも高くなるように５層積層し、５００μｍの積層正極板を作製する場合について述べる。 Here, five layers are laminated so that the concentration of the binder 3 on the side of the current collector foil 4 is higher than the concentration of the binder 3 on the surface side with the direction of the solidified positive electrode film of 100 μm (with the peeled surface as the back) in the same direction. A case where a 500 μm laminated positive electrode plate is manufactured will be described.
　まず、正極スラリの作製法について説明する。活物質としてリチウム遷移金属複合酸化物のリチウムマンガンコバルトニッケル複合酸化物粉末を用いた。このリチウムマンガンコバルトニッケル複合酸化物を８５重量部に対して、導電材として黒鉛粉末を９重量部およびカーボンブラックを２重量部とを混合して正極合剤として調製した。この正極合剤にポリフッ化ビニリデン（以下、ＰＶＤＦと略記する。）が４重量部となるようにポリフッ化ビニリデンを溶解したＮ－メチル－２－ピロリドン（以下、ＮＭＰと略記する。）溶液（バインダ溶液）を加えるとともにＮＭＰに分散させてスラリ状とした。 First, a method for producing a positive electrode slurry will be described. A lithium transition metal composite oxide lithium manganese cobalt nickel composite oxide powder was used as an active material. To 85 parts by weight of this lithium manganese cobalt nickel composite oxide, 9 parts by weight of graphite powder and 2 parts by weight of carbon black as a conductive material were mixed to prepare a positive electrode mixture. An N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) solution (binder) in which polyvinylidene fluoride is dissolved so that 4 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) is added to this positive electrode mixture. Solution) and dispersed in NMP to form a slurry.
　その後、上記で作製した正極膜用のスラリをポリプロピレンの基材フィルム表面へダイコータを使用し塗布する。続いて塗布正極膜を純水中に５秒間浸漬させバインダを固化させた後、基材フィルムを剥離し固化正極膜を形成する。固化正極膜の基材フィルムに接触していた側が集電箔側に来るように５層積層し、１２０度の熱間ロールプレスを用いて圧着を行った。その後、温風乾燥炉にて昇温速度３度/秒にて１２０度で残存した液体成分を乾燥させ、積層正極板を形成した。 Thereafter, the slurry for the positive electrode film prepared above is applied to the surface of the polypropylene base film using a die coater. Subsequently, the coated positive electrode film is immersed in pure water for 5 seconds to solidify the binder, and then the base film is peeled off to form a solidified positive electrode film. Five layers were laminated so that the side of the solidified positive electrode film that was in contact with the base film was on the current collector foil side, and pressure bonding was performed using a 120-degree hot roll press. Thereafter, the remaining liquid component was dried at 120 ° C. in a warm air drying furnace at a temperature rising rate of 3 ° / second to form a laminated positive electrode plate.
　作製した積層正極板のバインダ分布は図５に示すように、複数の層からなり、各層における集電箔側のバインダの量が表面近傍と比較して増加していた。各層の集電箔側のバインダの量は５．２％、表面側は４．２％と２４％多かった。 As shown in FIG. 5, the binder distribution of the produced laminated positive electrode plate was composed of a plurality of layers, and the amount of the binder on the current collector foil side in each layer was increased as compared with the vicinity of the surface. The amount of binder on the current collector foil side of each layer was 5.2%, and the surface side was 4.2%, which was 24% more.
　ここでは、１００μｍの固化正極膜の向き（剥離面を裏とする）を交互に５層積層し、集電箔４側のバインダ３の濃度が表面側のバインダ３の濃度よりも高い層と集電箔４側のバインダ３の濃度が表面側のバインダ３の濃度よりも低い層とが交互になるように５００μｍの積層正極板を作製する場合について述べる。 Here, five layers of 100 μm solidified positive electrode films (with the peeled surface as the back) are alternately stacked, and the concentration of the binder 3 on the current collecting foil 4 side is higher than the concentration of the binder 3 on the surface side. A case will be described in which a laminated positive electrode plate having a thickness of 500 μm is produced so that layers having a binder 3 concentration on the electric foil 4 side are alternately lower than the concentration of the binder 3 on the surface side.
　まず、正極スラリの作製法について説明する。活物質としてリチウム遷移金属複合酸化物のリチウムマンガンコバルトニッケル複合酸化物粉末を用いた。このリチウムマンガンコバルトニッケル複合酸化物を８５重量部に対して、導電材として黒鉛粉末を９重量部およびカーボンブラックを２重量部とを混合して正極合剤として調製した。この正極合剤にポリフッ化ビニリデン（以下、ＰＶＤＦと略記する。）が４重量部となるようにポリフッ化ビニリデンを溶解したＮ－メチル－２－ピロリドン（以下、ＮＭＰと略記する。）溶液（バインダ溶液）を加えるとともにＮＭＰに分散させてスラリ状とした。 First, a method for producing a positive electrode slurry will be described. A lithium transition metal composite oxide lithium manganese cobalt nickel composite oxide powder was used as an active material. To 85 parts by weight of this lithium manganese cobalt nickel composite oxide, 9 parts by weight of graphite powder and 2 parts by weight of carbon black as a conductive material were mixed to prepare a positive electrode mixture. An N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) solution (binder) in which polyvinylidene fluoride is dissolved so that 4 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) is added to this positive electrode mixture. Solution) and dispersed in NMP to form a slurry.
　その後、上記で作製した正極膜用のスラリをポリプロピレンの基材フィルム表面へダイコータを使用し塗布する。続いて塗布正極膜を純水中に５秒間浸漬させバインダを固化させた後、基材フィルムを剥離し固化正極膜を形成する。固化正極膜の基材フィルムに接触していた側（裏面）と表面側（表面）が交互になるように５層積層し、１２０度の熱間ロールプレスを用いて圧着を行った。このとき、最も集電箔に近い層は裏面が集電箔側になるように積層した。その後、温風乾燥炉にて昇温速度３度/秒にて１２０度で残存した液体成分を乾燥させ、積層正極板を形成した。 Thereafter, the slurry for the positive electrode film prepared above is applied to the surface of the polypropylene base film using a die coater. Subsequently, the coated positive electrode film is immersed in pure water for 5 seconds to solidify the binder, and then the base film is peeled off to form a solidified positive electrode film. Five layers were laminated so that the side (back surface) and the surface side (front surface) that were in contact with the base film of the solidified positive electrode film were alternated, and pressure bonding was performed using a 120-degree hot roll press. At this time, the layer closest to the current collector foil was laminated so that the back surface was on the current collector foil side. Thereafter, the remaining liquid component was dried at 120 ° C. in a warm air drying furnace at a temperature rising rate of 3 ° / second to form a laminated positive electrode plate.
　作製した積層正極板のバインダ分布は図５に示すように、複数の層からなり、最も集電箔に近い層における集電箔側のバインダの量が表面近傍と比較して増加していた。その上部の層は、表面側のバインダ量が集電箔側より多い層と表面側のバインダ量が集電箔側より少ない層が交互に存在していた。表面側と集電箔側のバインダ濃度の差はいずれも２４％であった。
（比較例１）
　ここでは実施例１の正極膜用のスラリをアルミニウムで形成された集電箔の表面へダイコータを使用し塗布する。続いて塗布正極膜を温風乾燥炉にて昇温速度３℃/秒にて１２０℃で乾燥させ、厚さ５００μｍの正極膜を形成した。 As shown in FIG. 5, the binder distribution of the produced laminated positive electrode plate was composed of a plurality of layers, and the amount of the binder on the side of the current collector foil in the layer closest to the current collector foil was increased as compared with the vicinity of the surface. In the upper layer, a layer having a larger amount of binder on the front side than that on the current collector foil side and a layer having a smaller amount of binder on the front side than that on the current collector foil side were alternately present. The difference in the binder concentration between the surface side and the current collector foil side was 24%.
(Comparative Example 1)
Here, the slurry for the positive electrode film of Example 1 is applied to the surface of the current collector foil formed of aluminum using a die coater. Subsequently, the coated positive electrode film was dried at 120 ° C. at a temperature rising rate of 3 ° C./second in a warm air drying furnace to form a positive electrode film having a thickness of 500 μm.
　作製した正極膜のバインダ分布は図６に示すように、集電箔側のバインダの量が表面近傍と比較して減少しており、正極膜の集電箔側のバインダの量は２．２％、表面側は６．５％と６６％少なかった。
（実施例１、２の効果）
　実施例１、２のように、バインダを固化させると、基材フィルム側のバインダ濃度が高くなる。実施例１、２では、いずれも集電箔側のバインダ濃度が表面側のバインダ濃度よりも高くなるように各電極膜層を積層した。このように電極膜層を集電箔に圧着すると、集電箔との密着性が高くなり、集電箔側の電極膜との剥離を防止することが可能となる。一方、比較例１のように温風乾燥炉にて乾燥を行うと、集電箔側のバインダ濃度が表面側のバインダ濃度よりも低くなり、表面へのバインダ偏析が顕著となり、集電箔の密着性が低下し、電極膜剥離の危険性がある。 As shown in FIG. 6, the binder distribution of the produced positive electrode film is such that the amount of the binder on the side of the current collector foil is smaller than that near the surface, and the amount of the binder on the side of the current collector foil of the positive electrode film is 2.2. %, And the surface side was 6.5%, 66% less.
(Effects of Examples 1 and 2)
When the binder is solidified as in Examples 1 and 2, the binder concentration on the base film side increases. In each of Examples 1 and 2, the electrode film layers were laminated so that the binder concentration on the current collector foil side was higher than the binder concentration on the surface side. When the electrode film layer is pressure-bonded to the current collector foil in this manner, the adhesiveness with the current collector foil is increased, and peeling from the electrode film on the current collector foil side can be prevented. On the other hand, when drying is performed in a warm air drying furnace as in Comparative Example 1, the binder concentration on the current collector foil side is lower than the binder concentration on the front surface side, and binder segregation on the surface becomes remarkable, and There is a risk of electrode film peeling due to reduced adhesion.
　また、実施例１、２では、いずれも各電極膜層の表面側と集電箔側のバインダ濃度の差は５０％以下であった。これにより、固化電極膜を複数重ねて厚膜化しても、より均一性に優れた厚膜電極を得ることができ、表面側のバインダ濃度も高く保つことにより、活物質等の脱落を抑制できる。 In Examples 1 and 2, the difference in binder concentration between the surface side of each electrode film layer and the current collector foil side was 50% or less. As a result, even if a plurality of solidified electrode films are stacked to increase the thickness, a thick film electrode with more uniformity can be obtained, and by keeping the binder concentration on the surface side high, dropping off of the active material can be suppressed. .
　以上より、実施例１、２によれば、バインダの量を多くせずに電極膜５との剥離を防止かつ表面近傍の可塑性も保つことができるため、電池容量の低下を抑制することが可能となる。 As described above, according to the first and second embodiments, it is possible to prevent the peeling from the electrode film 5 without increasing the amount of the binder and to maintain the plasticity in the vicinity of the surface. It becomes.
１　活物質
２　導電材
３　バインダ
４　集電箔
５　電極膜層
６　電極膜
７　気化した溶剤
８　バインダ濃縮部 DESCRIPTION OF SYMBOLS 1 Active material 2 Conductive material 3 Binder 4 Current collecting foil 5 Electrode film layer 6 Electrode film 7 Vaporized solvent 8 Binder concentration part

Claims (8)

  1. 　集電体としての集電箔と、
    　前記集電箔の表面に前記集電膜に接着するバインダが含まれる電極膜層が複数層積層された電極膜とを有し、
    　前記電極膜層は、前記集電箔側の前記バインダの濃度が前記集電箔の反対側の前記バインダの濃度よりも高い層を含むことを特徴とするリチウムイオン二次電池。     Current collector foil as a current collector;
    An electrode film in which a plurality of electrode film layers including a binder that adheres to the current collector film are stacked on the surface of the current collector foil;
    The lithium ion secondary battery, wherein the electrode film layer includes a layer in which the concentration of the binder on the side of the current collector foil is higher than the concentration of the binder on the side opposite to the current collector foil.
  2. 　前記電極膜は、前記集電箔側の前記バインダの濃度が前記集電箔の反対側の前記バインダの濃度よりも高い層と前記集電箔側の前記バインダの濃度が前記集電箔の反対側の前記バインダの濃度よりも低い層とを含むことを特徴とするリチウムイオン二次電池。 The electrode film has a layer in which the concentration of the binder on the side of the current collector foil is higher than the concentration of the binder on the side opposite to the current collector foil and the concentration of the binder on the side of the current collector foil is opposite to that of the current collector foil And a layer lower than the binder concentration on the side.
  3. 　前記電極膜層の前記集電箔側の前記バインダと反対側の前記バインダとの濃度差が50％以下であることを特徴とする請求項１または請求項２に記載のリチウムイオン二次電池。 3. The lithium ion secondary battery according to claim 1, wherein a concentration difference between the binder on the current collecting foil side and the binder on the opposite side of the electrode film layer is 50% or less. 4.
  4. 　前記バインダは、ポリビニリデンフルオライド系ポリマー、ゴム系ポリマーもしくはそれらの混合物であることを特徴とする請求項１または請求項２に記載のリチウムイオン二次電池。 3. The lithium ion secondary battery according to claim 1, wherein the binder is a polyvinylidene fluoride polymer, a rubber polymer, or a mixture thereof.
  5. 　前記バインダは、前記電極膜を固化させる成分を有することを特徴とする請求項１または請求項２に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1 or 2, wherein the binder has a component that solidifies the electrode film.
  6. 　前記固化剤は水、エタノール、イソプロピルアルコール、酢酸などに代表されるプロトン性溶剤もしくはこれらの混合液を含むことを特徴とする請求項５に記載のリチウムイオン二次電池。 6. The lithium ion secondary battery according to claim 5, wherein the solidifying agent contains a protic solvent typified by water, ethanol, isopropyl alcohol, acetic acid or the like, or a mixture thereof.
  7. 　集電体としての集電箔と電極膜とを接着するバインダと前記電極膜の材料とを第１の溶剤と混錬して電極スラリを作製する第１の工程と、
    　第２の溶剤を前記電極スラリに接触させ、前記バインダを析出させる第２の工程と、
    　前記集電箔上に前記電極膜層を複数層数積層させる第３の工程と、
    　前記電極膜層から液体成分を除去して乾燥する第４の工程とを含むことを特徴とするリチウムイオン二次電池の製造方法。     A first step of preparing an electrode slurry by kneading a binder for adhering a current collector foil as a current collector and an electrode film and a material of the electrode film with a first solvent;
    A second step of bringing a second solvent into contact with the electrode slurry and depositing the binder;
    A third step of laminating a plurality of the electrode film layers on the current collector foil;
    And a fourth step of removing the liquid component from the electrode film layer and drying it. A method for producing a lithium ion secondary battery, comprising:
  8. 　前記第１の溶剤はＮ－メチルピロリドン、ジメチルスルホキシド、プロピレンカーボネート、ジメチルホルムアミド、γ－ブチロラクトンなどに代表される非プロトン性極性溶剤もしくはこれらの混合液を含み、前記第２の溶剤は水、エタノール、イソプロピルアルコール、酢酸などに代表されるプロトン性溶剤もしくはこれらの混合液を含むことを特徴とする請求項７に記載のリチウムイオン二次電池の製造方法。 The first solvent includes an aprotic polar solvent represented by N-methylpyrrolidone, dimethyl sulfoxide, propylene carbonate, dimethylformamide, γ-butyrolactone, or a mixture thereof, and the second solvent is water, ethanol The method for producing a lithium ion secondary battery according to claim 7, comprising a protic solvent represented by isopropyl alcohol, acetic acid, or a mixture thereof.
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