WO2015098050A1 - Slurry composition for negative electrodes of lithium ion secondary batteries, negative electrode for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Slurry composition for negative electrodes of lithium ion secondary batteries, negative electrode for lithium ion secondary batteries, and lithium ion secondary battery Download PDF

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Publication number
WO2015098050A1
WO2015098050A1 PCT/JP2014/006310 JP2014006310W WO2015098050A1 WO 2015098050 A1 WO2015098050 A1 WO 2015098050A1 JP 2014006310 W JP2014006310 W JP 2014006310W WO 2015098050 A1 WO2015098050 A1 WO 2015098050A1
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Prior art keywords
negative electrode
lithium ion
ion secondary
secondary battery
mass
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PCT/JP2014/006310
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French (fr)
Japanese (ja)
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政憲 渋谷
園部　健矢
金田　拓也
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日本ゼオン株式会社
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Priority to CN201480068304.XA priority Critical patent/CN105830257B/en
Priority to JP2015554544A priority patent/JP6459977B2/en
Priority to KR1020167015619A priority patent/KR102272378B1/en
Publication of WO2015098050A1 publication Critical patent/WO2015098050A1/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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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 slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
  • Lithium ion secondary batteries are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.
  • the silicon-based negative electrode active material has a high theoretical capacity and can increase the battery capacity of the lithium ion secondary battery, it greatly expands and contracts with charge and discharge. Accordingly, in a negative electrode using a silicon-based negative electrode active material, deterioration of the silicon-based negative electrode active material itself (that is, structural destruction of the silicon-based negative electrode active material) due to expansion and contraction of the silicon-based negative electrode active material due to repeated charge / discharge. Miniaturization) and / or destruction of the electrode plate structure, and the conductive path in the electrode is destroyed. That is, a lithium ion secondary battery including a negative electrode using a silicon-based negative electrode active material has a problem in that cycle characteristics deteriorate due to large expansion and contraction of the silicon-based negative electrode active material.
  • the above-mentioned conventional technology cannot sufficiently suppress the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge, and it is a high dimension to increase the capacity of the lithium ion secondary battery and suppress the deterioration of the cycle characteristics. It was not possible to achieve both.
  • a negative electrode for a lithium ion secondary battery is prepared by applying a negative electrode slurry composition in which a negative electrode active material and a binder are dispersed in a dispersion medium on a current collector and drying the negative electrode active material and It is manufactured by forming a negative electrode composite material layer containing a binder on a current collector.
  • the viscosity of the slurry composition for negative electrode is increased when the blending amount or molecular weight of polyacrylic acid is increased in order to suppress the expansion and contraction of the silicon-based negative electrode active material.
  • the coating property was lowered due to the increase.
  • the present invention can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material that accompanies charge / discharge when used for the formation of the negative electrode, and is a lithium ion secondary that is excellent in coatability. It aims at providing the slurry composition for battery negative electrodes. Moreover, an object of this invention is to provide the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics. Another object of the present invention is to provide a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics.
  • the present inventor has intensively studied for the purpose of solving the above problems. And this inventor made the ratio of the silicon type negative electrode active material in a negative electrode active material into a predetermined range, and mix
  • the slurry composition for a lithium ion secondary battery negative electrode of the present invention comprises a negative electrode active material, polyacrylic acid, and water.
  • the negative electrode active material contains a silicon-based negative electrode active material in a proportion of 5% by mass to 40% by mass
  • the polyacrylic acid has a viscosity of 1% by mass aqueous solution with respect to the viscosity of the 0.5% by mass aqueous solution.
  • the ratio viscosity of 1% by mass aqueous solution / viscosity of 0.5% by mass aqueous solution) is 2.0 or more.
  • the polyacrylic acid in which the ratio of the viscosity of the 1% by mass aqueous solution to the viscosity of the 0.5% by mass aqueous solution satisfies the predetermined size, with the negative electrode active material having a silicon-based negative electrode active material content in the predetermined range.
  • the battery capacity can be increased while suppressing the expansion and contraction of the silicon-based negative electrode active material.
  • the slurry composition is excellent in coatability.
  • viscosity of an aqueous solution of polyacrylic acid is a condition of temperature 25 ° C., pH 8, rotor M4, rotation speed 60 rpm in accordance with JIS K7117-1, using a B-type viscometer. It refers to the viscosity of the polyacrylic acid aqueous solution measured below.
  • the slurry composition for a lithium ion secondary battery negative electrode of the present invention further contains a carboxymethyl cellulose salt. This is because the storage stability of the slurry composition can be improved by adding carboxymethylcellulose salt.
  • the negative electrode for lithium ion secondary batteries of this invention is either of the slurry composition for lithium ion secondary battery negative electrodes mentioned above. It has the negative mix layer obtained by using, It is characterized by the above-mentioned.
  • the negative electrode mixture layer formed using the lithium ion secondary battery negative electrode slurry composition expansion and contraction associated with charge and discharge of a silicon-based negative electrode active material having a high theoretical capacity can be suppressed. Therefore, if a negative electrode having the negative electrode composite material layer is used, a lithium ion secondary battery having excellent battery capacity and cycle characteristics can be provided.
  • the lithium ion secondary battery of this invention is the negative electrode for lithium ion secondary batteries mentioned above, a positive electrode, electrolyte solution, And a separator.
  • a lithium ion secondary battery using the negative electrode for a lithium ion secondary battery has a high battery capacity and excellent cycle characteristics.
  • a lithium ion secondary when used for forming a negative electrode, a lithium ion secondary that can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge and that is excellent in coatability.
  • a slurry composition for a battery negative electrode can be provided.
  • the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics can be provided.
  • a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics can be provided.
  • the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is used for forming a negative electrode of a lithium ion secondary battery.
  • the negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for lithium ion secondary batteries negative electrode of this invention.
  • the lithium ion secondary battery of the present invention is characterized by using the negative electrode for a lithium ion secondary battery of the present invention.
  • the lithium ion secondary battery negative electrode slurry composition of the present invention is an aqueous slurry composition containing a negative electrode active material, polyacrylic acid, and water.
  • the negative electrode active material of the slurry composition for lithium ion secondary battery negative electrodes of this invention contains a silicon type negative electrode active material in the ratio of 5 to 40 mass%.
  • the polyacrylic acid of the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is a ratio of the viscosity of a 1% by weight aqueous solution to the viscosity of a 0.5% by weight aqueous solution (viscosity of 1% by weight aqueous solution / 0.5% by weight % Aqueous solution) is 2.0 or more.
  • the slurry composition for lithium ion secondary battery negative electrodes of this invention may contain other components, such as a carboxymethylcellulose salt and a particulate binder other than a negative electrode active material and polyacrylic acid.
  • a negative electrode active material contains a silicon-type negative electrode active material in the ratio of 5 mass% or more, the battery capacity of a lithium ion secondary battery is raised.
  • a negative electrode that can be formed can be formed.
  • the negative electrode active material contains a silicon-based negative electrode active material in a proportion of 40% by mass or less, and the viscosity ratio of polyacrylic acid (1 (Viscosity of mass% aqueous solution / viscosity of 0.5 mass% aqueous solution) is 2.0 or more, so that when the negative electrode is formed, the decrease in the coating property of the slurry composition is suppressed. Expansion and contraction associated with charging / discharging can be suppressed.
  • each component contained in the said slurry composition for lithium ion secondary battery negative electrodes is demonstrated.
  • the negative electrode active material is a material that transfers electrons in the negative electrode of the lithium ion secondary battery. And as a negative electrode active material of a lithium ion secondary battery, the substance which can occlude and discharge
  • the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention uses a negative electrode active material containing a silicon-based negative electrode active material in order to increase the battery capacity of the lithium ion secondary battery. That is, in the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, a silicon-based negative electrode active material and another negative electrode active material are used in combination as the negative electrode active material.
  • the slurry composition for lithium ion secondary battery negative electrodes of this invention needs the ratio of the silicon type negative electrode active material in a negative electrode active material to be 5 mass% or more and 40 mass% or less. This is because when the ratio of the silicon-based negative electrode active material is less than 5% by mass, the capacity of the lithium ion secondary battery cannot be sufficiently increased. In addition, when the proportion of the silicon-based negative electrode active material is less than 5% by mass, the expansion and contraction of the entire negative electrode is small, so that the cycle characteristics are hardly deteriorated without using in combination with polyacrylic acid described later. When used in combination with acrylic acid, the negative electrode composite material layer becomes too hard and the cycle characteristics of the lithium ion secondary battery may be deteriorated.
  • the content ratio of the silicon-based negative electrode active material in the negative electrode active material is 35% by mass or less. It is preferably 30% by mass or less, more preferably 10% by mass or more, and further preferably 20% by mass or more.
  • the silicon-based negative electrode active material is an active material containing silicon.
  • silicon (Si) an alloy containing silicon, SiO, SiO x , a Si-containing material formed by coating or compounding a Si-containing material with conductive carbon, and conductive carbon. Examples include composites.
  • these silicon type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 types.
  • the alloy containing silicon examples include an alloy composition containing silicon and at least one element selected from the group consisting of titanium, iron, cobalt, nickel, and copper.
  • the alloy containing silicon examples include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing a rare earth element such as tin and yttrium.
  • a rare earth element such as tin and yttrium.
  • an alloy containing silicon (A) an amorphous phase containing silicon; (B) a nanocrystalline phase comprising tin, indium, and yttrium, lanthanide elements, actinide elements, or combinations thereof; Of the mixture.
  • an alloy containing silicon the following general formula: Si a Al b T c Sn d In e M f Li g [Wherein T is a transition metal, M is yttrium, a lanthanide element, an actinide element, or a combination thereof, and the sum of a + b + c + d + e + f is equal to 1, and 0.35 ⁇ a ⁇ 0.70, 0 .01 ⁇ b ⁇ 0.45, 0.05 ⁇ c ⁇ 0.25, 0.01 ⁇ d ⁇ 0.15, e ⁇ 0.15, 0.02 ⁇ f ⁇ 0.15, 0 ⁇ g ⁇ ⁇ 4.4 ⁇ (a + d + e) + b ⁇ ]
  • the alloy composition represented by these is mentioned.
  • Such an alloy can be prepared, for example, by a method described in JP2013-65569A, specifically, a melt spinning method.
  • SiO x is a compound containing at least one of SiO and SiO 2 and Si, and x is usually 0.01 or more and less than 2. Then, SiO x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or vapor after grinding and mixing SiO and optionally a polymer.
  • SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or
  • a composite of Si-containing material and conductive carbon for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam.
  • an organic gas and / or steam can be mentioned.
  • a method of coating the surface of the SiO particles by a chemical vapor deposition method using an organic gas a method of forming composite particles (granulation) of the SiO particles and graphite or artificial graphite by a mechanochemical method, etc. It can also be obtained by a known method.
  • the silicon-based negative electrode active material is preferably an alloy containing silicon and SiO x .
  • Examples of the negative electrode active material used in combination with the silicon negative electrode active material in the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention include a carbon negative electrode active material and a metal negative electrode active material.
  • the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”).
  • examples of the carbon-based negative electrode active material include carbonaceous materials and graphite. Quality materials.
  • the carbonaceous material is a material having a low degree of graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower.
  • the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.
  • the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon.
  • the graphitizable carbon for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned.
  • examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.
  • the graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher.
  • the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
  • the graphite material include natural graphite and artificial graphite.
  • the artificial graphite for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.
  • the metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more. Is an active material.
  • the metal-based negative electrode active material include simple metals other than Si that can form lithium metal and lithium alloys (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, and Sb). , Sn, Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, carbides, phosphides, and the like thereof.
  • the negative electrode active material is preferably a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material such as artificial graphite.
  • polyacrylic acid binds each component in the negative electrode mixture layer or each component and the current collector. At the same time, the expansion and contraction of the negative electrode active material accompanying charge / discharge are suppressed. That is, polyacrylic acid functions as a binder in the negative electrode mixture layer and breaks the conductive path due to the large expansion and contraction of the silicon negative electrode active material accompanying charge / discharge (structure of the silicon negative electrode active material). The reduction in cycle characteristics of the lithium ion secondary battery is suppressed by preventing miniaturization due to destruction and / or destruction of the electrode plate structure).
  • the polyacrylic acid used for the slurry composition for lithium ion secondary battery negative electrodes of this invention is ratio of the viscosity of 1 mass% aqueous solution with respect to the viscosity of 0.5 mass% aqueous solution (viscosity of 1 mass% aqueous solution / 0.5
  • the viscosity of the mass% aqueous solution needs to be 2.0 or more.
  • Polyacrylic acid having a ratio of the viscosity of the 1% by mass aqueous solution to the viscosity of the 0.5% by mass aqueous solution (hereinafter sometimes simply referred to as “viscosity ratio”) of 2.0 or more is a condition where the polyacrylic acid concentration is low.
  • the slurry composition for negative electrode containing polyacrylic acid having a viscosity ratio of 2.0 or more has low viscosity and good coatability in the state of the slurry composition having a low polyacrylic acid concentration.
  • the negative electrode mixture layer is formed by drying the slurry composition for negative electrode. High strength is exhibited in the composite layer, and the expansion and contraction of the negative electrode active material (particularly, the silicon-based negative electrode active material) is suppressed.
  • the viscosity ratio is preferably 3.0 or more, more preferably 6.0 or less, and still more preferably 4.5 or less.
  • the reasons for focusing on the viscosity of the 1% by mass aqueous solution and the viscosity of the 0.5% by mass aqueous solution are as follows. That is, when the concentration of the aqueous solution is less than 0.5% by mass, the measured value of the viscosity varies greatly. In addition, since polyacrylic acid having a viscosity ratio of 2.0 or more usually does not have high solubility in water, an aqueous solution having a concentration of more than 1% by mass may not be prepared.
  • the viscosity of 0.5 mass% aqueous solution of polyacrylic acid is 0.3 Pa.s or more and 10.0 Pa.s or less. It is because there exists a possibility that the applicability
  • the viscosity of the 1.0 mass% polyacrylic acid aqueous solution is 0.6 Pa.s or more and 15.0 Pa.s or less. It is because there exists a possibility that the applicability
  • the polyacrylic acid having the above-described viscosity property is not particularly limited, and can be obtained by copolymerizing acrylic acid or a salt thereof, a crosslinkable monomer, and optionally another polymerizable monomer.
  • Cross-linked polyacrylic acid can be mentioned.
  • 70 mass% or more of the whole monomer used for manufacture of a copolymer is acrylic acid or its salt.
  • the amount of the crosslinkable monomer used for the production of the crosslinkable polyacrylic acid is 2.0 parts by mass or less with respect to 100 parts by mass of the total amount of monomers other than the crosslinkable monomer. Preferably, it is 1.0 mass part or less.
  • acrylic acid or a salt thereof examples include acrylic acid and alkali metal salts such as sodium salt and potassium salt or ammonium salt thereof. These may be used alone or in combination of two or more.
  • crosslinkable monomer examples include polyalkenyl polyether monomers and polyvalent vinyl monomers. Specifically, tetraallyloxyethane, pentaerythritol tetraallyl ether, pentaerythritol triallyl ether, pentaerythritol diallyl ether, allyl saccharose, trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, ethylene glycol diallyl ether, glyceryl diallyl Examples include ether, glyceryl triallyl ether, triallyl isocyanurate, allyl acrylate, allyl methacrylate, diallyl phthalate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate.
  • crosslinkable monomer ethylene glycol dimethacrylate, tetraallyloxyethane, and pentaerythritol triallyl ether are preferable.
  • Examples of other polymerizable monomers include styrene, alkyl vinyl ether, vinylidene chloride, acrylic acid esters, methacrylic acid esters, acrylamides, methacrylamides, N-vinylformamide, N-vinylacetamide, vinyl acetate, Examples include vinyl pyrrolidone, acrylonitrile, and methacrylonitrile. These may be used alone or in combination of two or more.
  • acrylic esters and methacrylic esters include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylic.
  • (Meth) acrylic acid alkyl esters such as octyl acid;
  • (meth) acrylic acid esters having an ether bond such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate; 2-hydroxyethyl acrylate and 2-hydroxypropyl methacrylate Hydroxy group-containing (meth) acrylic acid esters; glycidyl methacrylate and the like.
  • acrylamides and methacrylamides examples include acrylamide, methacrylamide, dimethylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide and the like.
  • macromonomers such as terminal methacrylate polymethyl methacrylate, terminal styryl polymethyl methacrylate, terminal methacrylate polystyrene, terminal methacrylate polyethylene glycol, and terminal methacrylate acrylonitrile styrene copolymer can be used. is there.
  • esters such as maleic acid, fumaric acid and itaconic acid can be used, and trimethoxyvinylsilane, triethoxyvinylsilane, ⁇ -methacryloxypropyltrimethoxysilane and the like can also be used. Can be mentioned. These may be used alone or in combination of two or more.
  • acrylamides are preferable, and acrylamide is more preferable.
  • (meth) acryl means acryl and / or methacryl.
  • the above-mentioned cross-linked polyacrylic acid can be produced by using a general radical polymerization initiator and copolymerizing the above-described monomers.
  • the copolymerization is not particularly limited, and can be performed using a precipitation polymerization method in an organic solvent in which the monomer is dissolved but the polymer is not dissolved.
  • the radical polymerization initiator a compound selected from peroxides, azo initiators, and the like, or a mixture thereof can be used.
  • the cross-linked polyacrylic acid as the polyacrylic acid having the above-mentioned viscosity property can also be produced by mixing and reacting uncrosslinked polyacrylic acid and a cross-linking agent.
  • a specific production method for example, an aqueous solution of uncrosslinked polyacrylic acid is prepared, and a crosslinking agent capable of crosslinking polyacrylic acid is added thereto to add uncrosslinked polyacrylic acid and a crosslinking agent. The method of making it react is mentioned.
  • Uncrosslinked polyacrylic acid can be obtained by polymerizing acrylic acid or a salt thereof and optionally another polymerizable monomer by a known method.
  • acrylic acid or salt thereof and “other polymerizable monomer”
  • the above-mentioned “acrylic acid or salt thereof” and “other polymerizable monomer” can be used.
  • the number average molecular weight is 200,000 or more from the viewpoint of being excellent in dispersibility of the negative electrode active material and capable of suppressing precipitation and further improving the cycle characteristics of the lithium ion secondary battery.
  • Those having a number average molecular weight of 300,000 or more and 2 million or less are more preferable, and those having a number average molecular weight of 500,000 or more and 1,500,000 or less are particularly preferable.
  • “number average molecular weight” can be calculated
  • the ratio of uncrosslinked polyacrylic acid in the aqueous solution of uncrosslinked polyacrylic acid is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 10% by mass. Less than, more preferably less than 5% by mass.
  • Crosslinking agent examples include polyfunctional epoxy compounds, oxazoline compounds, and carbodiimide compounds.
  • a polyfunctional epoxy compound is a compound having two or more epoxy groups in one molecule. And as a polyfunctional epoxy compound, the compound which has an epoxy group preferably in less than 6 in a molecule
  • polyfunctional epoxy compound for example, polyfunctional glycidyl ether compounds such as aliphatic polyglycidyl ether, aromatic polyglycidyl ether, and diglycidyl ether are preferable.
  • the oxazoline compound is not particularly limited as long as it has two or more oxazoline groups.
  • 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-) is used.
  • 2,2′-bis (2-oxazoline) is preferable from the
  • Suitable examples include polycarbodiimides and / or modified polycarbodiimides having a repeating unit represented by the formula:
  • the modified polycarbodiimide refers to a resin obtained by reacting a reactive compound with polycarbodiimide.
  • the reactive compound one group having reactivity with polycarbodiimide (a group having an active hydrogen such as a carboxyl group or a primary or secondary amino group), and another functional group
  • examples of such carbodiimide compounds include SV-02, V-02 manufactured by Nisshinbo Chemical.
  • the crosslinking agent it is preferable to use an oxazoline compound or a carbodiimide compound from the viewpoint of allowing the crosslinking reaction to proceed uniformly throughout the system.
  • the amount of the crosslinking agent in the case of mixing and reacting the uncrosslinked polyacrylic acid and the crosslinking agent is preferably 0.1 parts by mass or more, more preferably, 100 parts by mass of the uncrosslinked polyacrylic acid. Is 0.5 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less. If the amount of the crosslinking agent is too small, the cycle characteristics of the resulting lithium ion secondary battery may be deteriorated. If the amount is too large, undissolved gel may remain when slurried and the negative electrode may be cracked. Because there is.
  • the viscosity ratio of the crosslinked polyacrylic acid obtained as described above, the viscosity of the 0.5 mass% aqueous solution, and the viscosity of the 1.0 mass% aqueous solution are, for example, the crosslinking density and crosslinking of the crosslinked polyacrylic acid. It can be adjusted by changing the distance between points. Specifically, for example, the viscosity ratio of cross-linked polyacrylic acid can be improved by increasing the cross-linking density by increasing the amount of cross-linkable monomer or cross-linking agent used.
  • the water absorption of the polyacrylic acid present in the negative electrode mixture layer prepared using the slurry composition for negative electrodes is increased. Can be lowered. As a result, it is possible to reduce hydrogen fluoride produced by the reaction between the electrolyte and the water in the negative electrode mixture layer when forming a lithium ion secondary battery, so that internal resistance, water absorption and gas generation amount Can be obtained.
  • the polyacrylic acid may be a polyacrylate. This is because when at least a part of the carboxyl group is neutralized, the molecular chain of polyacrylic acid is likely to spread, and the expansion and contraction of the negative electrode active material accompanying charge / discharge are easily suppressed.
  • the salt used for neutralization of polyacrylic acid is not particularly limited.
  • a monovalent base is preferable from the viewpoint of easily spreading the molecular chain of polyacrylic acid, and examples thereof include sodium hydroxide and lithium hydroxide.
  • lithium hydroxide is preferable from the viewpoint of the characteristics of the lithium ion secondary battery.
  • the degree of neutralization of the polyacrylic acid is preferably 0.4 or more and 1.0 or less, and 0.7 or more and 1.0 or less. More preferably.
  • the degree of neutralization of polyacrylic acid is preferably 0.4 or more and 1.0 or less, and 0.7 or more and 1.0 or less. More preferably it is.
  • the degree of neutralization can be measured according to the following method for measuring the degree of neutralization. [[Method for measuring degree of neutralization]]
  • the target neutralization degree is calculated from the value measured by the method according to JIS K0113-1997.
  • the method according to JIS K0113-1997 is a method in which a 0.1N potassium hydroxide aqueous solution is used as a titrant to perform potentiometric titration and the end point is determined by an inflection point method.
  • the neutralization degree of acrylic acid (number of moles of acrylate after neutralization ⁇ acrylic before neutralization)
  • the degree of neutralization can also be determined from the number of moles of acid.
  • the slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains polyacrylic acid in a proportion of 0.5 parts by mass or more per 100 parts by mass of the negative electrode active material. More preferably, it is contained at a rate of 10 parts by mass or less, more preferably at a rate of 5 parts by mass or less, particularly preferably at a rate of 3 parts by mass or less, Most preferably, it is contained in a proportion of 2 parts by mass or less.
  • the content of polyacrylic acid per 100 parts by mass of the negative electrode active material is 0.5 parts by mass or more, the expansion and contraction of the negative electrode active material (particularly, the silicon-based negative electrode active material) accompanying charge / discharge is sufficiently suppressed. be able to.
  • content of polyacrylic acid is 10 mass parts or less, it can fully suppress that the viscosity of a slurry composition rises and coating property falls.
  • the slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains a carboxymethyl cellulose salt.
  • a carboxymethyl cellulose salt By using polyacrylic acid and carboxymethylcellulose salt in combination, the dispersibility of the negative electrode active material and the like can be improved, and the storage stability of the negative electrode slurry composition can be improved.
  • carboxymethyl cellulose salt is not particularly limited, and a sodium salt or ammonium salt of carboxymethyl cellulose can be used.
  • the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose salt is preferably 1.0 Pa ⁇ s or more.
  • the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose salt is preferably 12 Pa ⁇ s or less, and preferably 10 Pa ⁇ s. More preferably, it is as follows.
  • the content of the carboxymethyl cellulose salt is preferably 0.1 to 9 times the content of polyacrylic acid, The content is more preferably 0.25 to 4 times the content, and still more preferably 0.25 to 2.3 times the polyacrylic acid content.
  • the content of the carboxymethyl cellulose salt is within the above range, it is possible to further suppress the expansion and contraction of the negative electrode active material accompanying charge / discharge while sufficiently increasing the storage stability of the slurry composition for negative electrode.
  • the slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains a particulate binder.
  • the particulate binder is composed of the components in the negative electrode mixture layer together with the polyacrylic acid described above. Alternatively, each component and the current collector are bound. Therefore, if a particulate binder is blended with the slurry composition for a negative electrode of a lithium ion secondary battery, the binding properties between the components in the negative electrode mixture layer or between each component and the current collector can be further improved.
  • a polymer such as a conjugated diene polymer or an acrylic polymer can be used as the particulate binder described above.
  • An acrylic polymer is a polymer containing a (meth) acrylic acid ester monomer unit.
  • the acrylic polymer includes a carboxyl group-containing monomer unit, an ⁇ , ⁇ -unsaturated nitrile monomer unit, and any other monomer unit. May be included.
  • “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.
  • (meth) acrylic acid ester monomers that can be used for the production of acrylic polymers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and t-butyl acrylate.
  • Alkyl acrylates such as pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate , Hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, etc.
  • acid alkyl esters Such as acid alkyl esters.
  • the ratio of the (meth) acrylic acid ester monomer unit in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, particularly preferably 58% by mass or more, and preferably 98% by mass. % Or less, more preferably 97% by mass or less, particularly preferably 96% by mass or less.
  • Examples of the carboxyl group-containing monomer that can be used for the production of the acrylic polymer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. It is done.
  • Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like.
  • Examples of the ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, ⁇ -chloro- ⁇ -E-methoxyacrylic.
  • Acid ⁇ -diaminoacrylic acid and the like.
  • ethylenically unsaturated dicarboxylic acid examples include maleic acid, fumaric acid, itaconic acid and the like.
  • acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like.
  • examples of ethylenically unsaturated dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate , Dodecyl maleate, octadecyl maleate, fluoroalkyl maleate and the like. These may be used alone or in combination of two or more.
  • the ratio of the carboxyl group-containing monomer unit in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 10% by mass or less, more preferably 5%. It is below mass%.
  • Examples of the ⁇ , ⁇ -unsaturated nitrile monomer that can be used in the production of the acrylic polymer include acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more.
  • the proportion of ⁇ , ⁇ -unsaturated nitrile monomer units in the acrylic polymer is preferably 1% by mass or more, more preferably 2% by mass or more, preferably 50% by mass or less, more preferably 35%. It is below mass%.
  • the monomer copolymerizable with the monomer mentioned above is mentioned.
  • the optional monomers include hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.
  • Crosslinkable monomer crosslinkable monomer: Styrene such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, ⁇ -methylstyrene, divinylbenzene Monomers; ethylene, propylene, etc.
  • diene 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
  • methyl vinyl ether vinyl ethers
  • Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone
  • Heterocycles such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole -Containing vinyl compounds
  • amino group-containing monomers such as aminoethyl vinyl ether and dimethylaminoethyl vinyl ether; These may be used alone or in combination of two or more.
  • the ratio of the arbitrary monomer unit in the acrylic polymer is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 0.5% by mass or more in total amount. Is preferable, and 1.0 mass% or more is more preferable.
  • the method for producing the acrylic polymer 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 may be used.
  • a solution polymerization method a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method
  • addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
  • the conjugated diene polymer is a polymer containing a conjugated diene monomer unit, and includes hydrogenated products thereof.
  • Specific examples of conjugated diene polymers include aliphatic conjugated diene polymers such as polybutadiene and polyisoprene; aromatic vinyl / aliphatic conjugated diene copolymers such as styrene / butadiene copolymer (SBR); acrylonitrile / butadiene.
  • Examples include vinyl cyanide / conjugated diene copolymers such as copolymers (NBR); hydrogenated SBR, hydrogenated NBR, and the like.
  • NBR copolymers
  • aromatic vinyl monomer, aliphatic conjugated diene monomer, carboxyl group-containing monomer, hydroxyl group-containing used for the production of aromatic vinyl / aliphatic conjugated diene copolymer preferred as conjugated diene polymer Monomers and other optional monomers will be described in detail.
  • examples of the aromatic vinyl monomer that can be used for the production of the aromatic vinyl / aliphatic conjugated diene copolymer include styrene, ⁇ -methylstyrene, vinyltoluene, and divinylbenzene. These may be used alone or in combination of two or more.
  • the ratio of the aromatic vinyl monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 30% by mass or more, more preferably 35% by mass or more, and preferably 79.5% by mass or less. More preferably, it is 69 mass% or less.
  • Examples of the aliphatic conjugated diene monomer that can be used in the production of the aromatic vinyl / aliphatic conjugated diene copolymer include 1,3-butadiene, 2-methyl-1,3-butadiene, and 2,3-dimethyl-1. , 3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. These may be used alone or in combination of two or more.
  • the ratio of the aliphatic conjugated diene monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 70% by mass or less. More preferably, it is 60 mass% or less, Most preferably, it is 55 mass% or less.
  • Examples of the carboxyl group-containing monomer that can be used for the production of the aromatic vinyl / aliphatic conjugated diene copolymer include those similar to those mentioned above that can be used for the production of the acrylic polymer. It is done.
  • the ratio of the carboxyl group-containing monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass. % Or less, more preferably 8% by mass or less.
  • the ratio of the hydroxyl group-containing monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass. % Or less, more preferably 8% by mass or less.
  • the monomer copolymerizable with the monomer mentioned above is mentioned.
  • the optional monomer from the above-mentioned acrylic polymers, those that can be used as other monomers, aromatic vinyl monomers, aliphatic conjugated diene monomers And those other than those corresponding to the hydroxyl group-containing monomer, and ⁇ , ⁇ -unsaturated nitrile monomers can be used. These other monomers may be used alone or in combination of two or more.
  • the proportion of any monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less in total. 0.5 mass% or more is preferable, and 1.0 mass% or more is more preferable.
  • the production method of the conjugated diene polymer 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 may be used.
  • a solution polymerization method a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method
  • addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
  • the slurry composition for lithium ion secondary battery negative electrodes of this invention contains a particulate binder in the ratio of 4 mass parts or more per 100 mass parts of polyacrylic acid, and is 20 mass parts or less. It is preferable to contain in a ratio, and it is still more preferable to contain in the ratio of 10 mass parts or less. If the content of the particulate binder per 100 parts by mass of polyacrylic acid is 4 parts by mass or more, the binding property is sufficiently increased, and the powder falling off from the negative electrode produced using the negative electrode slurry composition Occurrence can be suppressed.
  • the content of the particulate binder per 100 parts by mass of polyacrylic acid is 20 It is preferable to set it as a mass part or less.
  • the amount of the particulate binder is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more per 100 parts by mass of the negative electrode active material. 1.0 mass part or less, preferably 0.6 mass part or less, more preferably 0.5 mass part or less.
  • the particulate binder preferably has a gel content of 50% by mass or more, more preferably 80% by mass or more, preferably 98% by mass or less, more preferably 95% by mass or less.
  • the gel content of the particulate binder is less than 50% by mass, the cohesive force of the particulate binder may be reduced, and the adhesion strength with the current collector or the like may be insufficient.
  • the gel content of the particulate binder is more than 98% by mass, the particulate binder may lose toughness and become brittle, resulting in insufficient adhesion strength.
  • the “gel content” of the particulate binder can be measured using the measuring method described in the examples of the present specification.
  • the particulate binder has a glass transition temperature (Tg) of preferably ⁇ 30 ° C. or higher, more preferably ⁇ 20 ° C. or higher, preferably 80 ° C. or lower, more preferably 30 ° C. or lower.
  • Tg glass transition temperature
  • the components in the slurry composition for secondary battery negative electrode are prevented from aggregating and settling, and the stability of the slurry composition is ensured. be able to.
  • the glass transition temperature of a particulate-form binder is 80 degrees C or less.
  • the “glass transition temperature (Tg)” of the particulate binder can be measured using the measuring method described in the examples of the present specification.
  • the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention may contain components such as a conductive material, a reinforcing material, a leveling agent, and an electrolytic solution additive in addition to the above components. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
  • the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention can be prepared by dispersing each of the above components in an aqueous medium as a dispersion medium. Specifically, the above components and the aqueous medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or a fill mix. Thus, a slurry composition can be prepared.
  • water is usually used as the aqueous medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used.
  • the negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for negative electrodes of lithium ion secondary batteries of this invention.
  • the negative electrode for a lithium ion secondary battery of the present invention includes a current collector and a negative electrode mixture layer formed on the current collector, and the negative electrode mixture layer includes at least a negative electrode active material, Contains polyacrylic acid.
  • each component contained in the negative electrode composite material layer was contained in the slurry composition for a lithium ion secondary battery negative electrode of the present invention, and a suitable abundance ratio of each of these components is It is the same as the suitable abundance ratio of each component in the slurry composition for use.
  • the negative electrode mixture layer contains the above-described negative electrode active material containing a silicon-based negative electrode active material and the above-described polyacrylic acid.
  • the battery capacity can be improved while preventing the deterioration of the cycle characteristics of the battery.
  • the negative electrode for a lithium ion secondary battery of the present invention is applied, for example, to a step of applying the above-described slurry composition for a negative electrode of a lithium ion secondary battery on a current collector (application step), and a current collector.
  • the lithium ion secondary battery negative electrode slurry composition is dried to form a negative electrode mixture layer on the current collector (drying step).
  • a method for applying the slurry composition for a lithium ion secondary battery negative electrode on the current collector is not particularly limited, and a known method can be used. Specifically, as a 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 for negative electrode may be applied only to one side of the current collector, or may be applied to both sides.
  • the thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the negative electrode mixture layer obtained by drying.
  • the thickness of the negative electrode mixture layer can be preferably 1 to 200 ⁇ m, more preferably 3 to 100 ⁇ m.
  • the current collector to which the slurry composition for negative electrode is applied 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.
  • a copper foil is particularly preferable as the current collector used for the negative electrode.
  • the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
  • a method for drying the slurry composition for the negative electrode on the current collector is not particularly limited, and a known method can be used, for example, drying with hot air, hot air, low-humidity air, vacuum drying, infrared rays, electron beam, etc. The drying method by irradiation is mentioned.
  • a negative electrode mixture layer is formed on the current collector, and the negative electrode for a lithium ion secondary battery comprising the current collector and the negative electrode mixture layer Can be obtained.
  • the negative electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the negative electrode mixture layer and the current collector can be improved. Furthermore, when the negative electrode mixture layer contains a curable polymer, the polymer is preferably cured after the formation of the negative electrode mixture layer.
  • the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode for a lithium ion secondary battery of the present invention is used as the negative electrode. And since the lithium ion secondary battery of this invention uses the negative electrode for lithium ion secondary batteries of this invention, its battery capacity is high and it is excellent in cycling characteristics.
  • a positive electrode of a lithium ion secondary battery As a positive electrode of a lithium ion secondary battery, a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used. As the current collector, one made of a metal material such as aluminum can be used. As the positive electrode mixture layer, a layer containing a known positive electrode active material, a conductive material, and a binder can be used.
  • an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
  • the solvent an organic solvent capable of dissolving the electrolyte can be used.
  • the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, and ⁇ -butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
  • a lithium salt can be used as the electrolyte.
  • the lithium salt for example, those described in JP 2012-204303 A can be used.
  • LiPF 6 , LiClO 4 , and CF 3 SO 3 Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation.
  • ⁇ Separator> As the separator, for example, those described in JP 2012-204303 A can be used. Among these, the thickness of the separator as a whole can be reduced, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume.
  • a microporous film made of a series resin polyethylene, polypropylene, polybutene, polyvinyl chloride is preferred.
  • a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the battery shape as necessary, and placed in the battery container. It can manufacture by inject
  • an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary.
  • the shape of the lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.
  • ⁇ Viscosity ratio> About 0.5 mass% aqueous solution and 1.0 mass% aqueous solution of polyacrylic acid, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10M), temperature 25 ° C., pH 8.0, rotation speed 60 rpm The viscosity at (rotor: M4) was measured according to JIS K7117-1. Then, the viscosity ratio ( viscosity of 1 mass% aqueous solution / viscosity of 0.5 mass% aqueous solution) was calculated. The pH was adjusted using sodium hydroxide or lithium hydroxide.
  • ⁇ Glass transition temperature> The aqueous dispersion containing the particulate binder was dried for 3 days in an environment of 50% humidity and a temperature of 23 to 26 ° C. to obtain a film having a thickness of 1 ⁇ 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Then, using the dried film as a sample, in accordance with JIS K7121, measurement temperature: ⁇ 100 ° C. to 180 ° C., temperature increase rate: 5 ° C./min, a differential scanning calorimeter (DSC6220SII, manufactured by Nanotechnology, Inc.) ) was used to measure the glass transition temperature.
  • DSC6220SII differential scanning calorimeter
  • ⁇ Gel content> An aqueous dispersion containing a particulate binder was prepared, and the aqueous dispersion was dried in an environment of 50% humidity and a temperature of 23 to 25 ° C. to form a film having a thickness of 1 ⁇ 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Thereafter, the dried film was cut into 3 to 5 mm square, and about 1 g was precisely weighed. The mass of the film piece obtained by cutting is defined as w0. This film piece was immersed in 50 g of tetrahydrofuran (THF) for 24 hours.
  • THF tetrahydrofuran
  • Gel content (mass%) (w1 / w0) ⁇ 100 ⁇ Smoothness of negative electrode>
  • the coating amount was measured at 10 points every 10 mm in the length direction.
  • the difference between the minimum value and the maximum value of the 10 measured values was evaluated according to the following criteria. It shows that the coating property of the slurry composition for negative electrodes used for formation of a negative electrode is excellent, so that a difference is small.
  • Powder fall residual rate is 99.98% or more
  • B Powder fall residual rate is 99.96% or more and less than 99.98%
  • C Powder fall residual rate is less than 99.96% ⁇ Design capacity of negative electrode> The mass average theoretical capacity (mAh / g) of the used negative electrode active material was calculated and evaluated according to the following criteria.
  • Theoretical capacity exceeds 800 mAh / g
  • C Theoretical capacity is 470 mAh / g or less ⁇ Initial efficiency>
  • the laminated cell type lithium ion secondary battery thus prepared was allowed to stand at 25 ° C. for 5 hours after electrolyte injection, and then subjected to a cell voltage of 3.C under the condition of 25 ° C. by a constant current method of 0.2C.
  • the battery was charged to 65 V (the charge amount is defined as “C1 (mAh)”). Thereafter, an aging treatment is performed at a temperature of 60 ° C.
  • Initial efficiency ⁇ (D1 + D2) / (C1 + C2) ⁇ ⁇ 100 (%) A: Initial efficiency is 88% or more B: Initial efficiency is 85% or more and less than 88% C: Initial efficiency is 81% or more and less than 85% D: Initial efficiency is less than 81% ⁇ Cycle characteristics>
  • the lithium ion secondary battery used in the evaluation of the initial efficiency was discharged to a cell voltage of 2.75 V by a constant current method of 0.1 C under the condition of a temperature of 25 ° C. Thereafter, 100 cycles of charge / discharge operation were performed at a charge / discharge rate of charge voltage 4.2V, discharge voltage 2.75V, and 0.5C under the condition of a temperature of 45 ° C.
  • ⁇ C ′ (X2 / X1) ⁇ 100 (%). Evaluation was made according to the following criteria. The higher the value of the capacity change rate ⁇ C ′, the better the cycle characteristics. A: ⁇ C ′ is 85% or more B: ⁇ C ′ is 83% or more and less than 85% C: ⁇ C ′ is 80% or more and less than 83% D: ⁇ C ′ is less than 80%
  • Example 1 ⁇ Preparation of negative electrode active material> Artificial graphite (manufactured by Hitachi Chemical, theoretical capacity: 360 mAh / g) as a carbon-based negative electrode active material and SiO x (manufactured by Shin-Etsu Chemical, theoretical capacity: 2300 mAh / g) as a silicon-based negative electrode active material were prepared.
  • ⁇ Preparation of particulate binder> In a 5 MPa pressure vessel equipped with a stirrer, 62 parts of styrene as an aromatic vinyl monomer, 35 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 2 parts of itaconic acid as a carboxyl group-containing monomer, and a hydroxyl group-containing monomer 1 part of 2-hydroxyethyl acrylate (2-hydroxyethyl acrylate) as a monomer, 0.3 part of t-dodecyl mercaptan as a molecular weight regulator, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent And 1 part of potassium persulfate was added as a polymerization initiator, and after sufficiently stirring, the mixture was heated to 55 ° C.
  • the reaction was stopped by cooling.
  • the aqueous dispersion containing the polymer thus obtained was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution.
  • the unreacted monomer was removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion of the particulate binder.
  • the gel content and glass transition temperature were measured by the methods described above. As a result of the measurement, the gel content was 92% and the glass transition temperature (Tg) was 10 ° C.
  • ⁇ Preparation of slurry composition for negative electrode of lithium ion secondary battery> 90 parts of artificial graphite as a carbon-based negative electrode active material, 10 parts of SiO x (manufactured by Shin-Etsu Chemical) as a silicon-based negative electrode active material, cross-linked sodium polyacrylate (manufactured by Toagosei Co., Ltd., Rhegic 260H) 1 part by weight of a 1% by weight aqueous solution of 1.5 parts by weight, and 1.5 parts by weight of a 1% by weight aqueous solution of a carboxymethyl cellulose salt (MAC800LC, Nippon Paper Chemicals, sodium salt of carboxymethyl cellulose) in a solid content.
  • MAC800LC carboxymethyl cellulose salt
  • the obtained negative electrode raw material was pressed with a roll press so that the density was 1.63 to 1.67 g / cm 3, and further, under vacuum conditions for the purpose of removing moisture and further promoting crosslinking.
  • the negative electrode was obtained by placing in an environment of 120 ° C. for 10 hours. About the obtained negative electrode, smoothness and dust-proof property were evaluated. The results are shown in Table 1.
  • the obtained slurry composition for a lithium ion secondary battery positive electrode was applied with a comma coater onto an aluminum foil having a thickness of 20 ⁇ m so that the amount applied was 30.5 to 31.5 mg / cm 2 . Thereafter, the aluminum foil coated with the slurry composition for a positive electrode of a lithium ion secondary battery was dried by conveying it in an oven at a temperature of 60 ° C. at a rate of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material. The obtained positive electrode raw material was pressed with a roll press machine so that the density after pressing was 3.40 to 3.50 g / cm 3 , and further, the temperature was 120 ° C.
  • a single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 ⁇ m; manufactured by a dry method; porosity 55%) was prepared and cut into a 5 cm ⁇ 5 cm square.
  • the aluminum packaging material exterior was prepared as a battery exterior.
  • the produced positive electrode was cut out to 3.8cm x 2.8cm, and it has arrange
  • the square separator was placed on the surface of the positive electrode mixture layer of the positive electrode.
  • the produced negative electrode was cut out to 4.0 cm x 3.0 cm, and this was arrange
  • heat sealing at 150 ° C. was performed to seal and close the opening of the aluminum packaging material exterior, and a laminated cell type lithium ion secondary battery was manufactured. The initial efficiency and cycle characteristics of the lithium ion secondary battery were evaluated. The results are shown in Table 1.
  • Example 2 The negative electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the blending amount of the artificial graphite as the carbon-based negative electrode active material was 75 parts and the blending amount of SiO x as the silicon-based negative electrode active material was 25 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 3 The negative electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the compounding amount of the artificial graphite as the carbon-based negative electrode active material was 65 parts and the compounding amount of SiO x as the silicon-based negative electrode active material was 35 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 4 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the carboxymethyl cellulose salt was not blended. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 5 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the particulate binder was not blended. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 6 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the amount of the particulate binder was 0.225 parts corresponding to the solid content. Produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 7 Implemented except that 3 parts of polyacrylic acid 2 below was used in place of 1.5 parts of cross-linked sodium polyacrylate (Rheojic 260H) as polyacrylic acid, and carboxymethylcellulose salt and particulate binder were not added.
  • a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • ⁇ Preparation of polyacrylic acid 2> In a reaction vessel, uncrosslinked polyacrylic acid (manufactured by Aldrich, number average molecular weight: 1.25 million) was dissolved at a solid content concentration of 2% and stirred. Thereafter, the reaction vessel was heated to 60 ° C., and a carbodiimide compound (manufactured by Nisshinbo Chemical Co., Ltd., SV-02, diluted to a solid content concentration of 0.5%) was gradually added dropwise over 1 hour. Stir for 8 hours. Thereafter, the pH was adjusted to 8.0 with a 1% aqueous sodium hydroxide solution, and water was evaporated from the obtained aqueous solution under vacuum drying conditions at 60 ° C. to obtain polyacrylic acid 2.
  • uncrosslinked polyacrylic acid manufactured by Aldrich, number average molecular weight: 1.25 million
  • a carbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd., SV-02, diluted to a solid
  • Example 8 (Example 8) Implemented except that 3 parts of polyacrylic acid 3 below was used in place of 1.5 parts of cross-linked sodium polyacrylate (Rheodic 260H) as polyacrylic acid, and carboxymethyl cellulose salt and particulate binder were not added.
  • a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 9 A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary material were prepared in the same manner as in Example 1 except that the blending amount of a 1% by mass aqueous solution of carboxymethylcellulose salt was 0.375 parts corresponding to the solid content. A secondary battery was produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 1 (Comparative Example 1) In the same manner as in Example 1 except that only 100 parts of artificial graphite was used as the negative electrode active material and SiO x was not used as the silicon negative electrode active material, the slurry composition for the negative electrode of the lithium ion secondary battery, the negative electrode, A positive electrode and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 2 Lithium ion secondary battery negative electrode in the same manner as in Example 1 except that the amount of artificial graphite as the carbon-based negative electrode active material was 50 parts and the amount of SiO x as the silicon-based negative electrode active material was 50 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 5 The same procedure as in Example 1 was used except that polyacrylic acid 6 (manufactured by Toa Gosei Co., Ltd., cross-linked sodium polyacrylate, Rheotic 262L) was used as the polyacrylic acid instead of the cross-linked sodium polyacrylate (Rheodic 260H).
  • a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • Example 6 A slurry composition for a negative electrode of a lithium ion secondary battery in the same manner as in Example 1, except that no polyacrylic acid was blended and the blending amount of a 1% by weight aqueous solution of carboxymethylcellulose salt was 3.0 parts in terms of solid content. A negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
  • a lithium ion secondary when used for forming a negative electrode, a lithium ion secondary that can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge and that is excellent in coatability.
  • a slurry composition for a battery negative electrode can be provided.
  • the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics can be provided.
  • a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics can be provided.

Abstract

The purpose of the present invention is to provide a slurry composition for negative electrodes of lithium ion secondary batteries, which has excellent coatability and is capable of increasing battery capacity, while suppressing expansion and shrinkage of a silicon-based negative electrode active material, said expansion and shrinkage accompanying charge and discharge of a battery. A slurry composition for negative electrodes of lithium ion secondary batteries according to the present invention contains a negative electrode active material, a polyacrylic acid and water. The negative electrode active material contains a silicon-based negative electrode active material in an amount of 5-40% by mass. The ratio of the viscosity of a 1% by mass aqueous solution of the polyacrylic acid to the viscosity of a 0.5% by mass aqueous solution of the polyacrylic acid is 2.0 or more.

Description

リチウムイオン二次電池負極用スラリー組成物、リチウムイオン二次電池用負極およびリチウムイオン二次電池Slurry composition for negative electrode of lithium ion secondary battery, negative electrode for lithium ion secondary battery and lithium ion secondary battery
　本発明は、リチウムイオン二次電池負極用スラリー組成物、リチウムイオン二次電池用負極およびリチウムイオン二次電池に関するものである。 The present invention relates to a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
　リチウムイオン二次電池は、小型で軽量、且つエネルギー密度が高く、さら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、リチウムイオン二次電池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。 Lithium ion secondary batteries are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.
　具体的には、リチウムイオン二次電池の負極に用いる負極活物質としてシリコン系負極活物質を採用することによりリチウムイオン二次電池の電池容量を高めることが、検討されている。 Specifically, it has been studied to increase the battery capacity of the lithium ion secondary battery by adopting a silicon-based negative electrode active material as the negative electrode active material used for the negative electrode of the lithium ion secondary battery.
　しかし、シリコン系負極活物質は、高い理論容量を有してリチウムイオン二次電池の電池容量を高めることを可能にする一方で、充放電に伴って大きく膨張および収縮する。従って、シリコン系負極活物質を用いた負極には、充放電の繰り返しに伴うシリコン系負極活物質の膨張および収縮により、シリコン系負極活物質自体の劣化（即ち、シリコン系負極活物質の構造破壊による微細化）、及び／又は、極板構造の破壊が生じて電極内の導電パスが破壊されるという問題があった。即ち、シリコン系負極活物質を用いた負極を備えるリチウムイオン二次電池には、シリコン系負極活物質の大きな膨張および収縮に起因してサイクル特性が低下するという問題があった。 However, while the silicon-based negative electrode active material has a high theoretical capacity and can increase the battery capacity of the lithium ion secondary battery, it greatly expands and contracts with charge and discharge. Accordingly, in a negative electrode using a silicon-based negative electrode active material, deterioration of the silicon-based negative electrode active material itself (that is, structural destruction of the silicon-based negative electrode active material) due to expansion and contraction of the silicon-based negative electrode active material due to repeated charge / discharge. Miniaturization) and / or destruction of the electrode plate structure, and the conductive path in the electrode is destroyed. That is, a lithium ion secondary battery including a negative electrode using a silicon-based negative electrode active material has a problem in that cycle characteristics deteriorate due to large expansion and contraction of the silicon-based negative electrode active material.
　そこで、充放電に伴う膨張および収縮がシリコン系負極活物質よりも小さい炭素系負極活物質とシリコン系負極活物質とを併用する技術や、負極用結着材として所定のポリアクリル酸を用いる技術が提案されている（例えば、特許文献１～３参照）。 Therefore, a technology that uses a carbon-based negative electrode active material and a silicon-based negative electrode active material that are smaller in expansion and contraction due to charge / discharge than the silicon-based negative electrode active material, and a technology that uses a predetermined polyacrylic acid as a negative electrode binder Has been proposed (see, for example, Patent Documents 1 to 3).
特許第４６７２９８５号公報Japanese Patent No. 4672985 特許第４８７６４６８号公報Japanese Patent No. 4876468 特開２０００－３４８７３０号公報JP 2000-348730 A
　しかし、上記従来の技術では、充放電に伴うシリコン系負極活物質の膨張および収縮を十分に抑制することができず、リチウムイオン二次電池の高容量化とサイクル特性の低下抑制とを高い次元で両立することができなかった。 However, the above-mentioned conventional technology cannot sufficiently suppress the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge, and it is a high dimension to increase the capacity of the lithium ion secondary battery and suppress the deterioration of the cycle characteristics. It was not possible to achieve both.
　また、通常、リチウムイオン二次電池用負極は、負極活物質と結着材とを分散媒に分散させてなる負極用スラリー組成物を集電体上に塗布し、乾燥させて負極活物質および結着材を含む負極合材層を集電体上に形成することにより製造される。しかし、上記従来のポリアクリル酸を用いた技術には、シリコン系負極活物質の膨張および収縮を抑制するためにポリアクリル酸の配合量や分子量を増加させると、負極用スラリー組成物の粘度が高くなり、塗工性が低下するという問題もあった。 In general, a negative electrode for a lithium ion secondary battery is prepared by applying a negative electrode slurry composition in which a negative electrode active material and a binder are dispersed in a dispersion medium on a current collector and drying the negative electrode active material and It is manufactured by forming a negative electrode composite material layer containing a binder on a current collector. However, in the conventional technology using polyacrylic acid, the viscosity of the slurry composition for negative electrode is increased when the blending amount or molecular weight of polyacrylic acid is increased in order to suppress the expansion and contraction of the silicon-based negative electrode active material. There was also a problem that the coating property was lowered due to the increase.
　そこで、本発明は、負極の形成に使用した場合に充放電に伴うシリコン系負極活物質の膨張および収縮を抑制しつつ電池容量を高めることができ、且つ、塗工性に優れるリチウムイオン二次電池負極用スラリー組成物を提供することを目的とする。
　また、本発明は、優れた電池容量およびサイクル特性を有するリチウムイオン二次電池を提供することができるリチウムイオン二次電池用負極を提供することを目的とする。
　更に、本発明は、電池容量が高く、且つ、サイクル特性に優れるリチウムイオン二次電池を提供することを目的とする。 Therefore, the present invention can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material that accompanies charge / discharge when used for the formation of the negative electrode, and is a lithium ion secondary that is excellent in coatability. It aims at providing the slurry composition for battery negative electrodes.
Moreover, an object of this invention is to provide the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics.
Another object of the present invention is to provide a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics.
　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、負極活物質中のシリコン系負極活物質の割合を所定の範囲内にし、且つ、所定の粘度性状を有するポリアクリル酸を配合したリチウムイオン二次電池負極用スラリー組成物は、シリコン系負極活物質の膨張および収縮を抑制しつつ電池容量を高めることができ、更に塗工性にも優れていることを見出し、本発明を完成させた。 The present inventor has intensively studied for the purpose of solving the above problems. And this inventor made the ratio of the silicon type negative electrode active material in a negative electrode active material into a predetermined range, and mix | blended the polyacrylic acid which has a predetermined viscosity property, The slurry composition for lithium ion secondary battery negative electrodes Found that the battery capacity can be increased while suppressing the expansion and contraction of the silicon-based negative electrode active material, and that the coating property is also excellent, and the present invention has been completed.
　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、本発明のリチウムイオン二次電池負極用スラリー組成物は、負極活物質と、ポリアクリル酸と、水とを含み、前記負極活物質は、シリコン系負極活物質を５質量％以上４０質量％以下の割合で含有し、前記ポリアクリル酸は、０．５質量％水溶液の粘度に対する１質量％水溶液の粘度の比（１質量％水溶液の粘度／０．５質量％水溶液の粘度）が２．０以上であることを特徴とする。このように、シリコン系負極活物質の含有割合が所定の範囲内の負極活物質と、０．５質量％水溶液の粘度に対する１質量％水溶液の粘度の比が所定の大きさを満たすポリアクリル酸とを組み合わせて用いれば、スラリー組成物を使用して負極を形成した際に、シリコン系負極活物質の膨張および収縮を抑制しつつ電池容量を高めることができる。また、当該スラリー組成物は、塗工性にも優れている。
　ここで、本発明において、「ポリアクリル酸の水溶液の粘度」とは、Ｂ型粘度計を使用し、ＪＩＳ Ｋ７１１７－１に準拠して、温度２５℃、ｐＨ８、ローターＭ４、回転数６０ｒｐｍの条件下で測定したポリアクリル酸水溶液の粘度を指す。 That is, this invention aims to solve the above-mentioned problem advantageously, and the slurry composition for a lithium ion secondary battery negative electrode of the present invention comprises a negative electrode active material, polyacrylic acid, and water. The negative electrode active material contains a silicon-based negative electrode active material in a proportion of 5% by mass to 40% by mass, and the polyacrylic acid has a viscosity of 1% by mass aqueous solution with respect to the viscosity of the 0.5% by mass aqueous solution. The ratio (viscosity of 1% by mass aqueous solution / viscosity of 0.5% by mass aqueous solution) is 2.0 or more. Thus, the polyacrylic acid in which the ratio of the viscosity of the 1% by mass aqueous solution to the viscosity of the 0.5% by mass aqueous solution satisfies the predetermined size, with the negative electrode active material having a silicon-based negative electrode active material content in the predetermined range. When a negative electrode is formed using the slurry composition, the battery capacity can be increased while suppressing the expansion and contraction of the silicon-based negative electrode active material. In addition, the slurry composition is excellent in coatability.
Here, in the present invention, “viscosity of an aqueous solution of polyacrylic acid” is a condition of temperature 25 ° C., pH 8, rotor M4, rotation speed 60 rpm in accordance with JIS K7117-1, using a B-type viscometer. It refers to the viscosity of the polyacrylic acid aqueous solution measured below.
　ここで、本発明のリチウムイオン二次電池負極用スラリー組成物は、カルボキシメチルセルロース塩を更に含むことが好ましい。カルボキシメチルセルロース塩を配合すれば、スラリー組成物の保存安定性を向上させることができるからである。 Here, it is preferable that the slurry composition for a lithium ion secondary battery negative electrode of the present invention further contains a carboxymethyl cellulose salt. This is because the storage stability of the slurry composition can be improved by adding carboxymethylcellulose salt.
　また、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、本発明のリチウムイオン二次電池用負極は、上述したリチウムイオン二次電池負極用スラリー組成物の何れかを用いて得られる負極合材層を有することを特徴とする。上記リチウムイオン二次電池負極用スラリー組成物を用いて形成した負極合材層では、高い理論容量を有するシリコン系負極活物質の充放電に伴う膨張および収縮を抑制することができる。従って、当該負極合材層を有する負極を用いれば、優れた電池容量およびサイクル特性を有するリチウムイオン二次電池を提供することができる。 Moreover, this invention aims at solving the said subject advantageously, The negative electrode for lithium ion secondary batteries of this invention is either of the slurry composition for lithium ion secondary battery negative electrodes mentioned above. It has the negative mix layer obtained by using, It is characterized by the above-mentioned. In the negative electrode mixture layer formed using the lithium ion secondary battery negative electrode slurry composition, expansion and contraction associated with charge and discharge of a silicon-based negative electrode active material having a high theoretical capacity can be suppressed. Therefore, if a negative electrode having the negative electrode composite material layer is used, a lithium ion secondary battery having excellent battery capacity and cycle characteristics can be provided.
　更に、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、本発明のリチウムイオン二次電池は、上述したリチウムイオン二次電池用負極と、正極と、電解液と、セパレータとを備えることを特徴とする。上記リチウムイオン二次電池用負極を用いたリチウムイオン二次電池は、電池容量が高く、且つ、サイクル特性に優れている。 Furthermore, this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is the negative electrode for lithium ion secondary batteries mentioned above, a positive electrode, electrolyte solution, And a separator. A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery has a high battery capacity and excellent cycle characteristics.
　本発明によれば、負極の形成に使用した場合に充放電に伴うシリコン系負極活物質の膨張および収縮を抑制しつつ電池容量を高めることができ、且つ、塗工性に優れるリチウムイオン二次電池負極用スラリー組成物を提供することができる。
　また、本発明によれば、優れた電池容量およびサイクル特性を有するリチウムイオン二次電池を提供することができるリチウムイオン二次電池用負極を提供することができる。
　更に、本発明によれば、電池容量が高く、且つ、サイクル特性に優れるリチウムイオン二次電池を提供することができる。 According to the present invention, when used for forming a negative electrode, a lithium ion secondary that can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge and that is excellent in coatability. A slurry composition for a battery negative electrode can be provided.
Moreover, according to this invention, the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics can be provided.
Furthermore, according to the present invention, a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics can be provided.
　以下、本発明の実施形態について詳細に説明する。
　ここで、本発明のリチウムイオン二次電池負極用スラリー組成物は、リチウムイオン二次電池の負極の形成に用いられる。また、本発明のリチウムイオン二次電池用負極は、本発明のリチウムイオン二次電池負極用スラリー組成物を用いて製造することができる。更に、本発明のリチウムイオン二次電池は、本発明のリチウムイオン二次電池用負極を用いたことを特徴とする。 Hereinafter, embodiments of the present invention will be described in detail.
Here, the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is used for forming a negative electrode of a lithium ion secondary battery. Moreover, the negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for lithium ion secondary batteries negative electrode of this invention. Furthermore, the lithium ion secondary battery of the present invention is characterized by using the negative electrode for a lithium ion secondary battery of the present invention.
（リチウムイオン二次電池負極用スラリー組成物）
　本発明のリチウムイオン二次電池負極用スラリー組成物は、負極活物質と、ポリアクリル酸と、水とを含む水系のスラリー組成物である。そして、本発明のリチウムイオン二次電池負極用スラリー組成物の負極活物質は、シリコン系負極活物質を５質量％以上４０質量％以下の割合で含有する。また、本発明のリチウムイオン二次電池負極用スラリー組成物のポリアクリル酸は、０．５質量％水溶液の粘度に対する１質量％水溶液の粘度の比（１質量％水溶液の粘度／０．５質量％水溶液の粘度）が２．０以上である。なお、本発明のリチウムイオン二次電池負極用スラリー組成物は、負極活物質およびポリアクリル酸以外に、カルボキシメチルセルロース塩や粒子状結着材などのその他の成分を含有していてもよい。 (Slurry composition for negative electrode of lithium ion secondary battery)
The lithium ion secondary battery negative electrode slurry composition of the present invention is an aqueous slurry composition containing a negative electrode active material, polyacrylic acid, and water. And the negative electrode active material of the slurry composition for lithium ion secondary battery negative electrodes of this invention contains a silicon type negative electrode active material in the ratio of 5 to 40 mass%. Moreover, the polyacrylic acid of the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is a ratio of the viscosity of a 1% by weight aqueous solution to the viscosity of a 0.5% by weight aqueous solution (viscosity of 1% by weight aqueous solution / 0.5% by weight % Aqueous solution) is 2.0 or more. In addition, the slurry composition for lithium ion secondary battery negative electrodes of this invention may contain other components, such as a carboxymethylcellulose salt and a particulate binder other than a negative electrode active material and polyacrylic acid.
　そして、本発明のリチウムイオン二次電池負極用スラリー組成物によれば、負極活物質がシリコン系負極活物質を５質量％以上の割合で含有するので、リチウムイオン二次電池の電池容量を高めることが可能な負極を形成することができる。また、本発明のリチウムイオン二次電池負極用スラリー組成物によれば、負極活物質がシリコン系負極活物質を４０質量％以下の割合で含有し、且つ、ポリアクリル酸の粘度の比（１質量％水溶液の粘度／０．５質量％水溶液の粘度）が２．０以上であるので、スラリー組成物の塗工性の低下を抑制しつつ、負極を形成した際にシリコン系負極活物質の充放電に伴う膨張および収縮を抑制することができる。
　以下、上記リチウムイオン二次電池負極用スラリー組成物に含まれる各成分について説明する。 And according to the slurry composition for lithium ion secondary battery negative electrodes of this invention, since a negative electrode active material contains a silicon-type negative electrode active material in the ratio of 5 mass% or more, the battery capacity of a lithium ion secondary battery is raised. A negative electrode that can be formed can be formed. According to the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, the negative electrode active material contains a silicon-based negative electrode active material in a proportion of 40% by mass or less, and the viscosity ratio of polyacrylic acid (1 (Viscosity of mass% aqueous solution / viscosity of 0.5 mass% aqueous solution) is 2.0 or more, so that when the negative electrode is formed, the decrease in the coating property of the slurry composition is suppressed. Expansion and contraction associated with charging / discharging can be suppressed.
Hereinafter, each component contained in the said slurry composition for lithium ion secondary battery negative electrodes is demonstrated.
＜負極活物質＞
　負極活物質は、リチウムイオン二次電池の負極において電子の受け渡しをする物質である。そして、リチウムイオン二次電池の負極活物質としては、通常は、リチウムを吸蔵および放出し得る物質を用いる。 <Negative electrode active material>
The negative electrode active material is a material that transfers electrons in the negative electrode of the lithium ion secondary battery. And as a negative electrode active material of a lithium ion secondary battery, the substance which can occlude and discharge | release lithium is used normally.
　ここで、本発明のリチウムイオン二次電池負極用スラリー組成物は、リチウムイオン二次電池の電池容量を高めるために、シリコン系負極活物質を含む負極活物質を使用する。即ち、本発明のリチウムイオン二次電池負極用スラリー組成物では、負極活物質として、シリコン系負極活物質と、その他の負極活物質とを併用する。 Here, the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention uses a negative electrode active material containing a silicon-based negative electrode active material in order to increase the battery capacity of the lithium ion secondary battery. That is, in the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, a silicon-based negative electrode active material and another negative electrode active material are used in combination as the negative electrode active material.
　そして、本発明のリチウムイオン二次電池負極用スラリー組成物は、負極活物質中のシリコン系負極活物質の割合が５質量％以上４０質量％以下である必要がある。シリコン系負極活物質の割合が５質量％未満の場合、リチウムイオン二次電池を十分に高容量化することができないからである。また、シリコン系負極活物質の割合が５質量％未満であると、負極全体の膨張・収縮が小さいため後述するポリアクリル酸と組み合わせて用いなくても、サイクル特性が低下し難く、逆にポリアクリル酸と組み合わせて用いることで、負極合材層が硬くなり過ぎてリチウムイオン二次電池のサイクル特性が悪化する虞がある。一方、シリコン系負極活物質の割合が４０質量％超の場合、後述するポリアクリル酸を使用した場合であっても充放電に伴うシリコン系負極活物質の膨張および収縮を抑制することが困難になり、リチウムイオン二次電池のサイクル特性が悪化する虞があるからである。
　なお、リチウムイオン二次電池の高容量化とサイクル特性の低下抑制とを更に高い次元で両立する観点からは、負極活物質中のシリコン系負極活物質の含有割合は、３５質量％以下であることが好ましく、３０質量％以下であることが更に好ましく、１０質量％以上であることが好ましく、２０質量％以上であることが更に好ましい。 And the slurry composition for lithium ion secondary battery negative electrodes of this invention needs the ratio of the silicon type negative electrode active material in a negative electrode active material to be 5 mass% or more and 40 mass% or less. This is because when the ratio of the silicon-based negative electrode active material is less than 5% by mass, the capacity of the lithium ion secondary battery cannot be sufficiently increased. In addition, when the proportion of the silicon-based negative electrode active material is less than 5% by mass, the expansion and contraction of the entire negative electrode is small, so that the cycle characteristics are hardly deteriorated without using in combination with polyacrylic acid described later. When used in combination with acrylic acid, the negative electrode composite material layer becomes too hard and the cycle characteristics of the lithium ion secondary battery may be deteriorated. On the other hand, when the proportion of the silicon-based negative electrode active material is more than 40% by mass, it is difficult to suppress the expansion and contraction of the silicon-based negative electrode active material accompanying charge / discharge even when polyacrylic acid described later is used. This is because the cycle characteristics of the lithium ion secondary battery may be deteriorated.
In addition, from the viewpoint of achieving both higher capacity of the lithium ion secondary battery and suppression of reduction in cycle characteristics at a higher level, the content ratio of the silicon-based negative electrode active material in the negative electrode active material is 35% by mass or less. It is preferably 30% by mass or less, more preferably 10% by mass or more, and further preferably 20% by mass or more.
［シリコン系負極活物質］
　ここで、シリコン系負極活物質とは、ケイ素を含む活物質である。そして、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または複合化してなる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、これらのシリコン系負極活物質は、１種類を単独で用いてもよいし、２種類上を組み合わせて用いてもよい。 [Silicon negative electrode active material]
Here, the silicon-based negative electrode active material is an active material containing silicon. As the silicon-based negative electrode active material, for example, silicon (Si), an alloy containing silicon, SiO, SiO x , a Si-containing material formed by coating or compounding a Si-containing material with conductive carbon, and conductive carbon. Examples include composites. In addition, these silicon type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 types.
　ケイ素を含む合金としては、例えば、ケイ素と、チタン、鉄、コバルト、ニッケルおよび銅からなる群より選択される少なくとも一種の元素とを含む合金組成物が挙げられる。
　また、ケイ素を含む合金としては、例えば、ケイ素と、アルミニウムと、鉄などの遷移金属とを含み、さらにスズおよびイットリウム等の希土類元素を含む合金組成物も挙げられる。具体的には、ケイ素を含む合金としては、
（Ａ）シリコンを含む非晶相と、
（Ｂ）スズ、インジウム、並びに、イットリウム、ランタニド元素、アクチニド元素、または、これらの組み合わせを含むナノ結晶相と、
の混合物が挙げられる。より具体的には、ケイ素を含む合金としては、下記一般式：
ＳｉaＡｌbＴcＳｎdＩｎeＭfＬｉg
［式中、Ｔは、遷移金属であり、Ｍは、イットリウム、ランタニド元素、アクチニド元素、または、これらの組み合わせであり、ａ＋ｂ＋ｃ＋ｄ＋ｅ＋ｆの合計が１に等しく、０.３５≦ａ≦０.７０、０.０１≦ｂ≦０.４５、０.０５≦ｃ≦０.２５、０.０１≦ｄ≦０.１５、ｅ≦０.１５、０.０２≦ｆ≦０.１５、０＜ｇ≦｛４．４×（ａ＋ｄ＋ｅ）＋ｂ｝である］
で表される合金組成物が挙げられる。このような合金は、例えば特開２０１３－６５５６９号公報に記載の方法、具体的には溶融紡糸法（meltspun method）により調製することができる。 Examples of the alloy containing silicon include an alloy composition containing silicon and at least one element selected from the group consisting of titanium, iron, cobalt, nickel, and copper.
Examples of the alloy containing silicon include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing a rare earth element such as tin and yttrium. Specifically, as an alloy containing silicon,
(A) an amorphous phase containing silicon;
(B) a nanocrystalline phase comprising tin, indium, and yttrium, lanthanide elements, actinide elements, or combinations thereof;
Of the mixture. More specifically, as an alloy containing silicon, the following general formula:
Si a Al b T c Sn d In e M f Li g
[Wherein T is a transition metal, M is yttrium, a lanthanide element, an actinide element, or a combination thereof, and the sum of a + b + c + d + e + f is equal to 1, and 0.35 ≦ a ≦ 0.70, 0 .01 ≦ b ≦ 0.45, 0.05 ≦ c ≦ 0.25, 0.01 ≦ d ≦ 0.15, e ≦ 0.15, 0.02 ≦ f ≦ 0.15, 0 <g ≦ { 4.4 × (a + d + e) + b}]
The alloy composition represented by these is mentioned. Such an alloy can be prepared, for example, by a method described in JP2013-65569A, specifically, a melt spinning method.
　ＳｉＯxは、ＳｉＯおよびＳｉＯ2の少なくとも一方と、Ｓｉとを含有する化合物であり、ｘは、通常、０．０１以上２未満である。そして、ＳｉＯxは、例えば、一酸化ケイ素（ＳｉＯ）の不均化反応を利用して形成することができる。具体的には、ＳｉＯxは、ＳｉＯを、任意にポリビニルアルコールなどのポリマーの存在下で熱処理し、ケイ素と二酸化ケイ素とを生成させることにより、調製することができる。なお、熱処理は、ＳｉＯと、任意にポリマーとを粉砕混合した後、有機物ガスおよび／または蒸気を含む雰囲気下、９００℃以上、好ましくは１０００℃以上の温度で行うことができる。 SiO x is a compound containing at least one of SiO and SiO 2 and Si, and x is usually 0.01 or more and less than 2. Then, SiO x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or vapor after grinding and mixing SiO and optionally a polymer.
　Ｓｉ含有材料と導電性カーボンとの複合化物としては、例えば、ＳｉＯと、ポリビニルアルコールなどのポリマーと、任意に炭素材料との粉砕混合物を、例えば有機物ガスおよび／または蒸気を含む雰囲気下で熱処理してなる化合物を挙げることができる。また、ＳｉＯの粒子に対して、有機物ガスなどを用いた化学的蒸着法によって表面をコーティングする方法、ＳｉＯの粒子と黒鉛または人造黒鉛をメカノケミカル法によって複合粒子化（造粒化）する方法などの公知の方法でも得ることができる。 As a composite of Si-containing material and conductive carbon, for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam. Can be mentioned. In addition, a method of coating the surface of the SiO particles by a chemical vapor deposition method using an organic gas, a method of forming composite particles (granulation) of the SiO particles and graphite or artificial graphite by a mechanochemical method, etc. It can also be obtained by a known method.
　なお、リチウムイオン二次電池の高容量化の観点からは、シリコン系負極活物質としては、ケイ素を含む合金およびＳｉＯxが好ましい。 From the viewpoint of increasing the capacity of the lithium ion secondary battery, the silicon-based negative electrode active material is preferably an alloy containing silicon and SiO x .
［その他の負極活物質］
　本発明のリチウムイオン二次電池負極用スラリー組成物において上記シリコン系負極活物質と併用する負極活物質としては、炭素系負極活物質および金属系負極活物質などが挙げられる。 [Other negative electrode active materials]
Examples of the negative electrode active material used in combination with the silicon negative electrode active material in the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention include a carbon negative electrode active material and a metal negative electrode active material.
［［炭素系負極活物質］］
　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。 [[Carbon-based negative electrode active material]]
Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite. Quality materials.
　炭素質材料は、炭素前駆体を２０００℃以下で熱処理して炭素化させることによって得られる、黒鉛化度の低い（即ち、結晶性の低い）材料である。なお、炭素化させる際の熱処理温度の下限は特に限定されないが、例えば５００℃以上とすることができる。
　そして、炭素質材料としては、例えば、熱処理温度によって炭素の構造を容易に変える易黒鉛性炭素や、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、石油また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）、ハードカーボンなどが挙げられる。 The carbonaceous material is a material having a low degree of graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower. In addition, although the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.
Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. .
Here, as the graphitizable carbon, for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like.
In addition, examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.
　黒鉛質材料は、易黒鉛性炭素を２０００℃以上で熱処理することによって得られる、黒鉛に近い高い結晶性を有する材料である。なお、熱処理温度の上限は、特に限定されないが、例えば５０００℃以下とすることができる。
　そして、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。 The graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher. In addition, although the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
Examples of the graphite material include natural graphite and artificial graphite.
Here, as the artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.
［［金属系負極活物質］］
　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。金属系負極活物質としては、例えば、リチウム金属、リチウム合金を形成し得るＳｉ以外の単体金属（例えば、Ａｇ、Ａｌ、Ｂａ、Ｂｉ、Ｃｕ、Ｇａ、Ｇｅ、Ｉｎ、Ｎｉ、Ｐ、Ｐｂ、Ｓｂ、Ｓｎ、Ｓｒ、Ｚｎ、Ｔｉなど）およびその合金、並びに、それらの酸化物、硫化物、窒化物、炭化物、燐化物などが用いられる。 [[Metal negative electrode active material]]
The metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more. Is an active material. Examples of the metal-based negative electrode active material include simple metals other than Si that can form lithium metal and lithium alloys (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, and Sb). , Sn, Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, carbides, phosphides, and the like thereof.
　なお、負極活物質の膨張および収縮を抑制しつつリチウムイオン二次電池を十分に高容量化する観点からは、その他の負極活物質としては、炭素系負極活物質を用いることが好ましく、人造黒鉛を用いることがより好ましい。即ち、負極活物質は、シリコン系負極活物質と、人造黒鉛などの炭素系負極活物質との混合物であることが好ましい。 From the viewpoint of sufficiently increasing the capacity of the lithium ion secondary battery while suppressing expansion and contraction of the negative electrode active material, it is preferable to use a carbon-based negative electrode active material as the other negative electrode active material. It is more preferable to use That is, the negative electrode active material is preferably a mixture of a silicon-based negative electrode active material and a carbon-based negative electrode active material such as artificial graphite.
＜ポリアクリル酸＞
　ポリアクリル酸は、本発明のリチウムイオン二次電池負極用スラリー組成物を用いて形成した負極合材層において、負極合材層中の各成分同士または各成分と集電体とを結着させると共に、充放電に伴う負極活物質の膨張および収縮を抑制する。即ち、ポリアクリル酸は、負極合材層において、結着材として機能すると共に、充放電に伴うシリコン系負極活物質の大きな膨張および収縮に起因した導電パスの破壊（シリコン系負極活物質の構造破壊による微細化、及び／又は、極板構造の破壊）を防止してリチウムイオン二次電池のサイクル特性の低下を抑制する。 <Polyacrylic acid>
In the negative electrode mixture layer formed using the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention, polyacrylic acid binds each component in the negative electrode mixture layer or each component and the current collector. At the same time, the expansion and contraction of the negative electrode active material accompanying charge / discharge are suppressed. That is, polyacrylic acid functions as a binder in the negative electrode mixture layer and breaks the conductive path due to the large expansion and contraction of the silicon negative electrode active material accompanying charge / discharge (structure of the silicon negative electrode active material). The reduction in cycle characteristics of the lithium ion secondary battery is suppressed by preventing miniaturization due to destruction and / or destruction of the electrode plate structure).
　そして、本発明のリチウムイオン二次電池負極用スラリー組成物に用いるポリアクリル酸は、０．５質量％水溶液の粘度に対する１質量％水溶液の粘度の比（１質量％水溶液の粘度／０．５質量％水溶液の粘度）が２．０以上である必要がある。０．５質量％水溶液の粘度に対する１質量％水溶液の粘度の比（以下、単に「粘度比」と称することがある。）が２．０以上のポリアクリル酸は、ポリアクリル酸濃度が低い条件下では低粘度であるが、ポリアクリル酸濃度が上昇すると、粘度が大幅に増大する。即ち、粘度比が２．０以上のポリアクリル酸を含む負極用スラリー組成物は、ポリアクリル酸濃度が低いスラリー組成物の状態では、粘度が低く、塗工性が良好である。一方で、負極用スラリー組成物中の当該ポリアクリル酸は、ポリアクリル酸濃度が上昇すると粘度が大幅に増大するので、負極用スラリー組成物を乾燥させて負極合材層を形成すると、当該負極合材層中において高い強度を発揮し、負極活物質（特に、シリコン系負極活物質）の膨張および収縮を抑制する。従って、粘度比が２．０以上のポリアクリル酸を使用すれば、負極合材層の形成に使用した際に充放電に伴うシリコン系負極活物質の膨張および収縮を抑制することができ、且つ、塗工性に優れる負極用スラリー組成物を得ることができる。一方、粘度比が２．０未満のポリアクリル酸を使用した場合には、スラリー組成物の塗工性が低下すると共に、充放電に伴うシリコン系負極活物質の大きな膨張および収縮に起因した導電パスの破壊を十分に抑制することができず、リチウムイオン二次電池のサイクル特性が低下する。
　なお、粘度比は、３．０以上であることが好ましく、また、６．０以下であることが好ましく、４．５以下であることが更に好ましい。 And the polyacrylic acid used for the slurry composition for lithium ion secondary battery negative electrodes of this invention is ratio of the viscosity of 1 mass% aqueous solution with respect to the viscosity of 0.5 mass% aqueous solution (viscosity of 1 mass% aqueous solution / 0.5 The viscosity of the mass% aqueous solution) needs to be 2.0 or more. Polyacrylic acid having a ratio of the viscosity of the 1% by mass aqueous solution to the viscosity of the 0.5% by mass aqueous solution (hereinafter sometimes simply referred to as “viscosity ratio”) of 2.0 or more is a condition where the polyacrylic acid concentration is low. Below the viscosity is low, but as the polyacrylic acid concentration increases, the viscosity increases significantly. That is, the slurry composition for negative electrode containing polyacrylic acid having a viscosity ratio of 2.0 or more has low viscosity and good coatability in the state of the slurry composition having a low polyacrylic acid concentration. On the other hand, since the viscosity of the polyacrylic acid in the slurry composition for negative electrode increases significantly when the polyacrylic acid concentration increases, the negative electrode mixture layer is formed by drying the slurry composition for negative electrode. High strength is exhibited in the composite layer, and the expansion and contraction of the negative electrode active material (particularly, the silicon-based negative electrode active material) is suppressed. Therefore, if a polyacrylic acid having a viscosity ratio of 2.0 or more is used, expansion and contraction of the silicon-based negative electrode active material accompanying charge / discharge can be suppressed when used for forming the negative electrode mixture layer, and The slurry composition for negative electrodes which is excellent in coating property can be obtained. On the other hand, when polyacrylic acid having a viscosity ratio of less than 2.0 is used, the coating property of the slurry composition is lowered, and the conductivity due to the large expansion and contraction of the silicon-based negative electrode active material accompanying charge / discharge is reduced. The destruction of the path cannot be sufficiently suppressed, and the cycle characteristics of the lithium ion secondary battery are deteriorated.
The viscosity ratio is preferably 3.0 or more, more preferably 6.0 or less, and still more preferably 4.5 or less.
　ここで、本発明において、１質量％水溶液の粘度と、０．５質量％水溶液の粘度とに着目したのは、以下の理由による。即ち、水溶液の濃度が０．５質量％未満では、粘度の測定値のバラつきが大きくなるからである。また、粘度比が２．０以上のポリアクリル酸は、通常、水に対する溶解度が大きくないため、濃度が１質量％超の水溶液は調製できない場合がある一方、本発明者の種々の検討の結果、１質量％水溶液の粘度が０．５質量％水溶液の粘度の２．０倍以上であれば、負極活物質の膨張および収縮を十分に抑制し得ることが明らかとなったからである。 Here, in the present invention, the reasons for focusing on the viscosity of the 1% by mass aqueous solution and the viscosity of the 0.5% by mass aqueous solution are as follows. That is, when the concentration of the aqueous solution is less than 0.5% by mass, the measured value of the viscosity varies greatly. In addition, since polyacrylic acid having a viscosity ratio of 2.0 or more usually does not have high solubility in water, an aqueous solution having a concentration of more than 1% by mass may not be prepared. This is because when the viscosity of the 1% by mass aqueous solution is 2.0 times or more than the viscosity of the 0.5% by mass aqueous solution, it has become clear that expansion and contraction of the negative electrode active material can be sufficiently suppressed.
［０．５質量％水溶液の粘度］
　なお、ポリアクリル酸の０．５質量％水溶液の粘度は、０．３Ｐａ・ｓ以上１０．０Ｐａ・ｓ以下であることが好ましい。０．５質量％水溶液の粘度が大き過ぎると、スラリー組成物の塗工性が低下する虞があるからである。また、０．５質量％水溶液の粘度が小さ過ぎると、負極活物質の膨張および収縮を十分に抑制できない虞があるからである。 [Viscosity of 0.5 mass% aqueous solution]
In addition, it is preferable that the viscosity of 0.5 mass% aqueous solution of polyacrylic acid is 0.3 Pa.s or more and 10.0 Pa.s or less. It is because there exists a possibility that the applicability | paintability of a slurry composition may fall when the viscosity of 0.5 mass% aqueous solution is too large. Moreover, it is because there exists a possibility that expansion | swelling and shrinkage | contraction of a negative electrode active material cannot fully be suppressed when the viscosity of 0.5 mass% aqueous solution is too small.
［１．０質量％水溶液の粘度］
　また、ポリアクリル酸の１．０質量％水溶液の粘度は、０．６Ｐａ・ｓ以上１５．０Ｐａ・ｓ以下であることが好ましい。１．０質量％水溶液の粘度が大き過ぎると、スラリー組成物の塗工性が低下する虞があるからである。また、１．０質量％水溶液の粘度が小さ過ぎると、負極活物質の膨張および収縮を十分に抑制できない虞があるからである。 [Viscosity of 1.0 mass% aqueous solution]
Moreover, it is preferable that the viscosity of the 1.0 mass% polyacrylic acid aqueous solution is 0.6 Pa.s or more and 15.0 Pa.s or less. It is because there exists a possibility that the applicability | paintability of a slurry composition may fall when the viscosity of 1.0 mass% aqueous solution is too large. Moreover, it is because there exists a possibility that expansion | swelling and shrinkage | contraction of a negative electrode active material cannot fully be suppressed when the viscosity of 1.0 mass% aqueous solution is too small.
［ポリアクリル酸の調製方法（１）］
　上述した粘度性状を有するポリアクリル酸としては、特に限定されることなく、アクリル酸またはその塩と、架橋性単量体と、任意に他の重合性単量体とを共重合して得られる架橋型ポリアクリル酸が挙げられる。なお、架橋型ポリアクリル酸は、共重合体の製造に用いられる単量体全体の７０質量％以上が、アクリル酸またはその塩であることが好ましい。また、架橋型ポリアクリル酸の製造に用いられる架橋性単量体の量は、架橋性単量体以外の単量体の合計量１００質量部に対して２．０質量部以下であることが好ましく、１．０質量部以下であることが更に好ましい。 [Method for preparing polyacrylic acid (1)]
The polyacrylic acid having the above-described viscosity property is not particularly limited, and can be obtained by copolymerizing acrylic acid or a salt thereof, a crosslinkable monomer, and optionally another polymerizable monomer. Cross-linked polyacrylic acid can be mentioned. In addition, it is preferable that 70 mass% or more of the whole monomer used for manufacture of a copolymer is acrylic acid or its salt. The amount of the crosslinkable monomer used for the production of the crosslinkable polyacrylic acid is 2.0 parts by mass or less with respect to 100 parts by mass of the total amount of monomers other than the crosslinkable monomer. Preferably, it is 1.0 mass part or less.
［［アクリル酸またはその塩］］
　ここで、アクリル酸またはその塩としては、アクリル酸、並びに、そのナトリウム塩、カリウム塩等のアルカリ金属塩またはアンモニウム塩などが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。 [[Acrylic acid or its salt]]
Here, examples of acrylic acid or a salt thereof include acrylic acid and alkali metal salts such as sodium salt and potassium salt or ammonium salt thereof. These may be used alone or in combination of two or more.
［［架橋性単量体］］
　また、架橋性単量体としては、ポリアルケニルポリエーテル単量体、多価ビニル単量体などが挙げられる。具体的には、テトラアリルオキシエタン、ペンタエリスリトールテトラアリルエーテル、ペンタエリスリトールトリアリルエーテル、ペンタエリスリトールジアリルエーテル、アリルサッカロース、トリメチロールプロパンジアリルエーテル、トリメチロールプロパントリアリルエーテル、エチレングリコールジアリルエーテル、グリセリンジアリルエーテル、グリセリントリアリルエーテル、トリアリルイソシアヌレート、アクリル酸アリル、メタクリル酸アリル、ジアリルフタレート、エチレングリコールジアクリレート、ポリエチレングリコールジアクリレート、エチレングリコールジメタクリレートおよびポリエチレングリコールジメタクリレートなどが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。これらの中でも、架橋性単量体としては、エチレングリコールジメタクリレート、テトラアリルオキシエタンおよびペンタエリスリトールトリアリルエーテルが好ましい。 [[Crosslinkable monomer]]
Examples of the crosslinkable monomer include polyalkenyl polyether monomers and polyvalent vinyl monomers. Specifically, tetraallyloxyethane, pentaerythritol tetraallyl ether, pentaerythritol triallyl ether, pentaerythritol diallyl ether, allyl saccharose, trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, ethylene glycol diallyl ether, glyceryl diallyl Examples include ether, glyceryl triallyl ether, triallyl isocyanurate, allyl acrylate, allyl methacrylate, diallyl phthalate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate. These may be used alone or in combination of two or more. Among these, as the crosslinkable monomer, ethylene glycol dimethacrylate, tetraallyloxyethane, and pentaerythritol triallyl ether are preferable.
［［その他の重合性単量体］］
　その他の重合性単量体としては、例えば、スチレン、アルキルビニルエーテル、塩化ビニリデン、アクリル酸エステル類、メタクリル酸エステル類、アクリルアミド類、メタクリルアミド類、Ｎ－ビニルホルムアミド、Ｎ－ビニルアセトアミド、酢酸ビニル、ビニルピロリドン、アクリロニトリルおよびメタクリロニトリルなどが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。 [[Other polymerizable monomers]]
Examples of other polymerizable monomers include styrene, alkyl vinyl ether, vinylidene chloride, acrylic acid esters, methacrylic acid esters, acrylamides, methacrylamides, N-vinylformamide, N-vinylacetamide, vinyl acetate, Examples include vinyl pyrrolidone, acrylonitrile, and methacrylonitrile. These may be used alone or in combination of two or more.
　ここで、アクリル酸エステル類およびメタクリル酸エステル類の具体例としては、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸ブチル、（メタ）アクリル酸イソブチル、（メタ）アクリル酸オクチルなどの（メタ）アクリル酸アルキルエステル類；２－メトキシエチルアクリレート、２－エトキシエチルアクリレートなどのエーテル結合を有する（メタ）アクリル酸エステル類；２－ヒドロキシエチルアクリレート、２－ヒドロキシプロピルメタクリレートなどのヒドロキシ基含有（メタ）アクリル酸エステル類；グリシジルメタクリレートなどが挙げられる。
　また、アクリルアミド類およびメタアクリルアミド類としては、アクリルアミド、メタクリルアミド、ジメチルアクリルアミド、ジエチルアクリルアミド、ジメチルアミノプロピルアクリルアミドなどが挙げられる。
　さらに、その他の重合性単量体としては、末端メタクリレートポリメチルメタクリレート、末端スチリルポリメチルメタクリレート、末端メタクリレートポリスチレン、末端メタクリレートポリエチレングリコール、末端メタクリレートアクリロニトリルスチレン共重合体などのマクロモノマー類なども使用可能である。
　同様に、その他の重合性単量体としては、マレイン酸、フマル酸、イタコン酸などのエステル類なども使用でき、また、トリメトキシビニルシラン、トリエトキシビニルシラン、γ－メタクリロキシプロピルトリメトキシシランなども挙げられる。
　これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。これらの中でも、その他の重合性単量体としては、アクリルアミド類が好ましく、アクリルアミドがより好ましい。
　なお、本発明において、「（メタ）アクリル」とは、アクリル及び／又はメタクリルを意味する。 Here, specific examples of acrylic esters and methacrylic esters include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) acrylic. (Meth) acrylic acid alkyl esters such as octyl acid; (meth) acrylic acid esters having an ether bond such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate; 2-hydroxyethyl acrylate and 2-hydroxypropyl methacrylate Hydroxy group-containing (meth) acrylic acid esters; glycidyl methacrylate and the like.
Examples of acrylamides and methacrylamides include acrylamide, methacrylamide, dimethylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide and the like.
Furthermore, as other polymerizable monomers, macromonomers such as terminal methacrylate polymethyl methacrylate, terminal styryl polymethyl methacrylate, terminal methacrylate polystyrene, terminal methacrylate polyethylene glycol, and terminal methacrylate acrylonitrile styrene copolymer can be used. is there.
Similarly, as other polymerizable monomers, esters such as maleic acid, fumaric acid and itaconic acid can be used, and trimethoxyvinylsilane, triethoxyvinylsilane, γ-methacryloxypropyltrimethoxysilane and the like can also be used. Can be mentioned.
These may be used alone or in combination of two or more. Among these, as other polymerizable monomers, acrylamides are preferable, and acrylamide is more preferable.
In the present invention, “(meth) acryl” means acryl and / or methacryl.
　そして、上述した架橋型ポリアクリル酸は、一般的なラジカル重合開始剤を使用し、前述した単量体を共重合させて製造することができる。なお、共重合は、特に限定されることなく、単量体は溶解するが重合体は溶解しない有機溶剤中での沈殿重合法を用いて行うことができる。また、ラジカル重合開始剤としては、過酸化物、アゾ系開始剤などから選ばれた化合物またはそれらの混合物が使用できる。 The above-mentioned cross-linked polyacrylic acid can be produced by using a general radical polymerization initiator and copolymerizing the above-described monomers. The copolymerization is not particularly limited, and can be performed using a precipitation polymerization method in an organic solvent in which the monomer is dissolved but the polymer is not dissolved. Further, as the radical polymerization initiator, a compound selected from peroxides, azo initiators, and the like, or a mixture thereof can be used.
［ポリアクリル酸の調製方法（２）］
　また、上述した粘度性状を有するポリアクリル酸としての架橋型ポリアクリル酸は、未架橋型のポリアクリル酸と架橋剤とを混合し、反応させて製造することもできる。具体的な製造方法としては、例えば、未架橋型のポリアクリル酸の水溶液を用意し、これにポリアクリル酸を架橋可能な架橋剤を添加して未架橋型のポリアクリル酸と架橋剤とを反応させる方法が挙げられる。 [Method for preparing polyacrylic acid (2)]
The cross-linked polyacrylic acid as the polyacrylic acid having the above-mentioned viscosity property can also be produced by mixing and reacting uncrosslinked polyacrylic acid and a cross-linking agent. As a specific production method, for example, an aqueous solution of uncrosslinked polyacrylic acid is prepared, and a crosslinking agent capable of crosslinking polyacrylic acid is added thereto to add uncrosslinked polyacrylic acid and a crosslinking agent. The method of making it react is mentioned.
［［未架橋型のポリアクリル酸］］
　未架橋型のポリアクリル酸は、アクリル酸またはその塩と、任意に他の重合性単量体とを既知の手法で重合して得ることができる。なお、「アクリル酸またはその塩」および「他の重合性単量体」としては、上述した「アクリル酸またはその塩」および「その他の重合性単量体」を用いることができる。 [[Uncrosslinked polyacrylic acid]]
Uncrosslinked polyacrylic acid can be obtained by polymerizing acrylic acid or a salt thereof and optionally another polymerizable monomer by a known method. As the “acrylic acid or salt thereof” and “other polymerizable monomer”, the above-mentioned “acrylic acid or salt thereof” and “other polymerizable monomer” can be used.
　ここで、未架橋型のポリアクリル酸としては、負極活物質の分散性に優れると共に沈降を抑制でき、更にはリチウムイオン二次電池のサイクル特性を向上できる観点から、数平均分子量が２０万以上３００万以下のものを用いるのが好ましく、数平均分子量が３０万以上２００万以下のものを用いるのがより好ましく、数平均分子量が５０万以上１５０万以下のものを用いるのが特に好ましい。
　なお、「数平均分子量」は、ＧＰＣ（ゲル浸透クロマトグラフィー）を使用し、ポリスチレン換算値として求めることができる。 Here, as the uncrosslinked polyacrylic acid, the number average molecular weight is 200,000 or more from the viewpoint of being excellent in dispersibility of the negative electrode active material and capable of suppressing precipitation and further improving the cycle characteristics of the lithium ion secondary battery. Those having a number average molecular weight of 300,000 or more and 2 million or less are more preferable, and those having a number average molecular weight of 500,000 or more and 1,500,000 or less are particularly preferable.
In addition, "number average molecular weight" can be calculated | required as a polystyrene conversion value using GPC (gel permeation chromatography).
　そして、未架橋型のポリアクリル酸の水溶液における、未架橋型のポリアクリル酸の割合は、好ましくは０．１質量％以上、より好ましくは０．５質量％以上であり、好ましくは１０質量％未満、より好ましくは５質量％未満である。 The ratio of uncrosslinked polyacrylic acid in the aqueous solution of uncrosslinked polyacrylic acid is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 10% by mass. Less than, more preferably less than 5% by mass.
［［架橋剤］］
　未架橋型のポリアクリル酸と反応させる架橋剤としては、多官能エポキシ化合物、オキサゾリン化合物、カルボジイミド化合物等が挙げられる。 [[Crosslinking agent]]
Examples of the crosslinking agent to be reacted with uncrosslinked polyacrylic acid include polyfunctional epoxy compounds, oxazoline compounds, and carbodiimide compounds.
　多官能エポキシ化合物は、１分子中に２以上のエポキシ基を有する化合物である。そして、多官能エポキシ化合物としては、エポキシ基を、１分子中に好ましくは６未満、より好ましくは４未満有する化合物が好ましい。多官能エポキシ化合物としては、例えば脂肪族ポリグリシジルエーテル、芳香族ポリグリシジルエーテル、ジグリシジルエーテルなどの多官能グリシジルエーテル化合物が好ましい。 A polyfunctional epoxy compound is a compound having two or more epoxy groups in one molecule. And as a polyfunctional epoxy compound, the compound which has an epoxy group preferably in less than 6 in a molecule | numerator, More preferably, less than 4 is preferable. As the polyfunctional epoxy compound, for example, polyfunctional glycidyl ether compounds such as aliphatic polyglycidyl ether, aromatic polyglycidyl ether, and diglycidyl ether are preferable.
　オキサゾリン化合物としては、オキサゾリン基を２つ以上有するものであれば特に限定されるものではないが、例えば、２，２'－ビス（２－オキサゾリン）、２，２'－ビス（４－メチル－２－オキサゾリン）、２，２'－ビス（４，４－ジメチル－２－オキサゾリン）、２，２'－ビス（４－エチル－２－オキサゾリン）、２，２'－ビス（４，４'－ジエチル－２－オキサゾリン）、２，２'－ビス（４－プロピル－２－オキサゾリン）、２，２'－ビス（４－ブチル－２－オキサゾリン）、２，２'－ビス（４－ヘキシル－２－オキサゾリン）、２，２'－ビス（４－フェニル－２－オキサゾリン）、２，２'－ビス（４－シクロヘキシル－２－オキサゾリン）、２，２'－ビス（４－ベンジル－２－オキサゾリン）などが挙げられる。中でも、より剛直な架橋構造を形成する観点から、２，２'－ビス（２－オキサゾリン）が好ましい。 The oxazoline compound is not particularly limited as long as it has two or more oxazoline groups. For example, 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-) is used. 2-oxazoline), 2,2'-bis (4,4-dimethyl-2-oxazoline), 2,2'-bis (4-ethyl-2-oxazoline), 2,2'-bis (4,4 ' -Diethyl-2-oxazoline), 2,2'-bis (4-propyl-2-oxazoline), 2,2'-bis (4-butyl-2-oxazoline), 2,2'-bis (4-hexyl) -2-oxazoline), 2,2′-bis (4-phenyl-2-oxazoline), 2,2′-bis (4-cyclohexyl-2-oxazoline), 2,2′-bis (4-benzyl-2) -Oxazoline) and the like. Among these, 2,2′-bis (2-oxazoline) is preferable from the viewpoint of forming a more rigid cross-linked structure.
　カルボジイミド化合物は、分子中に一般式（１）：
－Ｎ＝Ｃ＝Ｎ－　・・・（１）
で表されるカルボジイミド基を有し、ポリアクリル酸間に架橋構造を形成し得る架橋性化合物であれば特に限定されない。そして、このようなカルボジイミド基を有するカルボジイミド化合物としては、例えば、カルボジイミド基を２つ以上有する化合物、具体的には、一般式（２）：
－Ｎ＝Ｃ＝Ｎ－Ｒ1　・・・（２）
［一般式（２）中、Ｒ1は２価の有機基を示す。］で表される繰返し単位を有するポリカルボジイミドおよび／または変性ポリカルボジイミドが好適に挙げられる。なお、本明細書において変性ポリカルボジイミドとは、ポリカルボジイミドに対して、反応性化合物を反応させることによって得られる樹脂をいう。そして、反応性化合物としては、ポリカルボジイミドとの反応性を有する基（カルボキシル基あるいは第一級もしくは第二級のアミノ基などの、活性水素を有する基）を１つと、さらに他の官能基を有する化合物、例えば特開２００５－４９３７０号公報に記載の化合物が挙げられる。
　このようなカルボジイミド化合物としては、例えば日清紡ケミカル製ＳＶ－０２，Ｖ－０２等をあげることができる。 The carbodiimide compound has a general formula (1) in the molecule:
-N = C = N- (1)
If it is a crosslinkable compound which has the carbodiimide group represented by and can form a crosslinked structure between polyacrylic acid, it will not specifically limit. And as such a carbodiimide compound having a carbodiimide group, for example, a compound having two or more carbodiimide groups, specifically, the general formula (2):
-N = C = N-R 1 (2)
[In General Formula (2), R 1 represents a divalent organic group. Suitable examples include polycarbodiimides and / or modified polycarbodiimides having a repeating unit represented by the formula: In the present specification, the modified polycarbodiimide refers to a resin obtained by reacting a reactive compound with polycarbodiimide. As the reactive compound, one group having reactivity with polycarbodiimide (a group having an active hydrogen such as a carboxyl group or a primary or secondary amino group), and another functional group For example, compounds described in JP-A-2005-49370.
Examples of such carbodiimide compounds include SV-02, V-02 manufactured by Nisshinbo Chemical.
　架橋剤としては、これらの中でも、架橋反応を系全体で均質的に進ませるという観点から、オキサゾリン化合物、カルボジイミド化合物を用いることが好ましい。 Among these, as the crosslinking agent, it is preferable to use an oxazoline compound or a carbodiimide compound from the viewpoint of allowing the crosslinking reaction to proceed uniformly throughout the system.
　未架橋型のポリアクリル酸と架橋剤とを混合し、反応させる場合における架橋剤の量は、未架橋型のポリアクリル酸１００質量部に対して、好ましくは０．１質量部以上、より好ましくは０．５質量部以上であり、好ましくは１０質量部以下、より好ましくは５質量部以下である。架橋剤の量が少なすぎると、得られるリチウムイオン二次電池のサイクル特性が低下する虞があり、多すぎるとスラリーにした際に未溶解のゲルが残留し、負極に割れが発生する虞があるからである。 The amount of the crosslinking agent in the case of mixing and reacting the uncrosslinked polyacrylic acid and the crosslinking agent is preferably 0.1 parts by mass or more, more preferably, 100 parts by mass of the uncrosslinked polyacrylic acid. Is 0.5 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less. If the amount of the crosslinking agent is too small, the cycle characteristics of the resulting lithium ion secondary battery may be deteriorated. If the amount is too large, undissolved gel may remain when slurried and the negative electrode may be cracked. Because there is.
［［粘度比の調整］］
　ここで、上述のようにして得られる架橋型ポリアクリル酸の粘度比、０．５質量％水溶液の粘度および１．０質量％水溶液の粘度は、例えば、架橋型ポリアクリル酸の架橋密度や架橋点間距離を変更することにより調整することができる。具体的には、例えば、架橋型ポリアクリル酸の粘度比は、使用する架橋性単量体や架橋剤の量を増加させて架橋密度を高めることにより向上させることができる。 [[Adjustment of viscosity ratio]]
Here, the viscosity ratio of the crosslinked polyacrylic acid obtained as described above, the viscosity of the 0.5 mass% aqueous solution, and the viscosity of the 1.0 mass% aqueous solution are, for example, the crosslinking density and crosslinking of the crosslinked polyacrylic acid. It can be adjusted by changing the distance between points. Specifically, for example, the viscosity ratio of cross-linked polyacrylic acid can be improved by increasing the cross-linking density by increasing the amount of cross-linkable monomer or cross-linking agent used.
　そして、ポリアクリル酸として上述した架橋型ポリアクリル酸を用いた負極用スラリー組成物によれば、負極用スラリー組成物を用いて調製した負極合材層中に存在するポリアクリル酸の吸水性を下げることができる。その結果、リチウムイオン二次電池を形成した際に電解液と負極合材層中の水分とが反応することにより生成するフッ化水素を減らすことができるので、内部抵抗、吸水性およびガス発生量の低い負極合材層を得ることができる。 And according to the slurry composition for negative electrodes using the cross-linked polyacrylic acid described above as the polyacrylic acid, the water absorption of the polyacrylic acid present in the negative electrode mixture layer prepared using the slurry composition for negative electrodes is increased. Can be lowered. As a result, it is possible to reduce hydrogen fluoride produced by the reaction between the electrolyte and the water in the negative electrode mixture layer when forming a lithium ion secondary battery, so that internal resistance, water absorption and gas generation amount Can be obtained.
［ポリアクリル酸の中和度］
　なお、本発明のリチウムイオン二次電池負極用スラリー組成物に用いるポリアクリル酸は、分子中に存在するカルボキシル基の少なくとも一部が中和されていることが好ましい。即ち、ポリアクリル酸はポリアクリル酸塩であってもよい。カルボキシル基の少なくとも一部が中和されていれば、ポリアクリル酸の分子鎖が広がり易く、充放電に伴う負極活物質の膨張および収縮を抑制し易いからである。
　ここで、ポリアクリル酸の中和に用いる塩は、特に限定されるものではない。特に好ましくは、ポリアクリル酸の分子鎖の広がりを得やすいという観点で、一価の塩基が好ましく、例えば水酸化ナトリウム、水酸化リチウムを挙げることができる。なお、リチウムイオン二次電池の特性の観点からは、水酸化リチウムが好ましい。 [Neutralization degree of polyacrylic acid]
In addition, it is preferable that at least one part of the carboxyl group which exists in the molecule | numerator is neutralized in the polyacrylic acid used for the slurry composition for lithium ion secondary battery negative electrodes of this invention. That is, the polyacrylic acid may be a polyacrylate. This is because when at least a part of the carboxyl group is neutralized, the molecular chain of polyacrylic acid is likely to spread, and the expansion and contraction of the negative electrode active material accompanying charge / discharge are easily suppressed.
Here, the salt used for neutralization of polyacrylic acid is not particularly limited. Particularly preferably, a monovalent base is preferable from the viewpoint of easily spreading the molecular chain of polyacrylic acid, and examples thereof include sodium hydroxide and lithium hydroxide. In addition, lithium hydroxide is preferable from the viewpoint of the characteristics of the lithium ion secondary battery.
　ここで、カルボキシル基が中和されてナトリウム塩を形成している場合、ポリアクリル酸の中和度は、０．４以上１．０以下であることが好ましく、０．７以上１．０以下であることが更に好ましい。また、カルボキシル基が中和されてリチウム塩を形成している場合、ポリアクリル酸の中和度は、０．４以上１．０以下であることが好ましく、０．７以上１．０以下であることが更に好ましい。なお、中和度は、下記の中和度の測定方法に従い測定することができる。
［［中和度の測定方法］］
　ＪＩＳ Ｋ０１１３－１９９７に準拠する方法によって測定した値から、目的とする中和度を算出する。ここで、ＪＩＳ Ｋ０１１３－１９９７に準拠する方法とは、０．１規定の水酸化カリウム水溶液を滴定液として使用して電位差滴定を行い、変曲点法によって終点を決定する方法である。
　なお、アクリル酸を中和した後に重合して得たポリアクリル酸の場合には、上記方法以外に、アクリル酸の中和度（中和後のアクリル酸塩のモル数÷中和前のアクリル酸のモル数）からも中和度を求めることができる。 Here, when the carboxyl group is neutralized to form a sodium salt, the degree of neutralization of the polyacrylic acid is preferably 0.4 or more and 1.0 or less, and 0.7 or more and 1.0 or less. More preferably. When the carboxyl group is neutralized to form a lithium salt, the degree of neutralization of polyacrylic acid is preferably 0.4 or more and 1.0 or less, and 0.7 or more and 1.0 or less. More preferably it is. The degree of neutralization can be measured according to the following method for measuring the degree of neutralization.
[[Method for measuring degree of neutralization]]
The target neutralization degree is calculated from the value measured by the method according to JIS K0113-1997. Here, the method according to JIS K0113-1997 is a method in which a 0.1N potassium hydroxide aqueous solution is used as a titrant to perform potentiometric titration and the end point is determined by an inflection point method.
In the case of polyacrylic acid obtained by polymerization after neutralizing acrylic acid, in addition to the above method, the neutralization degree of acrylic acid (number of moles of acrylate after neutralization ÷ acrylic before neutralization) The degree of neutralization can also be determined from the number of moles of acid.
［ポリアクリル酸の配合量］
　そして、本発明のリチウムイオン二次電池負極用スラリー組成物は、負極活物質１００質量部当たり、ポリアクリル酸を、０．５質量部以上の割合で含有することが好ましく、１質量部以上の割合で含有することが更に好ましく、１０質量部以下の割合で含有することが好ましく、５質量部以下の割合で含有することが更に好ましく、３質量部以下の割合で含有することが特に好ましく、２質量部以下の割合で含有することが最も好ましい。負極活物質１００質量部当たりのポリアクリル酸の含有量が０．５質量部以上であれば、充放電に伴う負極活物質（特に、シリコン系負極活物質）の膨張および収縮を十分に抑制することができる。また、ポリアクリル酸の含有量が１０質量部以下であれば、スラリー組成物の粘度が上昇して塗工性が低下するのを十分に抑制することができる。 [Amount of polyacrylic acid]
The slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains polyacrylic acid in a proportion of 0.5 parts by mass or more per 100 parts by mass of the negative electrode active material. More preferably, it is contained at a rate of 10 parts by mass or less, more preferably at a rate of 5 parts by mass or less, particularly preferably at a rate of 3 parts by mass or less, Most preferably, it is contained in a proportion of 2 parts by mass or less. When the content of polyacrylic acid per 100 parts by mass of the negative electrode active material is 0.5 parts by mass or more, the expansion and contraction of the negative electrode active material (particularly, the silicon-based negative electrode active material) accompanying charge / discharge is sufficiently suppressed. be able to. Moreover, if content of polyacrylic acid is 10 mass parts or less, it can fully suppress that the viscosity of a slurry composition rises and coating property falls.
＜カルボキシメチルセルロース塩＞
　本発明のリチウムイオン二次電池負極用スラリー組成物は、カルボキシメチルセルロース塩を含むことが好ましい。ポリアクリル酸とカルボキシメチルセルロース塩とを併用することで、負極活物質等の分散性を良好なものとし、負極用スラリー組成物の保存安定性を向上させることができる。 <Carboxymethylcellulose salt>
The slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains a carboxymethyl cellulose salt. By using polyacrylic acid and carboxymethylcellulose salt in combination, the dispersibility of the negative electrode active material and the like can be improved, and the storage stability of the negative electrode slurry composition can be improved.
［カルボキシメチルセルロース塩の種類］
　ここで、カルボキシメチルセルロース塩としては、特に限定されることなく、カルボキシメチルセルロースのナトリウム塩、アンモニウム塩を用いることができる。 [Types of carboxymethylcellulose salts]
Here, the carboxymethyl cellulose salt is not particularly limited, and a sodium salt or ammonium salt of carboxymethyl cellulose can be used.
［カルボキシメチルセルロース塩の１質量％水溶液粘度］
　なお、充放電に伴う負極活物質の膨張および収縮を更に抑制する観点からは、カルボキシメチルセルロース塩の１質量％水溶液粘度が、１．０Ｐａ・ｓ以上であることが好ましい。また、負極用スラリー組成物の過度な粘度上昇を抑制して塗工性を確保する観点からは、カルボキシメチルセルロース塩の１質量％水溶液粘度は、１２Ｐａ・ｓ以下であることが好ましく、１０Ｐａ・ｓ以下であることが更に好ましい。なお、カルボキシメチルセルロース塩の１質量％水溶液粘度は、ＪＩＳ Ｚ８８０３（１９９１）に準拠して、単一円筒形回転粘度計（温度２５℃、回転数６０ｒｐｍ、スピンドル形状＝１）により測定することができる。 [Viscosity of 1% by mass aqueous solution of carboxymethyl cellulose salt]
In addition, from the viewpoint of further suppressing expansion and contraction of the negative electrode active material due to charge / discharge, the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose salt is preferably 1.0 Pa · s or more. In addition, from the viewpoint of securing an applicability by suppressing an excessive increase in viscosity of the slurry composition for negative electrode, the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose salt is preferably 12 Pa · s or less, and preferably 10 Pa · s. More preferably, it is as follows. In addition, the 1 mass% aqueous solution viscosity of carboxymethylcellulose salt can be measured with a single cylindrical rotational viscometer (temperature 25 ° C., rotational speed 60 rpm, spindle shape = 1) according to JIS Z8803 (1991). .
［カルボキシメチルセルロース塩の配合量］
　そして、本発明のリチウムイオン二次電池負極用スラリー組成物は、カルボキシメチルセルロース塩の含有量が、ポリアクリル酸の含有量の０．１倍以上９倍以下であることが好ましく、ポリアクリル酸の含有量の０．２５倍以上４倍以下であることがより好ましく、ポリアクリル酸の含有量の０．２５倍以上２.３倍以下であることが更に好ましい。カルボキシメチルセルロース塩の含有量を上記範囲内とすれば、負極用スラリー組成物の保存安定性を十分に高めつつ、充放電に伴う負極活物質の膨張および収縮を更に抑制することができる。 [Amount of carboxymethyl cellulose salt]
In the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, the content of the carboxymethyl cellulose salt is preferably 0.1 to 9 times the content of polyacrylic acid, The content is more preferably 0.25 to 4 times the content, and still more preferably 0.25 to 2.3 times the polyacrylic acid content. When the content of the carboxymethyl cellulose salt is within the above range, it is possible to further suppress the expansion and contraction of the negative electrode active material accompanying charge / discharge while sufficiently increasing the storage stability of the slurry composition for negative electrode.
＜粒子状結着材＞
　本発明のリチウムイオン二次電池負極用スラリー組成物は、粒子状結着材を含むことが好ましい。ここで、粒子状結着材は、本発明のリチウムイオン二次電池負極用スラリー組成物を用いて形成した負極合材層において、上述したポリアクリル酸と共に、負極合材層中の各成分同士または各成分と集電体とを結着させる。従って、リチウムイオン二次電池負極用スラリー組成物に粒子状結着材を配合すれば、負極合材層中の各成分同士または各成分と集電体との結着性を更に高めて、負極用スラリー組成物を用いて製造した負極からの粉落ちの発生を抑制することができる。また、負極の柔軟性を確保しつつ、負極合材層と集電体との密着性を高めることができる。 <Particulate binder>
The slurry composition for a lithium ion secondary battery negative electrode of the present invention preferably contains a particulate binder. Here, in the negative electrode mixture layer formed using the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention, the particulate binder is composed of the components in the negative electrode mixture layer together with the polyacrylic acid described above. Alternatively, each component and the current collector are bound. Therefore, if a particulate binder is blended with the slurry composition for a negative electrode of a lithium ion secondary battery, the binding properties between the components in the negative electrode mixture layer or between each component and the current collector can be further improved. Generation | occurrence | production of the powder fall from the negative electrode manufactured using the slurry composition for water can be suppressed. Moreover, the adhesiveness of a negative electrode compound material layer and a collector can be improved, ensuring the softness | flexibility of a negative electrode.
［粒子状結着材の種類］
　ここで、上述した粒子状結着材としては、共役ジエン系重合体、アクリル系重合体等の重合体を用いることができる。 [Types of particulate binder]
Here, a polymer such as a conjugated diene polymer or an acrylic polymer can be used as the particulate binder described above.
［［アクリル系重合体]］
　ここで、粒子状結着材として好ましいアクリル系重合体について説明する。アクリル系重合体とは、（メタ）アクリル酸エステル単量体単位を含む重合体である。なお、アクリル系重合体は、（メタ）アクリル酸エステル単量体単位以外に、カルボキシル基含有単量体単位、α，β-不飽和ニトリル単量体単位、および、その他任意の単量体単位を含んでいてもよい。
　なお、本発明において「単量体単位を含む」とは、「その単量体を用いて得た重合体中に単量体由来の構造単位が含まれている」ことを意味する。 [[Acrylic polymer]]
Here, a preferable acrylic polymer as the particulate binder will be described. An acrylic polymer is a polymer containing a (meth) acrylic acid ester monomer unit. In addition to the (meth) acrylic acid ester monomer unit, the acrylic polymer includes a carboxyl group-containing monomer unit, an α, β-unsaturated nitrile monomer unit, and any other monomer unit. May be included.
In the present invention, “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.
　ここで、アクリル系重合体の製造に使用可能な（メタ）アクリル酸エステル単量体としては、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、ｔ－ブチルアクリレー卜、ペンチルアクリレート、ヘキシルアクリレート、ヘプチルアクリレート、オクチルアクリレート、２－エチルヘキシルアクリレート等のアクリル酸アルキルエステル；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、ｔ－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、ヘプチルメタクリレート、オクチルメタクリレート、２－エチルヘキシ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。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、アクリル系重合体における（メタ）アクリル酸エステル単量体単位の割合は、好ましくは５０質量％以上、より好ましくは５５質量％以上、特に好ましくは５８質量％以上であり、好ましくは９８質量％以下、より好ましくは９７質量％以下、特に好ましくは９６質量％以下である。 Here, (meth) acrylic acid ester monomers that can be used for the production of acrylic polymers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and t-butyl acrylate. , Alkyl acrylates such as pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate , Hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, etc. Such as acid alkyl esters. These may be used alone or in combination of two or more.
In addition, the ratio of the (meth) acrylic acid ester monomer unit in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, particularly preferably 58% by mass or more, and preferably 98% by mass. % Or less, more preferably 97% by mass or less, particularly preferably 96% by mass or less.
　また、アクリル系重合体の製造に使用可能なカルボキシル基含有単量体としては、エチレン性不飽和モノカルボン酸及びその誘導体、エチレン性不飽和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。
　エチレン性不飽和モノカルボン酸の例としては、アクリル酸、メタクリル酸、クロトン酸などが挙げられる。そして、エチレン性不飽和モノカルボン酸の誘導体の例としては、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、β－ジアミノアクリル酸などが挙げられる。
　エチレン性不飽和ジカルボン酸の例としては、マレイン酸、フマル酸、イタコン酸などが挙げられる。そして、エチレン性不飽和ジカルボン酸の酸無水物の例としては、無水マレイン酸、ジアクリル酸無水物、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。さらに、エチレン性不飽和ジカルボン酸の誘導体の例としては、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、マレイン酸ジフェニル、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が挙げられる。
　これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、アクリル系重合体におけるカルボキシル基含有単量体単位の割合は、好ましくは０．１質量％以上、より好ましくは０．５質量％以上であり、好ましくは１０質量％以下、より好ましくは５質量％以下である。 Examples of the carboxyl group-containing monomer that can be used for the production of the acrylic polymer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. It is done.
Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like. Examples of the ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic. Acid, β-diaminoacrylic acid and the like.
Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, diacrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like. In addition, examples of ethylenically unsaturated dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate , Dodecyl maleate, octadecyl maleate, fluoroalkyl maleate and the like.
These may be used alone or in combination of two or more.
In addition, the ratio of the carboxyl group-containing monomer unit in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, preferably 10% by mass or less, more preferably 5%. It is below mass%.
　また、アクリル系重合体の製造に使用可能なα，β－不飽和ニトリル単量体としては、アクリロニトリル、メタクリロニトリルが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、アクリル系重合体におけるα，β－不飽和ニトリル単量体単位の割合は、好ましくは１質量％以上、より好ましくは２質量％以上であり、好ましくは５０質量％以下、より好ましくは３５質量％以下である。 Examples of the α, β-unsaturated nitrile monomer that can be used in the production of the acrylic polymer include acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more.
The proportion of α, β-unsaturated nitrile monomer units in the acrylic polymer is preferably 1% by mass or more, more preferably 2% by mass or more, preferably 50% by mass or less, more preferably 35%. It is below mass%.
　任意の単量体としては、上述した単量体と共重合可能な単量体が挙げられる。具体的には、任意の単量体としては、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等のヒドロキシル基含有単量体；アクリルアミド－２－メチルプロパンスルホン酸等の硫酸エステル基含有単量体；アクリルアミド、メタクリルアミド等のアミド基含有単量体；アリルグリシジルエーテル、アリル（メタ）アクリレート、Ｎ－メチロールアクリルアミドなどの架橋性単量体（架橋可能な単量体）；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、ビニル安息香酸メチル、ビニルナフタレン、クロロメチルスチレン、α－メチルスチレン、ジビニルベンゼン等のスチレン系単量体；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、ブチルビエ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；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等のアミノ基含有単量体；などが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、アクリル系重合体における任意の単量体単位の割合は、特に限定されないが、合計量で好ましくは１０質量％以下であり、より好ましくは８質量％以下であり、０．５質量％以上が好ましく、１．０質量％以上がより好ましい。 As an arbitrary monomer, the monomer copolymerizable with the monomer mentioned above is mentioned. Specifically, the optional monomers include hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate. Monomers; sulfate group-containing monomers such as acrylamide-2-methylpropanesulfonic acid; amide group-containing monomers such as acrylamide and methacrylamide; allyl glycidyl ether, allyl (meth) acrylate, N-methylol acrylamide, etc. Crosslinkable monomer (crosslinkable monomer): Styrene such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, α-methylstyrene, divinylbenzene Monomers; ethylene, propylene, etc. Fins; diene 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; methyl vinyl ether; Vinyl ethers such as 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; Heterocycles such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole -Containing vinyl compounds; amino group-containing monomers such as aminoethyl vinyl ether and dimethylaminoethyl vinyl ether; These may be used alone or in combination of two or more.
The ratio of the arbitrary monomer unit in the acrylic polymer is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 0.5% by mass or more in total amount. Is preferable, and 1.0 mass% or more is more preferable.
　アクリル系重合体の製造方法は特に限定はされず、例えば、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を用いてもよい。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などの付加重合を用いることができる。 The method for producing the acrylic polymer 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 may be used. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
［[共役ジエン系重合体]］
　次に、粒子状結着材として好ましい共役ジエン系重合体について説明する。共役ジエン系重合体とは、共役ジエン単量体単位を含む重合体であり、それらの水素添加物も含まれる。
　共役ジエン系重合体の具体例としては、ポリブタジエンやポリイソプレンなどの脂肪族共役ジエン重合体；スチレン・ブタジエン共重合体（ＳＢＲ）などの芳香族ビニル・脂肪族共役ジエン共重合体；アクリロニトリル・ブタジエン共重合体（ＮＢＲ）などのシアン化ビニル・共役ジエン共重合体；水素化ＳＢＲ、水素化ＮＢＲ等が挙げられる。
　以下、共役ジエン系重合体として好ましい芳香族ビニル・脂肪族共役ジエン共重合体の製造に用いられる芳香族ビニル単量体、脂肪族共役ジエン単量体、カルボキシル基含有単量体、ヒドロキシル基含有単量体、その他任意の単量体について詳述する。 [[Conjugated Diene Polymer]]
Next, a preferred conjugated diene polymer as the particulate binder will be described. The conjugated diene polymer is a polymer containing a conjugated diene monomer unit, and includes hydrogenated products thereof.
Specific examples of conjugated diene polymers include aliphatic conjugated diene polymers such as polybutadiene and polyisoprene; aromatic vinyl / aliphatic conjugated diene copolymers such as styrene / butadiene copolymer (SBR); acrylonitrile / butadiene. Examples include vinyl cyanide / conjugated diene copolymers such as copolymers (NBR); hydrogenated SBR, hydrogenated NBR, and the like.
Hereinafter, aromatic vinyl monomer, aliphatic conjugated diene monomer, carboxyl group-containing monomer, hydroxyl group-containing used for the production of aromatic vinyl / aliphatic conjugated diene copolymer preferred as conjugated diene polymer Monomers and other optional monomers will be described in detail.
　ここで、芳香族ビニル・脂肪族共役ジエン共重合体の製造に使用可能な芳香族ビニル単量体としては、スチレン、α－メチルスチレン、ビニルトルエン、ジビニルベンゼンなどが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、芳香族ビニル・脂肪族共役ジエン共重合体における芳香族ビニル単量体単位の割合は、好ましくは３０質量％以上、より好ましくは３５質量％以上であり、好ましくは７９．５質量％以下、より好ましくは６９質量％以下である。 Here, examples of the aromatic vinyl monomer that can be used for the production of the aromatic vinyl / aliphatic conjugated diene copolymer include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. These may be used alone or in combination of two or more.
The ratio of the aromatic vinyl monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 30% by mass or more, more preferably 35% by mass or more, and preferably 79.5% by mass or less. More preferably, it is 69 mass% or less.
　芳香族ビニル・脂肪族共役ジエン共重合体の製造に使用可能な脂肪族共役ジエン単量体としては、１，３－ブタジエン、２－メチル－１，３－ブタジエン、２，３－ジメチル－１，３－ブタジエン、２－クロル－１，３－ブタジエン、置換直鎖共役ペンタジエン類、置換および側鎖共役ヘキサジエン類などが挙げられる。これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、芳香族ビニル・脂肪族共役ジエン共重合体における脂肪族共役ジエン単量体単位の割合は、好ましくは２０質量％以上、より好ましくは３０質量％以上であり、好ましくは７０質量％以下、より好ましくは６０質量％以下、特に好ましくは５５質量％以下である。 Examples of the aliphatic conjugated diene monomer that can be used in the production of the aromatic vinyl / aliphatic conjugated diene copolymer include 1,3-butadiene, 2-methyl-1,3-butadiene, and 2,3-dimethyl-1. , 3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. These may be used alone or in combination of two or more.
The ratio of the aliphatic conjugated diene monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 70% by mass or less. More preferably, it is 60 mass% or less, Most preferably, it is 55 mass% or less.
　芳香族ビニル・脂肪族共役ジエン共重合体の製造に使用可能なカルボキシル基含有単量体としては、上述のアクリル系重合体の製造に使用可能なものとした挙げたものと同様のものが挙げられる。
　なお、芳香族ビニル・脂肪族共役ジエン共重合体におけるカルボキシル基含有単量体単位の割合は、好ましくは０．５質量％以上、より好ましくは１．０質量％以上であり、好ましくは１０質量％以下、より好ましくは８質量％以下である。 Examples of the carboxyl group-containing monomer that can be used for the production of the aromatic vinyl / aliphatic conjugated diene copolymer include those similar to those mentioned above that can be used for the production of the acrylic polymer. It is done.
The ratio of the carboxyl group-containing monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass. % Or less, more preferably 8% by mass or less.
　芳香族ビニル・脂肪族共役ジエン共重合体の製造に使用可能なヒドロキシル基含有単量体としては、２－ヒドロキシエチルアクリレート、２－ヒドロキシエチルメタクリレート、ヒドロキシプロピルアクリレート、ヒドロキシプロピルメタクリレート、ヒドロキシブチルアクリレート、ヒドロキシブチルメタクリレート、３－クロロ－２－ヒドロキシプロピルメタクリレート、ジ－（エチレングリコール）マレエート、ジ－（エチレングリコール）イタコネート、２－ヒドロキシエチルマレエート、ビス（２－ヒドロキシエチル）マレエート、２－ヒドロキシエチルメチルフマレートなどが挙げられる。中でも、２－ヒドロキシエチルアクリレートが好ましい。なお、これらは、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、芳香族ビニル・脂肪族共役ジエン共重合体におけるヒドロキシル基含有単量体単位の割合は、好ましくは０．５質量％以上、より好ましくは１．０質量％以上であり、好ましくは１０質量％以下、より好ましくは８質量％以下である。 Examples of hydroxyl group-containing monomers that can be used for the production of aromatic vinyl / aliphatic conjugated diene copolymers include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, Hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl And methyl fumarate. Of these, 2-hydroxyethyl acrylate is preferred. In addition, these may be used individually by 1 type and may be used in combination of 2 or more types.
The ratio of the hydroxyl group-containing monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 10% by mass. % Or less, more preferably 8% by mass or less.
　任意の単量体としては、上述した単量体と共重合可能な単量体が挙げられる。具体的には、任意の単量体としては、上述のアクリル系重合体において、その他の単量体として使用可能なものとして挙げたものから、芳香族ビニル単量体、脂肪族共役ジエン単量体およびヒドロキシル基含有単量体に該当するものを除いたもの、並びに、α，β－不飽和ニトリル単量体が使用可能である。これらその他の単量体は、１種類を単独で用いてもよく、２種類以上を組み合わせて用いてもよい。
　なお、芳香族ビニル・脂肪族共役ジエン共重合体における任意の単量体単位の割合は、特に限定されないが、合計量で好ましくは１０質量％以下であり、より好ましくは８質量％以下であり、０．５質量％以上が好ましく、１．０質量％以上がより好ましい。 As an arbitrary monomer, the monomer copolymerizable with the monomer mentioned above is mentioned. Specifically, as the optional monomer, from the above-mentioned acrylic polymers, those that can be used as other monomers, aromatic vinyl monomers, aliphatic conjugated diene monomers And those other than those corresponding to the hydroxyl group-containing monomer, and α, β-unsaturated nitrile monomers can be used. These other monomers may be used alone or in combination of two or more.
The proportion of any monomer unit in the aromatic vinyl / aliphatic conjugated diene copolymer is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less in total. 0.5 mass% or more is preferable, and 1.0 mass% or more is more preferable.
　共役ジエン系重合体の製造方法は特に限定はされず、例えば、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を用いてもよい。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などの付加重合を用いることができる。 The production method of the conjugated diene polymer 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 may be used. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
［粒子状結着材の配合量］
　そして、本発明のリチウムイオン二次電池負極用スラリー組成物は、ポリアクリル酸１００質量部当たり、粒子状結着材を、４質量部以上の割合で含有することが好ましく、２０質量部以下の割合で含有することが好ましく、１０質量部以下の割合で含有することが更に好ましい。ポリアクリル酸１００質量部当たりの粒子状結着材の含有量が４質量部以上であれば、結着性を十分に高めて、負極用スラリー組成物を用いて製造した負極からの粉落ちの発生を抑制することができる。また、ポリアクリル酸の存在比が低下するのを抑制し、負極活物質の膨張よび収縮を良好に抑制する観点からは、ポリアクリル酸１００質量部当たりの粒子状結着材の含有量は２０質量部以下とすることが好ましい。
　なお、同様の理由により、粒子状結着材の配合量は、負極活物質１００質量部当たり、例えば０．０５質量部以上とすることが好ましく、０．１質量部以上とすることがより好ましく、１．０質量部以下とすることが好ましく、０．６質量部以下とすることがより好ましく、０．５質量部以下とすることが更に好ましい。 [Blending amount of particulate binder]
And it is preferable that the slurry composition for lithium ion secondary battery negative electrodes of this invention contains a particulate binder in the ratio of 4 mass parts or more per 100 mass parts of polyacrylic acid, and is 20 mass parts or less. It is preferable to contain in a ratio, and it is still more preferable to contain in the ratio of 10 mass parts or less. If the content of the particulate binder per 100 parts by mass of polyacrylic acid is 4 parts by mass or more, the binding property is sufficiently increased, and the powder falling off from the negative electrode produced using the negative electrode slurry composition Occurrence can be suppressed. Further, from the viewpoint of suppressing a decrease in the abundance ratio of polyacrylic acid and favorably suppressing expansion and contraction of the negative electrode active material, the content of the particulate binder per 100 parts by mass of polyacrylic acid is 20 It is preferable to set it as a mass part or less.
For the same reason, the amount of the particulate binder is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more per 100 parts by mass of the negative electrode active material. 1.0 mass part or less, preferably 0.6 mass part or less, more preferably 0.5 mass part or less.
［粒子状結着材の性状］
　粒子状結着材は、ゲル含有量が、好ましくは５０質量％以上、より好ましくは８０質量％以上であり、好ましくは９８質量％以下、より好ましくは９５質量％以下である。粒子状結着材のゲル含有量が５０質量％未満の場合、粒子状結着材の凝集力が低下して、集電体などとの密着強度が不十分となる場合がある。一方、粒子状結着材のゲル含有量が９８質量％超の場合、粒子状結着材が靱性を失って脆くなり、結果的に密着強度が不十分となる場合がある。なお、本発明において、粒子状結着材の「ゲル含有量」は、本明細書の実施例に記載の測定方法を用いて測定することができる。
　また、粒子状結着材は、ガラス転移温度（Ｔｇ）が、好ましくは－３０℃以上、より好ましくは－２０℃以上であり、好ましくは８０℃以下、より好ましくは３０℃以下である。粒子状結着材のガラス転移温度が－３０℃以上であることで、二次電池負極用スラリー組成物中の配合成分が凝集して沈降するのを防ぎ、スラリー組成物の安定性を確保することができる。また、粒子状結着材のガラス転移温度が８０℃以下であることで、二次電池負極用スラリー組成物を集電体上などに塗布する際の作業性を良好なものとすることができる。なお、本発明において、粒子状結着材の「ガラス転移温度（Ｔｇ）」は、本明細書の実施例に記載の測定方法を用いて測定することができる。 [Properties of particulate binder]
The particulate binder preferably has a gel content of 50% by mass or more, more preferably 80% by mass or more, preferably 98% by mass or less, more preferably 95% by mass or less. When the gel content of the particulate binder is less than 50% by mass, the cohesive force of the particulate binder may be reduced, and the adhesion strength with the current collector or the like may be insufficient. On the other hand, when the gel content of the particulate binder is more than 98% by mass, the particulate binder may lose toughness and become brittle, resulting in insufficient adhesion strength. In the present invention, the “gel content” of the particulate binder can be measured using the measuring method described in the examples of the present specification.
Further, the particulate binder has a glass transition temperature (Tg) of preferably −30 ° C. or higher, more preferably −20 ° C. or higher, preferably 80 ° C. or lower, more preferably 30 ° C. or lower. When the glass transition temperature of the particulate binder is −30 ° C. or higher, the components in the slurry composition for secondary battery negative electrode are prevented from aggregating and settling, and the stability of the slurry composition is ensured. be able to. Moreover, workability at the time of apply | coating the slurry composition for secondary battery negative electrodes on a collector etc. can be made favorable because the glass transition temperature of a particulate-form binder is 80 degrees C or less. . In the present invention, the “glass transition temperature (Tg)” of the particulate binder can be measured using the measuring method described in the examples of the present specification.
＜その他の成分＞
　本発明のリチウムイオン二次電池負極用スラリー組成物は、上記成分の他に、導電材、補強材、レベリング剤、電解液添加剤などの成分を含有していてもよい。これらは、電池反応に影響を及ぼさないものであれば特に限られず、公知のもの、例えば国際公開第２０１２／１１５０９６号に記載のものを使用することができる。これらの成分は、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。 <Other ingredients>
The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention may contain components such as a conductive material, a reinforcing material, a leveling agent, and an electrolytic solution additive in addition to the above components. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
（リチウムイオン二次電池負極用スラリー組成物の調製方法）
　本発明のリチウムイオン二次電池負極用スラリー組成物は、上記各成分を分散媒としての水系媒体中に分散させることにより調製することができる。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水系媒体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。
　ここで、水系媒体としては、通常は水を用いるが、任意の化合物の水溶液や、少量の有機媒体と水との混合溶液などを用いてもよい。 (Method for preparing slurry composition for negative electrode of lithium ion secondary battery)
The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention can be prepared by dispersing each of the above components in an aqueous medium as a dispersion medium. Specifically, the above components and the aqueous medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or a fill mix. Thus, a slurry composition can be prepared.
Here, water is usually used as the aqueous medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used.
（リチウムイオン二次電池用負極）
　本発明のリチウムイオン二次電池用負極は、本発明のリチウムイオン二次電池負極用スラリー組成物を使用して製造することができる。
　ここで、本発明のリチウムイオン二次電池用負極は、集電体と、集電体上に形成された負極合材層とを備え、負極合材層には、少なくとも、負極活物質と、ポリアクリル酸とが含まれている。なお、負極合材層中に含まれている各成分は、本発明のリチウムイオン二次電池負極用スラリー組成物中に含まれていたものであり、それら各成分の好適な存在比は、負極用スラリー組成物中の各成分の好適な存在比と同じである。
　そして、本発明のリチウムイオン二次電池用負極は、負極合材層が、シリコン系負極活物質を含む上述した負極活物質と、上述したポリアクリル酸とを含んでいるので、リチウムイオン二次電池のサイクル特性の低下を防止しつつ、電池容量を向上させることができる。 (Anode for lithium ion secondary battery)
The negative electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for negative electrodes of lithium ion secondary batteries of this invention.
Here, the negative electrode for a lithium ion secondary battery of the present invention includes a current collector and a negative electrode mixture layer formed on the current collector, and the negative electrode mixture layer includes at least a negative electrode active material, Contains polyacrylic acid. In addition, each component contained in the negative electrode composite material layer was contained in the slurry composition for a lithium ion secondary battery negative electrode of the present invention, and a suitable abundance ratio of each of these components is It is the same as the suitable abundance ratio of each component in the slurry composition for use.
In the negative electrode for a lithium ion secondary battery of the present invention, the negative electrode mixture layer contains the above-described negative electrode active material containing a silicon-based negative electrode active material and the above-described polyacrylic acid. The battery capacity can be improved while preventing the deterioration of the cycle characteristics of the battery.
　なお、本発明のリチウムイオン二次電池用負極は、例えば、上述したリチウムイオン二次電池負極用スラリー組成物を集電体上に塗布する工程（塗布工程）と、集電体上に塗布されたリチウムイオン二次電池負極用スラリー組成物を乾燥して集電体上に負極合材層を形成する工程（乾燥工程）とを経て製造される。 The negative electrode for a lithium ion secondary battery of the present invention is applied, for example, to a step of applying the above-described slurry composition for a negative electrode of a lithium ion secondary battery on a current collector (application step), and a current collector. The lithium ion secondary battery negative electrode slurry composition is dried to form a negative electrode mixture layer on the current collector (drying step).
［塗布工程］
　上記リチウムイオン二次電池負極用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、負極用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、乾燥して得られる負極合材層の厚みに応じて適宜に設定しうる。
　なお、負極合材層の厚さは、好ましくは１～２００μｍ、より好ましくは３～１００μｍとすることができる。 [Coating process]
A method for applying the slurry composition for a lithium ion secondary battery negative electrode on the current collector is not particularly limited, and a known method can be used. Specifically, as a 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 for negative electrode may be applied only to one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the negative electrode mixture layer obtained by drying.
The thickness of the negative electrode mixture layer can be preferably 1 to 200 μm, more preferably 3 to 100 μm.
　ここで、負極用スラリー組成物を塗布する集電体としては、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。中でも、負極に用いる集電体としては銅箔が特に好ましい。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。 Here, as the current collector to which the slurry composition for negative electrode is applied, 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. Among these, a copper foil is particularly preferable as the current collector used for the negative electrode. In addition, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
［乾燥工程］
　集電体上の負極用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、真空乾燥、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負極用スラリー組成物を乾燥することで、集電体上に負極合材層を形成し、集電体と負極合材層とを備えるリチウムイオン二次電池用負極を得ることができる。 [Drying process]
A method for drying the slurry composition for the negative electrode on the current collector is not particularly limited, and a known method can be used, for example, drying with hot air, hot air, low-humidity air, vacuum drying, infrared rays, electron beam, etc. The drying method by irradiation is mentioned. Thus, by drying the negative electrode slurry composition on the current collector, a negative electrode mixture layer is formed on the current collector, and the negative electrode for a lithium ion secondary battery comprising the current collector and the negative electrode mixture layer Can be obtained.
　なお、乾燥工程の後、金型プレスまたはロールプレスなどを用い、負極合材層に加圧処理を施してもよい。加圧処理により、負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。
　さらに、負極合材層が硬化性の重合体を含む場合は、負極合材層の形成後に前記重合体を硬化させることが好ましい。 Note that after the drying step, the negative electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the negative electrode mixture layer and the current collector can be improved.
Furthermore, when the negative electrode mixture layer contains a curable polymer, the polymer is preferably cured after the formation of the negative electrode mixture layer.
（リチウムイオン二次電池）
　本発明のリチウムイオン二次電池は、正極と、負極と、電解液と、セパレータとを備え、負極として、本発明のリチウムイオン二次電池用負極を用いたものである。そして、本発明のリチウムイオン二次電池は、本発明のリチウムイオン二次電池用負極を用いているので、電池容量が高く、且つ、サイクル特性に優れている。 (Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode for a lithium ion secondary battery of the present invention is used as the negative electrode. And since the lithium ion secondary battery of this invention uses the negative electrode for lithium ion secondary batteries of this invention, its battery capacity is high and it is excellent in cycling characteristics.
＜正極＞
　リチウムイオン二次電池の正極としては、リチウムイオン二次電池用正極として用いられる既知の正極を用いることができる。具体的には、正極としては、例えば、正極合材層を集電体上に形成してなる正極を用いることができる。
　なお、集電体としては、アルミニウム等の金属材料からなるものを用いることができる。また、正極合材層としては、既知の正極活物質と、導電材と、結着材とを含む層を用いることができる。 <Positive electrode>
As a positive electrode of a lithium ion secondary battery, a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used.
As the current collector, one made of a metal material such as aluminum can be used. As the positive electrode mixture layer, a layer containing a known positive electrode active material, a conductive material, and a binder can be used.
＜電解液＞
　電解液としては、溶媒に電解質を溶解した電解液を用いることができる。
　ここで、溶媒としては、電解質を溶解可能な有機溶媒を用いることができる。具体的には、溶媒としては、エチレンカーボネート、プロピレンカーボネート、γ－ブチロラクトン等のアルキルカーボネート系溶媒に、２，５－ジメチルテトラヒドロフラン、テトラヒドロフラン、ジエチルカーボネート、エチルメチルカーボネート、ジメチルカーボネート、酢酸メチル、ジメトキシエタン、ジオキソラン、プロピオン酸メチル、ギ酸メチル等の粘度調整溶媒を添加したものを用いることができる。
　電解質としては、リチウム塩を用いることができる。リチウム塩としては、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。これらのリチウム塩の中でも、有機溶媒に溶解しやすく、高い解離度を示すという点より、電解質としてはＬｉＰＦ6、ＬｉＣｌＯ4、ＣＦ3ＳＯ3Ｌｉが好ましい。 <Electrolyte>
As the electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
Here, as the solvent, an organic solvent capable of dissolving the electrolyte can be used. Specifically, examples of the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, and γ-butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
A lithium salt can be used as the electrolyte. As the lithium salt, for example, those described in JP 2012-204303 A can be used. Among these lithium salts, LiPF 6 , LiClO 4 , and CF 3 SO 3 Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation.
＜セパレータ＞
　セパレータとしては、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、リチウムイオン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、ポリオレフィン系の樹脂（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）からなる微多孔膜が好ましい。 <Separator>
As the separator, for example, those described in JP 2012-204303 A can be used. Among these, the thickness of the separator as a whole can be reduced, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume. A microporous film made of a series resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred.
（リチウムイオン二次電池の製造方法）
　本発明のリチウムイオン二次電池は、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。リチウムイオン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。リチウムイオン二次電池の形状は、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 producing lithium ion secondary battery)
In the lithium ion secondary battery of the present invention, for example, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the battery shape as necessary, and placed in the battery container. It can manufacture by inject | pouring electrolyte solution into and sealing. In order to prevent an increase in pressure inside the lithium ion secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.
　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。
　実施例および比較例において、ポリアクリル酸の粘度比、粒子状結着材のゲル含有率およびガラス転移温度、負極の平滑性、耐粉落ち性および設計容量、並びに、リチウムイオン二次電池の初期効率およびサイクル特性は、それぞれ以下の方法を使用して評価した。 EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the viscosity ratio of polyacrylic acid, the gel content and the glass transition temperature of the particulate binder, the smoothness of the negative electrode, the dust resistance and the design capacity, and the initial stage of the lithium ion secondary battery Efficiency and cycle characteristics were each evaluated using the following methods.
＜粘度比＞
　ポリアクリル酸の０．５質量％水溶液および１．０質量％水溶液について、Ｂ型粘度計（東機産業株式会社製、TVB-10M）を用いて、温度２５℃、ｐＨ８．０、回転速度６０ｒｐｍ（ローター：Ｍ４）での粘度をＪＩＳ Ｋ７１１７－１に準拠して測定した。そして、粘度比（＝１質量％水溶液の粘度／０．５質量％水溶液の粘度）を算出した。なお、ｐＨの調整は、水酸化ナトリウムまたは水酸化リチウムを用いて行った。
＜ガラス転移温度＞
　粒子状結着材を含む水分散液を、湿度５０％、温度２３～２６℃の環境下で３日間乾燥させて、厚み１±０．３ｍｍのフィルムを得た。このフィルムを、温度６０℃の真空乾燥機で１０時間乾燥させた。その後、乾燥させたフィルムをサンプルとして、ＪＩＳ Ｋ７１２１に準拠し、測定温度：－１００℃～１８０℃、昇温速度：５℃／分の条件下、示差走査熱量分析計（ナノテクノロジー社製、ＤＳＣ６２２０ＳＩＩ）を用いてガラス転移温度を測定した。
＜ゲル含有量＞
　粒子状結着材を含む水分散液を用意し、この水分散液を湿度５０％、温度２３～２５℃の環境下で乾燥させて、厚み１±０．３ｍｍのフィルムに成膜した。このフィルムを、温度６０℃の真空乾燥機で１０時間乾燥させた。その後、乾燥させたフィルムを３～５ｍｍ角に裁断し、約１ｇを精秤した。裁断により得られたフィルム片の質量をｗ０とする。
　このフィルム片を、５０ｇのテトラヒドロフラン（ＴＨＦ）に２４時間浸漬した。その後、ＴＨＦから引き揚げたフィルム片を温度１０５℃で３時間真空乾燥して、不溶分の質量ｗ１を計測した。
　そして、下記式に従ってゲル含有量（質量％）を算出した。
　ゲル含有量（質量％）＝（ｗ１／ｗ０）×１００
＜負極の平滑性＞
　負極原反について、塗布量を長さ方向に１０ｍｍ毎に１０点測定した。１０点の測定値の最小値と最大値の差を下記基準に従って評価した。差が小さいほど、負極の形成に用いた負極用スラリー組成物の塗工性が優れていることを示す。
　Ａ：差が０．５ｍｇ／ｃｍ2未満
　Ｂ：差が０．５ｍｇ／ｃｍ2以上
＜負極の耐粉落ち性＞
　シート状負極を１０ｃｍ角に切断して、得られた試料片の質量（Ｙ０）を測定した。その後、φ１６ｍｍの円形打ち抜き機を用いて試料片を５か所打ち抜いた。その後、エアーブラシをかけ、打ち抜いた試料片と、打ち抜かれた試料片との合計の質量（Ｙ１）を測定し、下記式に従って粉落ち残存率を算出した。
　粉落ち残存率＝（Ｙ１／Ｙ０）×１００（％）
　そして、下記基準に従って耐粉落ち性を評価した。粉落ち残存率の値が大きいほど、負極の端部の割れ、はがれが少ないことを示す。
　Ａ：粉落ち残存率が９９．９８％以上
　Ｂ：粉落ち残存率が９９．９６％以上９９．９８％未満
　Ｃ：粉落ち残存率が９９．９６％未満
＜負極の設計容量＞
　用いた負極活物質の質量平均の理論容量（ｍＡｈ／ｇ）を算出し、以下の基準で評価した。
　Ａ：理論容量が８００ｍＡｈ／ｇを超える
　Ｂ：理論容量が４７０ｍＡｈ／ｇを超え、８００ｍＡｈ／ｇ以下
　Ｃ：理論容量が４７０ｍＡｈ／ｇ以下
＜初期効率＞
　作製したラミネートセル型のリチウムイオン二次電池を、電解液注液後、温度２５℃で５時間静置してから、温度２５℃の条件下、０．２Ｃの定電流法によってセル電圧３．６５Ｖまで充電（充電量を「Ｃ１(ｍＡｈ)」と定義する。）した。その後、温度６０℃で１２時間エージング処理を行い、温度２５℃の条件下、０．２Ｃの定電流法によってセル電圧２．７５Ｖまで放電（放電量を「Ｄ１(ｍＡｈ)」と定義する。）した。
　その後、０．２Ｃの定電流にてＣＣ－ＣＶ充電（上限セル電圧４．２０Ｖ）を行い（充電量を「Ｃ２(ｍＡｈ)」と定義する。）、０．２Ｃの定電流にてＣＣ放電（下限セル電圧２．７５Ｖ）を実施（放電量を「Ｄ２(ｍＡｈ)」と定義する）した。
　初期効率を下記式に従って算出し、以下の基準により評価した。
　初期効率＝｛（Ｄ１＋Ｄ２）／（Ｃ１＋Ｃ２）｝×１００（％）
　Ａ：初期効率が８８％以上
　Ｂ：初期効率が８５％以上８８％未満
　Ｃ：初期効率が８１％以上８５％未満
　Ｄ：初期効率が８１％未満
＜サイクル特性＞
　初期効率の評価で用いたリチウムイオン二次電池を、温度２５℃の条件下、０．１Ｃの定電流法にてセル電圧２．７５Ｖまで放電した。その後、温度４５℃の条件下、充電電圧４．２Ｖ、放電電圧２．７５Ｖ、０．５Ｃの充放電レートにて１００サイクル充放電の操作を行った。そのとき、１サイクル目の放電容量（初期放電容量Ｘ１）および１００サイクル目の放電容量Ｘ２を測定し、ΔＣ´＝（Ｘ２／Ｘ１）×１００（％）で示される容量変化率ΔＣ´を求め、以下の基準により評価した。この容量変化率ΔＣ´の値が高いほど、サイクル特性に優れることを示す。
　Ａ：ΔＣ´が８５％以上
　Ｂ：ΔＣ´が８３％以上８５％未満
　Ｃ：ΔＣ´が８０％以上８３％未満
　Ｄ：ΔＣ´が８０％未満 <Viscosity ratio>
About 0.5 mass% aqueous solution and 1.0 mass% aqueous solution of polyacrylic acid, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10M), temperature 25 ° C., pH 8.0, rotation speed 60 rpm The viscosity at (rotor: M4) was measured according to JIS K7117-1. Then, the viscosity ratio (= viscosity of 1 mass% aqueous solution / viscosity of 0.5 mass% aqueous solution) was calculated. The pH was adjusted using sodium hydroxide or lithium hydroxide.
<Glass transition temperature>
The aqueous dispersion containing the particulate binder was dried for 3 days in an environment of 50% humidity and a temperature of 23 to 26 ° C. to obtain a film having a thickness of 1 ± 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Then, using the dried film as a sample, in accordance with JIS K7121, measurement temperature: −100 ° C. to 180 ° C., temperature increase rate: 5 ° C./min, a differential scanning calorimeter (DSC6220SII, manufactured by Nanotechnology, Inc.) ) Was used to measure the glass transition temperature.
<Gel content>
An aqueous dispersion containing a particulate binder was prepared, and the aqueous dispersion was dried in an environment of 50% humidity and a temperature of 23 to 25 ° C. to form a film having a thickness of 1 ± 0.3 mm. This film was dried with a vacuum dryer at a temperature of 60 ° C. for 10 hours. Thereafter, the dried film was cut into 3 to 5 mm square, and about 1 g was precisely weighed. The mass of the film piece obtained by cutting is defined as w0.
This film piece was immersed in 50 g of tetrahydrofuran (THF) for 24 hours. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass w1 of insoluble matter was measured.
And gel content (mass%) was computed according to the following formula.
Gel content (mass%) = (w1 / w0) × 100
<Smoothness of negative electrode>
About the negative electrode original fabric, the coating amount was measured at 10 points every 10 mm in the length direction. The difference between the minimum value and the maximum value of the 10 measured values was evaluated according to the following criteria. It shows that the coating property of the slurry composition for negative electrodes used for formation of a negative electrode is excellent, so that a difference is small.
A: Difference is less than 0.5 mg / cm 2 B: Difference is 0.5 mg / cm 2 or more <Powder resistance of negative electrode>
The sheet-like negative electrode was cut into 10 cm square, and the mass (Y0) of the obtained sample piece was measured. Thereafter, five sample pieces were punched using a φ16 mm circular punching machine. Thereafter, an air brush was applied to measure the total mass (Y1) of the punched sample piece and the punched sample piece, and the residual rate of powder removal was calculated according to the following formula.
Residual rate of powder fall = (Y1 / Y0) × 100 (%)
And dust-proof property was evaluated according to the following reference | standard. It shows that there are few cracks and peeling of the edge part of a negative electrode, so that the value of a powder fall residual rate is large.
A: Powder fall residual rate is 99.98% or more B: Powder fall residual rate is 99.96% or more and less than 99.98% C: Powder fall residual rate is less than 99.96% <Design capacity of negative electrode>
The mass average theoretical capacity (mAh / g) of the used negative electrode active material was calculated and evaluated according to the following criteria.
A: Theoretical capacity exceeds 800 mAh / g B: Theoretical capacity exceeds 470 mAh / g, 800 mAh / g or less C: Theoretical capacity is 470 mAh / g or less <Initial efficiency>
The laminated cell type lithium ion secondary battery thus prepared was allowed to stand at 25 ° C. for 5 hours after electrolyte injection, and then subjected to a cell voltage of 3.C under the condition of 25 ° C. by a constant current method of 0.2C. The battery was charged to 65 V (the charge amount is defined as “C1 (mAh)”). Thereafter, an aging treatment is performed at a temperature of 60 ° C. for 12 hours, and discharge is performed to a cell voltage of 2.75 V by a constant current method of 0.2 C under a temperature of 25 ° C. (the discharge amount is defined as “D1 (mAh)”) did.
Then, CC-CV charge (upper limit cell voltage 4.20V) is performed at a constant current of 0.2C (the charge amount is defined as “C2 (mAh)”), and CC discharge is performed at a constant current of 0.2C. (Lower limit cell voltage 2.75 V) was carried out (the amount of discharge is defined as “D2 (mAh)”).
The initial efficiency was calculated according to the following formula and evaluated according to the following criteria.
Initial efficiency = {(D1 + D2) / (C1 + C2)} × 100 (%)
A: Initial efficiency is 88% or more B: Initial efficiency is 85% or more and less than 88% C: Initial efficiency is 81% or more and less than 85% D: Initial efficiency is less than 81% <Cycle characteristics>
The lithium ion secondary battery used in the evaluation of the initial efficiency was discharged to a cell voltage of 2.75 V by a constant current method of 0.1 C under the condition of a temperature of 25 ° C. Thereafter, 100 cycles of charge / discharge operation were performed at a charge / discharge rate of charge voltage 4.2V, discharge voltage 2.75V, and 0.5C under the condition of a temperature of 45 ° C. At that time, the discharge capacity at the first cycle (initial discharge capacity X1) and the discharge capacity X2 at the 100th cycle are measured to obtain a capacity change rate ΔC ′ represented by ΔC ′ = (X2 / X1) × 100 (%). Evaluation was made according to the following criteria. The higher the value of the capacity change rate ΔC ′, the better the cycle characteristics.
A: ΔC ′ is 85% or more B: ΔC ′ is 83% or more and less than 85% C: ΔC ′ is 80% or more and less than 83% D: ΔC ′ is less than 80%
（実施例１）
＜負極活物質の準備＞
　炭素系負極活物質としての人造黒鉛（日立化成製、理論容量：３６０ｍＡｈ／ｇ）と、シリコン系負極活物質としてのＳｉＯx（信越化学製、理論容量：２３００ｍＡｈ／ｇ）とを準備した。
＜ポリアクリル酸１の準備＞
　架橋型ポリアクリル酸ナトリウム（東亜合成株式会社製、レオジック２６０Ｈ）の１質量％水溶液を準備した。
＜カルボキシメチルセルロース塩の準備＞
　カルボキシメチルセルロース塩としてＭＡＣ８００ＬＣ（日本製紙ケミカル製、カルボキシメチルセルロースのナトリウム塩、１質量％水溶液粘度６．７～９．２Ｐａ・ｓ）を準備した。
＜粒子状結着材の調製＞
　攪拌機付き５ＭＰａ耐圧容器に、芳香族ビニル単量体としてスチレン６２部、脂肪族共役ジエン単量体として１，３－ブタジエン３５部、カルボキシル基含有単量体としてイタコン酸２部、ヒドロキシル基含有単量体としてアクリル酸－２－ヒドロキシエチル（２－ヒドロキシエチルアクリレート）１部、分子量調整剤としてｔ－ドデシルメルカプタン０．３部、乳化剤としてドデシルベンゼンスルホン酸ナトリウム５部、溶媒としてイオン交換水１５０部、及び重合開始剤として過硫酸カリウム１部を入れ、十分に攪拌した後、５５℃に加温して重合を開始した。
　モノマー消費量が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液に、５％水酸化ナトリウム水溶液を添加して、ｐＨ８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、３０℃以下まで冷却し、粒子状結着材の水分散液を得た。得られた粒子状結着材の水分散液を用いて、上述した方法により、ゲル含有量、及び、ガラス転移温度を測定した。測定の結果、ゲル含有量は９２％、ガラス転移温度（Ｔｇ）は１０℃であった。
＜リチウムイオン二次電池負極用スラリー組成物の調製＞
　プラネタリーミキサーに、炭素系負極活物質としての人造黒鉛９０部、シリコン系負極活物質としてのＳｉＯx（信越化学製）１０部、架橋型ポリアクリル酸ナトリウム（東亜合成株式会社製、レオジック２６０Ｈ）の１質量％水溶液を固形分相当で１．５部、カルボキシメチルセルロース塩（ＭＡＣ８００ＬＣ、日本製紙ケミカル製、カルボキシメチルセルロースのナトリウム塩）の１質量％水溶液を固形分相当で１．５部投入し、回転速度４０ｒｐｍで３０分間混合した。その後、粒子状結着材の水分散液を固形分相当で０．１０部投入し、Ｂ型粘度計（東機産業株式会社製、TVB-10M）を用いて、温度２５℃、回転速度６０ｒｐｍ（ローターＭ４）の条件でスラリー組成物の粘度が４．０Ｐａ・ｓとなるようにイオン交換水を加えて混合し、負極活物質、架橋型ポリアクリル酸ナトリウム、カルボキシメチルセルロース塩（ＣＭＣ）、粒子状結着材を含んでなるリチウムイオン二次電池負極用スラリー組成物を調製した。
＜負極の製造＞
　上述のリチウムイオン二次電池負極用スラリー組成物を、コンマコーターで、厚さ２０μｍの銅箔（集電体）の上に塗付量が９．２～９．８ｍｇ／ｃｍ2となるように塗布した。このリチウムイオン二次電池負極用スラリー組成物が塗布された銅箔を、０．２ｍ／分の速度で、温度６０℃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、銅箔上のスラリー組成物を乾燥させ、負極原反を得た。
　そして、得られた負極原反をロールプレス機にて密度が１．６３～１．６７ｇ／ｃｍ3となるようプレスし、さらに、水分の除去および架橋のさらなる促進を目的として、真空条件下、温度１２０℃の環境に１０時間置き、負極を得た。得られた負極について、平滑性および耐粉落ち性を評価した。結果を表１に示す。
＜正極の製造＞
　プラネタリーミキサーに、正極活物質としてのＬｉＣｏＯ2１００部、導電材としてのアセチレンブラック２部（電気化学工業（株）製、ＨＳ－１００）、結着材としてのＰＶＤＦ（ポリフッ化ビニリデン、（株）クレハ化学製、ＫＦ－１１００）２部、および溶媒としての２－メチルピリロドンを、全固形分濃度が６７％となるように加えて混合し、リチウムイオン二次電池正極用スラリー組成物を調製した。
　得られたリチウムイオン二次電池正極用スラリー組成物を、コンマコーターで、厚さ２０μｍのアルミ箔の上に塗付量が３０．５～３１．５ｍｇ／ｃｍ2となるように塗布した。その後、リチウムイオン二次電池正極用スラリー組成物が塗布されたアルミ箔を、０．５ｍ／分の速度で温度６０℃のオーブン内を２分間かけて搬送することにより、乾燥させた。その後、温度１２０℃にて２分間加熱処理して、正極原反を得た。
　得られた正極原反をロールプレス機にてプレス後の密度が３．４０～３．５０ｇ／ｃｍ3になるようにプレスし、さらに、水分の除去を目的として、真空条件下、温度１２０℃の環境に３時間置き、正極を得た。
＜リチウムイオン二次電池の製造＞
　単層のポリプロピレン製セパレータ（幅６５ｍｍ、長さ５００ｍｍ、厚さ２５μｍ；乾式法により製造；気孔率５５％）を用意し、５ｃｍ×５ｃｍの正方形に切り抜いた。また、電池の外装として、アルミ包材外装を用意した。
　そして、作製した正極を、３．８ｃｍ×２．８ｃｍに切り出し、集電体側の表面がアルミ包材外装に接するように配置した。次に、正極の正極合材層の面上に、上記の正方形のセパレータを配置した。さらに、作製した負極を、４．０ｃｍ×３．０ｃｍに切り出し、これをセパレータ上に、負極合材層側の表面がセパレータに向かい合うよう配置した。その後、電解液として濃度１．０ＭのＬｉＰＦ6溶液（溶媒はエチレンカーボネート（ＥＣ）／エチルメチルカーボネート（ＥＭＣ）＝３／７（体積比）の混合溶媒、添加剤としてビニレンカーボネート２体積％含有）を充填した。さらに、１５０℃のヒートシールをしてアルミ包材外装の開口を密封閉口し、ラミネートセル型のリチウムイオン二次電池を製造した。そして、リチウムイオン二次電池の初期効率およびサイクル特性を評価した。結果を表１に示す。 Example 1
<Preparation of negative electrode active material>
Artificial graphite (manufactured by Hitachi Chemical, theoretical capacity: 360 mAh / g) as a carbon-based negative electrode active material and SiO x (manufactured by Shin-Etsu Chemical, theoretical capacity: 2300 mAh / g) as a silicon-based negative electrode active material were prepared.
<Preparation of polyacrylic acid 1>
A 1 mass% aqueous solution of cross-linked sodium polyacrylate (manufactured by Toagosei Co., Ltd., Rheojic 260H) was prepared.
<Preparation of carboxymethyl cellulose salt>
MAC800LC (manufactured by Nippon Paper Chemical Co., Ltd., sodium salt of carboxymethylcellulose, 1 mass% aqueous solution viscosity 6.7 to 9.2 Pa · s) was prepared as the carboxymethylcellulose salt.
<Preparation of particulate binder>
In a 5 MPa pressure vessel equipped with a stirrer, 62 parts of styrene as an aromatic vinyl monomer, 35 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 2 parts of itaconic acid as a carboxyl group-containing monomer, and a hydroxyl group-containing monomer 1 part of 2-hydroxyethyl acrylate (2-hydroxyethyl acrylate) as a monomer, 0.3 part of t-dodecyl mercaptan as a molecular weight regulator, 5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent And 1 part of potassium persulfate was added as a polymerization initiator, 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. The aqueous dispersion containing the polymer thus obtained was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, the unreacted monomer was removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion of the particulate binder. Using the obtained aqueous dispersion of the particulate binder, the gel content and glass transition temperature were measured by the methods described above. As a result of the measurement, the gel content was 92% and the glass transition temperature (Tg) was 10 ° C.
<Preparation of slurry composition for negative electrode of lithium ion secondary battery>
In a planetary mixer, 90 parts of artificial graphite as a carbon-based negative electrode active material, 10 parts of SiO x (manufactured by Shin-Etsu Chemical) as a silicon-based negative electrode active material, cross-linked sodium polyacrylate (manufactured by Toagosei Co., Ltd., Rhegic 260H) 1 part by weight of a 1% by weight aqueous solution of 1.5 parts by weight, and 1.5 parts by weight of a 1% by weight aqueous solution of a carboxymethyl cellulose salt (MAC800LC, Nippon Paper Chemicals, sodium salt of carboxymethyl cellulose) in a solid content. Mix for 30 minutes at a speed of 40 rpm. Thereafter, 0.10 parts of an aqueous dispersion of the particulate binder was added in an amount corresponding to the solid content, and using a B-type viscometer (TVB-10M, manufactured by Toki Sangyo Co., Ltd.), the temperature was 25 ° C. and the rotation speed was 60 rpm. Ion exchange water is added and mixed so that the viscosity of the slurry composition is 4.0 Pa · s under the conditions of (Rotor M4), negative electrode active material, cross-linked sodium polyacrylate, carboxymethylcellulose salt (CMC), particles A slurry composition for a negative electrode of a lithium ion secondary battery comprising a binder was prepared.
<Manufacture of negative electrode>
Apply the above slurry composition for a negative electrode of a lithium ion secondary battery on a copper foil (current collector) having a thickness of 20 μm with a comma coater so that the coating amount is 9.2 to 9.8 mg / cm 2. Applied. The copper foil coated with the lithium ion secondary battery negative electrode slurry composition was applied at a speed of 0.2 m / min in an oven at a temperature of 60 ° C. for 2 minutes and further in an oven at a temperature of 110 ° C. for 2 minutes. By carrying, the slurry composition on copper foil was dried and the negative electrode original fabric was obtained.
Then, the obtained negative electrode raw material was pressed with a roll press so that the density was 1.63 to 1.67 g / cm 3, and further, under vacuum conditions for the purpose of removing moisture and further promoting crosslinking. The negative electrode was obtained by placing in an environment of 120 ° C. for 10 hours. About the obtained negative electrode, smoothness and dust-proof property were evaluated. The results are shown in Table 1.
<Production of positive electrode>
In a planetary mixer, 100 parts of LiCoO 2 as a positive electrode active material, 2 parts of acetylene black as a conductive material (HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride, as a binder) Kleha Chemical Co., Ltd., KF-1100) 2 parts, and 2-methylpyrrhodone as a solvent were added and mixed so that the total solid concentration was 67%, and a slurry composition for a positive electrode of a lithium ion secondary battery was prepared. Prepared.
The obtained slurry composition for a lithium ion secondary battery positive electrode was applied with a comma coater onto an aluminum foil having a thickness of 20 μm so that the amount applied was 30.5 to 31.5 mg / cm 2 . Thereafter, the aluminum foil coated with the slurry composition for a positive electrode of a lithium ion secondary battery was dried by conveying it in an oven at a temperature of 60 ° C. at a rate of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material.
The obtained positive electrode raw material was pressed with a roll press machine so that the density after pressing was 3.40 to 3.50 g / cm 3 , and further, the temperature was 120 ° C. under vacuum conditions for the purpose of removing moisture. For 3 hours to obtain a positive electrode.
<Manufacture of lithium ion secondary batteries>
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm; manufactured by a dry method; porosity 55%) was prepared and cut into a 5 cm × 5 cm square. Moreover, the aluminum packaging material exterior was prepared as a battery exterior.
And the produced positive electrode was cut out to 3.8cm x 2.8cm, and it has arrange | positioned so that the surface by the side of a collector may touch the aluminum packaging material exterior. Next, the square separator was placed on the surface of the positive electrode mixture layer of the positive electrode. Furthermore, the produced negative electrode was cut out to 4.0 cm x 3.0 cm, and this was arrange | positioned so that the surface by the side of the negative electrode compound-material layer might face a separator on a separator. Thereafter, a LiPF 6 solution having a concentration of 1.0 M as an electrolytic solution (a solvent is a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3/7 (volume ratio), vinylene carbonate is contained as an additive in 2% by volume)) Filled. Furthermore, heat sealing at 150 ° C. was performed to seal and close the opening of the aluminum packaging material exterior, and a laminated cell type lithium ion secondary battery was manufactured. The initial efficiency and cycle characteristics of the lithium ion secondary battery were evaluated. The results are shown in Table 1.
（実施例２）
　炭素系負極活物質としての人造黒鉛の配合量を７５部とし、シリコン系負極活物質としてのＳｉＯxの配合量を２５部とした以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Example 2)
The negative electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the blending amount of the artificial graphite as the carbon-based negative electrode active material was 75 parts and the blending amount of SiO x as the silicon-based negative electrode active material was 25 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（実施例３）
　炭素系負極活物質としての人造黒鉛の配合量を６５部とし、シリコン系負極活物質としてのＳｉＯxの配合量を３５部とした以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 Example 3
The negative electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the compounding amount of the artificial graphite as the carbon-based negative electrode active material was 65 parts and the compounding amount of SiO x as the silicon-based negative electrode active material was 35 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（実施例４）
　カルボキシメチルセルロース塩を配合しなかった以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 Example 4
A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the carboxymethyl cellulose salt was not blended. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（実施例５）
　粒子状結着材を配合しなかった以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Example 5)
A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the particulate binder was not blended. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（実施例６）
　粒子状結着材の配合量を固形分相当で０．２２５部とした以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Example 6)
A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the amount of the particulate binder was 0.225 parts corresponding to the solid content. Produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（実施例７）
　ポリアクリル酸として架橋型ポリアクリル酸ナトリウム（レオジック２６０Ｈ）１．５部に替えて下記のポリアクリル酸２を３部用い、さらにカルボキシメチルセルロース塩および粒子状結着材を配合しなかった以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。
＜ポリアクリル酸２の準備＞
　反応容器に、未架橋型のポリアクリル酸（アルドリッチ製、数平均分子量：１２５万）を固形分濃度２％で溶解し、撹拌した。その後、反応容器を６０℃に加熱し、カルボジイミド化合物（日清紡ケミカル社製、ＳＶ－０２、固形分濃度０．５％に希釈したもの）を１時間かけて徐々に滴下し、滴下終了後、さらに８時間撹拌した。その後、１％水酸化ナトリウム水溶液にて、ｐＨ＝８．０に調整し、得られた水溶液を６０℃、真空乾燥条件下で水を蒸発させて、ポリアクリル酸２を得た。 (Example 7)
Implemented except that 3 parts of polyacrylic acid 2 below was used in place of 1.5 parts of cross-linked sodium polyacrylate (Rheojic 260H) as polyacrylic acid, and carboxymethylcellulose salt and particulate binder were not added. In the same manner as in Example 1, a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of polyacrylic acid 2>
In a reaction vessel, uncrosslinked polyacrylic acid (manufactured by Aldrich, number average molecular weight: 1.25 million) was dissolved at a solid content concentration of 2% and stirred. Thereafter, the reaction vessel was heated to 60 ° C., and a carbodiimide compound (manufactured by Nisshinbo Chemical Co., Ltd., SV-02, diluted to a solid content concentration of 0.5%) was gradually added dropwise over 1 hour. Stir for 8 hours. Thereafter, the pH was adjusted to 8.0 with a 1% aqueous sodium hydroxide solution, and water was evaporated from the obtained aqueous solution under vacuum drying conditions at 60 ° C. to obtain polyacrylic acid 2.
（実施例８）
　ポリアクリル酸として架橋型ポリアクリル酸ナトリウム（レオジック２６０Ｈ）１．５部に替えて下記のポリアクリル酸３を３部用い、さらにカルボキシメチルセルロース塩および粒子状結着材を配合しなかった以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。
＜ポリアクリル酸３の準備＞
　反応容器に、未架橋型のポリアクリル酸（アルドリッチ製、数平均分子量：１２５万）を固形分濃度２％で溶解し、撹拌した。その後、反応容器を６０℃に加熱し、カルボジイミド化合物（日清紡ケミカル社製、ＳＶ－０２、固形分濃度０．５％に希釈したもの）を１時間かけて徐々に滴下し、滴下終了後、さらに８時間撹拌した。その後、１％水酸化リチウム水溶液にて、ｐＨ＝８．０に調整し、得られた水溶液を６０℃、真空乾燥条件下で水を蒸発させて、ポリアクリル酸３を得た。 (Example 8)
Implemented except that 3 parts of polyacrylic acid 3 below was used in place of 1.5 parts of cross-linked sodium polyacrylate (Rheodic 260H) as polyacrylic acid, and carboxymethyl cellulose salt and particulate binder were not added. In the same manner as in Example 1, a slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of polyacrylic acid 3>
In a reaction vessel, uncrosslinked polyacrylic acid (manufactured by Aldrich, number average molecular weight: 1.25 million) was dissolved at a solid content concentration of 2% and stirred. Thereafter, the reaction vessel was heated to 60 ° C., and a carbodiimide compound (manufactured by Nisshinbo Chemical Co., Ltd., SV-02, diluted to a solid content concentration of 0.5%) was gradually added dropwise over 1 hour. Stir for 8 hours. Thereafter, the pH was adjusted to 8.0 with a 1% aqueous lithium hydroxide solution, and water was evaporated from the obtained aqueous solution under vacuum drying conditions at 60 ° C. to obtain polyacrylic acid 3.
（実施例９）
　カルボキシメチルセルロース塩の１質量％水溶液の配合量を固形分相当で０．３７５部とした以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 Example 9
A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary material were prepared in the same manner as in Example 1 except that the blending amount of a 1% by mass aqueous solution of carboxymethylcellulose salt was 0.375 parts corresponding to the solid content. A secondary battery was produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例１）
　負極活物質として人造黒鉛１００部のみを使用し、シリコン系負極活物質としてのＳｉＯxを使用しなかった以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Comparative Example 1)
In the same manner as in Example 1 except that only 100 parts of artificial graphite was used as the negative electrode active material and SiO x was not used as the silicon negative electrode active material, the slurry composition for the negative electrode of the lithium ion secondary battery, the negative electrode, A positive electrode and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例２）
　炭素系負極活物質としての人造黒鉛の配合量を５０部とし、シリコン系負極活物質としてのＳｉＯxの配合量を５０部とした以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Comparative Example 2)
Lithium ion secondary battery negative electrode in the same manner as in Example 1 except that the amount of artificial graphite as the carbon-based negative electrode active material was 50 parts and the amount of SiO x as the silicon-based negative electrode active material was 50 parts. Slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were prepared. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例３）
　ポリアクリル酸として架橋型ポリアクリル酸ナトリウム（レオジック２６０Ｈ）に替えてポリアクリル酸４（アルドリッチ製、非架橋型ポリアクリル酸ナトリウム、重量平均分子量＝４５万、１質量％水溶液をＮａＯＨ（和光純薬、特級試薬）でｐＨ＝８に調整したもの）を使用した以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Comparative Example 3)
Polyacrylic acid 4 (manufactured by Aldrich, non-crosslinked sodium polyacrylate, weight average molecular weight = 450,000, 1% by weight aqueous solution NaOH (Wako Pure Chemical Industries) instead of crosslinked polysodium acrylate (Rheojic 260H) as polyacrylic acid A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the pH adjusted to 8 with a special grade reagent) was used. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例４）
　ポリアクリル酸として架橋型ポリアクリル酸ナトリウム（レオジック２６０Ｈ）に替えてポリアクリル酸５（アルドリッチ製、非架橋型ポリアクリル酸ナトリウム、重量平均分子量＝３００万、１質量％水溶液をＮａＯＨ（和光純薬、特級試薬）でｐＨ＝８に調整したもの）を使用した以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Comparative Example 4)
Polyacrylic acid 5 (manufactured by Aldrich, non-crosslinked sodium polyacrylate, weight average molecular weight = 3 million, 1% by weight NaOH as a polyacrylic acid instead of cross-linked sodium polyacrylate (Rheojic 260H) A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the pH adjusted to 8 with a special grade reagent) was used. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例５）
　ポリアクリル酸として架橋型ポリアクリル酸ナトリウム（レオジック２６０Ｈ）に替えてポリアクリル酸６（東亜合成株式会社製、架橋型ポリアクリル酸ナトリウム、レオジック２６２Ｌ）を使用した以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。 (Comparative Example 5)
The same procedure as in Example 1 was used except that polyacrylic acid 6 (manufactured by Toa Gosei Co., Ltd., cross-linked sodium polyacrylate, Rheotic 262L) was used as the polyacrylic acid instead of the cross-linked sodium polyacrylate (Rheodic 260H). A slurry composition for a negative electrode of a lithium ion secondary battery, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
（比較例６）
　ポリアクリル酸を配合せず、カルボキシメチルセルロース塩の１質量％水溶液の配合量を固形分相当で３．０部とした以外は実施例１と同様にして、リチウムイオン二次電池負極用スラリー組成物、負極、正極およびリチウムイオン二次電池を作製した。そして、実施例１と同様にして評価を行った。結果を表１に示す。
(Comparative Example 6)
A slurry composition for a negative electrode of a lithium ion secondary battery in the same manner as in Example 1, except that no polyacrylic acid was blended and the blending amount of a 1% by weight aqueous solution of carboxymethylcellulose salt was 3.0 parts in terms of solid content. A negative electrode, a positive electrode, and a lithium ion secondary battery were produced. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１より、実施例１～９では、電池容量が高く、且つ、サイクル特性に優れるリチウムイオン二次電池が得られることが分かる。一方、表１より、比較例１では、電池容量を十分に高めることができず、比較例２～６ではサイクル特性が低下してしまうことが分かる。
　なお、表１より、特に実施例１～３および９では、負極の耐粉落ち性に優れると共に、電池容量、初期効率およびサイクル特性の全てに優れるリチウムイオン二次電池が得られることが分かる。 From Table 1, it can be seen that in Examples 1 to 9, lithium ion secondary batteries having high battery capacity and excellent cycle characteristics can be obtained. On the other hand, it can be seen from Table 1 that in Comparative Example 1, the battery capacity cannot be sufficiently increased, and in Comparative Examples 2 to 6, the cycle characteristics deteriorate.
From Table 1, it can be seen that in Examples 1 to 3 and 9 in particular, lithium ion secondary batteries having excellent negative electrode dust resistance and excellent battery capacity, initial efficiency, and cycle characteristics can be obtained.
　本発明によれば、負極の形成に使用した場合に充放電に伴うシリコン系負極活物質の膨張および収縮を抑制しつつ電池容量を高めることができ、且つ、塗工性に優れるリチウムイオン二次電池負極用スラリー組成物を提供することができる。
　また、本発明によれば、優れた電池容量およびサイクル特性を有するリチウムイオン二次電池を提供することができるリチウムイオン二次電池用負極を提供することができる。
　更に、本発明によれば、電池容量が高く、且つ、サイクル特性に優れるリチウムイオン二次電池を提供することができる。 According to the present invention, when used for forming a negative electrode, a lithium ion secondary that can increase the battery capacity while suppressing the expansion and contraction of the silicon-based negative electrode active material due to charge / discharge and that is excellent in coatability. A slurry composition for a battery negative electrode can be provided.
Moreover, according to this invention, the negative electrode for lithium ion secondary batteries which can provide the lithium ion secondary battery which has the outstanding battery capacity and cycling characteristics can be provided.
Furthermore, according to the present invention, a lithium ion secondary battery having a high battery capacity and excellent cycle characteristics can be provided.

Claims (4)

  1. 　負極活物質と、ポリアクリル酸と、水とを含み、
    　前記負極活物質は、シリコン系負極活物質を５質量％以上４０質量％以下の割合で含有し、
    　前記ポリアクリル酸は、０．５質量％水溶液の粘度に対する１質量％水溶液の粘度の比（１質量％水溶液の粘度／０．５質量％水溶液の粘度）が２．０以上である、
    リチウムイオン二次電池負極用スラリー組成物。     Including a negative electrode active material, polyacrylic acid, and water;
    The negative electrode active material contains a silicon-based negative electrode active material in a proportion of 5% by mass to 40% by mass,
    The polyacrylic acid has a ratio of the viscosity of the 1% by weight aqueous solution to the viscosity of the 0.5% by weight aqueous solution (viscosity of the 1% by weight aqueous solution / viscosity of the 0.5% by weight aqueous solution) is 2.0 or more.
    A slurry composition for a negative electrode of a lithium ion secondary battery.
  2. 　カルボキシメチルセルロース塩を更に含む、請求項１に記載のリチウムイオン二次電池負極用スラリー組成物。 The slurry composition for a lithium ion secondary battery negative electrode according to claim 1, further comprising a carboxymethylcellulose salt.
  3. 　請求項１または２に記載のリチウムイオン二次電池負極用スラリー組成物を用いて得られる負極合材層を有する、リチウムイオン二次電池用負極。 A negative electrode for a lithium ion secondary battery having a negative electrode mixture layer obtained by using the slurry composition for a negative electrode of a lithium ion secondary battery according to claim 1 or 2.
  4. 　請求項３に記載のリチウムイオン二次電池用負極と、正極と、電解液と、セパレータとを備えるリチウムイオン二次電池。 A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 3, a positive electrode, an electrolytic solution, and a separator.
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