WO2014024937A1 - 二次電池用負極、二次電池、スラリー組成物、及び製造方法 - Google Patents
二次電池用負極、二次電池、スラリー組成物、及び製造方法 Download PDFInfo
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- WO2014024937A1 WO2014024937A1 PCT/JP2013/071417 JP2013071417W WO2014024937A1 WO 2014024937 A1 WO2014024937 A1 WO 2014024937A1 JP 2013071417 W JP2013071417 W JP 2013071417W WO 2014024937 A1 WO2014024937 A1 WO 2014024937A1
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- active material
- water
- secondary battery
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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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- H01M4/134—Electrodes based on metals, Si or alloys
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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
- H01M4/139—Processes of manufacture
- H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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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
- H01M4/36—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
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- 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 negative electrode for a secondary battery, a secondary battery, a slurry composition, and a method for producing a negative electrode for a secondary battery.
- the electrode is usually a liquid composition in which a polymer serving as a binder (binder) is dispersed or dissolved in a solvent such as water or an organic solvent, an electrode active material, and optionally conductive carbon or the like.
- a solvent such as water or an organic solvent
- an electrode active material such as water or an organic solvent
- optionally conductive carbon or the like an electrode active material
- the conductive agent is mixed to obtain a slurry composition, and this slurry composition is applied to a current collector and dried.
- binders and various additives for binding the electrode active material and the like to the current collector for example, Patent Document 1). To 4).
- Patent Document 1 and Patent Document 2 describe a slurry for a negative electrode of a non-aqueous secondary battery including a binder composed of a carbon material active material, a water-dispersed emulsion resin, and a water-soluble polymer compound.
- a binder composed of a carbon material active material, a water-dispersed emulsion resin, and a water-soluble polymer compound.
- water-soluble polymer compounds polyvinyl alcohol, carboxymethyl cellulose, sodium polyacrylate, and the like are described. According to this, it is described that the coating film strength and the coating film density of the battery are improved.
- Patent Document 3 includes 0.02 to 13% by weight of a fluorine-containing unsaturated monomer, 10 to 38% by weight of an aliphatic conjugated diene monomer, and 0.1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer.
- a binder for a secondary battery electrode comprising a copolymer latex obtained by emulsion polymerization of a monomer composition composed of 49 to 88.88% by weight of other monomers copolymerizable therewith.
- a binder for a secondary battery electrode comprising a copolymer latex obtained by emulsion polymerization of a monomer composition composed of 49 to 88.88% by weight of other monomers copolymerizable therewith.
- Patent Document 4 describes a secondary battery electrode binder made of a polymer having a monomer unit derived from a fluorine atom-containing monomer such as (fluoro) alkyl (meth) acrylate. And it describes that a cellulose polymer, polyacrylate, etc. can be added in order to improve applicability
- the particles of the electrode active material contained in the negative electrode may expand and contract with charge / discharge. When such expansion and contraction are repeated, the negative electrode gradually expands and the secondary battery may be deformed. Therefore, development of a technique capable of suppressing the swelling of the negative electrode as described above is desired.
- some conventional secondary batteries have a reduced capacity when stored in a high temperature environment of, for example, 60 ° C. Therefore, it is desired to develop a technology that can suppress a decrease in the capacity of the secondary battery even when the secondary battery is stored in a high temperature environment.
- secondary batteries are required to have good characteristics such as cycle characteristics and output characteristics in both high temperature and low temperature environments.
- the present invention was devised in view of the above-mentioned problems, can suppress the swelling of the negative electrode due to charge and discharge, hardly reduces the capacity even when stored in a high temperature environment, and has characteristics in both a high temperature environment and a low temperature environment.
- a negative electrode for a secondary battery capable of realizing a good secondary battery, a slurry composition for a negative electrode capable of producing the negative electrode for a secondary battery, a method for producing a negative electrode for a secondary battery, and the negative electrode for a secondary battery An object is to provide a secondary battery provided.
- the present inventor has obtained a sulfonic acid group-containing monomer unit and a fluorine-containing (meth) acrylate monomer unit in the electrode active material layer of the secondary battery negative electrode. And a water-soluble polymer containing a specific ratio of each of the above, the swelling of the negative electrode accompanying charging and discharging can be suppressed, and the capacity can be made difficult to decrease even when stored in a high temperature environment. Completed. That is, according to the present invention, the following [1] to [11] are provided.
- a negative electrode for a secondary battery comprising a negative electrode active material, a particulate binder and a water-soluble polymer,
- the water-soluble polymer is 0.1% to 15% by weight of sulfonic acid group-containing monomer units, and 0.5% to 10% by weight of fluorine-containing (meth) acrylic acid ester monomer units
- the negative electrode for secondary batteries which is a copolymer containing this.
- the metal is silicon.
- a secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the negative electrode is the negative electrode for a secondary battery according to any one of [1] to [7].
- a slurry composition comprising a negative electrode active material, a particulate binder, and a water-soluble polymer, The water-soluble polymer is 0.1% to 15% by weight of a sulfonic acid group-containing monomer unit
- a slurry composition for secondary battery negative electrode which is a copolymer containing 0.5 to 10% by weight of a fluorine-containing (meth) acrylic acid ester monomer unit.
- a method for producing a secondary battery negative electrode comprising applying the slurry composition for a secondary battery negative electrode according to [9] or [10] onto a current collector and drying.
- the swelling of the negative electrode accompanying charging and discharging can be suppressed, the capacity is not easily reduced even when stored in a high temperature environment, and the characteristics are good in both a high temperature environment and a low temperature environment.
- a secondary battery can be realized.
- the secondary battery of the present invention can suppress swelling of the negative electrode accompanying charging / discharging, hardly reduces the capacity even when stored in a high temperature environment, and has good characteristics in both a high temperature environment and a low temperature environment. If the slurry composition for negative electrodes of this invention is used, the negative electrode for secondary batteries of this invention can be manufactured.
- the slurry composition for negative electrodes of the present invention has high stability, it can be stored for a long period of time and is easy to use. According to the method for producing a negative electrode for a secondary battery of the present invention, the negative electrode for a secondary battery of the present invention can be produced.
- (meth) acrylic acid means acrylic acid and methacrylic acid.
- a substance is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.
- a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.
- the negative electrode for a secondary battery of the present invention includes a negative electrode active material, a particulate binder, and a water-soluble polymer.
- the negative electrode of the present invention includes a current collector and a negative electrode active material layer formed on the surface of the current collector, and the negative electrode active material layer includes the negative electrode active material, particulate binder, and water-soluble polymer. including.
- the negative electrode active material is an electrode active material for a negative electrode, and is a material that transfers electrons in the negative electrode of the secondary battery.
- a material that can occlude and release lithium is usually used as the negative electrode active material.
- An example of a suitable negative electrode active material is carbon. Examples of carbon include natural graphite, artificial graphite, and carbon black. Among these, natural graphite is preferably used.
- a suitable negative electrode active material is a material containing a metal.
- a negative electrode active material containing at least one selected from the group consisting of tin, silicon, germanium and lead is preferable. This is because a negative electrode active material containing these elements has a small irreversible capacity.
- a negative electrode active material containing silicon is preferable.
- the electric capacity of the lithium ion secondary battery can be increased.
- a negative electrode active material containing silicon expands and contracts greatly (for example, about 5 times) with charge and discharge.
- battery performance due to expansion and contraction of the negative electrode active material containing silicon is increased. The decrease can be suppressed.
- Examples of the active material containing silicon include an active material made of metallic silicon, an active material made of a compound of silicon and another element (hereinafter sometimes referred to as “silicon-based active material”), and made of metallic silicon. Examples include a combination of an active material and a silicon-based active material.
- one type of negative electrode active material may be used alone, or two or more types may be used in combination at any ratio. Therefore, two or more of the negative electrode active materials can be used in combination.
- a negative electrode active material containing a combination of carbon and an active material containing silicon it is preferable to use a negative electrode active material containing a combination of carbon and an active material containing silicon.
- a combination of carbon and an active material containing silicon is used as the negative electrode active material, insertion and desorption of Li into one or both of metal silicon and silicon-based active material occurs at a high potential, and at a low potential. It is assumed that Li insertion and desorption from carbon occurs. For this reason, since expansion and contraction are suppressed, the cycle characteristics of the lithium ion secondary battery can be improved.
- silicon-based active material examples include SiO, SiO 2 , SiO x (0.01 ⁇ x ⁇ 2), SiC, SiOC, and the like, and SiO x , SiC, and SiC are preferable.
- SiO x is a compound that can be formed from one or both of SiO and SiO 2 and metallic silicon. This SiO x can be produced, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of SiO 2 and metal silicon.
- the active material containing silicon is preferably combined with conductive carbon.
- conductive carbon By combining with conductive carbon, swelling of the negative electrode active material itself can be suppressed.
- a method of compounding for example, a method of compounding by coating an active material containing silicon with carbon; a method of compounding by granulating a mixture containing conductive carbon and an active material containing silicon; Etc.
- the amount of silicon atoms in the negative electrode active material is 0.1 to 50 parts by weight with respect to 100 parts by weight of the total carbon atoms. It is preferable. Thereby, a conductive path is formed satisfactorily and the conductivity of the negative electrode can be improved.
- the weight ratio of carbon to the active material containing silicon (“weight of carbon” / “weight of active material containing silicon”) is: Preferably it is 50/50 or more, More preferably, it is 70/30 or more, Preferably it is 97/3 or less, More preferably, it is 90/10 or less. Thereby, the cycle characteristics of the secondary battery can be improved.
- the negative electrode active material is preferably sized in the form of particles.
- the volume average particle diameter is appropriately selected in consideration of other constituent elements of the secondary battery, and is usually 0.1 ⁇ m or more, preferably 1 ⁇ m or more, more preferably 5 ⁇ m or more. Usually, it is 100 ⁇ m or less, preferably 50 ⁇ m or less, more preferably 30 ⁇ m or less.
- the volume average particle diameter employs a particle diameter at which the cumulative volume calculated from the small diameter side is 50% in the particle size distribution measured by the laser diffraction method.
- the specific surface area of the negative electrode active material is usually 2 m 2 / g or more, preferably 3 m 2 / g or more, more preferably 5 m 2 / g or more, and usually 20 m 2 / g or less, preferably from the viewpoint of improving the output density. It is 15 m 2 / g or less, more preferably 10 m 2 / g or less.
- the specific surface area of the negative electrode active material can be measured by, for example, the BET method.
- the particulate binder is a component that binds the electrode active material to the surface of the current collector in the negative electrode.
- the particulate binder binds the negative electrode active material, so that the detachment of the negative electrode active material from the negative electrode active material layer is reduced.
- the particulate binder also serves to bind particles other than the negative electrode active material contained in the negative electrode active material layer and maintain the strength of the negative electrode active material layer.
- the particulate binder it is preferable to use a binder that is excellent in performance of holding the negative electrode active material and has high adhesion to the current collector.
- a binder that is excellent in performance of holding the negative electrode active material and has high adhesion to the current collector.
- those containing a polymer are used, and in particular, those substantially consisting of a polymer can be used.
- the polymer of the particulate binder may be a homopolymer or a copolymer.
- the polymer of the particulate binder preferably contains an aliphatic conjugated diene monomer unit.
- the aliphatic conjugated diene monomer unit is a flexible repeating unit having low rigidity. Therefore, sufficient adhesion between the negative electrode active material layer and the current collector can be obtained by using a polymer containing an aliphatic conjugated diene monomer unit as a particulate binder.
- the aliphatic conjugated diene monomer unit is a repeating unit obtained by polymerizing an aliphatic conjugated diene monomer.
- aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. Substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. Of these, 1,3-butadiene is preferred.
- One type of aliphatic conjugated diene monomer may be used alone, or two or more types may be used in combination at any ratio. Therefore, the polymer of the particulate binder may contain only one type of aliphatic conjugated diene monomer unit, or may contain two or more types in combination at any ratio.
- the ratio of the aliphatic conjugated diene monomer unit is preferably 20% by weight or more, more preferably 30% by weight or more, preferably 70% by weight or less, more preferably 60% by weight. Hereinafter, it is particularly preferably 55% by weight or less.
- the polymer of the particulate binder preferably contains an aromatic vinyl monomer unit.
- the aromatic vinyl monomer unit is stable, and the negative electrode active material layer can be stabilized by reducing the solubility of the polymer containing the aromatic vinyl monomer unit in the electrolytic solution.
- the aromatic vinyl monomer unit is a repeating unit obtained by polymerizing an aromatic vinyl monomer.
- the aromatic vinyl monomer include styrene, ⁇ -methylstyrene, vinyl toluene, divinylbenzene and the like. Of these, styrene is preferred.
- the polymer of the particulate binder preferably includes an aromatic vinyl monomer unit, and as already described, the polymer of the particulate binder preferably includes an aliphatic conjugated diene monomer unit such as butadiene.
- the polymer of the particulate binder is preferably a polymer containing an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit, and for example, a styrene / butadiene copolymer is preferable.
- An aromatic vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the polymer of the particulate binder may contain only one type of aromatic vinyl monomer, or may contain two or more types in combination at any ratio.
- the particulate binder polymer may contain unreacted aliphatic conjugated diene monomer and unreacted aromatic vinyl monomer as residual monomers.
- the amount of the unreacted aliphatic conjugated diene monomer contained in the particulate binder polymer is preferably 50 ppm or less, more preferably 10 ppm or less, and the unreacted aroma contained in the particulate binder polymer.
- the amount of the group vinyl monomer is preferably 1000 ppm or less, more preferably 200 ppm or less.
- the negative electrode slurry composition according to the present invention is applied to the surface of the current collector and dried to produce a negative electrode. Furthermore, it is possible to prevent the surface of the negative electrode from being roughened by foaming or causing an environmental load due to odor. In addition, when the amount of the aromatic vinyl monomer contained in the particulate binder polymer is kept within the above range, the environmental load and roughness of the negative electrode surface caused by drying conditions can be suppressed, and further the particulate binder polymer. The electrolytic solution resistance can be improved.
- the ratio of the aromatic vinyl monomer unit is preferably 30% by weight or more, more preferably 35% by weight or more, preferably 79.5% by weight or less, more preferably 69% by weight. % Or less.
- the polymer of the particulate binder preferably contains an ethylenically unsaturated carboxylic acid monomer unit.
- the ethylenically unsaturated carboxylic acid monomer unit includes a carboxyl group (—COOH group) that enhances the adsorptivity to the negative electrode active material and the current collector, and is a repeating unit having high strength. Desorption of the negative electrode active material can be stably prevented, and the strength of the negative electrode can be improved.
- the ethylenically unsaturated carboxylic acid monomer unit is a repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer.
- the ethylenically unsaturated carboxylic acid monomer include monocarboxylic and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and anhydrides thereof.
- An ethylenically unsaturated carboxylic acid monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the polymer of the particulate binder may contain only one type of ethylenically unsaturated carboxylic acid monomer unit, or may contain two or more types in combination at any ratio.
- the ratio of the ethylenically unsaturated carboxylic acid monomer unit is preferably 0.5% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more, preferably Is 10% by weight or less, more preferably 8% by weight or less, and particularly preferably 7% by weight or less.
- the polymer of the particulate binder may contain arbitrary repeating units other than those described above as long as the effects of the present invention are not significantly impaired.
- the monomer corresponding to the arbitrary repeating unit include a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, an unsaturated monomer containing a hydroxyalkyl group, and an unsaturated carboxylic acid. And acid amide monomers. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- vinyl cyanide monomer examples include acrylonitrile, methacrylonitrile, ⁇ -chloroacrylonitrile, ⁇ -ethylacrylonitrile and the like. Of these, acrylonitrile and methacrylonitrile are preferable. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaco. Nate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. Of these, methyl methacrylate, ethyl acrylate, and butyl acrylate are preferable. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- Examples of unsaturated monomers containing a hydroxyalkyl group include ⁇ -hydroxyethyl acrylate, ⁇ -hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2- Examples thereof include hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate. Of these, ⁇ -hydroxyethyl acrylate is preferred. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like. Of these, acrylamide and methacrylamide are preferable. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- the monomer constituting the particulate binder polymer for example, ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride and the like used in ordinary emulsion polymerization are used. May be. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- the weight average molecular weight of the particulate binder polymer is preferably 10,000 or more, more preferably 20,000 or more, preferably 2,000,000 or less, more preferably 500,000 or less.
- the weight average molecular weight of the particulate binder polymer can be determined by gel permeation chromatography (GPC) as a value in terms of polystyrene using tetrahydrofuran as a developing solvent.
- the glass transition temperature of the particulate binder is preferably ⁇ 75 ° C. or higher, more preferably ⁇ 55 ° C. or higher, particularly preferably ⁇ 35 ° C. or higher, preferably 40 ° C. or lower, preferably 30 ° C. or lower, more preferably 20 C. or lower, particularly preferably 15 C or lower.
- characteristics such as flexibility, binding and winding properties of the negative electrode, and adhesion between the negative electrode active material layer and the current collector are highly balanced and suitable. is there.
- the particulate binder is a water-insoluble polymer. Therefore, in the slurry composition for negative electrodes of the present invention, the particulate binder is not dissolved in water as a solvent but is dispersed as particles. When the particulate binder is soluble in water and an organic solvent (for example, N-methyl-2-pyrrolidone), the binder is adsorbed on the negative electrode active material, and as a result, the output characteristics of the secondary battery are reduced. End up. When the particulate binder is a water-insoluble polymer, the above problems can be prevented. In the negative electrode slurry composition, the particulate binder is preferably dispersed in water in the form of particles.
- the binder When a negative electrode slurry composition is used in which the binder is dissolved in an organic solvent such as NMP (N-methyl-2-pyrrolidone) and does not maintain the particulate shape, the binder is not present on the surface of the negative electrode active material. Adsorption causes output characteristics to deteriorate.
- NMP N-methyl-2-pyrrolidone
- the number average particle diameter of the particles of the particulate binder is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less.
- the presence of particles can be easily measured by transmission electron microscopy, Coulter counter, laser diffraction scattering, or the like.
- the particulate binder is produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent.
- the ratio of each monomer in the monomer composition is usually the repeating unit in the polymer of the particulate binder (eg, aliphatic conjugated diene monomer unit, aromatic vinyl monomer unit, ethylenically unsaturated). Carboxylic acid monomer units, etc.)
- the aqueous solvent is not particularly limited as long as the particles of the particulate binder can be dispersed.
- the boiling point at normal pressure is usually 80 ° C. or higher, preferably 100 ° C. or higher, and usually 350 ° C.
- it is preferably selected from aqueous solvents at 300 ° C. or lower. Examples of the aqueous solvent will be given below.
- the number in parentheses after the solvent name is the boiling point (unit: ° C) at normal pressure, and the value after the decimal point is a value rounded off or rounded down.
- aqueous solvent examples include water (100); ketones such as diacetone alcohol (169) and ⁇ -butyrolactone (204); ethyl alcohol (78), isopropyl alcohol (82), and normal propyl alcohol (97).
- Alcohols propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (171), 3-methoxy-3-methyl-1-butanol (174) , Ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (1 Glycol ethers such as 8); 1,3-dioxolane (75), 1,4-dioxolane (101), ethers such as tetrahydrofuran (66); and the like.
- water is particularly preferred from the viewpoint that it is not flammable and a dispersion of particulate binder particles can be easily obtained.
- Water may be used as the main solvent, and an aqueous solvent other than the above-described water may be mixed and used within a range in which the dispersed state of the particulate binder particles can be ensured.
- the polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used.
- the polymerization method any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. It is easy to obtain a high molecular weight product, and since the polymer is obtained in a state of being dispersed in water as it is, no redispersion treatment is required, and it can be used for production of the negative electrode slurry composition according to the present invention. From the viewpoint of production efficiency, the emulsion polymerization method is particularly preferable.
- the emulsion polymerization method is usually performed by a conventional method.
- the method is described in “Experimental Chemistry Course” Vol. 28, (Publisher: Maruzen Co., Ltd., edited by The Chemical Society of Japan). That is, water, an additive such as a dispersant, an emulsifier, a crosslinking agent, a polymerization initiator, and a monomer are added to a sealed container equipped with a stirrer and a heating device so as to have a predetermined composition, and the composition in the container
- a product is stirred to emulsify monomers and the like in water, and the temperature is increased while stirring to initiate polymerization.
- it is the method of putting into a sealed container and starting reaction similarly.
- polymerization initiator examples include organic compounds such as lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, and 3,3,5-trimethylhexanoyl peroxide.
- Peroxides examples include azo compounds such as ⁇ , ⁇ ′-azobisisobutyronitrile; ammonium persulfate; potassium persulfate.
- a polymerization initiator may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- Emulsifiers, dispersants, polymerization initiators, and the like are generally used in these polymerization methods, and the amount used is generally the amount generally used.
- seed polymerization may be performed using seed particles.
- the polymerization temperature and the polymerization time can be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator. Usually, the polymerization temperature is about 30 ° C. or more, and the polymerization time is about 0.5 to 30 hours. Further, additives such as amines may be used as a polymerization aid.
- an aqueous dispersion of particulate binder particles obtained by these methods is used, for example, alkali metal (eg, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (eg, NH 4 Cl). Etc.) and a basic aqueous solution containing an organic amine compound (eg, ethanolamine, diethylamine, etc.) may be mixed to adjust the pH to a range of usually 5 to 10, preferably 5 to 9.
- pH adjustment with an alkali metal hydroxide is preferable because it improves the binding property (peel strength) between the current collector and the negative electrode active material.
- the particulate binder particles described above may be composite polymer particles composed of two or more types of polymers.
- the composite polymer particles are also obtained by a method (two-stage polymerization method) in which at least one monomer component is polymerized by a conventional method and then at least one other monomer component is polymerized by a conventional method. be able to. In this way, by polymerizing the monomer stepwise, it is possible to obtain core-shell structured particles having a core layer present inside the particle and a shell layer covering the core layer.
- the amount of the particulate binder is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, preferably 8 parts by weight or less, more preferably 4 parts by weight with respect to 100 parts by weight of the negative electrode active material. Part or less, particularly preferably 2 parts by weight or less.
- the water-soluble polymer contained in the negative electrode active material layer includes a predetermined proportion of a sulfonic acid group-containing monomer unit and a predetermined proportion of a fluorine-containing (meth) acrylate monomer unit. It is a copolymer.
- the coating property when the negative electrode slurry composition of the present invention is applied to a current collector, and the collection of the negative electrode active material layer in the secondary battery of the present invention are provided. Adhesiveness to the electric body, high temperature cycle characteristics and low temperature output characteristics are usually excellent.
- the dispersion stability of the negative electrode active material can be improved, the detachment of the negative electrode active material from the negative electrode active material layer can be prevented, or the negative electrode active material Since the chemical change of itself can be suppressed, the high temperature storage characteristic and the low temperature output characteristic of the secondary battery can be improved.
- the water-soluble polymer contains a fluorine-containing (meth) acrylic acid ester monomer unit, the water-soluble polymer can be swelled in water (when the water-soluble polymer is immersed in water, The degree to which the coalescence swells by absorbing water is improved, and the water-soluble polymer can be elastically deformed. As a result, the properties of the slurry are improved, and the performance of the battery is improved. It is considered that the effects described above are achieved by combining these actions.
- the water-soluble polymer when the negative electrode active material expands or contracts in the negative electrode, the water-soluble polymer can be elastically deformed following the expansion or contraction of the negative electrode active material, so that swelling of the negative electrode accompanying charge / discharge can be suppressed.
- the particulate binder when the negative electrode active material repeatedly expands and contracts, the particulate binder cannot adhere to the negative electrode active material, and a gap is generated between the negative electrode active materials or between the negative electrode active material and the conductive agent.
- the electrical connection between the active material and the conductive agent may be impaired. If the electrical connection is impaired, the electric capacity of the secondary battery may be reduced.
- the water-soluble polymer can be elastically deformed following the expansion or contraction of the negative electrode active material, the generation of the gap can be suppressed and the electrical connection can be maintained, so that the cycle characteristics can be improved.
- the water-soluble polymer can be adsorbed on the surface of the negative electrode active material to cover the negative electrode active material and form a protective layer.
- this protective layer decomposition of the electrolytic solution under a high temperature environment and decomposition of the electrolytic solution accompanying charge / discharge can be suppressed.
- bubbles are generated around the negative electrode active material, which may hinder the transfer of electrons and reduce the electric capacity of the secondary battery.
- the decomposition of the electrolytic solution can be suppressed by the water-soluble polymer, the decrease in electric capacity as described above can be suppressed, and the high temperature storage characteristics and the high temperature cycle characteristics can be improved.
- the protective layer formed of the water-soluble polymer has higher ionic conductivity than the protective layer formed of a conventional additive such as carboxymethyl cellulose (hereinafter referred to as “CMC” as appropriate).
- CMC carboxymethyl cellulose
- the water-soluble polymer has swelling properties with respect to the electrolytic solution (when the water-soluble polymer is immersed in the electrolytic solution, the water-soluble polymer swells by absorbing the electrolytic solution).
- the ionic conductivity is high, the diffusion resistance (that is, the resistance that hinders the diffusion of ions) is reduced, so that the secondary battery of the present invention has high output characteristics, particularly excellent low-temperature output characteristics.
- the solvent of the electrolyte solution is swollen to such an extent that it cannot easily pass through the protective layer. Is done.
- the water-soluble polymer has high solubility in water and can be easily adsorbed on the negative electrode active material. For this reason, in the whole slurry composition for negative electrodes of this invention, a water-soluble polymer can cover the surface of the particle
- the water-soluble polymer is highly flexible and soft, it easily adheres to the surface of the current collector and the surface of the negative electrode active material without any gap. For this reason, the water-soluble polymer can supplement the binding of the particulate binder to the current collector and the negative electrode active material, thereby increasing the adhesion. Therefore, the adhesion of the negative electrode active material layer to the current collector can be improved.
- the sulfonic acid group-containing monomer unit contained in the water-soluble polymer is a repeating unit obtained by polymerizing a monomer containing a sulfonic acid group (—SO 3 H).
- monomers containing sulfonic acid include sulfonic acid group-containing monomers having no functional group other than sulfonic acid groups or salts thereof, monomers containing amide groups and sulfonic acid groups, or Examples thereof include a salt thereof and a monomer containing a hydroxyl group and a sulfonic acid group or a salt thereof.
- the water-soluble polymer may contain only one type of sulfonic acid group-containing monomer unit, or may contain two or more types in combination at any ratio.
- the sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group examples include a monomer obtained by sulfonating one of conjugated double bonds of a diene compound such as isoprene and butadiene, vinyl sulfonic acid, Examples thereof include styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, and sulfobutyl methacrylate.
- the salt lithium salt, sodium salt, potassium salt etc. are mentioned, for example. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- Examples of the monomer containing an amide group and a sulfonic acid group include 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
- AMPS 2-acrylamido-2-methylpropanesulfonic acid
- salt lithium salt, sodium salt, potassium salt etc. are mentioned, for example. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- Examples of the monomer containing a hydroxyl group and a sulfonic acid group include 3-allyloxy-2-hydroxypropanesulfonic acid (HAPS).
- HAPS 3-allyloxy-2-hydroxypropanesulfonic acid
- salt lithium salt, sodium salt, potassium salt etc. are mentioned, for example. One of these may be used alone, or two or more of these may be used in combination at any ratio.
- styrene sulfonic acid 2-acrylamido-2-methylpropane sulfonic acid (AMPS)
- AMPS 2-acrylamido-2-methylpropane sulfonic acid
- the ratio of the sulfonic acid group-containing monomer units in the water-soluble polymer is 0.1% by weight or more, preferably 1% by weight or more, while 15% by weight or less, preferably 10% by weight or less.
- the dispersibility of the slurry for the negative electrode is improved when the density of sulfonic acid groups in the water-soluble polymer is increased.
- a sulfonic acid group usually undergoes a crosslinking reaction when producing the negative electrode of the present invention, a crosslinked structure is formed by the sulfonic acid group in the negative electrode active material layer.
- the water-soluble polymer since the water-soluble polymer has a sufficient amount of sulfonic acid groups, the number of cross-linked structures is increased to increase the strength of the negative electrode active material layer, and the secondary battery has high temperature storage characteristics and low temperature output. The characteristics can be improved. Therefore, the water-soluble polymer preferably contains a large amount of sulfonic acid group-containing monomer units as described above. However, if there are too many sulfonic acid group-containing monomer units, the other monomer units are relatively reduced, and the adsorptivity and strength of the water-soluble polymer to the negative electrode active material can be reduced. The amount of the group-containing monomer unit is preferably not more than the upper limit of the above range.
- the fluorine-containing (meth) acrylate monomer unit contained in the water-soluble polymer is a unit other than the sulfonic acid group-containing monomer unit described above, and the fluorine-containing (meth) acrylate monomer Is a repeating unit obtained by polymerization.
- Examples of the fluorine-containing (meth) acrylic acid ester monomer include monomers represented by the following formula (I).
- R 1 represents a hydrogen atom or a methyl group.
- R 2 represents a hydrocarbon group containing a fluorine atom.
- the carbon number of the hydrocarbon group is usually 1 or more and usually 18 or less.
- the number of fluorine atoms contained in R 2 may be one or two or more.
- fluorine-containing (meth) acrylic acid ester monomers represented by formula (I) are: (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, (meth) acrylic acid fluoride Aralkyl etc. are mentioned. Of these, alkyl fluoride (meth) acrylate is preferable.
- Such monomers include trifluoromethyl (meth) acrylate, 2,2,2-trifluoroethyl (meth) acrylate, ⁇ - (perfluorooctyl) ethyl (meth) acrylate, (Meth) acrylic acid 2,2,3,3-tetrafluoropropyl, (meth) acrylic acid 2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 9H-par Fluoro-1-nonyl, 1H, 1H, 11H-perfluoroundecyl (meth) acrylate, perfluorooctyl (meth) acrylate, 3 [4 [1-trifluoromethyl-2,2- (meth) acrylic acid (Meth) acrylic acid perfluoroalkyl esters such as bis [bis (trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl Etc.
- One type of fluorine-containing (meth) acrylic acid ester monomer may be used alone, or two or more types may be used in combination at any ratio. Therefore, the water-soluble polymer may contain only one type of fluorine-containing (meth) acrylic acid ester monomer unit, or may contain two or more types in combination at any ratio.
- the ratio of fluorine-containing (meth) acrylic acid ester monomer units in the water-soluble polymer is 0.5% by weight or more, preferably 1% by weight or more, 10% by weight or less, preferably 5% by weight or less. .
- the water-soluble polymer may contain repeating units other than the above-described sulfonic acid group-containing monomer units and fluorine-containing (meth) acrylate monomer units as long as the effects of the present invention are not significantly impaired.
- a repeating unit can be a repeating unit obtained by polymerizing a monomer copolymerizable with a sulfonic acid group-containing monomer and a fluorine-containing (meth) acrylate monomer.
- the water-soluble polymer can include ethylenically unsaturated carboxylic acid monomer units.
- the ethylenically unsaturated carboxylic acid monomer unit is a repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer.
- Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof.
- ethylenically unsaturated monocarboxylic acid is preferable because it can further increase the dispersibility of the resulting water-soluble polymer in water.
- the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like.
- Examples of derivatives of ethylenically unsaturated monocarboxylic acids include 2-ethylacrylic acid, isocrotonic acid, ⁇ -acetoxyacrylic acid, ⁇ -trans-aryloxyacrylic acid, ⁇ -chloro- ⁇ -E-methoxyacrylic acid, Examples thereof include ⁇ -diaminoacrylic acid.
- Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like.
- Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like.
- Examples of derivatives of ethylenically unsaturated dicarboxylic acids include maleic acid substituted with hydrocarbon groups such as methylmaleic acid, dimethylmaleic acid and phenylmaleic acid; halogens such as chloromaleic acid, dichloromaleic acid and fluoromaleic acid Maleic acid; methyl allyl maleate; and maleic acid esters such as diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, fluoroalkyl maleate, and the like.
- ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. It is because the dispersibility with respect to water of the obtained water-soluble polymer can be improved more.
- One type of ethylenically unsaturated carboxylic acid monomer may be used alone, or two or more types may be used in combination at any ratio. Therefore, the water-soluble polymer may contain only one type of ethylenically unsaturated carboxylic acid monomer unit, or may contain two or more types in combination at any ratio.
- the ratio of the ethylenically unsaturated carboxylic acid monomer unit is preferably 5% by weight or more, more preferably 10% by weight or more, preferably 35% by weight or less, more preferably 30% by weight. It is as follows. By making the amount of the ethylenically unsaturated carboxylic acid monomer unit more than the lower limit of the above range, the adsorptivity of the water-soluble polymer to the negative electrode active material is improved, and the dispersibility of the negative electrode active material and the current collector are increased. Adhesion can be increased. In addition, since the flexibility of the water-soluble polymer can be increased by setting it to the upper limit or less, the flexibility of the negative electrode is improved to prevent the negative electrode from being chipped or cracked, thereby improving the durability. Can do.
- the water-soluble polymer may contain a (meth) acrylic acid ester monomer unit.
- a (meth) acrylic acid ester monomer unit is a repeating unit obtained by polymerizing a (meth) acrylic acid ester monomer.
- those corresponding to the above-mentioned sulfonic acid group-containing monomers or fluorine-containing (meth) acrylic acid ester monomers are used for the calculation of the quantitative ratio. It is included in the monomer or fluorine-containing (meth) acrylate monomer, and is not included in the (meth) acrylate monomer.
- those containing fluorine are distinguished from (meth) acrylate monomers as fluorine-containing (meth) acrylate monomers.
- Examples of (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, Acrylic acid alkyl esters such as 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t- Butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl Meth
- (Meth) acrylic acid ester monomer may be used alone or in combination of two or more at any ratio. Therefore, the water-soluble polymer may contain only one type of (meth) acrylic acid ester monomer unit, or may contain two or more types in combination at any ratio.
- the ratio of the (meth) acrylic acid ester monomer unit is preferably 30% by weight or more, more preferably 35% by weight or more, particularly preferably 40% by weight or more, and preferably 70%. % By weight or less.
- the water-soluble polymer may contain a crosslinkable monomer unit.
- the crosslinkable monomer unit is a structural unit capable of forming a crosslinked structure during or after polymerization by heating or irradiating energy with the crosslinkable monomer.
- the water-soluble polymer can be cross-linked, so that the strength and stability of the film formed of the water-soluble polymer can be increased.
- crosslinkable monomer a monomer capable of forming a crosslinked structure upon polymerization can be used.
- the crosslinkable monomer include monomers having two or more reactive groups per molecule. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.
- thermally crosslinkable groups contained in the monofunctional monomer include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof.
- an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.
- crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond examples include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl.
- Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, glycy Unsaturated carboxylic acids such as ru-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidy
- crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.
- crosslinkable monomer having an oxetanyl group as a thermally crosslinkable group and having an olefinic double bond examples include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl) ) -4-trifluoromethyloxetane.
- crosslinkable monomer having an oxazoline group as a heat crosslinkable group and having an olefinic double bond examples include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and And 2-isopropenyl-5-ethyl-2-oxazoline.
- multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl
- Examples include ethers, allyl or vinyl ethers of polyfunctional alcohols other than those described above, triallylamine, methylenebisacrylamide, and divinylbenzene.
- ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are particularly preferred as the crosslinkable monomer.
- the content of the crosslinkable monomer unit is preferably 0.1% or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 2%. % By weight or less, more preferably 1.5% by weight or less, particularly preferably 1% by weight or less.
- the ratio of the crosslinkable monomer unit in the water-soluble polymer usually coincides with the ratio (charge ratio) of the crosslinkable monomer in all the monomers of the water-soluble polymer.
- the water-soluble polymer may contain a reactive surfactant monomer unit.
- the reactive surfactant monomer unit is a structural unit obtained by polymerizing a reactive surfactant monomer.
- the reactive surfactant monomer unit constitutes a part of the water-soluble polymer and can function as a surfactant.
- the reactive surfactant monomer is a monomer having a polymerizable group that can be copolymerized with other monomers and having a surfactant group (hydrophilic group and hydrophobic group).
- the reactive surfactant monomer has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization.
- the polymerizable unsaturated group that the reactive surfactant monomer has include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group.
- One kind of the polymerizable unsaturated group may be used alone, or two or more kinds may be used in combination at any ratio.
- the reactive surfactant monomer usually has a hydrophilic group as a portion that exhibits hydrophilicity.
- Reactive surfactant monomers are classified into anionic, cationic and nonionic surfactants depending on the type of hydrophilic group.
- Examples of the anionic hydrophilic group include —SO 3 M, —COOM, and —PO (OM) 2 .
- M represents a hydrogen atom or a cation.
- Examples of cations include alkali metal ions such as lithium, sodium and potassium; alkaline earth metal ions such as calcium and magnesium; ammonium ions; ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; and And ammonium ions of alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.
- Examples of cationic hydrophilic groups include primary amine salts such as —NH 2 HX, secondary amine salts such as —NHCH 3 HX, tertiary amine salts such as —N (CH 3 ) 2 HX, And quaternary amine salts such as —N + (CH 3 ) 3 X — .
- X represents a halogen group.
- An example of a nonionic hydrophilic group is —OH.
- Suitable reactive surfactant monomers include compounds represented by the following formula (II).
- R represents a divalent linking group. Examples of R include —Si—O— group, methylene group and phenylene group.
- R 3 represents a hydrophilic group. An example of R 3 includes —SO 3 NH 4 .
- n represents an integer of 1 to 100.
- a suitable reactive surfactant has a structural unit having a structure formed by polymerizing ethylene oxide and a structural unit having a structure formed by polymerizing butylene oxide.
- Examples thereof include compounds having an alkenyl group having a terminal double bond and —SO 3 NH 4 (for example, trade names “Latemul PD-104” and “Latemul PD-105”, manufactured by Kao Corporation).
- a reactive surfactant monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the content of the reactive surfactant unit is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably It is 5% by weight or less, more preferably 4% by weight or less, and particularly preferably 2% by weight or less.
- the dispersibility of the slurry composition can be improved by setting the content ratio of the reactive surfactant unit to be equal to or higher than the lower limit of the above range.
- durability of an electrode can be improved by setting it as below an upper limit.
- Examples of arbitrary units that can be contained in the water-soluble polymer include, in addition to those listed above, repeating units obtained by polymerizing various arbitrary copolymerizable monomers.
- Examples of the copolymerizable monomer include carboxylic acid ester monomers having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; styrene Styrene monomers such as chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, ⁇ -methylstyrene, divinylbenzene; acrylamide, N -Amide monomers such as methylolacrylamide; ⁇ , ⁇ -unsaturated nitrile compound monomers such as acrylon
- the above copolymerizable monomers may be used alone or in combination of two or more at any ratio. Therefore, the water-soluble polymer may contain only one type of units based on such copolymerizable monomers, or may contain two or more types in combination at any ratio.
- the proportion of units based on the copolymerizable monomer is preferably 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight.
- the weight average molecular weight of the water-soluble polymer is usually smaller than that of the polymer to be a particulate binder, preferably 500 or more, more preferably 700 or more, particularly preferably 1000 or more, preferably 500000 or less, more preferably 250,000 or less, particularly preferably 100,000 or less.
- the water-soluble polymer can be softened by setting it to the upper limit value or less of the above range, for example, it is possible to suppress swelling of the negative electrode and improve adhesion of the negative electrode active material layer to the current collector.
- the weight average molecular weight of the water-soluble polymer can be determined by GPC as a value in terms of polystyrene using a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide.
- the glass transition temperature of the water-soluble polymer is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, preferably 100 ° C. or lower, more preferably 50 ° C. or lower.
- the glass transition temperature of the water-soluble polymer can be adjusted by combining various monomers.
- the water-soluble polymer has a viscosity of 0.1 mPa ⁇ s or more, preferably 1 mPa ⁇ s or more, more preferably 10 mPa ⁇ s or more, and usually 20000 mPa ⁇ s or less, preferably 1 wt% aqueous solution. It is 10,000 mPa ⁇ s or less, more preferably 5000 mPa ⁇ s or less.
- the viscosity can be adjusted by, for example, the molecular weight of the water-soluble polymer.
- the viscosity is a value when measured at 25 ° C. and a rotation speed of 60 rpm using a B-type viscometer.
- Method for producing water-soluble polymer for example, a monomer composition containing the above-described sulfonic acid group-containing monomer, fluorine-containing (meth) acrylic acid ester monomer, and any monomer as required
- the product can be produced by polymerization in an aqueous solvent.
- the aqueous solvent and the polymerization method are the same as, for example, the production of the particulate binder.
- an aqueous solution in which a water-soluble polymer is usually dissolved in an aqueous solvent is obtained.
- the water-soluble polymer may be taken out from the aqueous solution thus obtained.
- a negative electrode slurry composition is produced using the water-soluble polymer dissolved in an aqueous solvent, and the negative electrode slurry composition is prepared. To produce a negative electrode.
- the aqueous solution containing the water-soluble polymer in an aqueous solvent is usually acidic, it may be alkalized to pH 7 to pH 13 as necessary. Thereby, the handleability of aqueous solution can be improved and the coating property of the slurry composition for negative electrodes can be improved.
- Examples of the method for alkalinizing to pH 7 to pH 13 include alkali metal aqueous solutions such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution and potassium hydroxide aqueous solution; alkaline earth metal aqueous solutions such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution; The method of mixing aqueous alkali solution, such as aqueous ammonia solution, is mentioned.
- One kind of the alkaline aqueous solution may be used alone, or two or more kinds may be used in combination at any ratio.
- the amount of the water-soluble polymer is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, particularly preferably 1 part by weight or more with respect to 100 parts by weight of the negative electrode active material, preferably 10 parts by weight. It is 5 parts by weight or less, more preferably 5 parts by weight or less.
- the negative electrode active material layer may contain optional components in addition to the negative electrode active material, the particulate binder, and the water-soluble polymer described above.
- optional components include a viscosity modifier, a conductive agent, a reinforcing material, a leveling agent, an electrolytic solution additive, and the like. These are not particularly limited as long as they do not affect the battery reaction. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the viscosity modifier is a component used for adjusting the viscosity of the negative electrode slurry composition of the present invention to improve the dispersibility and coating property of the negative electrode slurry composition.
- the viscosity modifier contained in the negative electrode slurry composition remains in the negative electrode active material layer.
- a water-soluble polysaccharide as the viscosity modifier.
- polysaccharides include natural polymer compounds and cellulose semisynthetic polymer compounds.
- a viscosity modifier may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- natural polymer compounds include plant- and animal-derived polysaccharides and proteins. Moreover, the natural high molecular compound by which the fermentation process by the microorganisms etc., the process by heat
- plant-based natural polymer compounds examples include gum arabic, gum tragacanth, galactan, guar gum, carob gum, caraya gum, carrageenan, pectin, agar, quince seed (quince), alge colloid (brown algae extract), starch (rice, corn, Potato, those derived from wheat, etc.), glycyrrhizin and the like.
- animal-based natural polymer compounds include collagen, casein, albumin, and gelatin.
- examples of the microbial natural polymer compound include xanthan gum, dextran, succinoglucan, and pullulan.
- Cellulosic semisynthetic polymer compounds can be classified into nonionic, anionic and cationic.
- Nonionic cellulose semisynthetic polymer compounds include, for example, alkylcelluloses such as methylcellulose, methylethylcellulose, ethylcellulose, and microcrystalline cellulose; hydroxyethylcellulose, hydroxybutylmethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxy And hydroxyalkylcelluloses such as propylmethylcellulose stearoxy ether, carboxymethylhydroxyethylcellulose, alkylhydroxyethylcellulose, and nonoxynylhydroxyethylcellulose;
- anionic cellulose semi-synthetic polymer compound examples include alkyl celluloses obtained by substituting the above nonionic cellulose semi-synthetic polymer compound with various derivative groups, and sodium salts and ammonium salts thereof. Specific examples include sodium cellulose sulfate, methyl cellulose, methyl ethyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC) and salts thereof.
- Examples of the cationic cellulose semisynthetic polymer compound include low nitrogen hydroxyethyl cellulose dimethyl diallylammonium chloride (polyquaternium-4), O- [2-hydroxy-3- (trimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium). -10) and O- [2-hydroxy-3- (lauryldimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium-24).
- cellulose-based semi-synthetic polymer compounds sodium salts thereof and ammonium salts thereof are preferable because they can have cationic, anionic and amphoteric characteristics.
- anionic cellulose semisynthetic polymer compounds are particularly preferable from the viewpoint of dispersibility of the negative electrode active material.
- the degree of etherification of the cellulose semisynthetic polymer compound is preferably 0.5 or more, more preferably 0.6 or more, preferably 1.0 or less, more preferably 0.8 or less.
- the degree of etherification refers to the degree of substitution of hydroxyl groups (three) per anhydroglucose unit in cellulose with a substitution product such as a carboxymethyl group.
- the degree of etherification can theoretically take a value of 0-3.
- the degree of etherification is in the above range, the cellulose semi-synthetic polymer compound is adsorbed on the surface of the negative electrode active material and is compatible with water, so it has excellent dispersibility, and the negative electrode active material is the primary particle. Can be finely dispersed to the level.
- the average degree of polymerization of the viscosity modifier calculated from the intrinsic viscosity obtained from the Ubbelohde viscometer is preferably 500 or more, more preferably 1000 or more, preferably It is 2500 or less, more preferably 2000 or less, and particularly preferably 1500 or less.
- the average degree of polymerization of the viscosity modifier may affect the fluidity of the negative electrode slurry composition of the present invention, the film uniformity of the negative electrode active material layer, and the process in the process. By making the average degree of polymerization within the above range, the stability of the negative electrode slurry composition of the present invention over time can be improved, and coating without agglomerates and without thickness unevenness becomes possible.
- the amount of the viscosity modifier is preferably 0 part by weight or more and preferably 0.5 part by weight or less with respect to 100 parts by weight of the negative electrode active material.
- the conductive agent is a component that improves electrical contact between the negative electrode active materials. By including the conductive agent, the discharge rate characteristics of the secondary battery of the present invention can be improved.
- a conductive agent for example, acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber, conductive carbon such as carbon nanotube, and the like can be used.
- a electrically conductive agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the amount of the conductive agent is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.
- the reinforcing material for example, various inorganic and organic spherical, plate, rod or fiber fillers can be used.
- a reinforcing material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- a tough and flexible negative electrode can be obtained, and a secondary battery exhibiting excellent long-term cycle characteristics can be realized.
- the amount of the reinforcing material is usually 0.01 parts by weight or more, preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 10 parts by weight or less, with respect to 100 parts by weight of the negative electrode active material.
- leveling agent examples include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants.
- a leveling agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using a leveling agent, it is possible to prevent the repelling that occurs during the application of the negative electrode slurry composition or to improve the smoothness of the negative electrode.
- the amount of the leveling agent is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.
- the leveling agent is in the above range, the productivity, smoothness, and battery characteristics during the production of the negative electrode are excellent.
- the dispersibility of the negative electrode active material and the like in the negative electrode slurry composition can be improved, and the smoothness of the negative electrode obtained thereby can be improved.
- Examples of the electrolytic solution additive include vinylene carbonate.
- One electrolyte solution additive may be used alone, or two or more electrolyte solution additives may be used in combination at any ratio.
- the amount of the electrolytic solution additive is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material. By setting the amount of the electrolytic solution additive in the above range, a secondary battery excellent in cycle characteristics and high temperature characteristics can be realized.
- the negative electrode active material layer may contain nanoparticles, such as fumed silica and fumed alumina, for example.
- nanoparticles such as fumed silica and fumed alumina
- One kind of nanoparticles may be used alone, or two or more kinds of nanoparticles may be used in combination at any ratio.
- the thixotropy of the negative electrode slurry composition can be adjusted, so that the leveling property of the negative electrode of the present invention obtained thereby can be improved.
- the amount of the nanoparticles is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material. When the nanoparticles are in the above range, the stability and productivity of the negative electrode slurry composition can be improved, and high battery characteristics can be realized.
- the negative electrode of the present invention usually includes a current collector and a negative electrode active material layer provided on the surface of the current collector.
- the negative electrode active material layer comprises a negative electrode active material, a particulate binder, and a water-soluble polymer.
- the current collector is usually in the form of a sheet, and the negative electrode active material layer may be provided on at least one side of the sheet-like current collector, but is preferably provided on both sides.
- the current collector for the negative electrode is not particularly limited as long as it has electrical conductivity and is electrochemically durable, but a metal material is preferable because of its heat resistance.
- a metal material is preferable because of its heat resistance.
- the material for the current collector for the negative electrode include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum.
- copper is particularly preferable as the current collector used for the secondary battery negative electrode.
- the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.
- the current collector may be used after roughening the surface in advance.
- the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.
- a mechanical polishing method usually, a polishing cloth with an abrasive particle fixed thereto, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used.
- an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity of the negative electrode active material layer.
- the thickness of the negative electrode active material layer provided on the surface of the current collector is usually 5 ⁇ m or more, preferably 30 ⁇ m or more, and usually 300 ⁇ m or less, preferably 250 ⁇ m or less. When the thickness of the negative electrode active material layer is in the above range, load characteristics and cycle characteristics can be improved.
- the content ratio of the negative electrode active material in the negative electrode active material layer is preferably 85% by weight or more, more preferably 88% by weight or more, preferably 99% by weight or less, more preferably 97% by weight or less.
- the negative electrode for secondary battery of the present invention can be produced by any production method, but preferably, the slurry composition for secondary battery negative electrode of the present invention described below (hereinafter referred to as “the slurry composition for negative electrode of the present invention as appropriate”). Can be produced by a method for producing a negative electrode for a secondary battery of the present invention described below (hereinafter referred to as “method for producing a negative electrode of the present invention” as appropriate).
- the negative electrode slurry composition of the present invention is a slurry-like composition containing a negative electrode active material, a particulate binder, and a water-soluble polymer.
- the negative electrode slurry composition of the present invention usually further contains a solvent.
- the solvent it is preferable to use water or a mixture of water and a liquid other than water from the viewpoint of reducing environmental load.
- Water functions as a solvent or a dispersion medium in the negative electrode slurry composition, and can disperse the negative electrode active material, disperse the particulate binder, or dissolve the water-soluble polymer. It is preferable to combine a liquid that dissolves the particulate binder and the water-soluble polymer because the dispersion of the negative electrode active material is stabilized by adsorbing the particulate binder and the water-soluble polymer on the surface of the negative electrode active material.
- the type of liquid to be combined with water is preferably selected from the viewpoint of drying speed and environment.
- Preferred examples include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, butyl acetate, ⁇ -butyrolactone, Esters such as ⁇ -caprolactone; Acylonitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether: Alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; N— Examples include amides such as methylpyrrolidone and N, N-dimethylformamide, among which N-methylpyrrolidone (NMP) is preferable.
- the amount of the solvent in the negative electrode slurry composition is preferably adjusted so that the viscosity of the negative electrode slurry composition of the present invention is suitable for coating.
- the concentration of the solid content of the slurry composition for negative electrode of the present invention is preferably 30% by weight or more, more preferably 40% by weight or more, preferably 90% by weight or less, more preferably 80% by weight. It is used by adjusting to the following amount.
- the slurry composition for negative electrode may contain optional components other than the negative electrode active material, the particulate binder, the water-soluble polymer, and the solvent as necessary.
- the amount of the optional component is usually the same as the amount of the optional component contained in the negative electrode active material layer.
- a part of the water-soluble polymer is usually dissolved in water, but another part of the water-soluble polymer is adsorbed on the surface of the negative electrode active material.
- the negative electrode active material is covered with a stable layer of a water-soluble polymer, and the dispersibility of the negative electrode active material in the solvent is improved. For this reason, the slurry composition for negative electrodes of this invention has the favorable coating property at the time of apply
- the method for preparing the slurry composition for negative electrode of the present invention is not particularly limited, and can be manufactured by mixing a negative electrode active material, a particulate binder, a water-soluble polymer, a solvent, and optional components used as necessary.
- the mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type.
- a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.
- the negative electrode slurry of the present invention is produced by applying the slurry composition for negative electrode of the present invention to the surface of the current collector and drying it as necessary to form a negative electrode active material layer on the surface of the current collector. Can do.
- the method for applying the negative electrode slurry composition of the present invention to the surface of the current collector is not particularly limited.
- Examples of the method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.
- drying method examples include, for example, drying with warm air, hot air, low-humidity air, vacuum drying, and drying method by irradiation with (far) infrared rays or electron beams.
- the drying time is usually 1 minute to 40 minutes, and the drying temperature is usually 40 ° C. to 180 ° C.
- the negative electrode active material layer after applying and drying the negative electrode slurry composition on the surface of the current collector, it is preferable to subject the negative electrode active material layer to a pressure treatment using, for example, a die press or a roll press, if necessary. .
- the porosity of the negative electrode active material layer can be lowered.
- the porosity is preferably 5% or more, more preferably 7% or more, preferably 30% or less, more preferably 20% or less.
- the negative electrode active material layer contains a curable polymer
- the secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode is the negative electrode of the present invention. Since the negative electrode of the present invention is provided, the secondary battery of the present invention can suppress swelling of the negative electrode accompanying charging / discharging, or make it difficult to reduce the capacity even when stored in a high temperature environment. Moreover, normally, the high-temperature cycle characteristics and low-temperature output characteristics of the secondary battery of the present invention can be improved, and the adhesion of the negative electrode active material layer to the current collector can be improved.
- the positive electrode usually includes a current collector and a positive electrode active material layer including a positive electrode active material and a positive electrode binder formed on the surface of the current collector.
- the current collector of the positive electrode is not particularly limited as long as it is a material having electrical conductivity and electrochemical durability.
- the current collector for the positive electrode for example, the current collector used for the negative electrode of the present invention may be used. Among these, aluminum is particularly preferable.
- the positive electrode active material for example, when the secondary battery of the present invention is a lithium ion secondary battery, a material capable of inserting and removing lithium ions is used.
- Such positive electrode active materials are roughly classified into those made of inorganic compounds and those made of organic compounds.
- Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and the like.
- Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.
- transition metal oxide examples include MnO, MnO 2 , V 2 O 5 , V 6 O 13 , TiO 2 , Cu 2 V 2 O 3 , amorphous V 2 O—P 2 O 5 , MoO 3 , V 2 O 5 , V 6 O 13 and the like can be mentioned. Among them, MnO, V 2 O 5 , V 6 O 13 and TiO 2 are preferable from the viewpoint of cycle stability and capacity.
- transition metal sulfide examples include TiS 2 , TiS 3 , amorphous MoS 2 , FeS, and the like.
- lithium-containing composite metal oxide examples include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.
- lithium-containing composite metal oxide having a layered structure examples include lithium-containing cobalt oxide (LiCoO 2 ), lithium-containing nickel oxide (LiNiO 2 ), lithium composite oxide of Co—Ni—Mn, Ni—Mn— Examples thereof include lithium composite oxides of Al and lithium composite oxides of Ni—Co—Al.
- lithium-containing composite metal oxide having a spinel structure examples include Li [Mn 3/2 M 1/2 ] O 4 in which lithium manganate (LiMn 2 O 4 ) or a part of Mn is substituted with another transition metal. (Where M is Cr, Fe, Co, Ni, Cu, etc.).
- lithium-containing composite metal oxide having an olivine type structure examples include Li X MPO 4 (wherein M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti).
- Examples of the positive electrode active material made of an organic compound include conductive polymers such as polyacetylene and poly-p-phenylene.
- the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
- a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and this composite material may be used as a positive electrode active material.
- Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
- you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
- a positive electrode active material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the volume average particle diameter of the positive electrode active material particles is usually 1 ⁇ m or more, preferably 2 ⁇ m or more, and usually 50 ⁇ m or less, preferably 30 ⁇ m or less.
- the volume average particle diameter of the positive electrode active material particles is usually 1 ⁇ m or more, preferably 2 ⁇ m or more, and usually 50 ⁇ m or less, preferably 30 ⁇ m or less.
- the content ratio of the positive electrode active material in the positive electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, preferably 99.9% by weight or less, more preferably 99% by weight or less.
- binder for the positive electrode examples include polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, and polyacrylonitrile derivatives.
- Resins; Soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers, and vinyl soft polymers can be used.
- a binder may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- the positive electrode active material layer may contain components other than the positive electrode active material and the binder as necessary. Examples thereof include a viscosity modifier, a conductive agent, a reinforcing material, a leveling agent, an electrolytic solution additive, and the like. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the thickness of the positive electrode active material layer is usually 5 ⁇ m or more, preferably 10 ⁇ m or more, and usually 300 ⁇ m or less, preferably 250 ⁇ m or less. When the thickness of the positive electrode active material layer is in the above range, high characteristics can be realized in both load characteristics and energy density.
- the positive electrode can be manufactured, for example, by the same manufacturing method as the above-described negative electrode.
- Electrolyte As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used.
- the lithium salt include LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlCl 4 , LiClO 4 , CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi , (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 ) NLi, and other lithium salts.
- LiPF 6 , LiClO 4 , and CF 3 SO 3 Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used.
- One of these may be used alone, or two or more of these may be used in combination at any ratio.
- the amount of the supporting electrolyte is usually 1% by weight or more, preferably 5% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the secondary battery may be lowered.
- the solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte.
- the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC); Esters such as butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide;
- dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide.
- a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- an additive may be included in the electrolytic solution as necessary.
- carbonate compounds such as vinylene carbonate (VC) are preferable.
- an additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution; an inorganic solid electrolyte such as lithium sulfide, LiI, and Li 3 N; Can do.
- separator As the separator, a porous substrate having a pore portion is usually used.
- separators include (a) a porous separator having pores, (b) a porous separator having a polymer coating layer formed on one or both sides, and (c) a porous resin coat containing inorganic ceramic powder. And a porous separator having a layer formed thereon.
- these include solid polymer electrolytes such as polypropylene, polyethylene, polyolefin, or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymers.
- a polymer film for a gel polymer electrolyte a separator coated with a gelled polymer coat layer; a separator coated with a porous film layer composed of an inorganic filler and an inorganic filler dispersant; and the like.
- the manufacturing method of the secondary battery of the present invention is not particularly limited.
- the above-described negative electrode and positive electrode are overlapped via a separator, and this is wound according to the shape of the battery, folded into a battery container, injected into the battery container, and sealed by injecting an electrolyte.
- a battery can be manufactured.
- an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge.
- the shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.
- Adhesive strength The negative electrodes produced in Examples and Comparative Examples were cut into rectangles having a length of 100 mm and a width of 10 mm to obtain test pieces. A cellophane tape was affixed on the surface of the negative electrode active material layer of the test piece with the surface of the negative electrode active material layer facing down. At this time, a cellophane tape defined in JIS Z1522 was used. The cellophane tape was fixed on a horizontal test bench. Then, the stress when one end of the current collector was pulled vertically upward at a pulling speed of 50 mm / min and peeled was measured. This measurement was performed 3 times, the average value was calculated
- Coating property Apply the slurry composition for negative electrode manufactured in Examples and Comparative Examples on a 20 ⁇ m thick copper foil as a current collector so that the film thickness after drying is about 150 ⁇ m, and then dry. It was. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode. The obtained negative electrode was cut out with a size of 10 ⁇ 10 cm, and the number of pinholes having a diameter of 0.1 mm or more was visually measured. The smaller the number of pinholes, the better the coatability.
- Viscosity of 1% aqueous solution of water-soluble polymer The water-soluble polymers produced in the examples and comparative examples were diluted with 10% ammonia water and ion-exchanged water so that the pH would be 8. % Aqueous solution was prepared. The viscosity of this aqueous solution was measured with a B-type viscometer.
- Example 1 (1-1. Production of water-soluble polymer) In a 5 MPa pressure vessel equipped with a stirrer, 65.5 parts of ethyl acrylate as a (meth) acrylic acid ester monomer, 30 parts of methacrylic acid as an ethylenically unsaturated carboxylic acid monomer, a single amount of fluorine-containing (meth) acrylic acid ester 2.5 parts of trifluoromethyl methacrylate as a body, 2 parts of 2-acrylamido-2-methylpropanesulfonic acid as a sulfonic acid group-containing monomer, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, And 0.5 part of potassium persulfate was put as a polymerization initiator, and after stirring sufficiently, it heated at 60 degreeC and started superposition
- the reaction was stopped by cooling to obtain an aqueous solution containing a water-soluble polymer.
- the aqueous solution containing the water-soluble polymer thus obtained was adjusted to pH 8 by adding 10% ammonia water to obtain an aqueous solution containing the desired water-soluble polymer. It was 12800 when the weight average molecular weight of the obtained water-soluble polymer was measured.
- the viscosity of a 1% aqueous solution of the water-soluble polymer was measured and found to be 1500 mPa ⁇ s.
- aqueous dispersion containing a particulate binder composed of a styrene butadiene copolymer (hereinafter referred to as “SBR” as appropriate).
- SBR styrene butadiene copolymer
- a 5% aqueous sodium hydroxide solution was added to adjust the pH to 8, and then the unreacted monomer was removed by heating under reduced pressure. Then, it cooled to 30 degrees C or less, and obtained the aqueous dispersion containing a desired particulate binder. It was 1500,000 when the weight average molecular weight of the obtained particulate binder was measured.
- the number average particle diameter of the particulate binder measured by a laser diffraction / scattering particle size distribution apparatus was 150 nm.
- the aqueous solution containing the water-soluble polymer obtained in the step (1-1) was diluted with water to adjust the concentration to 5%.
- a planetary mixer with a disper 50 parts of SiOC (volume average particle diameter: 12 ⁇ m) as an anode active material and 50 parts of artificial graphite (volume average particle diameter: 24.5 ⁇ m) having a specific surface area of 4 m 2 / g, A 1% portion of a 5% aqueous solution of a polymer was added in an amount corresponding to the solid content, adjusted to a solid content concentration of 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting the solid content concentration to 52% with ion-exchanged water, the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.
- the slurry composition for negative electrode obtained in the step (1-3) was applied onto a 20 ⁇ m thick copper foil as a current collector by a comma coater so that the film thickness after drying was about 150 ⁇ m. , Dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material.
- This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 80 ⁇ m.
- the adhesion strength of the obtained negative electrode was evaluated. The results are shown in Table 1.
- a 40% aqueous dispersion of an acrylate polymer having a glass transition temperature Tg of ⁇ 40 ° C. and a number average particle size of 0.20 ⁇ m was prepared.
- the acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 78% by weight of 2-ethylhexyl acrylate, 20% by weight of acrylonitrile, and 2% by weight of methacrylic acid.
- LiFePO 4 having a volume average particle size of 0.5 ⁇ m and having an olivine crystal structure as a positive electrode active material and a 1% aqueous solution of carboxymethyl cellulose (“BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a dispersant 1 part at a time and a 40% aqueous dispersion of the above acrylate polymer as a binder are mixed with 5 parts at a solid content, and ion-exchanged water is added to this so that the total solid content concentration is 40%.
- the slurry composition for positive electrodes was prepared by mixing with a planetary mixer.
- the above positive electrode slurry composition was applied onto a 20 ⁇ m thick aluminum foil as a current collector with a comma coater so that the film thickness after drying was about 200 ⁇ m, and dried. This drying was performed by transporting the aluminum foil in an oven at 60 ° C. at a speed 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. This positive electrode raw material was rolled with a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 70 ⁇ m.
- the negative electrode obtained in the step (1-4) was cut into a 4.2 mm ⁇ 4.2 mm rectangle.
- the positive electrode obtained in step (1-5) was cut into a 4 mm ⁇ 4 mm rectangle.
- the separator of step (1-6) was cut into a 5 mm ⁇ 5 mm rectangle.
- the rectangular positive electrode was placed so that the surface of the current collector was in contact with the aluminum packaging exterior.
- a rectangular separator was disposed on the surface of the positive electrode active material layer of the rectangular positive electrode.
- the rectangular negative electrode was placed on a rectangular separator so that the surface of the negative electrode active material layer faced the separator.
- capacitance initial capacity
- Example 2 In the production of the water-soluble polymer in the step (1-1), styrene sulfonic acid (Example 2) or vinyl sulfonic acid (Example 2) instead of 2-acrylamido-2-methylpropane sulfonic acid is used as a sulfonic acid group-containing monomer.
- styrene sulfonic acid Example 2
- vinyl sulfonic acid Example 2
- 2-acrylamido-2-methylpropane sulfonic acid is used as a sulfonic acid group-containing monomer.
- a lithium ion secondary battery and its components were produced and evaluated in the same manner as in Example 1 except that Example 3) was used. The results are shown in Table 1.
- Example 4 In the production of the water-soluble polymer in the step (1-1), as a fluorine-containing (meth) acrylic acid ester monomer, trifluoromethyl acrylate (Example 4) or perfluorooctyl methacrylate ( A lithium ion secondary battery and its components were produced and evaluated in the same manner as in Example 1 except that Example 5) was used. The results are shown in Table 1.
- Example 6 to 12 In the production of the water-soluble polymer in the step (1-1), the ratio of ethyl acrylate, methacrylic acid, trifluoromethyl methacrylate, and 2-acrylamido-2-methylpropanesulfonic acid was changed as shown in Table 1 and Table 2.
- the lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
- Example 13 In the production of the negative electrode slurry composition in the step (1-3), lithium ion two-component was performed in the same manner as in Example 1, except that 50 parts of SiOC and 50 parts of artificial graphite were used as the negative electrode active material. The secondary battery and its components were manufactured and evaluated. The results are shown in Table 2.
- Example 14 In the production of the slurry composition for negative electrode in the step (1-3), lithium ion was prepared in the same manner as in Example 1, except that 100 parts of artificial graphite was used as the negative electrode active material instead of 50 parts of SiOC and 50 parts of artificial graphite. An ion secondary battery and its components were manufactured and evaluated. The results are shown in Table 2.
- Example 15-1 Production of nanosilica active material A
- argon gas was introduced and the inside of the processing furnace was replaced with argon, and then the temperature was increased to 1200 ° C. at a temperature increase rate of 300 ° C./hr while flowing argon at 2 NL / min, and held for 3 hours.
- the temperature was lowered, and after reaching room temperature, the powder was recovered and used as Si-based active material A.
- step (1-3) Manufacture and evaluation of lithium ion secondary battery and its components
- 5 parts of Si-based active material A and artificial graphite obtained in step (15-1) were used instead of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material.
- a lithium ion secondary battery and its constituent elements were produced and evaluated in the same manner as in Example 1 except that 95 parts were used. The results are shown in Table 2.
- TFMMA trifluoromethyl methacrylate
- TFMA trifluoromethyl acrylate
- PFOMA perfluorooctyl methacrylate
- AMPS 2-acrylamido-2methylpropane sulfonic acid
- SS styrene sulfonic acid
- VS vinyl sulfonic acid
- A nanosilica prepared in Example 15
- Active material A Si-based B nanosilica active material B produced in Example 16
- Binder Binder type
- EA amount Addition amount of ethyl acrylate (parts)
- Fluorine monomer type Fluorine-containing (meth) acrylate monomer type
- Fluorine monomer amount Fluorine-containing (meth) acrylate monomer addition amount (parts)
- Type of sulfone monomer Type of sulfonic acid group-containing monomer
- Type of sulfone monomer Addition amount of sulfonic acid group-containing monomer
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Abstract
Description
すなわち、本発明によれば以下の〔1〕~〔11〕が提供される。
〔1〕 負極活物質、粒子状バインダー及び水溶性重合体を含む二次電池用負極であって、
前記水溶性重合体が、
スルホン酸基含有単量体単位0.1重量%~15重量%、及び
フッ素含有(メタ)アクリル酸エステル単量体単位0.5重量%~10重量%
を含む共重合体である二次電池用負極。
〔2〕 前記水溶性重合体が、エチレン性不飽和カルボン酸単量体単位を含む〔1〕に記載の二次電池用負極。
〔3〕 前記エチレン性不飽和カルボン酸単量体が、エチレン性不飽和モノカルボン酸単量体である、〔2〕記載の二次電池用負極。
〔4〕 前記負極活物質が、リチウムを吸蔵及び放出でき、金属を含む、〔1〕~〔3〕のいずれか1項に記載の二次電池用負極。
〔5〕 前記金属が、ケイ素である、〔4〕に記載の二次電池用負極。
〔6〕 前記粒子状バインダーが、脂肪族共役ジエン単量体単位を含む重合体を含む、〔1〕~〔5〕のいずれか1項に記載の二次電池用負極。
〔7〕 前記脂肪族共役ジエン単量体単位を含む重合体が、芳香族ビニル単量体単位をさらに含む、〔6〕に記載の二次電池用負極。
〔8〕 正極、負極、電解液及びセパレーターを備え、前記負極が、〔1〕~〔7〕のいずれか1項に記載の二次電池用負極である、二次電池。
〔9〕 負極活物質、粒子状バインダー及び水溶性重合体を含むスラリー組成物であって、
前記水溶性重合体が、
スルホン酸基含有単量体単位0.1重量%~15重量%、
フッ素含有(メタ)アクリル酸エステル単量体単位0.5重量%~10重量%を含む共重合体である二次電池負極用スラリー組成物。
〔10〕 前記水溶性重合体が、エチレン性不飽和カルボン酸単量体単位を含む、〔9〕に記載の負極用スラリー組成物。
〔11〕 〔9〕又は〔10〕に記載の二次電池負極用スラリー組成物を、集電体上に塗布し、乾燥することを含む、二次電池用負極の製造方法。
本発明の二次電池は、充放電に伴う負極の膨らみを抑制でき、高温環境で保存した場合でも容量を低下し難く、且つ高温環境及び低温環境のいずれにおいても特性が良好である。
本発明の負極用スラリー組成物を用いれば、本発明の二次電池用負極を製造できる。さらに、本発明の負極用スラリー組成物は、安定性が高いため、長期保存が可能であり、使用が容易である。
本発明の二次電池用負極の製造方法によれば、本発明の二次電池用負極を製造できる。
本発明の二次電池用負極(以下、適宜「本発明の負極」という。)は、負極活物質、粒子状バインダー及び水溶性重合体を含む。通常、本発明の負極は、集電体と、前記集電体の表面に形成された負極活物質層とを備え、負極活物質層が前記の負極活物質、粒子状バインダー及び水溶性重合体を含む。
負極活物質は、負極用の電極活物質であり、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。
例えば本発明の二次電池がリチウムイオン二次電池である場合には、負極活物質として、通常は、リチウムを吸蔵及び放出しうる物質を用いる。
好適な負極活物質の例としては、炭素が挙げられる。炭素としては、例えば、天然黒鉛、人造黒鉛、カーボンブラック等が挙げられ、中でも天然黒鉛を用いることが好ましい。
この中でも、ケイ素を含む負極活物質が好ましい。ケイ素を含む負極活物質を用いることにより、リチウムイオン二次電池の電気容量を大きくすることが可能となる。また、一般にケイ素を含む負極活物質は充放電に伴って大きく(例えば5倍程度に)膨張及び収縮するが、本発明の負極においては、ケイ素を含む負極活物質の膨張及び収縮による電池性能の低下を抑制することができる。
ケイ素を含む活物質の例としては、金属ケイ素からなる活物質、ケイ素と他の元素との化合物からなる活物質(以下において「ケイ素系活物質」ということがある。)、及び金属ケイ素からなる活物質とケイ素系活物質との組み合わせが挙げられる。
複合化の方法としては、例えば、ケイ素を含む活物質をカーボンによりコーティングすることにより複合化する方法;導電性カーボンとケイ素を含む活物質とを含む混合物を造粒することにより複合化する方法;等が挙げられる。
負極活物質は、粒子状に整粒されたものが好ましい。粒子の形状が球形であると、電極成形時に、より高密度な電極が形成できる。
負極活物質が粒子である場合、その体積平均粒子径は、二次電池の他の構成要件との兼ね合いで適宜選択され、通常0.1μm以上、好ましくは1μm以上、より好ましくは5μm以上であり、通常100μm以下、好ましくは50μm以下、より好ましくは30μm以下である。ここで、体積平均粒子径は、レーザー回折法で測定された粒度分布において小径側から計算した累積体積が50%となる粒子径を採用する。
粒子状バインダーは、負極において電極活物質を集電体の表面に結着させる成分である。本発明の負極では、粒子状バインダーが負極活物質を結着することにより、負極活物質層からの負極活物質の脱離が低減される。また、粒子状バインダーは通常は負極活物質層に含まれる負極活物質以外の粒子をも結着し、負極活物質層の強度を維持する役割も果たす。
脂肪族共役ジエン単量体は1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。したがって、粒子状バインダーの重合体は、脂肪族共役ジエン単量体単位を、1種類だけ含んでいてもよく、2種類以上を任意の比率で組み合わせて含んでいてもよい。
芳香族ビニル単量体は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。したがって、粒子状バインダーの重合体は、芳香族ビニル単量体を、1種類だけ含んでいてもよく、2種類以上を任意の比率で組み合わせて含んでいてもよい。
エチレン性不飽和カルボン酸単量体は1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。したがって、粒子状バインダーの重合体は、エチレン性不飽和カルボン酸単量体単位を、1種類だけ含んでいてもよく、2種類以上を任意の比率で組み合わせて含んでいてもよい。
単量体組成物中の各単量体の比率は、通常、粒子状バインダーの重合体における繰り返し単位(例えば、脂肪族共役ジエン単量体単位、芳香族ビニル単量体単位、エチレン性不飽和カルボン酸単量体単位等)の比率と同様にする。
また、アミン類などの添加剤を重合助剤として用いてもよい。
本発明の負極において、負極活物質層が含有する水溶性重合体は、所定割合のスルホン酸基含有単量体単位と、所定割合のフッ素含有(メタ)アクリル酸エステル単量体単位とを含む共重合体である。本発明の負極が水溶性重合体を含むことにより、充放電に伴う負極の膨らみを抑制でき、且つ、高温環境で保存した場合でも容量が低下し難い二次電池を実現できる。また、かかる水溶性重合体を用いたことにより、本発明の負極用スラリー組成物を集電体に塗布する際の塗工性、及び、本発明の二次電池における、負極活物質層の集電体への密着性、並びに、高温サイクル特性及び低温出力特性が、通常優れたものとなる。
水溶性重合体が含むスルホン酸基含有単量体単位は、スルホン酸基(-SO3H)を含有する単量体を重合して得られる繰り返し単位である。スルホン酸を含有する単量体の例を挙げると、スルホン酸基以外に官能基をもたないスルホン酸基含有単量体またはその塩、アミド基とスルホン酸基とを含有する単量体またはその塩、並びに、ヒドロキシル基とスルホン酸基とを含有する単量体またはその塩が挙げられる。これらは1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。したがって、水溶性重合体は、スルホン酸基含有単量体単位を、1種類だけ含んでいてもよく、2種類以上を任意の比率で組み合わせて含んでいてもよい。
水溶性重合体が含むフッ素含有(メタ)アクリル酸エステル単量体単位は、上に述べたスルホン酸基含有単量体単位以外の単位であって、フッ素含有(メタ)アクリル酸エステル単量体を重合して得られる繰り返し単位である。
フッ素含有(メタ)アクリル酸エステル単量体としては、例えば、下記の式(I)で表される単量体が挙げられる。
前記の式(I)において、R2は、フッ素原子を含有する炭化水素基を表す。炭化水素基の炭素数は、通常1以上であり、通常18以下である。また、R2が含有するフッ素原子の数は、1個でもよく、2個以上でもよい。
水溶性重合体は、本発明の効果を著しく損なわない限りにおいて、上述したスルホン酸基含有単量体単位及びフッ素含有(メタ)アクリル酸エステル単量体単位以外の繰り返し単位を含みうる。このような繰り返し単位は、スルホン酸基含有単量体及びフッ素含有(メタ)アクリル酸エステル単量体と共重合可能な単量体を重合して得られる繰り返し単位としうる。
例えば、水溶性重合体は、エチレン性不飽和カルボン酸単量体単位を含みうる。エチレン性不飽和カルボン酸単量体単位は、エチレン性不飽和カルボン酸単量体を重合して得られる繰り返し単位である。
エチレン性不飽和カルボン酸単量体としては、例えば、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。これらのうち、エチレン性不飽和モノカルボン酸が、得られる水溶性重合体の水に対する分散性をより高めることができるため好ましい。
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。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。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、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。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等の炭化水素基で置換されたマレイン酸;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等のハロゲン化マレイン酸;マレイン酸メチルアリル;並びに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等のマレイン酸エステルなどが挙げられる。これらの中でも、アクリル酸、メタクリル酸等のエチレン性不飽和モノカルボン酸が好ましい。得られる水溶性重合体の水に対する分散性がより高めることができるからである。
また例えば、水溶性重合体は、(メタ)アクリル酸エステル単量体単位を含みうる。(メタ)アクリル酸エステル単量体単位は、(メタ)アクリル酸エステル単量体を重合して得られる繰り返し単位である。ただし、(メタ)アクリル酸エステル単量体の中でも上述したスルホン酸基含有単量体又はフッ素含有(メタ)アクリル酸エステル単量体に該当するものは、量比の計算にあたりスルホン酸基含有単量体又はフッ素含有(メタ)アクリル酸エステル単量体に含め、(メタ)アクリル酸エステル単量体には含めない。例えば、(メタ)アクリル酸エステル単量体のうちフッ素を含有するものは、フッ素含有(メタ)アクリル酸エステル単量体として(メタ)アクリル酸エステル単量体とは区別する。
また、例えば、水溶性重合体は、架橋性単量体単位を含んでいてもよい。架橋性単量体単位は、架橋性単量体を加熱又はエネルギー照射することにより、重合中又は重合後に架橋構造を形成しうる構造単位である。架橋性単量体単位を含むことにより、水溶性重合体を架橋させることができるので、水溶性重合体で形成される被膜の強度及び安定性を高めることができる。
さらに、例えば、水溶性重合体は、反応性界面活性剤単量体単位を含んでいてもよい。反応性界面活性剤単量体単位は、反応性界面活性剤単量体を重合して得られる構造単位である。反応性界面活性剤単量体単位は、水溶性重合体の一部を構成し、且つ界面活性剤として機能しうる。
カチオン系の親水基の例としては、-NH2HXなどの第1級アミン塩、-NHCH3HXなどの第2級アミン塩、-N(CH3)2HXなどの第3級アミン塩、-N+(CH3)3X-などの第4級アミン塩などが挙げられる。ここでXは、ハロゲン基を表す。
ノニオン系の親水基の例としては、-OHが挙げられる。
式(II)において、R3は親水性基を表す。R3の例としては、-SO3NH4が挙げられる。
式(II)において、nは1以上100以下の整数を表す。
反応性界面活性剤単量体は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
水溶性重合体が含みうる任意の単位の例としては、上に挙げたものに加えて、種々の任意の共重合可能な単量体を重合して得られる繰り返し単位を挙げうる。かかる共重合可能な単量体としては、例えば、エチレングリコールジメタクリレート、ジエチレングリコールジメタクリレート、トリメチロールプロパントリアクリレート等の、2つ以上の炭素-炭素二重結合を有するカルボン酸エステル単量体;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、ビニル安息香酸メチル、ビニルナフタレン、クロロメチルスチレン、ヒドロキシメチルスチレン、α-メチルスチレン、ジビニルベンゼン等のスチレン系単量体;アクリルアミド、N-メチロールアクリルアミド等のアミド系単量体;アクリロニトリル、メタクリロニトリル等のα,β-不飽和ニトリル化合物単量体;エチレン、プロピレン等のオレフィン類単量体;塩化ビニル、塩化ビニリデン等の、(フッ素含有(メタ)アクリル酸エステル単量体以外の)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単量体;メチルビニルエーテル、エチルビニルエーテル、ブチルビニルエーテル等のビニルエーテル類単量体;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単量体;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単量体などが挙げられる。
水溶性重合体の重量平均分子量は、通常は粒子状バインダーとなる重合体よりも小さく、好ましくは500以上、より好ましくは700以上、特に好ましくは1000以上であり、好ましくは500000以下、より好ましくは250000以下、特に好ましくは100000以下である。水溶性重合体の重量平均分子量を上記範囲の下限値以上とすることにより水溶性重合体の強度を高くして負極活物質を覆う安定な保護層を形成できるので、例えば負極活物質の分散性及び二次電池の高温保存特性などを改善できる。また、上記範囲の上限値以下とすることにより水溶性重合体を柔らかくできるので、例えば負極の膨らみの抑制、負極活物質層の集電体への密着性の改善などが可能となる。水溶性重合体の重量平均分子量は、GPCによって、ジメチルホルムアミドの10体積%水溶液に0.85g/mlの硝酸ナトリウムを溶解させた溶液を展開溶媒としたポリスチレン換算の値として求めうる。
水溶性重合体の製造方法としては、例えば、上述したスルホン酸基含有単量体、フッ素含有(メタ)アクリル酸エステル単量体、及び必要に応じて任意の単量体を含む単量体組成物を、水系溶媒中で重合して製造しうる。水系溶媒及び重合方法は、例えば、粒子状バインダーの製造と同様としる。これにより、通常は水系溶媒に水溶性重合体が溶解した水溶液が得られる。こうして得られた水溶液から水溶性重合体を取り出してもよいが、通常は、水系溶媒に溶解した状態の水溶性重合体を用いて負極用スラリー組成物を製造し、その負極用スラリー組成物を用いて負極を製造する。
水溶性重合体の量は、負極活物質100重量部に対して、好ましくは0.1重量部以上、より好ましくは0.5重量部以上、特に好ましくは1重量部以上であり、好ましくは10重量部以下、より好ましくは5重量部以下である。水溶性重合体の量を前記の範囲にすることにより、充放電に伴う負極の膨らみの抑制;二次電池の高温保存特性、高温サイクル特性及び低温出力特性の改善;負極用スラリー組成物を集電体に塗布する際の塗工性の改善;並びに、負極活物質層の集電体への密着性の改善などの上述した効果を安定して発揮できる。
本発明の負極において、負極活物質層には、上述した負極活物質、粒子状バインダー及び水溶性重合体以外に任意成分が含まれていてもよい。任意成分の例を挙げると、粘度調整剤、導電剤、補強材、レベリング剤、電解液添加剤等が挙げられる。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ない。また、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。
電解液添加剤の量は、負極活物質の量100重量部に対して、好ましくは0.01重量部~10重量部である。電解液添加剤の量を上記範囲にすることにより、サイクル特性及び高温特性に優れた二次電池を実現できる。
ナノ微粒子の量は、負極活物質の量100重量部に対して、好ましくは0.01重量部~10重量部である。ナノ微粒子が上記範囲であることにより、負極用スラリー組成物の安定性及び生産性を改善し、高い電池特性を実現できる。
本発明の負極は、通常、集電体と、集電体の表面に設けられた負極活物質層とを含み、この負極活物質層が、負極活物質、粒子状バインダー及び水溶性重合体を含む。集電体は、通常シート状の形状であり、負極活物質層は、かかるシート状の集電体の少なくとも片面に設けられていればよいが、両面に設けられていることが好ましい。
集電体は、負極活物質層との接着強度を高めるため、表面に予め粗面化処理して使用してもよい。粗面化方法としては、例えば、機械的研磨法、電解研磨法、化学研磨法などが挙げられる。機械的研磨法においては、通常、研磨剤粒子を固着した研磨布紙、砥石、エメリバフ、鋼線などを備えたワイヤーブラシ等が使用される。また、負極活物質層の接着強度や導電性を高めるために、集電体の表面に中間層を形成してもよい。
本発明の二次電池用負極は、任意の製造方法により製造しうるが、好ましくは、以下に述べる本発明の二次電池負極用スラリー組成物(以下、適宜「本発明の負極用スラリー組成物」という。)を用い、以下に述べる本発明の二次電池用負極の製造方法(以下、適宜「本発明の負極の製造方法」という。)により製造しうる。
本発明の負極用スラリー組成物は、負極活物質、粒子状バインダー、水溶性重合体を含むスラリー状の組成物である。
本発明の負極用スラリー組成物は、通常、さらに溶媒を含む。溶媒としては、水、又は水と水以外の液体との混合物を用いることが、環境負荷の低減の観点から好ましい。
本発明の負極用スラリー組成物を、集電体の表面に塗布し、必要に応じ乾燥させることにより、集電体の表面に負極活物質層を形成して、本発明の負極を製造することができる。
本発明の二次電池は、正極、負極、電解液及びセパレーターを備え、前記負極が、本発明の負極である。
本発明の負極を備えるので、本発明の二次電池では、充放電に伴う負極の膨らみを抑制できたり、高温環境で保存した場合でも容量を低下し難くしたりできる。また、通常、本発明の二次電池の高温サイクル特性及び低温出力特性を改善したり、負極活物質層の集電体への密着性を高めたりすることもできる。
正極は、通常、集電体と、集電体の表面に形成された、正極活物質及び正極用のバインダーを含む正極活物質層とを備える。
上記の遷移金属としては、例えばTi、V、Cr、Mn、Fe、Co、Ni、Cu、Mo等が挙げられる。
遷移金属硫化物としては、例えば、TiS2、TiS3、非晶質MoS2、FeS等が挙げられる。
層状構造を有するリチウム含有複合金属酸化物としては、例えば、リチウム含有コバルト酸化物(LiCoO2)、リチウム含有ニッケル酸化物(LiNiO2)、Co-Ni-Mnのリチウム複合酸化物、Ni-Mn-Alのリチウム複合酸化物、Ni-Co-Alのリチウム複合酸化物等が挙げられる。
スピネル構造を有するリチウム含有複合金属酸化物としては、例えば、マンガン酸リチウム(LiMn2O4)又はMnの一部を他の遷移金属で置換したLi[Mn3/2M1/2]O4(ここでMは、Cr、Fe、Co、Ni、Cu等)等が挙げられる。
オリビン型構造を有するリチウム含有複合金属酸化物としては、例えば、LiXMPO4(式中、Mは、Mn、Fe、Co、Ni、Cu、Mg、Zn、V、Ca、Sr、Ba、Ti、Al、Si、B及びMoからなる群より選ばれる少なくとも1種を表し、Xは0≦X≦2を満たす数を表す。)で表されるオリビン型燐酸リチウム化合物が挙げられる。
さらに、前記の化合物を部分的に元素置換したものを正極活物質として用いてもよい。また、上記の無機化合物と有機化合物の混合物を正極活物質として用いてもよい。
なお、正極活物質は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
電解液としては、例えば、非水系の溶媒に支持電解質としてリチウム塩を溶解したものを使用しうる。リチウム塩としては、例えば、LiPF6、LiAsF6、LiBF4、LiSbF6、LiAlCl4、LiClO4、CF3SO3Li、C4F9SO3Li、CF3COOLi、(CF3CO)2NLi、(CF3SO2)2NLi、(C2F5SO2)NLiなどのリチウム塩が挙げられる。特に溶媒に溶けやすく高い解離度を示すLiPF6、LiClO4、CF3SO3Liは好適に用いられる。これらは1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。
セパレーターとしては、通常、気孔部を有する多孔性基材を用いる。セパレーターの例を挙げると、(a)気孔部を有する多孔性セパレーター、(b)片面または両面に高分子コート層が形成された多孔性セパレーター、(c)無機セラミック粉末を含む多孔質の樹脂コート層が形成された多孔性セパレーター、などが挙げられる。これらの例としては、ポリプロピレン系、ポリエチレン系、ポリオレフィン系、またはアラミド系多孔性セパレーター、ポリビニリデンフルオリド、ポリエチレンオキシド、ポリアクリロニトリルまたはポリビニリデンフルオリドヘキサフルオロプロピレン共重合体などの固体高分子電解質用またはゲル状高分子電解質用の高分子フィルム;ゲル化高分子コート層がコートされたセパレーター;無機フィラーと無機フィラー用分散剤とからなる多孔膜層がコートされたセパレーター;などが挙げられる。
本発明の二次電池の製造方法は、特に限定されない。例えば、上述した負極と正極とをセパレーターを介して重ね合わせ、これを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、二次電池を製造しうる。さらに、必要に応じてエキスパンドメタル;ヒューズ、PTC素子などの過電流防止素子;リード板などを入れ、電池内部の圧力上昇、過充放電の防止をしてもよい。電池の形状は、例えば、ラミネートセル型、コイン型、ボタン型、シート型、円筒型、角形、扁平型などいずれであってもよい。
以下の説明において、量を表す「%」及び「部」は、別に断らない限り重量基準である。また、以下に説明する操作は、別に断らない限り、常温及び常圧の条件において行った。特に、電池の評価の操作は、別に断らない限り、25℃において行った。
実施例及び比較例における特性の評価は、下記の通り行った。
実施例および比較例で製造した負極を、長さ100mm、幅10mmの長方形に切り出して試験片とした。この試験片を、負極活物質層の表面を下にして、負極活物質層の表面にセロハンテープを貼り付けた。この際、セロハンテープとしてはJIS Z1522に規定されるものを用いた。また、セロハンテープは水平な試験台に固定しておいた。その後、集電体の一端を鉛直上方に引張り速度50mm/分で引っ張って剥がしたときの応力を測定した。この測定を3回行い、その平均値を求めて、当該平均値をピール強度(N/m)とした。ピール強度が大きいほど、負極活物質層の集電体への結着力が大きいこと、すなわち、密着強度が大きいことを示す。
実施例および比較例で製造した負極用スラリー組成物について、B型粘度計により、25℃、回転数60rpmにおける粘度η0を測定した。
その後、負極用スラリー組成物を、5℃で72時間静置したのち、25℃に戻し、再び前記と同様に粘度η1を測定した。静置前後の粘度を比較して、粘度変化率(=(η1-η0)/η0×100)が10%増加未満であればA、10%増加以上~30%増加未満であればB、30%増加以上であればCとした。
実施例および比較例で製造した負極用スラリー組成物を、集電体である厚さ20μmの銅箔の上に、乾燥後の膜厚が150μm程度になるように塗布し、乾燥させた。この乾燥は、銅箔を0.5m/分の速度で60℃のオーブン内を2分間かけて搬送することにより行った。その後、120℃にて2分間加熱処理して負極を得た。得られた負極を10×10cmの寸法で切り出し、目視にて直径0.1mm以上のピンホールの個数を測定した。ピンホールの個数が小さいほど、塗工性に優れることを示す。
(1)高温保存特性
実施例および比較例で製造したラミネート型セルのリチウムイオン二次電池を、25℃環境下で24時間静置させた後に、25℃環境下で、0.1Cの定電流法により、4.2Vに充電し、3.0Vまで放電する充放電の操作を行い、初期容量C0を測定した。さらに、4.2Vに充電し、60℃で7日間保存した後、25℃環境下で0.1Cの定電流法により、4.2Vに充電し、3.0Vまで放電する充放電の操作を行い、高温保存後の容量C1を測定した。高温保存特性は、ΔCS=C1/C0×100(%)で示す容量変化率ΔCSにて評価した。この容量変化率ΔCSの値が高いほど、高温保存特性に優れることを示す。
実施例および比較例で製造したラミネート型セルのリチウムイオン二次電池を、25℃環境下で24時間静置させた後に、25℃環境下で、0.1Cの定電流法により、4.2Vに充電し、3.0Vまで放電する充放電の操作を行い、初期容量C0を測定した。さらに、60℃の環境下で1Cの定電流法により、4.2Vに充電し、3.0Vまで放電する充放電操作を繰り返し、100サイクル後の容量C2を測定した。高温サイクル特性は、ΔCC=C2/C0×100(%)で示す容量変化率ΔCCにて評価した。この容量変化率ΔCCの値が高いほど、高温サイクル特性に優れることを示す。
前記の「(1)高温保存特性」の評価の後でリチウムイオン二次電池のセルを解体し、負極の極板の厚みd1を測定した。リチウムイオン二次電池のセルの作製前における負極の極板の厚みをd0として、負極の極板膨らみ率(d1-d0)/d0×100(%)を算出した。この値が低いほど、極板膨らみ特性に優れることを示す。
実施例および比較例で製造したラミネート型セルのリチウムイオン二次電池を、25℃環境下で24時間静置させた後に、4.2V、1Cの充電レートにて充電の操作を行った。その後、-10℃の環境下で、1Cの放電レートにて放電の操作を行い、放電開始15秒後の電圧V15を測定した。低温出力特性は、ΔV=4.2V-V15(mV)で示す電圧変化ΔVにて評価した。この電圧変化ΔVの値が小さいほど、低温出力特性に優れることを示す。
実施例および比較例で製造した水溶性重合体を、pHが8となるように、10%アンモニア水およびイオン交換水により希釈し、水溶性重合体の1%水溶液を調製した。この水溶液の粘度を、B型粘度計により測定した。
(1-1.水溶性重合体の製造)
攪拌機付き5MPa耐圧容器に、(メタ)アクリル酸エステル単量体としてアクリル酸エチル65.5部、エチレン性不飽和カルボン酸単量体としてメタクリル酸30部、フッ素含有(メタ)アクリル酸エステル単量体としてトリフルオロメチルメタクリレート2.5部、スルホン酸基含有単量体として2-アクリルアミド-2-メチルプロパンスルホン酸2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1.0部、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0.5部を入れ、十分に攪拌した後、60℃に加温して重合を開始した。重合転化率が96%になった時点で冷却し反応を停止して、水溶性重合体を含む水溶液を得た。こうして得られた水溶性重合体を含む水溶液に、10%アンモニア水を添加してpH8に調整し、所望の水溶性重合体を含む水溶液を得た。得られた水溶性重合体の重量平均分子量を測定したところ、12800であった。
得られた水溶性重合体を含む水溶液を試料として、水溶性重合体の1%水溶液の粘度を測定したところ1500mPa・sであった。
攪拌機付き5MPa耐圧容器に、脂肪族共役ジエン単量体である1,3-ブタジエン33部、エチレン性不飽和カルボン酸単量体であるメタクリル酸1.5部、芳香族ビニル系単量体であるスチレン65.5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4部、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0.5部を入れ、十分に攪拌した後、50℃に加温して重合を開始した。重合転化率が96%になった時点で冷却し反応を停止して、スチレンブタジエン共重合体(以下、適宜「SBR」という。)からなる粒子状バインダーを含む水系分散液を得た。こうして得られた粒子状バインダーを含む水系分散液に、5%水酸化ナトリウム水溶液を添加して、pH8に調整後、加熱減圧蒸留によって未反応単量体の除去を行った。その後、30℃以下まで冷却し、所望の粒子状バインダーを含む水系分散液を得た。得られた粒子状バインダーの重量平均分子量を測定したところ、1500000であった。また、レーザー回折散乱方式粒度分布装置により測定した粒子状バインダーの個数平均粒径は、150nmであった。
工程(1-1)で得られた水溶性重合体を含む水溶液を水で希釈して濃度を5%に調整した。
ディスパー付きのプラネタリーミキサーに、負極活物質としてSiOC(体積平均粒子径:12μm)50部及び比表面積4m2/gの人造黒鉛(体積平均粒子径:24.5μm)50部と、上記の水溶性重合体の5%水溶液を固形分相当で1部とをそれぞれ加え、イオン交換水で固形分濃度55%に調整した後、25℃で60分混合した。次に、イオン交換水で固形分濃度52%に調整した後、さらに25℃で15分混合し混合液を得た。
得られた負極用スラリー組成物について、安定性及び塗工性の評価を行った。結果を表1に示す。
工程(1-3)で得られた負極用スラリー組成物を、コンマコーターで、集電体である厚さ20μmの銅箔の上に、乾燥後の膜厚が150μm程度になるように塗布し、乾燥させた。この乾燥は、銅箔を0.5m/分の速度で60℃のオーブン内を2分間かけて搬送することにより行った。その後、120℃にて2分間加熱処理して負極原反を得た。この負極原反をロールプレスで圧延して、負極活物質層の厚みが80μmの負極を得た。
得られた負極について、密着強度の評価を行った。結果を表1に示す。
正極用のバインダーとして、ガラス転移温度Tgが-40℃で、数平均粒子径が0.20μmのアクリレート重合体の40%水分散体を用意した。前記のアクリレート重合体は、アクリル酸2-エチルヘキシル78重量%、アクリロニトリル20重量%、及びメタクリル酸2重量%を含む単量体混合物を乳化重合して得られる共重合体である。
単層のポリプロピレン製セパレーター(幅65mm、長さ500mm、厚さ25μm、乾式法により製造、気孔率55%)を用意した。
電池の外装として、アルミ包材外装を用意した。工程(1-4)で得た負極を4.2mm×4.2mmの矩形に切り出した。工程(1-5)で得た正極を4mm×4mmの矩形に切り出した。工程(1-6)のセパレーターを5mm×5mmの矩形に切り出した。
上記の矩形の正極を、集電体の表面がアルミ包材外装に接するように配置した。矩形の正極の正極活物質層の面上に、矩形のセパレーターを配置した。さらに、矩形のセパレーター上に、上記の矩形の負極を、負極活物質層の表面がセパレーターに向かい合うよう配置した。アルミ包材内に、電解液として濃度1.0MのLiPF6溶液(溶媒はEC/DEC=1/2(体積比))の混合溶媒を充填した。さらに、アルミ包材の開口を密封するために、150℃のヒートシールをしてアルミ外装を閉口し、リチウムイオン二次電池を製造した。
得られた電池について、高温保存特性、高温サイクル特性及び極板膨らみ特性を評価し、更に、低温出力特性を評価した。結果を表1に示す。
また、得られたリチウムイオン二次電池を4.2V、0.1Cの充放電レートで最初に充放電させたときの容量(初期容量)は50mAhであった。
工程(1-1)の水溶性重合体の製造において、スルホン酸基含有単量体として、2-アクリルアミド-2-メチルプロパンスルホン酸に代えてスチレンスルホン酸(実施例2)またはビニルスルホン酸(実施例3)を用いた他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表1に示す。
工程(1-1)の水溶性重合体の製造において、フッ素含有(メタ)アクリル酸エステル単量体として、トリフルオロメチルメタクリレートに代えてトリフルオロメチルアクリレート(実施例4)またはパーフルオロオクチルメタクリレート(実施例5)を用いた他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表1に示す。
工程(1-1)の水溶性重合体の製造において、アクリル酸エチル、メタクリル酸、トリフルオロメチルメタクリレート、及び2-アクリルアミド-2-メチルプロパンスルホン酸の割合を表1及び表2に示す通り変更した他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表1及び表2に示す。
工程(1-3)の負極用スラリー組成物の製造で、負極活物質としてSiOC50部及び人造黒鉛50部に代えて、SiOC100部を用いた他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表2に示す。
工程(1-3)の負極用スラリー組成物の製造で、負極活物質としてSiOC50部及び人造黒鉛50部に代えて、人造黒鉛100部を用いた他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表2に示す。
(15-1.ナノシリカ活物質Aの製造)
平均粒子径3μm、BET比表面積12m2/gの酸化ケイ素粉末(SiOx:x=1.02)を、窒化ケイ素製トレイに200g仕込んだ後、雰囲気を保持できる処理炉内に静置した。次にアルゴンガスを流入させ、処理炉内をアルゴン置換した後、アルゴンガスを2NL/min流入させつつ300℃/hrの昇温速度で1200℃まで昇温し、3時間保持した。保持終了後、降温を開始し、室温到達後、粉末を回収し、Si系活物質Aとした。得られたSi系活物質Aは、平均粒子径3.5μm、BET比表面積11m2/gの粉末であり、この粉末のCu-Kα線によるX線回折パターンより、2θ=28.4°付近のSi(111)に帰属される回折線が存在し、この回折線の半価幅よりシェーラー法により求めた二酸化ケイ素中に分散したケイ素の結晶の大きさが40nmであるケイ素複合体粉末であることが確認された。
工程(1-3)の負極用スラリー組成物の製造で、負極活物質としてSiOC50部及び人造黒鉛50部に代えて、工程(15-1)で得たSi系活物質A 5部及び人造黒鉛95部を用いた他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表2に示す。
(16-1.ナノシリカ活物質Bの製造)
内温800℃の流動層内に多結晶ケイ素微粒子を導入し、モノシランを送入することで製造した粒状多結晶ケイ素をジェットミルを用いて粉砕した後、分級機にて分級し、D50=10.2μmの多結晶ケイ素粉末を得て、これをSi系活物質Bとした。X線回折線の半値全幅よりシェーラー法で、Si系活物質Bの結晶子サイズが44nmであることを確認した。
工程(1-3)の負極用スラリー組成物の製造で、負極活物質としてSiOC50部及び人造黒鉛50部に代えて、工程(16-1)で得たSi系活物質B 5部及び人造黒鉛95部を用いた他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表2に示す。
工程(1-1)の水溶性重合体の製造において、アクリル酸エチル、メタクリル酸、トリフルオロメチルメタクリレート、及び2-アクリルアミド-2-メチルプロパンスルホン酸の割合を表3に示す通り変更した他は、実施例1と同様にして、リチウムイオン二次電池及びその構成要素を製造し評価した。結果を表3に示す。
TFMMA:トリフルオロメチルメタクリレート
TFMA:トリフルオロメチルアクリレート
PFOMA:パーフルオロオクチルメタクリレート
AMPS:2-アクリルアミド-2メチルプロパンスルホン酸
SS:スチレンスルホン酸
VS:ビニルスルホン酸
Si系A:実施例15で製造したナノシリカ活物質A
Si系B:実施例16で製造したナノシリカ活物質B
バインダー:バインダー種別
EA量:アクリル酸エチル添加量(部)
フッ素単量体種類:フッ素含有(メタ)アクリル酸エステル単量体種類
フッ素単量体量:フッ素含有(メタ)アクリル酸エステル単量体添加量(部)
スルホン単量体種類:スルホン酸基含有単量体種類
スルホン単量体量:スルホン酸基含有単量体添加量(部)
MAA量:メタクリル酸添加量(部)
1%水溶液粘度:水溶性重合体の1%水溶液の粘度(mPa・s)
水溶性重合体分子量:水溶性重合体の重量平均分子量
負極活物質:負極活物質種類
活物質割合:それぞれの活物質の添加量(部)
密着強度:負極ピール強度平均値(N/m)
スラリー安定性:粘度変化率の評価結果 A:変化率10%増未満、B:10%増以上30%増未満、C:30%増以上
塗工性:負極用スラリー塗布後のピンホール個数(個)
高温保存特性:電池の容量変化率ΔCS(%)
高温サイクル特性:電池の容量変化率ΔCC(%)
極板膨らみ特性:高温保存特性評価後の負極の極板膨らみ率(%)
低温出力特性:低温での電圧変化ΔV(mV)
表1~表3の結果から明らかな通り、本願実施例1~16においては、本願発明の要件のいずれかを満たさない比較例に比べて、充放電に伴う負極の膨らみが抑制され、且つ各種の特性のいずれについてもバランスよく良好であった。また、水溶性重合体の添加量が少ない実施例8以外の実施例においては、スラリーの安定性にも優れていた。
Claims (11)
- 負極活物質、粒子状バインダー及び水溶性重合体を含む二次電池用負極であって、
前記水溶性重合体が、
スルホン酸基含有単量体単位0.1重量%~15重量%、及び
フッ素含有(メタ)アクリル酸エステル単量体単位0.5重量%~10重量%
を含む共重合体である二次電池用負極。 - 前記水溶性重合体が、エチレン性不飽和カルボン酸単量体単位を含む請求項1に記載の二次電池用負極。
- 前記エチレン性不飽和カルボン酸単量体が、エチレン性不飽和モノカルボン酸単量体である、請求項2記載の二次電池用負極。
- 前記負極活物質が、リチウムを吸蔵及び放出でき、金属を含む、請求項1~3のいずれか1項に記載の二次電池用負極。
- 前記金属が、ケイ素である、請求項4に記載の二次電池用負極。
- 前記粒子状バインダーが、脂肪族共役ジエン単量体単位を含む重合体を含む、請求項1~5のいずれか1項に記載の二次電池用負極。
- 前記脂肪族共役ジエン単量体単位を含む重合体が、芳香族ビニル単量体単位をさらに含む、請求項6に記載の二次電池用負極。
- 正極、負極、電解液及びセパレーターを備え、前記負極が、請求項1~7のいずれか1項に記載の二次電池用負極である、二次電池。
- 負極活物質、粒子状バインダー及び水溶性重合体を含むスラリー組成物であって、
前記水溶性重合体が、
スルホン酸基含有単量体単位0.1重量%~15重量%、
フッ素含有(メタ)アクリル酸エステル単量体単位0.5重量%~10重量%を含む共重合体である二次電池負極用スラリー組成物。 - 前記水溶性重合体が、エチレン性不飽和カルボン酸単量体単位を含む、請求項9に記載の負極用スラリー組成物。
- 請求項9又は10に記載の二次電池負極用スラリー組成物を、集電体上に塗布し、乾燥することを含む、二次電池用負極の製造方法。
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