WO2016171028A1 - 非水電解質二次電池電極用バインダー及びその用途 - Google Patents
非水電解質二次電池電極用バインダー及びその用途 Download PDFInfo
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- WO2016171028A1 WO2016171028A1 PCT/JP2016/061729 JP2016061729W WO2016171028A1 WO 2016171028 A1 WO2016171028 A1 WO 2016171028A1 JP 2016061729 W JP2016061729 W JP 2016061729W WO 2016171028 A1 WO2016171028 A1 WO 2016171028A1
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- secondary battery
- binder
- monomer
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- nonaqueous electrolyte
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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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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/04—Acids; Metal salts or ammonium salts thereof
- C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F220/10—Esters
- C08F220/26—Esters containing oxygen in addition to the carboxy oxygen
- C08F220/28—Esters containing oxygen in addition to the carboxy oxygen containing no aromatic rings in the alcohol moiety
- C08F220/281—Esters containing oxygen in addition to the carboxy oxygen containing no aromatic rings in the alcohol moiety and containing only one oxygen, e.g. furfuryl (meth)acrylate or 2-methoxyethyl (meth)acrylate
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- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
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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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0568—Liquid materials characterised by the solutes
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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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0569—Liquid materials characterised by the solvents
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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- H—ELECTRICITY
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- 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
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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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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- 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
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
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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
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
- H01M2300/0028—Organic electrolyte characterised by the solvent
- H01M2300/0037—Mixture of solvents
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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
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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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
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
Definitions
- the present invention relates to a binder for a non-aqueous electrolyte secondary battery electrode that can be used for a lithium ion secondary battery or the like and its use. Specifically, a binder for a non-aqueous electrolyte secondary battery electrode, a composition for a non-aqueous electrolyte secondary battery electrode mixture layer obtained using the binder, a non-aqueous electrolyte secondary battery electrode, and a non-aqueous electrolyte two Next battery.
- a lithium ion secondary battery As a nonaqueous electrolyte secondary battery, for example, a lithium ion secondary battery is well known. Lithium ion secondary batteries are superior in energy density, output density, charge / discharge cycle characteristics, etc. compared to other secondary batteries such as lead-acid batteries, so mobiles such as smartphones, tablet terminals and laptop computers Used in terminals, it contributes to reducing the size and weight of terminals and improving their performance. On the other hand, secondary batteries for electric vehicles and hybrid vehicles (on-vehicle secondary batteries) have not yet achieved sufficient performance in terms of input / output characteristics, required charging time, and the like.
- the non-aqueous electrolyte secondary battery is composed of a pair of electrodes disposed via a separator and a non-aqueous electrolyte solution.
- the electrode is composed of a current collector and a mixture layer formed on the surface thereof, and the mixture layer is coated with a composition (slurry) for the electrode mixture layer containing an active material and a binder on the current collector. And formed by drying or the like.
- a composition for an electrode mixture layer there is an increasing demand for water-based treatment from the viewpoints of environmental protection and cost reduction.
- SBR styrene butadiene rubber
- CMC carboxymethyl cellulose
- a binder is used.
- further improvement is desired in order to cope with high-rate characteristics and cycle characteristics required for in-vehicle applications.
- a solvent-based binder such as polyvinylidene fluoride (PVDF) using an organic solvent such as N-methyl-2-pyrrolidone (NMP) is mainly used, and the above requirements are sufficiently satisfied. No water-based binder has been proposed.
- Components constituting the lithium ion secondary battery electrode include active materials such as graphite and hard carbon (HC), and carbon-based materials such as conductive additives such as ketjen black (KC) and acetylene black (AB). Often used. In general, these carbon-based materials have poor wettability to an aqueous medium, and in order to obtain a composition for an electrode mixture layer that is uniform and excellent in dispersion stability, an aqueous system excellent in the dispersion stabilization effect of the carbon-based material is used. A binder is desired. In the electrode manufacturing process, operations such as winding, rewinding, cutting, and winding are performed.
- Patent Document 1 discloses an acrylic acid polymer crosslinked with polyalkenyl ether as a binder for forming a negative electrode coating film of a lithium ion secondary battery. Further, in Patent Document 2, a polymer obtained by crosslinking polyacrylic acid with a specific crosslinking agent is used as a binder, so that the electrode structure is not destroyed even when an active material containing silicon is used. It is described that an excellent capacity retention ratio can be obtained.
- Patent Document 3 includes a structural unit derived from an ethylenically unsaturated carboxylate monomer and a structural unit derived from an ethylenically unsaturated carboxylic acid ester monomer, and contains a water-soluble polymer having a specific aqueous solution viscosity.
- An aqueous electrode binder for a secondary battery is disclosed.
- Patent Document 1 and Patent Document 2 both disclose the use of cross-linked polyacrylic acid as a binder, but are not sufficient in terms of flexibility, and improvements in bending resistance and the like are desired. It was a thing. Further, in the detailed description of the invention of Patent Document 1, when the blending composition ratio of the acrylic acid polymer in the binder exceeds 95% by weight, the particle surface of the carbon material is coated to reduce the conductivity. It has been described that it has a problem of inhibiting the movement of lithium ions. The binder described in Patent Document 3 is improved in terms of flexibility, but is not sufficiently satisfactory in terms of dispersion stability and binding properties. Also, none of Patent Documents 1 to 3 describes high rate characteristics.
- the present invention has been made in view of such circumstances, and it is possible to obtain an electrode that satisfies both electrode characteristics such as high-rate characteristics and durability (cycle characteristics) and has excellent bending resistance.
- Another object of the present invention is to provide a binder for a nonaqueous electrolyte secondary battery electrode and a method for producing an acrylic cross-linked polymer used in the binder.
- Another object of the present invention is to provide a composition for a non-aqueous electrolyte secondary battery electrode mixture layer, a non-aqueous electrolyte secondary battery electrode and a non-aqueous electrolyte secondary battery obtained using the binder. It is.
- the amount of the binder serving as a resistance component is as small as possible. Therefore, it is possible to stably disperse the active material and the conductive additive even in a small amount, and the binding force between the active materials and between the active material and the current collector is large (as a result, the mixture layer and the current collector Therefore, a binder that is excellent in durability of the obtained electrode is desired. Furthermore, the binder is required to be such that it does not hinder the entry or escape of lithium ions even if it is present on the active material surface.
- a binder that reduces resistance (interface resistance) associated with penetration of lithium ions into the active material or escape from the active material due to excellent lithium ion desolvation effect and lithium ion conductivity is preferable.
- a binder having high flexibility is required.
- the inventors of the present invention have a specific value for the SP value of the ethylenically unsaturated carboxylic acid monomer and the homopolymer, and are ethylenic having no carboxyl group.
- An acrylic cross-linked polymer having an unsaturated monomer as a constituent monomer, and an acrylic cross-linked polymer or a salt thereof having a high ratio of a monomer having an acryloyl group in the total amount of the constituent monomer In the case of the binder to be included, the present inventors have obtained knowledge that the high rate characteristics can be improved since excellent binding properties are exhibited even in a small amount.
- the said binder is excellent in binding property and flexibility, it discovered that it was effective also with respect to the durability (cycle characteristic) and the improvement of bending resistance of an electrode. Furthermore, since the composition for a mixture layer containing the binder has a viscosity suitable for electrode preparation, it is possible to obtain a nonaqueous electrolyte secondary battery electrode having a uniform mixture layer and good electrode characteristics. It was. The present invention has been completed based on these findings.
- a binder for a nonaqueous electrolyte secondary battery electrode containing an acrylic crosslinked polymer or a salt thereof The acrylic cross-linked polymer has (a) component: 30 to 90% by weight of ethylenically unsaturated carboxylic acid monomer and (b) component: homopolymer SP value in all the constituent monomers. 9.0 to 12.5 (cal / cm 3 ) 1/2 and an ethylenically unsaturated monomer having no carboxyl group in the range of 10 to 70% by weight,
- the acrylic cross-linked polymer is cross-linked with a cross-linkable monomer, and the amount of the cross-linkable monomer used is 0.1 to 2 with respect to the total amount of non-cross-linkable monomers.
- Non-aqueous electrolyte secondary battery electrode binder [5] The binder for a nonaqueous electrolyte secondary battery electrode according to any one of [1] to [4], wherein the component (b) includes a monomer having an ether group. [6] The binder for a nonaqueous electrolyte secondary battery electrode according to any one of [1] to [5], wherein the component (b) includes a monomer having an amide group.
- a method for producing an acrylic crosslinked polymer used for a binder for a nonaqueous electrolyte secondary battery electrode (A) Component: 30 to 90% by weight of ethylenically unsaturated carboxylic acid monomer, and (b) Component: homopolymer SP value is 9.0 to 12.5 (cal / cm 3 ) 1/2 And an ethylenically unsaturated monomer having no carboxyl group in the range of 10 to 70% by weight, Furthermore, a method for producing an acrylic crosslinked polymer by precipitation polymerization of a monomer component having an acryloyl group-containing monomer content of 70% by weight or more in an aqueous medium.
- a composition for a non-aqueous electrolyte secondary battery electrode mixture layer comprising the binder, active material and water according to any one of [1] to [7] above.
- a non-aqueous electrolyte secondary battery electrode comprising a mixture layer formed on the current collector surface from the composition for a non-aqueous electrolyte secondary battery electrode mixture layer according to [9].
- a nonaqueous electrolyte secondary battery comprising the nonaqueous electrolyte secondary battery electrode according to [10], a separator, and a nonaqueous electrolyte solution.
- the binder for nonaqueous electrolyte secondary battery electrodes of the present invention is excellent in flexibility and exhibits excellent binding properties even in a small amount. For this reason, it becomes possible to reduce the binder content in the composition for the mixture layer, and it is possible to obtain an electrode having high high-rate characteristics and excellent durability (cycle characteristics) and bending resistance. Moreover, since the composition for a nonaqueous electrolyte secondary battery electrode mixture layer of the present invention has a viscosity suitable for electrode production, the nonaqueous electrolyte secondary battery electrode has a uniform mixture layer and good electrode characteristics. Can be obtained.
- (meth) acryl means acryl and / or methacryl
- (meth) acrylate means acrylate and / or methacrylate
- the “(meth) acryloyl group” means an acryloyl group and / or a methacryloyl group.
- the binder for nonaqueous electrolyte secondary battery electrodes of the present invention contains an acrylic crosslinked polymer or a salt thereof, and can be made into an electrode mixture layer composition by mixing with an active material and water.
- the composition described above may be in a slurry state that can be applied to the current collector, or may be prepared in a wet powder state so that it can be applied to pressing on the surface of the current collector.
- a nonaqueous electrolyte secondary battery electrode of the present invention is obtained by forming a mixture layer formed from the above composition on the surface of a current collector such as a copper foil or an aluminum foil.
- Binder for secondary battery electrode method for producing acrylic cross-linked polymer used for the binder, composition for non-aqueous electrolyte secondary battery electrode mixture layer obtained using the binder, non-aqueous electrolyte secondary battery
- the electrode and the nonaqueous electrolyte secondary battery will be described in detail.
- the binder of the present invention contains an acrylic crosslinked polymer or a salt thereof.
- the acrylic cross-linked polymer has, as its constituent monomers, an SP value of (a) component: ethylenically unsaturated carboxylic acid monomer and (b) component: homopolymer of 9.0-12. 5 (cal / cm 3 ) 1/2 and an ethylenically unsaturated monomer having no carboxyl group.
- the constituent monomer is such that the proportion of the monomer having an acryloyl group in the total amount is 70% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more. .
- the ratio of the monomer having an acryloyl group is 70% by weight or more, the polymerization rate is sufficiently high and a polymer having a long primary chain length can be obtained. Thus, a binder having a good binding property and dispersion stability can be obtained. Can do.
- the upper limit of the ratio of the monomer having an acryloyl group is 100% by weight.
- ethylenically unsaturated carboxylic acid monomers include acrylic acid; acrylamide alkyl carboxylic acids such as acrylamide hexanoic acid and acrylamide dodecanoic acid; monohydroxy succinate Examples thereof include ethylenically unsaturated monomers having a carboxyl group such as ethyl acrylate, ⁇ -carboxy-caprolactone monoacrylate, ⁇ -carboxyethyl acrylate and the like, and (partially) alkali neutralized products thereof. You may use individually and may be used in combination of 2 or more type.
- acrylic acid is preferable in that the primary chain length of the obtained polymer is long and the binding force of the binder is good.
- the types of salts include alkali metal salts such as lithium, sodium and potassium; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as magnesium salts and aluminum salts; ammonium salts and organic amine salts Is mentioned.
- alkali metal salt and a magnesium salt are preferable, an alkali metal salt is more preferable, and a lithium salt is most preferable because an adverse effect on battery characteristics is less likely to occur.
- the ratio of the ethylenically unsaturated carboxylic acid monomer (component (a)) to the total amount of the constituent monomers of the acrylic crosslinked polymer is in the range of 30 to 90% by weight, and 40 to 90% by weight. The range is preferable, and the range of 50 to 90% by weight is more preferable.
- the acrylic cross-linked polymer has a carboxyl group, the adhesion to the current collector is improved, and since the lithium ion desolvation effect and ion conductivity are excellent, the resistance is small, and an electrode with high rate characteristics is excellent. can get. Moreover, since water swelling property is provided, dispersion stability of the active material etc. in a mixture layer composition can be improved.
- the ratio of the ethylenically unsaturated carboxylic acid monomer in the total amount of the constituent monomers is less than 30% by weight, the dispersion stability, the binding property and the durability as a battery may be insufficient. Moreover, when it exceeds 90 weight%, there exists a possibility that the bending resistance of the electrode obtained and the high-rate characteristic as a battery may become inadequate.
- acryloyl Specific compounds having a group include methyl acrylate (SP value: 10.6), ethyl acrylate (SP value: 10.2), butyl acrylate (SP value: 9.77), isobutyl acrylate ( SP value: 9.57), 2-ethylhexyl acrylate (SP value: 9.22), cyclohexyl acrylate (SP value: 10.8), 2-methoxyethyl acrylate (SP value: 10.2), acrylic Acrylic acid esters such as ethoxyethoxyethyl acid (SP value: 9.82); isopropylacrylamide (SP value: 12.0), t-butylacrylamide (SP value: 11.4), N- N-alkylacrylamide compounds such as n-butoxymethylacrylamide (SP value: 11.5) and
- SP value described about each compound was calculated based on the method which Fedors advocated later mentioned.
- compounds having an ether bond such as alkoxyalkyl acrylates such as 2-methoxyethyl acrylate and ethoxyethoxyethyl acrylate are preferred, since lithium ion conductivity is high and high rate characteristics are further improved.
- the acid 2-methoxyethyl is more preferred.
- compounds having an amide group such as an N-alkylacrylamide compound and an N, N-dialkylacrylamide compound are preferable in terms of further improving the binding property.
- a compound having a glass transition temperature (Tg) of the homopolymer of 0 ° C. or lower is preferable in that the obtained electrode has good bending resistance.
- the SP value of the above homopolymer in the total amount of constituent monomers of the acrylic crosslinked polymer is 9.0 to 12.5 (cal / cm 3 ) 1/2 and ethylenic acid having no carboxyl group
- the proportion of the unsaturated monomer (component (b)) is in the range of 10 to 70% by weight, preferably in the range of 10 to 60% by weight, more preferably in the range of 10 to 50% by weight, and 20 to 40% by weight. % Range is more preferred.
- the acrylic cross-linked polymer is polyacrylic acid consisting only of the component (a)
- the affinity for the electrolytic solution is not so high.
- the above component (b) whose homopolymer has an SP value of 9.0 to 12.5 (cal / cm 3 ) 1/2 is close to the SP value of the electrolytic solution, so the component (b) is copolymerized.
- the affinity for the electrolytic solution is increased, and the acrylic crosslinked polymer is appropriately plasticized.
- the proportion of the component (b) is less than 10% by weight, the above effect may not be sufficiently obtained.
- the main compounds used in the electrolyte and their SP values include ethylene carbonate (SP value: 14.7, hereinafter also referred to as “EC”), propylene carbonate (SP value: 13.3, hereinafter also referred to as “PC”).
- DMC Dimethyl carbonate
- DEC diethyl carbonate
- EMC ethyl methyl carbonate
- non-crosslinkable monomers other than the above components (a) and (b) can be used in combination as monomer components.
- Other non-crosslinkable monomers include methacrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, monobutyl itaconic acid, monobutyl maleate, cyclohexanedicarboxylic acid and other vinyl-based monomers.
- a crosslinkable monomer in addition to the non-crosslinkable monomer, a crosslinkable monomer may be used.
- the crosslinkable monomer include a polyfunctional polymerizable monomer having two or more polymerizable unsaturated groups, and a monomer having a self-crosslinkable functional group such as a hydrolyzable silyl group.
- the polyfunctional polymerizable monomer is a compound having two or more polymerizable functional groups such as (meth) acryloyl group and alkenyl group in the molecule, and is a polyfunctional (meth) acrylate compound, polyfunctional alkenyl compound, ( Examples include compounds having both a (meth) acryloyl group and an alkenyl group.
- These compounds may be used alone or in combination of two or more.
- a compound having one or more alkenyl groups in the molecule such as a polyfunctional alkenyl compound and a compound having both a (meth) acryloyl group and an alkenyl group is preferable in that a uniform crosslinked structure can be easily obtained.
- a compound having both a (meth) acryloyl group and an alkenyl group is more preferable because the reactivity is good and an unreacted product hardly remains.
- the coating properties of the mixture layer composition and This is particularly preferable since the binding property and the bending resistance of the obtained electrode are more excellent.
- Polyfunctional (meth) acrylate compounds include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di ( Di (meth) acrylates of dihydric alcohols such as (meth) acrylate; trimethylolpropane tri (meth) acrylate, trimethylolpropane ethylene oxide modified tri (meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol tri ( Poly (meth) acrylates such as tri (meth) acrylates and tetra (meth) acrylates of trihydric or higher polyhydric alcohols such as (meth) acrylates and pentaerythritol tetra (meth) acrylates And the like can be given Relate.
- polyfunctional alkenyl compound examples include trimethylolpropane diallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, polyallyl saccharose and the like; polyfunctional allyl compounds such as diallyl phthalate; divinyl Examples thereof include polyfunctional vinyl compounds such as benzene.
- Examples of the compound having both (meth) acryloyl group and alkenyl group include allyl (meth) acrylate, isopropenyl (meth) acrylate, butenyl (meth) acrylate, pentenyl (meth) acrylate, (meth) acrylic acid. 2- (2-vinyloxyethoxy) ethyl and the like can be mentioned.
- Examples of other polyfunctional polymerizable monomers include bisamides such as methylene bisacrylamide and hydroxyethylene bisacrylamide.
- the monomer having a crosslinkable functional group capable of self-crosslinking include hydrolyzable silyl group-containing vinyl monomers, N-methylol (meth) acrylamide, N-methoxyalkyl (meth) acrylate, and the like. Is mentioned. These compounds can be used alone or in combination of two or more.
- the hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group.
- vinyl silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinyldimethylmethoxysilane
- silyl such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, and methyldimethoxysilylpropyl acrylate Group-containing acrylic acid esters
- silyl group-containing methacrylates such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, dimethylmethoxysilylpropyl methacrylate
- trimethoxysilylpropyl vinyl ether etc.
- the amount of the cross-linkable monomer used is a monomer other than the cross-linkable monomer (non-cross-linkable single monomer).
- Body is preferably 0.1 to 2.0 mol%, more preferably 0.3 to 1.5 mol%. If the usage-amount of a crosslinkable monomer is the said range, the binder which has the more outstanding binding force can be obtained.
- the acrylic cross-linked polymer of the present invention may be cross-linked by a compound having two or more functional groups capable of reacting with a carboxyl group introduced into the polymer in addition to the cross-linkable monomer.
- the compound having two or more functional groups capable of reacting with a carboxyl group include the following compounds. i) A compound that forms a covalent bond with a carboxyl group such as an epoxy group, a carbodiimide group, or an oxazoline group. ii) A compound having Ca 2+ , Mg 2+ and the like and forming an ionic bond with a carboxyl group. iii) A compound having Zn 2+ , Al 3+ , Fe 3+ and the like and forming a coordinate bond with a carboxyl group.
- the viscosity is preferably in the range of 1,000 to 40,000 mPa ⁇ s.
- the viscosity is measured by the B-type viscosity at the liquid temperature 25 (rotor rotation speed 20 rpm).
- the viscosity of the 0.5 wt% aqueous dispersion is more preferably in the range of 2,000 to 40,000 mPa ⁇ s, and still more preferably in the range of 5,000 to 40,000 mPa ⁇ s.
- the viscosity is 1,000 mPa ⁇ s or more, it is possible to obtain an electrode having a uniform mixture layer by sufficiently exhibiting dispersion stability of the active material or the like.
- the viscosity is 40,000 mPa ⁇ s or less, the kneading operation in preparing the composition for electrode mixture layer is easy, and a uniform mixture layer composition is obtained.
- the cross-linked polymer is not neutralized or has a neutralization degree of less than 90 mol%, it is neutralized in an aqueous medium with an alkali compound to a neutralization degree of 90 mol%, and after making a 0.5 wt% aqueous dispersion, the viscosity is taking measurement.
- the toughness increases, it becomes possible to obtain high binding properties, and the viscosity of the aqueous dispersion increases.
- a crosslinked polymer (salt) obtained by subjecting a polymer having a long primary chain length to a relatively small amount of crosslinking exists as a microgel body swollen in water in water.
- the viscosity of the aqueous dispersion also increases.
- the water swellability of the crosslinked polymer is limited, and as a result, the viscosity of the aqueous dispersion tends to decrease.
- a thickening effect and a dispersion stabilizing effect are expressed by the interaction of the microgel bodies.
- the interaction of the microgel body varies depending on the water swelling degree of the microgel body and the strength of the microgel body, and these are controlled by the crosslinking degree of the crosslinked polymer.
- the degree of crosslinking is too low, the strength of the microgel is insufficient, and the dispersion stabilizing effect and the binding property may be insufficient.
- the degree of crosslinking is too high, the degree of swelling of the microgel may be insufficient and the dispersion stabilizing effect and binding properties may be insufficient.
- the cross-linked polymer is desirably a micro-crosslinked polymer obtained by appropriately crosslinking a polymer having a sufficiently long primary chain length.
- the degree of crosslinking of the crosslinked polymer of the present invention is relatively low, even an aqueous dispersion having a low concentration of 0.5% by weight exhibits a viscosity of 1,000 mPa ⁇ s or more due to the packing of the microgel. Therefore, it is assumed that the primary chain length is sufficiently long and has an appropriate degree of crosslinking. Since the binder made of such a crosslinked polymer exhibits excellent binding properties, the amount of the binder used can be reduced, and the high rate characteristics of the electrode can be improved.
- the crosslinked polymer of the present invention is used as a salt form in which an acid group such as a carboxyl group derived from an ethylenically unsaturated carboxylic acid monomer is neutralized so that the degree of neutralization is 20 to 100 mol%. Is preferred.
- the neutralization degree is more preferably 50 to 100 mol%, and further preferably 60 to 95 mol%. When the degree of neutralization is 20 mol% or more, water swellability is good and a dispersion stabilizing effect is easily obtained.
- the acrylic crosslinked polymer of the present invention can use a known polymerization method such as solution polymerization, precipitation polymerization, suspension polymerization, reverse phase emulsion polymerization, etc., but has a long primary chain length and is appropriately crosslinked.
- Precipitation polymerization is preferred in that the produced polymer can be produced efficiently.
- Precipitation polymerization is a method for producing a polymer by carrying out a polymerization reaction in a solvent that dissolves an unsaturated monomer as a raw material but does not substantially dissolve the produced polymer.
- the polymer particles become larger due to aggregation and growth, and a dispersion of polymer particles in which primary particles of several tens to several hundreds of nm are aggregated to several ⁇ m to several tens of ⁇ m is obtained.
- a dispersion stabilizer can also be used to control the particle size of the polymer.
- the polymerization solvent may be a solvent selected from water and various organic solvents in consideration of the type of monomer used. In order to obtain a polymer having a longer primary chain length, it is preferable to use a solvent having a small chain transfer constant.
- specific polymerization solvents when the ethylenically unsaturated carboxylic acid monomer is polymerized in an unneutralized state, examples thereof include benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane, and n-heptane. These can be used alone or in combination of two or more.
- water-soluble solvents such as methanol, t-butyl alcohol, acetone and tetrahydrofuran can be used.
- methanol, t-butyl alcohol, acetone and tetrahydrofuran can be used.
- One of these may be used alone or 2
- a combination of more than one species can be used.
- the water-soluble solvent refers to a solvent having a solubility in water at 20 ° C. of more than 10 g / 100 ml.
- a (partial) neutralized product of an ethylenically unsaturated carboxylic acid monomer is precipitated in an aqueous medium containing water and a water-soluble solvent because a polymer having excellent dispersion stability of the active material is obtained.
- a polymerization method is preferred. At this time, by controlling the type and amount of the water-soluble solvent and the amount of water according to the type and amount of the monomer used, the precipitation and aggregation of the polymer are controlled, and the dispersion stability of the precipitated particles is ensured. Thus, the polymerization can be completed stably.
- the ratio of the water-soluble solvent contained in the aqueous medium is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and still more preferably 90 to 100% by weight with respect to the total amount of the aqueous medium.
- the polymerization initiator may be a known polymerization initiator such as an azo compound, an organic peroxide, or an inorganic peroxide, but is not particularly limited.
- the conditions of use can be adjusted by a known method such as thermal initiation, redox initiation using a reducing agent in combination, UV initiation, or the like so as to obtain an appropriate radical generation amount.
- thermal initiation redox initiation using a reducing agent in combination
- UV initiation or the like so as to obtain an appropriate radical generation amount.
- Examples of the azo compound include 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (N-butyl-2-methylpropionamide), 2- (tert-butylazo) -2. -Cyanopropane, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (2-methylpropane), etc., and one or more of these are used be able to.
- organic peroxide examples include 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane (manufactured by NOF Corporation, trade name “Pertetra A”), 1,1-di (t- Hexylperoxy) cyclohexane (same as “Perhexa HC”), 1,1-di (t-butylperoxy) cyclohexane (same as “PerhexaC”), n-butyl-4,4-di (t-butylperoxy) Valerate ("Perhexa V"), 2,2-di (t-butylperoxy) butane ("Perhexa 22"), t-butyl hydroperoxide ("Perbutyl H”), cumene hydroperoxide (Japan) Made by Oil Co., Ltd., trade name “Park Mill H”), 1,1,3,3-tetramethylbutyl hydroperoxide (“Perocta H”), t-
- inorganic peroxide examples include potassium persulfate, sodium persulfate, and ammonium persulfate.
- potassium persulfate sodium persulfate
- sodium persulfate sodium persulfate
- ammonium persulfate sodium sulfite, sodium thiosulfate, sodium formaldehyde sulfoxylate, ascorbic acid, sulfurous acid gas (SO 2 ), ferrous sulfate and the like can be used as a reducing agent.
- the preferred use amount of the polymerization initiator is 0.001 to 2 parts by weight, more preferably 0.005 to 1 part by weight, further preferably 100 parts by weight based on the total amount of monomer components to be used. Is 0.01 to 0.1 parts by weight.
- the amount of the polymerization initiator used is 0.001 part or more, the polymerization reaction can be stably performed, and when it is 2 parts or less, a polymer having a long primary chain length is easily obtained.
- the concentration of the monomer component is usually in the range of about 2 to 30% by weight.
- Polymerization takes place at The monomer concentration at the start of polymerization is preferably 5 to 30% by weight, more preferably 15 to 30% by weight, and even more preferably 20 to 30% by weight.
- the polymerization temperature is preferably 0 to 100 ° C., more preferably 20 to 80 ° C., although it depends on conditions such as the type and concentration of the monomer used.
- the polymerization temperature may be constant or may change during the polymerization reaction.
- the polymerization time is preferably 1 minute to 10 hours, more preferably 10 minutes to 5 hours, and further preferably 30 minutes to 2 hours.
- composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention includes the binder containing the acrylic crosslinked polymer and a salt thereof, an active material, and water.
- active materials a lithium salt of a transition metal oxide is mainly used as a positive electrode active material.
- a layered rock salt type and a spinel type lithium-containing metal oxide can be used.
- Specific compounds of the positive electrode active material of layered rock-salt, lithium cobaltate, lithium nickelate, and, NCM ⁇ Li (Ni x, Co y, Mn z), x + y + z 1 ⁇ called ternary and NCA ⁇ Li (Ni 1-ab Co a Al b ) ⁇ and the like.
- the spinel positive electrode active material include lithium manganate.
- oxides, phosphates, silicates, sulfur and the like are used, and examples of the phosphate include olivine type lithium iron phosphate.
- the positive electrode active material one of the above may be used alone, or two or more may be used in combination as a mixture or a composite.
- the dispersion When the layered rock salt type positive electrode active material is dispersed in water, the dispersion exhibits alkalinity by exchanging lithium ions on the surface of the active material and hydrogen ions in water. For this reason, there exists a possibility that the aluminum foil (Al) etc. which are general collector materials for positive electrodes may be corroded. In such a case, it is preferable to neutralize the alkali content eluted from the active material by using an unneutralized or partially neutralized crosslinked polymer as a binder. The amount of unneutralized or partially neutralized cross-linked polymer is used so that the amount of unneutralized carboxyl groups in the cross-linked polymer is equal to or greater than the amount of alkali eluted from the active material. It is preferable.
- any positive electrode active material has low electrical conductivity, it is common to add a conductive auxiliary agent.
- the conductive assistant include carbon-based materials such as carbon black, carbon nanotube, carbon fiber, graphite fine powder, and carbon fiber. Among these, carbon black, carbon nanotube, and carbon fiber are easy to obtain excellent conductivity. Are preferred. Moreover, as carbon black, ketjen black and acetylene black are preferable.
- the conductive assistant one of the above may be used alone, or two or more may be used in combination.
- the amount of the conductive aid used is preferably 2 to 20% by weight and more preferably 2 to 10% by weight with respect to the total amount of the active material from the viewpoint of achieving both conductivity and energy density.
- the positive electrode active material may be a surface coated with a conductive carbon-based material.
- examples of the negative electrode active material include carbon materials, lithium metals, lithium alloys, metal oxides, and the like, and one or more of them can be used in combination.
- active materials composed of carbon-based materials such as natural graphite, artificial graphite, hard carbon, and soft carbon (hereinafter, also referred to as “carbon-based active material”) are preferable, graphite such as natural graphite and artificial graphite, and Hard carbon is more preferable.
- carbon-based active material such as natural graphite, artificial graphite, hard carbon, and soft carbon
- graphite such as natural graphite and artificial graphite
- Hard carbon is more preferable.
- spheroidized graphite is preferably used from the viewpoint of battery performance, and the preferred particle size range is 1 to 20 ⁇ m, and the more preferred range is 5 to 15 ⁇ m.
- silicon has a higher capacity than graphite, and an active material composed of silicon-based materials such as silicon, silicon alloys and silicon oxides such as silicon monoxide (SiO) (hereinafter referred to as “silicon-based active material”).
- silicon-based active material has a high capacity, but has a large volume change due to charge / discharge. For this reason, it is preferable to use together with the carbon-based active material.
- the compounding amount of the silicon-based active material is large, the electrode material may be collapsed and the cycle characteristics (durability) may be greatly reduced.
- the amount used is preferably 60% by mass or less, and more preferably 30% by mass or less with respect to the carbon-based active material.
- the carbon-based active material itself has good electrical conductivity, it is not always necessary to add a conductive additive.
- a conductive additive is added for the purpose of further reducing resistance, the amount used is preferably 10% by weight or less, preferably 5% by weight or less based on the total amount of the active material from the viewpoint of energy density. Is more preferable.
- the amount of the active material used is preferably in the range of 10 to 75% by weight, preferably 30 to 65% by weight, based on the total amount of the composition. More preferably, it is the range.
- the amount of the active material used is 10% by weight or more, the migration of the binder and the like is suppressed, and the medium drying cost is advantageous.
- it is 75 weight% or less, the fluidity
- the amount of the active material used is preferably in the range of 60 to 97% by weight, preferably 70 to 90% by weight with respect to the total amount of the composition. A range is more preferable. Further, from the viewpoint of energy density, it is preferable that the non-volatile components other than the active material such as the binder and the conductive assistant are as small as possible within a range in which necessary binding properties and conductivity are ensured.
- the composition for a nonaqueous electrolyte secondary battery electrode mixture layer of the present invention uses water as a medium.
- water-soluble organic solvents such as lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, tetrahydrofuran, N-methylpyrrolidone, etc. It is good also as a mixed solvent.
- the proportion of water in the mixed medium is preferably 50% by weight or more, and more preferably 70% by weight or more.
- the content of the medium containing water in the entire composition is determined from the viewpoints of slurry coating properties, energy costs required for drying, and productivity. Is preferably in the range of 25 to 90% by weight, more preferably in the range of 35 to 70% by weight. Further, in the case of a pressable wet powder state, the content of the medium is preferably in the range of 3 to 40% by weight, more preferably in the range of 10 to 30% by weight from the viewpoint of the uniformity of the mixture layer after pressing. .
- the amount of the crosslinked polymer and its salt used in the composition for electrode mixture layer of the present invention is 0.5 to 5.0% by weight based on the total amount of the active material.
- the amount used is preferably 1.0 to 5.0% by weight, more preferably 1.5 to 5.0% by weight, and still more preferably 2.0 to 5.0 parts by weight.
- the amount of the crosslinked polymer and its salt used is less than 0.5% by weight, sufficient binding properties may not be obtained. Further, the dispersion stability of the active material or the like becomes insufficient, and the uniformity of the formed mixture layer may be lowered.
- the usage-amount of a crosslinked polymer and its salt exceeds 5.0 weight%, the composition for electrode mixture layers may become high viscosity, and the coating property to a collector may fall. As a result, bumps and irregularities are generated in the obtained mixture layer, which may adversely affect the electrode characteristics. In addition, the interface resistance increases, and there is a concern that the high-rate characteristics will deteriorate. If the use amount of the crosslinked polymer and its salt is within the above range, a composition having excellent dispersion stability can be obtained, and a mixture layer having extremely high adhesion to the current collector can be obtained. As a result, the durability of the battery is improved. Furthermore, since the amount used is as small as 0.5 to 5.0% by weight with respect to the active material, and the polymer has a carboxy anion, an electrode having low interface resistance and excellent high rate characteristics can be obtained. .
- the binder of the present invention may be composed of only the above-mentioned acrylic crosslinked polymer or a salt thereof, but other than this, such as styrene / butadiene latex (SBR), acrylic latex, and polyvinylidene fluoride latex.
- SBR styrene / butadiene latex
- acrylic latex acrylic latex
- polyvinylidene fluoride latex Other binder components may be used in combination.
- the amount used is preferably 5% by weight or less, more preferably 2% by weight or less, still more preferably 1% by weight or less based on the active material. .
- the amount of other binder components used exceeds 5% by weight, the resistance increases and the high rate characteristics may be insufficient.
- the composition for a non-aqueous electrolyte secondary battery electrode mixture layer of the present invention comprises the above active material, water and binder as essential components, and by mixing each component using known means. can get.
- the mixing method of each component is not particularly limited, and a known method can be adopted.
- a method of mixing and dispersing and kneading with a dispersion medium such as the above is preferable.
- the composition for an electrode mixture layer is obtained in a slurry state, it is preferable to finish the slurry without any poor dispersion or aggregation.
- a mixing means known mixers such as a planetary mixer, a thin film swirl mixer, and a self-revolving mixer can be used, but a thin film swirl mixer is used because a good dispersion state can be obtained in a short time. It is preferable to carry out.
- a thin film swirling mixer it is preferable to perform preliminary dispersion with a stirrer such as a disper in advance.
- the viscosity of the slurry is preferably in the range of 500 to 100,000 mPa ⁇ s, and more preferably in the range of 1,000 to 50,000 mPa ⁇ s as the B-type viscosity at 60 rpm.
- the electrode mixture layer composition when obtained in a wet powder state, it is preferably kneaded to a uniform state with no density unevenness using a planetary mixer, a biaxial kneader or the like.
- the electrode for nonaqueous electrolyte secondary batteries of the present invention comprises a mixture layer formed from the above composition for an electrode mixture layer on the surface of a current collector such as copper or aluminum.
- the mixture layer is formed by coating the surface of the current collector with the composition for electrode mixture layer of the present invention, and then drying and removing a medium such as water.
- the method for applying the mixture layer composition is not particularly limited, and a known method such as a doctor blade method, a dip method, a roll coat method, a comma coat method, a curtain coat method, a gravure coat method, and an extrusion method is adopted. be able to.
- the said drying can be performed by well-known methods, such as hot air spraying, pressure reduction, (far) infrared rays, and microwave irradiation.
- the mixture layer obtained after drying is subjected to a compression treatment by a die press, a roll press or the like.
- a compression treatment by a die press, a roll press or the like.
- the strength of the mixture layer and the adhesiveness to the current collector can be improved. It is preferable to adjust the thickness of the mixture layer by compression to about 30 to 80% before compression, and the thickness of the mixture layer after compression is generally about 4 to 200 ⁇ m.
- the nonaqueous electrolyte secondary battery of the present invention comprises the electrode for a nonaqueous electrolyte secondary battery according to the present invention, a separator, and a nonaqueous electrolyte solution.
- the separator is disposed between the positive electrode and the negative electrode of the battery, and plays a role of ensuring ionic conductivity by preventing a short circuit due to contact between both electrodes and holding an electrolytic solution.
- the separator is preferably a film-like insulating microporous film having good ion permeability and mechanical strength.
- polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene, and the like can be used.
- non-aqueous electrolyte solution a known one generally used for non-aqueous electrolyte secondary batteries can be used.
- the solvent include cyclic carbonates having a high dielectric constant such as propylene carbonate and ethylene carbonate and high electrolyte dissolving ability, and low-viscosity chain carbonates such as ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate. These can be used alone or as a mixed solvent.
- the non-aqueous electrolyte solution is used by dissolving lithium salts such as LiPF 6 , LiSbF 6 , LiBF 4 , LiClO 4 , LiAlO 4 in these solvents.
- the non-aqueous electrolyte secondary battery of the present invention can be obtained by storing a positive electrode plate and a negative electrode plate partitioned by a separator in a spiral or laminated structure in a case or the like.
- the polymer separated by filtration was washed with twice the amount of methanol as the polymerization reaction solution, and then the filter cake was recovered and vacuum dried at 100 ° C. for 6 hours to obtain a powdery acrylic crosslinked polymer R-1. .
- the degree of neutralization of the acrylic crosslinked polymer R-1 is 90 mol%. Since acrylic crosslinked polymer R-1 has a hygroscopic property, it was hermetically stored in a container having a water vapor barrier property.
- the mixture was mixed with water so that the concentration of the acrylic cross-linked polymer R-1 obtained above was 0.5% by weight, and stirred until it became a transparent uniform dispersed (swelled) state.
- the viscosity at a rotor rotational speed of 20 rpm was measured using a B-type viscometer, TVB-10 (manufactured by Toki Sangyo Co., Ltd.). The results are shown in Table 1.
- AA acrylic acid MAA: methacrylic acid 2-MEA: 2-methoxyethyl acrylate BA: butyl acrylate NIPAM: isopropylacrylamide TBAM: t-butylacrylamide AAm: acrylamide AMA: allyl methacrylate P-30: pentaerythritol triallyl ether (Product name “Neoallyl P-30”, manufactured by Daiso Corporation) 1,6-HDDA: 1,6-hexanediol diacrylate ACVA: 4,4′-azobiscyanovaleric acid (manufactured by Otsuka Chemical Co., Ltd.)
- Nonaqueous Electrolyte Secondary Battery Electrode Example 1-1 Regarding the composition for the mixture layer using graphite as the negative electrode active material and the acrylic cross-linked polymer R-1 as the binder, the coating property and the peel strength between the formed mixture layer / current collector (that is, the binder) (Binding property) was measured. 100 parts of artificial graphite (made by Nippon Graphite Co., Ltd., trade name “CGB-10”) and 2.0 parts of powdered acrylic cross-linked polymer R-1 were mixed well in advance, and then 102 parts of ion-exchanged water were added.
- artificial graphite made by Nippon Graphite Co., Ltd., trade name “CGB-10”
- powdered acrylic cross-linked polymer R-1 were mixed well in advance, and then 102 parts of ion-exchanged water were added.
- this dispersion is performed for 15 seconds at a peripheral speed of 20 m / sec using a thin film swirling mixer (manufactured by Primics, FM-56-30), so that a slurry-like negative electrode A composition for the mixture layer was obtained.
- the mixture layer composition was coated on a 20 ⁇ m thick copper foil (manufactured by Nihon Foil Co., Ltd.) so that the film thickness after drying was 50 ⁇ m, and then immediately in the ventilation dryer. The mixture layer was formed by drying at 100 ° C. for 10 minutes.
- the mixture layer density was adjusted to 1.7 ⁇ 0.05 g / cm 3 with a roll press machine to prepare an electrode, and then cut into a 25 mm width strip to prepare a peel test sample.
- the mixture layer surface of the above sample was attached to a double-sided tape fixed to a horizontal surface, 90 ° peeling was performed at a tensile speed of 50 mm / min, and the peel strength between the mixture layer and the copper foil was measured.
- the peel strength was as high as 10.8 N / m.
- Examples 1-2 to 1-13 and Comparative Examples 1-1 to 1-5 A mixture layer composition was prepared by performing the same operation as in Example 1-1 except that the crosslinked polymer used as the binder was used as shown in Tables 2 and 3, and coating properties, 90 ° peel strength and The bending resistance was evaluated. The results are shown in Tables 2 and 3.
- Examples 1-1 to 1-13 are electrode mixture layer compositions containing a binder for a nonaqueous electrolyte secondary battery electrode belonging to the present invention, and electrodes produced using the same.
- the coating property of each mixture layer composition (slurry) is good, and the peel strength between the mixture layer of the obtained electrode and the current collector (copper foil) is 1.0 N / m or more. It was obtained and showed excellent binding properties. Moreover, it was confirmed that the bending resistance of the electrode is at a satisfactory level. Further, comparing the types of crosslinkable monomers used in the respective acrylic cross-linked polymers, compared to Example 1-11, a crosslinkable monomer having one or more alkenyl groups in the molecule was used.
- Example 1-10 the coating property and binding property of the mixture layer composition and the bending resistance of the obtained electrode were better.
- Example 1-2 in which a compound having a plurality of allyl ether groups in the molecule and a compound having both a (meth) acryloyl group and an alkenyl group are used in combination, each performance is good at a high level in a balanced manner. It was confirmed.
- Comparative Example 1-1 using a non-crosslinked polymer has poor coating stability due to insufficient dispersion stability, and further has a very low binder binding property, so that a good mixture layer can be obtained. There wasn't.
- Comparative Example 1-2 is an experimental example using a polymer (R-13) in which the proportion of the monomer having an acryloyl group in the monomer component is less than 70% by weight. The coating property of (slurry) was poor, and the binding property was also insufficient. Further, Comparative Example 1-3 using the acrylic cross-linked polymer (R-14) in which the amount of the monomer corresponding to the component (b) of the present invention was large was greatly inferior in binding force. On the other hand, in Comparative Example 1-4 using the acrylic crosslinked polymer (R-15) obtained without using the component (b), the mixture layer was brittle and the result was inferior in bending resistance. In Comparative Example 1-5, the SP value of the homopolymer of the monomer (AAm) copolymerized with the component (a) is outside the range specified in the present invention (SP value: 19.2), and the obtained electrode Was inferior in bending resistance.
- Example 2-1 A lithium ion secondary battery was prepared using a composition for a mixture layer containing hard carbon as a negative electrode material, acetylene black as a conductive additive, and a crosslinked polymer R-1 as a binder, and the battery characteristics were evaluated.
- Hard carbon (trade name “LBV-1001” manufactured by Sumitomo Bakelite Co., Ltd.) 100 parts, acetylene black (trade name “HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) 2 parts, and powdered acrylic cross-linked polymer R- Take 2 parts of 1 and mix well beforehand, add 104 parts of ion-exchanged water, preliminarily disperse with a disper, and then use a thin film swirling mixer (FM-56-30, manufactured by Primics Co., Ltd.) This dispersion was carried out for 15 seconds under the condition of / sec, to obtain a slurry-like negative electrode mixture layer composition.
- a thin film swirling mixer FM-56-30, manufactured by Primics Co., Ltd.
- the above mixture layer composition was coated on both sides with a coating width of 120 mm on a 20 ⁇ m thick copper foil (manufactured by Nippon Foil Co., Ltd.) as a current collector. After drying, roll press treatment was performed to prepare a negative electrode having a mixture layer on both sides of the current collector.
- the adhesion amount of the mixture layer was 4.96 mg / cm 2 (for one side), and the density was 1.0 g / cm 3 .
- NCM manufactured by Nippon Chemical Industry Co., Ltd.
- HS-100 as the conductive additive
- polyvinylidene fluoride manufactured by Kureha Co., Ltd., trade name “KF # 1000”
- the adhesion amount of the positive electrode mixture layer was 6.80 mg / cm 2 (for one side), and the density was 2.78 g / cm 3 .
- Both the positive electrode and the negative electrode were vacuum-dried at 120 ° C. for 12 hours, and then the positive electrode was slit to a size of 96 ⁇ 84 mm and the negative electrode was 100 ⁇ 88 mm.
- Examples 2-2 to 2-6 and comparative examples 2-1 to 2-4 A laminate cell was assembled by performing the same operation as in Example 2-1, except that the crosslinked polymer used as the binder was used as shown in Table 4, and the battery characteristics were evaluated. The results are shown in Table 4.
- Comparative Example 2-4 the following styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as binders.
- SBR manufactured by JSR, trade name “TRD2001”, 1.5 parts used as solid content
- CMC manufactured by Daicel Finechem, Inc., trade name “CMC2200”, used 1.5 parts as solid content
- Examples 2-1 to 2-6 belong to the non-aqueous electrolyte secondary battery of the present invention, and the discharge capacity retention rate after the cycle test was as high as 91 to 96%, and the results of excellent cycle characteristics were obtained. .
- each example showed good high rate characteristics. This is because the internal resistance of the battery is small because the interface resistance value is small due to the characteristics of the used crosslinked polymer, the uniform dispersibility of the active material and the conductive assistant is good, and the electronic resistance is small.
- Example 2-3 using the acrylic cross-linked polymer (R-2) had a higher discharge capacity retention rate under high current density conditions, and was excellent in high rate characteristics.
- Comparative Example 2-1 had poor cycle characteristics, had a low discharge capacity retention rate during the low temperature rate test, and had poor high rate characteristics.
- Comparative Examples 2-2 and 2-3 have larger interface resistance values and discharge capacity maintenance ratios than Examples 2-1 2-2, 2-5, and 2-6 in which the amount of binder used is the same. Low. In other words, it was confirmed that the high rate characteristics were inferior.
- Comparative Example 2-4 is an experimental example using SBR and CMC as a binder, but it is understood that the high rate characteristics are inferior to those of the examples. In Comparative Example 2-4, since the binder does not have sufficient carboxyl groups, the interface resistance is increased, and as a result, it is presumed that the high rate characteristics are decreased.
- the binder for a nonaqueous electrolyte secondary battery electrode of the present invention has an excellent binding force and exhibits an effect of reducing battery resistance. For this reason, the nonaqueous electrolyte secondary battery provided with the electrode obtained by using the binder exhibits excellent high-rate characteristics and durability (cycle characteristics), and is expected to be applied to an in-vehicle secondary battery. . Moreover, since the binder of this invention is excellent in a softness
Abstract
Description
一方、近年、上記電極合剤層用組成物については、環境保全及びコストダウン等の観点から水系化の要望が高まっている。この点に関してリチウムイオン二次電池では、活物質として黒鉛等の炭素系材料を用いる負極向け電極合剤層用組成物のバインダーとして、スチレンブタジエンゴム(SBR)及びカルボキシメチルセルロース(CMC)を用いた水系バインダーが使用されている。しかし、車載用途に求められる高度なハイレート特性及びサイクル特性に対応すべく、さらなる改善が望まれている。また、リチウムイオン二次電池の正極に関しては、N-メチル-2-ピロリドン(NMP)等の有機溶剤を用いたポリフッ化ビニリデン(PVDF)等の溶剤系バインダーが主流であり、上記要求を十分満足する水系バインダーは未だ提案されていない。
このような状況の下、リチウムイオン二次電池電極への適用が可能な水系バインダーがいくつか提案されている。
特許文献1では、リチウムイオン二次電池の負極塗膜を形成する結着剤としてポリアルケニルエーテルにより架橋したアクリル酸重合体が開示されている。また、特許文献2には、特定の架橋剤によりポリアクリル酸を架橋したポリマーを結着剤として用いることにより、シリコンを含む活物質を用いた場合であっても電極構造が破壊されることなく、優れた容量維持率が得られることが記載されている。特許文献3には、エチレン性不飽和カルボン酸塩単量体由来の構造単位及びエチレン性不飽和カルボン酸エステル単量体由来の構造単位を含み、特定の水溶液粘度を有する水溶性高分子を含有する二次電池用水系電極バインダーが開示されている。
また、特許文献1~3ともに、ハイレート特性に関しては何ら記載されていない。
さらに、バインダーに対しては、活物質表面に存在していてもリチウムイオンの侵入や脱出を妨げないようなものであることが要求される。すなわち、リチウムイオンの脱溶媒和効果やリチウムイオン伝導度に優れることにより、リチウムイオンの活物質への侵入、もしくは活物質からの脱出に伴う抵抗(界面抵抗)が小さくなるようなバインダーが好ましい。
一方、耐屈曲性に優れた電極を得るためには、可撓性を備えた合剤層を形成する必要があり、柔軟性の高いバインダーが求められる。
〔1〕アクリル系架橋重合体又はその塩を含有する非水電解質二次電池電極用バインダーであって、
前記アクリル系架橋重合体は、その全構成単量体中に、(a)成分:エチレン性不飽和カルボン酸単量体を30~90重量%、及び(b)成分:ホモポリマーのSP値が9.0~12.5(cal/cm3)1/2であり、且つ、カルボキシル基を有さないエチレン性不飽和単量体を10~70重量%の範囲で含み、
前記全構成単量体に占めるアクリロイル基を有する単量体の割合が、70重量%以上であることを特徴とする非水電解質二次電池電極用バインダー。
〔2〕上記アクリル系架橋重合体が、架橋性単量体により架橋されたものであり、該架橋性単量体の使用量が非架橋性単量体の総量に対して0.1~2.0モル%である上記〔1〕に記載の非水電解質二次電池電極用バインダー。
〔3〕上記架橋性単量体が、分子内にアルケニル基を1つ以上有する化合物である上記〔1〕又は〔2〕に記載の非水電解質二次電池電極用バインダー。
〔4〕上記架橋性単量体が、分子内に複数のアリルエーテル基を有する化合物、並びに、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物を併用するものである上記〔3〕に記載の非水電解質二次電池電極用バインダー。
〔5〕上記(b)成分が、エーテル基を有する単量体を含む上記〔1〕~〔4〕のいずれかに記載の非水電解質二次電池電極用バインダー。
〔6〕上記(b)成分が、アミド基を有する単量体を含む上記〔1〕~〔5〕のいずれかに記載の非水電解質二次電池電極用バインダー。
〔7〕中和度90モル%における前記架橋重合体の0.5重量%水分散液の粘度が1,000~40,000mPa・sである上記〔1〕~〔6〕のいずれかに記載の非水電解質二次電池電極用バインダー。
〔8〕非水電解質二次電池電極用バインダーに用いられるアクリル系架橋重合体の製造方法であって、
(a)成分:エチレン性不飽和カルボン酸単量体を30~90重量%、及び(b)成分:ホモポリマーのSP値が9.0~12.5(cal/cm3)1/2であり、且つ、カルボキシル基を有さないエチレン性不飽和単量体を10~70重量%の範囲で含み、
さらに、アクリロイル基を有する単量体の割合が70重量%以上である単量体成分を、水性媒体中で沈殿重合することによりアクリル系架橋重合体を製造する方法。
〔9〕上記〔1〕~〔7〕のいずれかに記載のバインダー、活物質及び水を含む非水電解質二次電池電極合剤層用組成物。
〔10〕集電体表面に、上記〔9〕に記載の非水電解質二次電池電極合剤層用組成物から形成される合剤層を備えた非水電解質二次電池電極。
〔11〕上記〔10〕に記載の非水電解質二次電池電極、セパレータ及び非水電解質液を備えた非水電解質二次電池。
以下に、本発明の非水電解質二次電池電極用バインダー及び該バインダーに用いられるアクリル系架橋重合体の製造方法、並びに、該バインダーを用いて得られる非水電解質二次電池電極合剤層用組成物、非水電解質二次電池電極及び非水電解質二次電池の各々について詳細に説明する。
本発明のバインダーは、アクリル系架橋重合体又はその塩を含有する。また、上記アクリル系架橋重合体は、その構成単量体として、(a)成分:エチレン性不飽和カルボン酸単量体、及び(b)成分:ホモポリマーのSP値が9.0~12.5(cal/cm3)1/2であり、且つ、カルボキシル基を有さないエチレン性不飽和単量体を含む。
また、上記構成単量体は、その総量に占めるアクリロイル基を有する単量体の割合が70重量%以上であり、80重量%以上であることが好ましく、90重量%以上であることがより好ましい。アクリロイル基を有する単量体の割合が70重量%以上であれば、重合速度が十分速く、一次鎖長の長い重合体が得られるため、結着性及び分散安定性の良好なバインダーを得ることができる。アクリロイル基を有する単量体の割合の上限は100重量%である。
また、塩の種類としてはリチウム、ナトリウム、カリウム等のアルカリ金属塩;カルシウム塩及びバリウム塩等のアルカリ土類金属塩;マグネシウム塩、アルミニウム塩等のその他の金属塩;アンモニウム塩及び有機アミン塩等が挙げられる。これらの中でも電池特性への悪影響が生じにくい点からアルカリ金属塩及びマグネシウム塩が好ましく、アルカリ金属塩がより好ましく、リチウム塩が最も好ましい。
上記の中でも、リチウムイオン伝導性が高く、ハイレート特性がより向上する点から、アクリル酸2-メトキシエチル及びアクリル酸エトキシエトキシエチルなどのアクリル酸アルコキシアルキル類等、エーテル結合を有する化合物が好ましく、アクリル酸2-メトキシエチルがより好ましい。
また、N-アルキルアクリルアミド化合物及びN,N-ジアルキルアクリルアミド化合物等のアミド基を有する化合物は、結着性がより向上する点で好ましい。
さらに、上記のうちでも、ホモポリマーのガラス転移温度(Tg)が0℃以下の化合物は、得られる電極の耐屈曲性が良好となる点で好ましい。
例えば、アクリル系架橋重合体が上記(a)成分のみからなるポリアクリル酸の場合、電解液に対する親和性はあまり高くない。しかし、ホモポリマーのSP値が9.0~12.5(cal/cm3)1/2である上記(b)成分は、電解液のSP値に近いため、該(b)成分を共重合することにより電解液に対する親和性が高まり、アクリル系架橋重合体は適度に可塑化される。これにより、リチウムイオンが電解液からアクリル系架橋重合体で被覆された活物質内に侵入する際の抵抗(界面抵抗)が小さくなるため、ハイレート特性が向上する。(b)成分の割合が10重量%未満の場合には、上記の効果が十分得られないことがある。一方、(b)成分の割合が70重量%を超えた場合には、アクリル系架橋重合体が過剰に可塑化される結果、結着力が大きく低下して耐久性が不十分となったり、(a)成分量が少なくなることによって脱溶媒和効果が不足し、ハイレート特性が低下する虞がある。
電解液に使用される主な化合物及びそのSP値としては、エチレンカーボネート(SP値:14.7、以下「EC」ともいう)、プロピレンカーボネート(SP値:13.3、以下「PC」ともいう)、ジメチルカーボネート(SP値:9.9、以下「DMC」ともいう)、ジエチルカーボネート(SP値:8.8、以下「DEC」ともいう)、エチルメチルカーボネート(以下「EMC」ともいう)等が挙げられる。なお、各化合物のSP値は「Polymer Handbook」に記載された値を転載した。EMCのSP値については上記「Polymer Handbook」に記載されていないが、DMCとDECの間の値になると推定される。実際の電解液としては、EC/DEC=1/3(v/v)、EC/EMC=1/3(v/v)のように混合溶媒として使用される。
ΔEvap :各原子団のモル蒸発熱(cal/mol)
V :各原子団のモル体積(cm3/mol)
上記多官能重合性単量体は、(メタ)アクリロイル基、アルケニル基等の重合性官能基を分子内に2つ以上有する化合物であり、多官能(メタ)アクリレート化合物、多官能アルケニル化合物、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物等が挙げられる。これらの化合物は、1種のみを単独で用いてもよいし、2種以上を組み合わせて用いてもよい。これらの内でも、均一な架橋構造を得やすい点で多官能アルケニル化合物、並びに、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物等の分子内にアルケニル基を1つ以上有する化合物が好ましい。また、反応性が良好であり、未反応物が残り難いことから、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物がより好ましい。さらに、架橋性単量体として分子内に複数のアリルエーテル基を有する化合物、並びに、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物を併用した場合、合剤層組成物の塗工性及び結着性、並びに、得られる電極の耐屈曲性がより優れたものとなることから特に好ましい。
その他の多官能重合性単量体としては、メチレンビスアクリルアミド、ヒドロキシエチレンビスアクリルアミド等のビスアミド類を挙げることができる。
カルボキシル基と反応し得る官能基を2個以上有する化合物としては、以下のような化合物を挙げることができる。
i)エポキシ基、カルボジイミド基及びオキサゾリン基等のカルボキシル基と共有結合を形成する化合物。
ii)Ca2+、Mg2+等を有し、カルボキシル基とイオン結合を形成する化合物。
iii)Zn2+、Al3+、Fe3+等を有し、カルボキシル基と配位結合を形成する化合物。
架橋重合体が未中和若しくは中和度90モル%未満の場合は、水媒体中でアルカリ化合物により中和度90モル%に中和し、0.5重量%水分散液とした後に粘度を測定する。架橋重合体の中和度が90モル%を超えている場合、当該中和度のまま、若しくは硫酸等の適当な酸を加えて中和度を90モル%に調製した後の0.5重量%水分散液の粘度を測定する。
上記の通り、本発明の架橋重合体の架橋度は比較的低いものの、0.5重量%という低濃度の水分散液であってもミクロゲルのパッキングにより1,000mPa・s以上の粘度を示す。よって、その一次鎖長は十分に長く、適切な架橋度であると推察される。このような架橋重合体からなるバインダーは優れた結着性を発揮するため、バインダーの使用量を低減することが可能となり、電極のハイレート特性を向上することができる。
本発明のアクリル系架橋重合体は、溶液重合、沈殿重合、懸濁重合、逆相乳化重合等の公知の重合方法を使用することが可能であるが、一次鎖長が長く、かつ適度に架橋された重合体を効率よく製造できる点で、沈殿重合が好ましい。
沈殿重合は、原料である不飽和単量体を溶解するが、生成する重合体を実質溶解しない溶媒中で重合反応を行うことにより重合体を製造する方法である。重合の進行とともにポリマー粒子は凝集及び成長により大きくなり、数十nm~数百nmの一次粒子が数μm~数十μmに凝集したポリマー粒子の分散液が得られる。ポリマーの粒子サイズを制御するために分散安定剤を使用することもできる。また、重合後に反応液に濾過又は遠心分離等の処理を施すことによりポリマー粒子を溶媒から分離してもよい。
具体的な重合溶媒として、エチレン性不飽和カルボン酸単量体を未中和の状態で重合する場合は、ベンゼン、酢酸エチル、ジクロロエタン、n-ヘキサン、シクロヘキサン及びn-ヘプタン等が挙げられ、これらの1種を単独であるいは2種以上を組み合わせて用いることができる。
エチレン性不飽和カルボン酸単量体の(部分)中和物を重合する場合は、メタノール、t-ブチルアルコール、アセトン及びテトラヒドロフラン等の水溶性溶剤が挙げられ、これらの1種を単独であるいは2種以上を組み合わせて用いることができる。又は、これらと水との混合溶媒として用いてもよい。本発明において水溶性溶剤とは、20℃における水への溶解度が10g/100mlより大きいものを指す。
これらの内、活物質の分散安定性に優れた重合体が得られる点から、水及び水溶性溶剤を含む水性媒体中でエチレン性不飽和カルボン酸単量体の(部分)中和物を沈殿重合する方法が好ましい。この際、使用するモノマーの種類及び量に応じて水溶性溶剤の種類及び量、並びに水の量を調整することにより、ポリマーの析出及び凝集を制御し、析出粒子の分散安定性を確保することにより安定に重合を完結することができる。上記水性媒体に含まれる水溶性溶剤の割合は、水性媒体全量に対して50~100重量%が好ましく、70~100重量%がより好ましく、90~100重量%がさらに好ましい。
また、レドックス開始の場合、亜硫酸ナトリウム、チオ硫酸ナトリウム、ナトリウムホルムアルデヒドスルホキシレート、アスコルビン酸、亜硫酸ガス(SO2)、硫酸第一鉄等を還元剤として用いることができる。
重合温度は、使用する単量体の種類及び濃度等の条件にもよるが、0~100℃が好ましく、20~80℃がより好ましい。重合温度は一定であってもよいし、重合反応の期間において変化するものであってもよい。また、重合時間は1分間~10時間が好ましく、10分間~5時間がより好ましく、30分間~2時間がさらに好ましい。
本発明の非水電解質二次電池電極合剤層用組成物は、上記アクリル系架橋重合体及びその塩を含有するバインダー、活物質及び水を含む。
上記活物質の内、正極活物質としては主に遷移金属酸化物のリチウム塩が用いられ、例えば、層状岩塩型及びスピネル型のリチウム含有金属酸化物を使用することができる。層状岩塩型の正極活物質の具体的な化合物としては、コバルト酸リチウム、ニッケル酸リチウム、並びに、三元系と呼ばれるNCM{Li(Nix,Coy,Mnz)、x+y+z=1}及びNCA{Li(Ni1-a-bCoaAlb)}等が挙げられる。また、スピネル型の正極活物質としてはマンガン酸リチウム等が挙げられる。酸化物以外にもリン酸塩、ケイ酸塩及び硫黄等が使用され、リン酸塩としては、オリビン型のリン酸鉄リチウム等が挙げられる。正極活物質としては、上記のうちの1種を単独で使用してもよく、2種以上を組み合わせて混合物又は複合物として使用してもよい。
尚、層状岩塩型の正極活物質を水に分散させた場合、活物質表面のリチウムイオンと水中の水素イオンとが交換されることにより、分散液がアルカリ性を示す。このため、一般的な正極用集電体材料であるアルミ箔(Al)等が腐食される虞がある。このような場合には、バインダーとして未中和又は部分中和された架橋重合体を用いることにより、活物質から溶出するアルカリ分を中和することが好ましい。また、未中和又は部分中和された架橋重合体の使用量は、架橋重合体の中和されていないカルボキシル基量が活物質から溶出するアルカリ量に対して等量以上となるように用いることが好ましい。
また正極活物質は導電性を有する炭素系材料で表面コーティングしたものを使用してもよい。
また、エネルギー密度を高くするために、ケイ素やスズなどのリチウムを吸蔵できる金属又は金属酸化物等を負極活物質として使用することも好ましい。その中でも、ケイ素は黒鉛に比べて高容量であり、ケイ素、ケイ素合金及び一酸化ケイ素(SiO)等のケイ素酸化物のようなケイ素系材料からなる活物質(以下、「ケイ素系活物質」ともいう)を用いることができる。しかし、上記ケイ素系活物質は高容量である反面充放電に伴う体積変化が大きい。このため、上記炭素系活物質と併用するのが好ましい。この場合、ケイ素系活物質の配合量が多いと電極材料の崩壊を招き、サイクル特性(耐久性)が大きく低下する場合がある。このような観点から、ケイ素系活物質を併用する場合、その使用量は炭素系活物質に対して60質量%以下であることが好ましく、30質量%以下であることがより好ましい。
また、湿粉状態で電極合剤層用組成物を調製する場合、活物質の使用量は、組成物全量に対して60~97重量%の範囲であることが好ましく、70~90重量%の範囲であることがより好ましい。
また、エネルギー密度の観点から、バインダーや導電助剤等の活物質以外の不揮発成分は、必要な結着性や導電性が担保される範囲内で出来る限り少ない方がよい。
本発明の非水電解質二次電池電極合剤層用組成物は、媒体として水を使用する。また、組成物の性状及び乾燥性等を調整する目的で、メタノール及びエタノール等の低級アルコール類、エチレンカーボネート等のカーボネート類、アセトン等のケトン類、テトラヒドロフラン、N-メチルピロリドン等の水溶性有機溶剤との混合溶媒としてもよい。混合媒体中の水の割合は50重量%以上が好ましく、70重量%以上がより好ましい。
電極合剤層用組成物を塗工可能なスラリー状態とする場合、組成物全体に占める水を含む媒体の含有量は、スラリーの塗工性、および乾燥に必要なエネルギーコスト、生産性の観点から25~90重量%の範囲が好ましく、35~70重量%の範囲がより好ましい。また、プレス可能な湿粉状態とする場合、上記媒体の含有量はプレス後の合剤層の均一性の観点から3~40重量%の範囲が好ましく、10~30重量%の範囲がより好ましい。
架橋重合体及びその塩の使用量が上記範囲内であれば、分散安定性に優れた組成物が得られるとともに、集電体への密着性が極めて高い合剤層を得ることができ、結果として電池の耐久性が向上する。さらに、上記使用量が活物質に対して0.5~5.0重量%と少なく、かつ、上記重合体はカルボキシアニオンを有することから、界面抵抗が小さく、ハイレート特性に優れた電極が得られる。
本発明の非水電解質二次電池電極合剤層用組成物は、上記の活物質、水及びバインダーを必須の構成成分とするものであり、公知の手段を用いて各成分を混合することにより得られる。各成分の混合方法は特段制限されるものではなく、公知の方法を採用することができるが、活物質、導電助剤及びバインダーである架橋重合体粒子等の粉末成分をドライブレンドした後、水等の分散媒と混合し、分散混練する方法が好ましい。
電極合剤層用組成物をスラリー状態で得る場合、分散不良や凝集のないスラリーに仕上げることが好ましい。混合手段としては、プラネタリーミキサー、薄膜旋回式ミキサー及び自公転式ミキサー等の公知のミキサーを使用することができるが、短時間で良好な分散状態が得られる点で薄膜旋回式ミキサーを使用して行うことが好ましい。また、薄膜旋回式ミキサーを用いる場合は、予めディスパー等の攪拌機で予備分散を行うことが好ましい。
また、上記スラリーの粘度は、60rpmにおけるB型粘度として500~100,000mPa・sの範囲が好ましく、1,000~50,000mPa・sの範囲がより好ましい。
本発明の非水電解質二次電池用電極は、銅又はアルミニウム等の集電体表面に上記電極合剤層用組成物から形成される合剤層を備えてなるものである。合剤層は、集電体の表面に本発明の電極合剤層用組成物を塗工した後、水等の媒体を乾燥除去することにより形成される。合剤層組成物を塗工する方法は特に限定されず、ドクターブレード法、ディップ法、ロールコート法、コンマコート法、カーテンコート法、グラビアコート法及びエクストルージョン法などの公知の方法を採用することができる。また、上記乾燥は、温風吹付け、減圧、(遠)赤外線、マイクロ波照射等の公知の方法により行うことができる。
通常、乾燥後に得られた合剤層には、金型プレス及びロールプレス等による圧縮処理が施される。圧縮することにより活物質及びバインダーを密着させ、合剤層の強度及び集電体への密着性を向上させることができる。圧縮により合剤層の厚みを圧縮前の30~80%程度に調整することが好ましく、圧縮後の合剤層の厚みは4~200μm程度が一般的である。
本発明の非水電解質二次電池について説明する。本発明の非水電解質二次電池は、本発明による非水電解質二次電池用電極、セパレータ及び非水電解質液を備えてなる。
セパレータは電池の正極及び負極間に配され、両極の接触による短絡の防止や電解液を保持してイオン導電性を確保する役割を担う。セパレータにはフィルム状の絶縁性微多孔膜であって、良好なイオン透過性及び機械的強度を有するものが好ましい。具体的な素材としては、ポリエチレン及びポリプロピレン等のポリオレフィン、ポリテトラフルオロエチレン等を使用することができる。
本発明の非水電解質二次電池は、セパレータで仕切られた正極板及び負極板を渦巻き状又は積層構造にしてケース等に収納することにより得られる。
重合には、攪拌翼、温度計、還流冷却器及び窒素導入管を備えた反応器を用いた。
反応器内にメタノール342部、アクリル酸(以下「AA」という)80部、アクリル酸2-メトキシエチル(以下「2-MEA」という)20部、メタクリル酸アリル(三菱ガス化学社製、以下「AMA」という)0.5部及びペンタエリスリトールトリアリルエーテル(ダイソー社製、商品名「ネオアリルP-30」)1.0部を仕込んだ。次いで、撹拌下、苛性ソーダフレーク22.22部、及びイオン交換水16部を内温が40℃以下に維持されるようゆっくりと添加した。
反応器内を十分に窒素置換した後、加温して内温を68℃まで昇温した。内温が68℃で安定したことを確認した後、重合開始剤として4,4’-アゾビスシアノ吉草酸(大塚化学社製、商品名「ACVA」)0.01部を添加したところ、反応液に白濁が認められたため、この点を重合開始点とした。溶媒が穏やかに還流するように外温(水バス温度)を調整しながら重合反応を継続し、重合開始点から3時間経過した時点でACVA0.01部、重合開始点から6時間経過した時点でACVA0.03部を追加で添加するとともに、引き続き溶媒の還流を維持した。重合開始点から9時間を経過したところで反応液の冷却を開始し、内温が30℃まで低下した後、苛性ソーダフレーク17.78部を内温が50℃を超えないようにゆっくりと添加した。苛性ソーダフレークの添加を完了し、内温を30℃以下に冷却した後、吸引濾過により重合反応液(重合体スラリー)の濾過を行った。濾別した重合体を重合反応液の2倍量のメタノールで洗浄した後、濾過ケーキを回収し、100℃で6時間真空乾燥することにより粉末状のアクリル系架橋重合体R-1を得た。アクリル系架橋重合体R-1の中和度は90モル%である。アクリル系架橋重合体R-1は吸湿性を有するため、水蒸気バリア性を有する容器に密封保管した。
各原料の仕込み量を表1に記載の通りとした以外は製造例1と同様の操作を行い、粉末状のアクリル系架橋重合体R-2~R-16を得た。
AA:アクリル酸
MAA:メタクリル酸
2-MEA:アクリル酸2-メトキシエチル
BA:アクリル酸ブチル
NIPAM:イソプロピルアクリルアミド
TBAM:t-ブチルアクリルアミド
AAm:アクリルアミド
AMA:メタクリル酸アリル
P-30:ペンタエリスリトールトリアリルエーテル(ダイソー社製、商品名「ネオアリルP-30」)
1,6-HDDA:1,6-ヘキサンジオールジアクリレート
ACVA:4,4’-アゾビスシアノ吉草酸(大塚化学社製)
実施例1-1
負極活物質として黒鉛、バインダーとしてアクリル系架橋重合体R-1を用いた合剤層用組成物について、その塗工性及び形成された合剤層/集電体間の剥離強度(すなわちバインダーの結着性)を測定した。
人造黒鉛(日本黒鉛社製、商品名「CGB-10」)100部、及び粉末状のアクリル系架橋重合体R-1を2.0部採り、予めよく混合した後、イオン交換水102部を加えてディスパーで予備分散を行った後、薄膜旋回式ミキサー(プライミクス社製、FM-56-30)を用いて周速度20m/秒の条件で本分散を15秒間行うことにより、スラリー状の負極合剤層用組成物を得た。
可変式アプリケーターを用いて、厚さ20μmの銅箔(日本製箔社製)上に上記合剤層用組成物を乾燥後の膜厚が50μmとなるように塗工した後、直ちに通風乾燥機内で100℃×10分間の乾燥を行うことにより合剤層を形成した。得られた合剤層の外観を目視により観察し、以下の基準に基づいて塗工性を評価した結果、「○」と判断された。
<塗工性判定基準>
○:表面に筋ムラ、ブツ等の外観異常がまったく認められない。
△:表面に筋ムラ、ブツ等の外観異常がわずかに認められる。
×:表面に筋ムラ、ブツ等の外観異常が顕著に認められる。
さらに、ロールプレス機にて合剤層密度を1.7±0.05g/cm3に調整して電極を作成した後、25mm幅の短冊状に裁断して剥離試験用試料を作成した。水平面に固定された両面テープに上記試料の合剤層面を貼付け、引張速度50mm/分における90°剥離を行い、合剤層と銅箔間の剥離強度を測定した。剥離強度は10.8N/mと高く、良好であった。
一般に、電極を裁断、加工して電池セルの組み立てを行う際、合剤層が集電体(銅箔)から剥がれ落ちるという不具合を避けるためには、1.0N/m以上の剥離強度が必要とされる。剥離強度が高いということは、使用したバインダーが活物質間及び活物質と電極間の結着性に優れているということを意味するものであり、充放電サイクル試験時の容量低下が小さく、耐久性に優れた電池が得られるということが示唆された。
上記90°剥離強度と同様の電極試料を用いて評価した。電極試料をφ2.0mmのSUS棒に巻き付け、湾曲した合剤層の様子を観察し、以下の基準に基づいて耐屈曲性を評価した結果、「△」と判断された。
○:合剤層に外観異常がまったく認められない。
△:合剤層に微細なクラックが認められる。
×:合剤層に明確な割れが観察される。または、合剤層の一部が剥がれ落ちる。
バインダーとして使用する架橋重合体を表2及び表3の通り用いた以外は実施例1-1と同様の操作を行うことにより合剤層組成物を調製し、塗工性、90°剥離強度及び耐屈曲性を評価した。結果を表2及び表3に示す。
また、各アクリル系架橋重合体に用いられた架橋性単量体の種類について比較すると、実施例1-11に比較して、分子内にアルケニル基を1つ以上有する架橋性単量体を用いた実施例1-1~1-10は、合剤層組成物の塗工性及び結着性、並びに、得られた電極の耐屈曲性においてより良好であった。中でも、分子内に複数のアリルエーテル基を有する化合物、並びに、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物を併用した実施例1-2では、各性能がバランスよく高いレベルで良好となることが確認された。
これに対し、非架橋重合体を用いた比較例1-1は、分散安定性が不足するために塗工性が悪く、さらにバインダーの結着性も極めて低く、良好な合剤層が得られなかった。比較例1-2は、単量体成分中に占めるアクリロイル基を有する単量体の割合が70重量%未満である重合体(R-13)を用いた実験例であり、合剤層組成物(スラリー)の塗工性に劣り、結着性も不十分なものであった。
また、本発明の(b)成分に相当する単量体の使用量が多いアクリル系架橋重合体(R-14)を用いた比較例1-3は、結着力に大きく劣るものであった。一方、(b)成分を用いずに得られたアクリル系架橋重合体(R-15)を用いた比較例1-4は、合剤層が脆く、耐屈曲性に劣る結果が得られた。比較例1-5は、(a)成分と共重合させる単量体(AAm)のホモポリマーのSP値が本発明で規定する範囲外(SP値:19.2)であり、得られた電極は耐屈曲性に劣るものであった。
負極物質としてハードカーボン、導電助剤としてアセチレンブラック、バインダーとして架橋重合体R-1を含む合剤層用組成物を用いてリチウムイオン二次電池を作製し、その電池特性を評価した。
ハードカーボン(住友ベークライト社製、商品名「LBV-1001」)100部、アセチレンブラック(電気化学工業社製、商品名「HS-100」)2部、及び粉末状のアクリル系架橋重合体R-1を2部採り、予めよく混合した後、イオン交換水104部を加えてディスパーで予備分散を行った後、薄膜旋回式ミキサー(プライミクス社製、FM-56-30)を用いて周速度20m/秒の条件で本分散を15秒間行うことにより、スラリー状の負極用合剤層組成物を得た。
乾燥炉を有するダイレクトコート方式の塗工機を用いて、集電体となる厚さ20μmの銅箔(日本製箔社製)に上記合剤層組成物を塗工幅120mmで両面塗工し、乾燥後、ロールプレス処理を行い、集電体の両面に合剤層を有する負極を作製した。合剤層の付着量は4.96mg/cm2(片面分)、密度は1.0g/cm3であった。
なお、正極には、活物質としてNCM(日本化学工業社製)、導電助剤としてHS-100、バインダーとしてポリフッ化ビニリデン(クレハ社製、商品名「KF#1000」)を85.5/4.5/10(重量比)の比率で含む合剤層用組成物から形成された合剤層を、集電体となる厚さ15μmのアルミ箔(日本製箔社製)の両面に有するものを使用した。正極の合剤層の付着量は6.80mg/cm2(片面分)、密度は2.78g/cm3であった。
上記で作製したラミネートセルについて、以下の電池特性評価を実施した。
充放電装置SD8(北斗電工社製)を用い、以下の条件にて初期充放電容量を測定した。
測定に際し、電池状態を安定化させるために1サイクル充放電した後、2サイクル目の充放電を行い、充放電容量が設計容量(700~800mAh)内で安定していることを確認した。
測定温度:25℃
充電:0.1C-CC/Cut-off4.2V ⇒ CV/終止レート0.01C
放電:0.1C-CC/Cut-off3.0V
2サイクル
1サイクル目の充電容量は1153mAh、放電容量は776mAh、2サイクル目の充電容量は776mAh、放電容量は760mAhであった。
初期充放電試験を行ったセルについて、以下の条件、順序にて低温レート試験及び交流インピーダンス測定を行った。尚、測定には充放電装置SD8(北斗電工社製)及び交流インピーダンス測定装置VSP(Bio-Logic社製)を使用した。
測定温度:-15℃
(1)0.1C充放電(低温初期充放電)
充電:0.1C-CC/Cut-off4.2V
(休止時間10分)
放電:0.1C-CC/Cut-off3.0V
(2)交流インピーダンス測定
充電:0.1C、2時間
印加電圧:10mV
周波数:1000kHz~10mHz
(残放電処理 3Vまで0.1C)
(3)0.5C充放電
充電:0.5C-CC/Cut-off4.2V
(休止時間10分)
放電:0.5C-CC/Cut-off3.0V
(残放電処理 3Vまで0.1C)
(4)1C充放電
充電:1C-CC/Cut-off4.2V
(休止時間10分)
放電:1C-CC/Cut-off3.0V
(残放電処理 3Vまで0.1C)
(5)2C充放電
充電:2C-CC/Cut-off4.2V
(休止時間10分)
放電:2C-CC/Cut-off3.0V
(残放電処理 3Vまで0.1C)
(6)3C充放電
充電:3C-CC/Cut-off4.2V
(休止時間10分)
放電:3C-CC/Cut-off3.0V
(残放電処理 3Vまで0.1C)
(7)4C充放電
充電:4C-CC/Cut-off4.2V
(休止時間10分)
放電:4C-CC/Cut-off3.0V
(残放電処理 3Vまで0.1C)
上記(1)の測定結果は、低温初期充放電容量621mAh、放電容量604mAhであった。
上記(2)の測定結果より、ナイキストプロットを作成し、その円弧の大きさより界面抵抗値を見積った結果、0.35Ωであった。
上記(3)~上記(7)の測定により得られた放電容量を、上記(1)の測定で得られた放電容量で除することにより、各Cレートでの放電容量維持率を計算した結果、0.5C:71%、1C:49%、2C:23%、3C:6%、4C:0%であった。なお0%とは過電圧による電圧降下により放電開始直後にCut-off電圧(3.0V)に到達したことを意味する。
初期充放電試験を行ったセルについて、下記条件にてサイクル試験を行った。
測定温度:25℃
充電:1C-CC/Cut-off4.2V
放電:1C-CC/Cut-off3.0V
200サイクル
200サイクル目の放電容量を1サイクル目の放電容量で除することで、200サイクル放電容量維持率を計算した結果、95%であった。
バインダーとして使用する架橋重合体を表4の通り用いた以外は実施例2-1と同様の操作を行うことによりラミネートセルを組み立て、電池特性評価を行った。結果を表4に示す。
なお、比較例2-4については、バインダーとして以下のスチレンブタジエンゴム(SBR)及びカルボキシメチルセルロース(CMC)を使用した。
SBR:JSR社製、商品名「TRD2001」、固形分として1.5部使用
CMC:ダイセルファインケム社製、商品名「CMC2200」、固形分として1.5部使用
LBV-1001:ハードカーボン(住友ベークライト社製)
HS-100:アセチレンブラック(電気化学工業社製)
これに対し、比較例2-1はサイクル特性が悪く、さらに低温レート試験時の放電容量維持率が低く、ハイレート特性も不良であることが確認された。これはバインダーとして使用したR-14の構成単量体におけるエチレン性不飽和カルボン酸単量体の割合が25重量%と低いため、集電体との結着性(剥離強度)が低く、電解液に過度に膨潤し、さらにカルボキシル基の脱溶媒和効果が十分ではないためと推察される。また比較例2-2及び2-3は、バインダー使用量が同一の実施例2-1、2-2、2-5、2-6と比べると、界面抵抗値が大きく、放電容量維持率も低い。つまりハイレート特性に劣ることが確認された。これは比較例2-2及び2-3で使用した架橋重合体R-15及びR-16は、構成単量体として、SP値が9.0~12.5(cal/cm3)1/2であり、且つ、カルボキシル基を有さないエチレン性不飽和単量体を有しないために、電解液との親和性が実施例で使用した架橋重合体よりも低く、Liイオンが活物質に出入りする際に必要なエネルギーが大きくなった為と推定される。比較例2-4は、バインダーとしてSBR及びCMCを使用した実験例であるが、各実施例に比較してハイレート特性に劣るものであることが分かる。比較例2-4では、バインダーが十分なカルボキシル基を持たないことから界面抵抗が増加し、その結果ハイレート特性が低下したものと推察される。
また、本発明のバインダーは柔軟性に優れるため、電極合剤層に良好な耐屈曲性を付与することができる。このため、電極製造時のトラブルが低減され、歩留まり向上に繋がる。
Claims (11)
- アクリル系架橋重合体又はその塩を含有する非水電解質二次電池電極用バインダーであって、
前記アクリル系架橋重合体は、その全構成単量体中に、(a)成分:エチレン性不飽和カルボン酸単量体を30~90重量%、及び(b)成分:ホモポリマーのSP値が9.0~12.5(cal/cm3)1/2であり、且つ、カルボキシル基を有さないエチレン性不飽和単量体を10~70重量%の範囲で含み、
前記全構成単量体に占めるアクリロイル基を有する単量体の割合が、70重量%以上であることを特徴とする非水電解質二次電池電極用バインダー。 - 前記アクリル系架橋重合体が、架橋性単量体により架橋されたものであり、該架橋性単量体の使用量が非架橋性単量体の総量に対して0.1~2.0モル%である請求項1に記載の非水電解質二次電池電極用バインダー。
- 前記架橋性単量体が、分子内にアルケニル基を1つ以上有する化合物である請求項1又は2に記載の非水電解質二次電池電極用バインダー。
- 前記架橋性単量体が、分子内に複数のアリルエーテル基を有する化合物、並びに、(メタ)アクリロイル基及びアルケニル基の両方を有する化合物を併用するものである請求項3に記載の非水電解質二次電池電極用バインダー。
- 前記(b)成分が、エーテル基を有する単量体を含む請求項1~4のいずれか1項に記載の非水電解質二次電池電極用バインダー。
- 前記(b)成分が、アミド基を有する単量体を含む請求項1~5のいずれか1項に記載の非水電解質二次電池電極用バインダー。
- 中和度90モル%における前記架橋重合体の0.5重量%水分散液の粘度が1,000~40,000mPa・sである請求項1~6のいずれか1項に記載の非水電解質二次電池電極用バインダー。
- 非水電解質二次電池電極用バインダーに用いられるアクリル系架橋重合体の製造方法であって、
(a)成分:エチレン性不飽和カルボン酸単量体を30~90重量%、及び(b)成分:ホモポリマーのSP値が9.0~12.5(cal/cm3)1/2であり、且つ、カルボキシル基を有さないエチレン性不飽和単量体を10~70重量%の範囲で含み、
さらに、アクリロイル基を有する単量体の割合が70重量%以上である単量体成分を、水性媒体中で沈殿重合することによりアクリル系架橋重合体を製造する方法。 - 請求項1~7のいずれか1項に記載のバインダー、活物質及び水を含む非水電解質二次電池電極合剤層用組成物。
- 集電体表面に、請求項9に記載の非水電解質二次電池電極合剤層用組成物から形成される合剤層を備えた非水電解質二次電池電極。
- 請求項10に記載の非水電解質二次電池電極、セパレータ及び非水電解質液を備えた非水電解質二次電池。
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EP3288105A4 (en) | 2018-12-26 |
KR20170140253A (ko) | 2017-12-20 |
KR102524363B1 (ko) | 2023-04-21 |
CN107534150A (zh) | 2018-01-02 |
US20180102542A1 (en) | 2018-04-12 |
EP3288105A1 (en) | 2018-02-28 |
JP6465323B2 (ja) | 2019-02-06 |
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