WO2014188724A1 - 二次電池用バインダー組成物、二次電池電極用スラリー組成物、二次電池用負極、および、二次電池 - Google Patents
二次電池用バインダー組成物、二次電池電極用スラリー組成物、二次電池用負極、および、二次電池 Download PDFInfo
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- WO2014188724A1 WO2014188724A1 PCT/JP2014/002700 JP2014002700W WO2014188724A1 WO 2014188724 A1 WO2014188724 A1 WO 2014188724A1 JP 2014002700 W JP2014002700 W JP 2014002700W WO 2014188724 A1 WO2014188724 A1 WO 2014188724A1
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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
-
- 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
- C08F212/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring
- C08F212/02—Monomers containing only one unsaturated aliphatic radical
- C08F212/04—Monomers containing only one unsaturated aliphatic radical containing one ring
- C08F212/06—Hydrocarbons
- C08F212/08—Styrene
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/16—Nitrogen-containing compounds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
- C08L1/08—Cellulose derivatives
- C08L1/26—Cellulose ethers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L25/00—Compositions of, homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Compositions of derivatives of such polymers
- C08L25/02—Homopolymers or copolymers of hydrocarbons
- C08L25/04—Homopolymers or copolymers of styrene
- C08L25/08—Copolymers of styrene
- C08L25/10—Copolymers of styrene with conjugated dienes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L33/00—Compositions of homopolymers or 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 of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
- C08L33/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L53/00—Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
- C08L53/02—Compositions of block copolymers containing at least one sequence of a polymer obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers of vinyl-aromatic monomers and conjugated dienes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—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
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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
-
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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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
-
- 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 binder composition for a secondary battery, a slurry composition for a secondary battery electrode, a negative electrode for a secondary battery, and a secondary battery.
- Secondary batteries such as lithium ion secondary batteries are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of secondary batteries.
- a battery member such as a porous film provided for the purpose of improving heat resistance and strength on the electrode (positive electrode and negative electrode) of the secondary battery or on the electrode or the separator is a component included in these battery members.
- it is formed by binding the component and a base material (for example, a current collector, an electrode, or a separator) with a binder.
- a negative electrode of a secondary battery usually includes a current collector and a negative electrode mixture layer formed on the current collector.
- the negative electrode mixture layer is formed by, for example, applying a slurry composition for an electrode in which a binder composition containing a particulate polymer and a negative electrode active material are dispersed in a dispersion medium on a current collector, and drying. And formed by binding a negative electrode active material or the like with a particulate polymer.
- a slurry composition for an electrode in which a binder composition containing a particulate polymer and a negative electrode active material are dispersed in a dispersion medium on a current collector, and drying. And formed by binding a negative electrode active material or the like with a particulate polymer.
- a crosslinking agent is blended in a binder composition or electrode slurry composition used for forming an electrode for a secondary battery, and an electrode is formed using the binder composition or electrode slurry composition.
- a crosslinking agent is blended in a binder composition or electrode slurry composition used for forming an electrode for a secondary battery, and an electrode is formed using the binder composition or electrode slurry composition.
- a crosslinking agent such as carboxymethylcellulose, and a melamine resin, urea formalin resin, tannic acid, glyoxal resin, dimethylol compound, and PVA.
- Patent Document 2 discloses a functional group-containing resin fine particle obtained by emulsion polymerization of an ethylenically unsaturated monomer containing a keto group-containing ethylenically unsaturated monomer, and a polyfunctional hydrazide compound as a crosslinking agent. And a binder composition for a secondary battery electrode is proposed, and it is disclosed that functional group-containing resin fine particles are cross-linked via a polyfunctional hydrazide compound.
- Patent Document 3 has a porous film on at least one of a positive electrode and a negative electrode, and the positive electrode or the negative electrode has a water-soluble polymer material having a hydroxyl group and a functional group that reacts with the hydroxyl group.
- a lithium ion secondary battery formed using a binder composed of a crosslinking agent has been proposed, and it is disclosed that water-soluble polymer materials are crosslinked via a crosslinking agent.
- Patent Document 4 discloses a non-aqueous secondary battery electrode including functional group-containing crosslinked resin fine particles obtained by copolymerizing a monomer containing an ethylenically unsaturated monomer having a specific functional group.
- a binder composition has been proposed, and a compound having at least one functional group selected from an epoxy group, an amide group, a hydroxyl group, and an oxazoline group and a functional group-containing crosslinked resin fine particle are crosslinked via a crosslinking agent. Is disclosed.
- the binder composition used for forming the battery member described above has good binding properties, and the secondary battery is good when the battery member formed using the binder composition is applied to the secondary battery. Therefore, it is required to exhibit excellent electrical characteristics (for example, cycle characteristics).
- the binder composition of the above prior art has room for improvement in terms of improving the binding properties and the electrical characteristics of the secondary battery using the binder composition.
- this invention aims at providing the binder composition for secondary batteries which is excellent in binding property and can improve the electrical characteristic of a secondary battery when it is used for formation of a battery member.
- the present invention also provides a slurry composition for a secondary battery electrode that can be used for forming an electrode mixture layer that has excellent adhesion to a current collector and can improve the electrical characteristics of the secondary battery.
- the purpose is to provide.
- An object of the present invention is to provide a negative electrode for a secondary battery that is excellent in adhesion between the current collector and the negative electrode mixture layer and that can improve the electrical characteristics of the secondary battery.
- an object of the present invention is to provide a secondary battery that has excellent adhesion between the current collector and the negative electrode composite material layer and is excellent in electrical characteristics.
- the present inventor has intensively studied to achieve the above object. And this inventor is the functional group and specific which react with the water-soluble thickener (A) which has a hydroxyl group or a carboxyl group, the crosslinking agent (B) which has a carbodiimide group or an oxazoline group, and the said crosslinking agent (B). And a particulate polymer (C) having a main chain structure, and the blending ratio of the crosslinking agent (B) and the particulate polymer (C) to the water-soluble thickener (A) in a specific range.
- the present inventors have newly found that the binder composition described above has excellent binding properties and can improve the electrical characteristics of the secondary battery when used in the formation of battery members.
- the binder composition for secondary batteries of this invention is the water-soluble thickener (A) which has a hydroxyl group or a carboxyl group, A crosslinking agent (B) having a carbodiimide group or an oxazoline group, and a particulate polymer (C), the particulate polymer (C) has a functional group that reacts with the crosslinking agent (B); And it contains an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit, and 0.001 part by mass or more and 100 parts by mass of the crosslinking agent (B) per 100 parts by mass of the water-soluble thickener (A).
- the particulate polymer (C) is contained in an amount of 10 parts by weight or more and less than 500 parts by weight.
- it has a water-soluble thickener (A) having a hydroxyl group or a carboxyl group, a crosslinking agent (B) having a carbodiimide group or an oxazoline group, a functional group that reacts with the crosslinking agent, and a specific main chain structure.
- a binder composition capable of improving the electrical characteristics of the secondary battery when used for forming a battery member.
- the water-soluble thickener (A) includes carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polycarboxylic acid, and these It is preferably at least one selected from the group consisting of salts.
- the workability when applying the slurry composition containing the binder composition onto a substrate such as a current collector is good. can do.
- the binder composition for secondary batteries of this invention is a functional group which reacts with the said crosslinking agent (B) in the said particulate polymer (C), a carboxyl group, a hydroxyl group, a glycidyl ether group, and a thiol group. It is preferable that it is at least 1 sort (s) selected from the group which consists of.
- the functional group that reacts with the crosslinking agent (B) in the particulate polymer (C) is at least one selected from the above group, the cycle characteristics of a secondary battery obtained using the binder composition, etc. The electrical characteristics can be improved.
- the slurry composition for secondary battery electrodes of this invention is a water-soluble thickener (A) which has a hydroxyl group or a carboxyl group, and , A crosslinking agent (B) having a carbodiimide group or an oxazoline group, a particulate polymer (C), an electrode active material, and water, and the particulate polymer (C) comprises the crosslinking agent (B).
- the cross-linking agent (B) per 100 parts by weight of the water-soluble thickener (A), which has a functional group that reacts with the aliphatic conjugated diene monomer unit and the aromatic vinyl monomer unit.
- the particulate polymer (C) is contained by 10 parts by mass or more and less than 500 parts by mass.
- it has a water-soluble thickener (A) having a hydroxyl group or a carboxyl group, a crosslinking agent (B) having a carbodiimide group or an oxazoline group, a functional group that reacts with the crosslinking agent, and a specific main chain structure.
- the particulate polymer (C) is blended, and further, the current-collecting ratio is obtained by setting the blending ratio of the crosslinking agent (B) and the particulate polymer (C) to the water-soluble thickener (A) within a specific range.
- a slurry composition for a secondary battery electrode capable of forming an electrode mixture layer that has excellent adhesion to the body and can improve the electrical characteristics of the secondary battery is obtained.
- the negative electrode for secondary batteries of this invention is the slurry composition for said secondary battery electrodes whose said electrode active material is a negative electrode active material It has the negative mix layer obtained from a thing, It is characterized by the above-mentioned.
- the adhesion between the current collector and the negative electrode mixture layer is excellent, and the secondary A negative electrode for a secondary battery that can improve the electrical characteristics of the battery is obtained.
- the negative electrode mixture layer preferably has a crosslinked structure formed from the water-soluble thickener (A), the crosslinking agent (B), and the particulate polymer (C). That is, the crosslinking agent (B) is suitable for connecting the water-soluble thickeners (A), the water-soluble thickener (A) and the particulate polymer (C), and the particulate polymers (C).
- the crosslinking agent (B) is suitable for connecting the water-soluble thickeners (A), the water-soluble thickener (A) and the particulate polymer (C), and the particulate polymers (C).
- the secondary battery of this invention is either the negative electrode for secondary batteries mentioned above, a positive electrode, electrolyte solution, a separator, It is characterized by providing.
- a secondary battery using the above-described negative electrode for a secondary battery has excellent electrical characteristics and excellent adhesion between the current collector and the negative electrode mixture layer.
- the binder composition for a secondary battery of the present invention good binding properties can be obtained, and the electrical characteristics of a secondary battery using a battery member formed using the binder composition can be improved. it can.
- the slurry composition for secondary battery electrodes of the present invention an electrode mixture layer that has excellent adhesion to the current collector and can improve the electrical characteristics of the secondary battery is formed. be able to.
- the negative electrode for secondary batteries of this invention while improving the adhesiveness of a collector and a negative mix layer, the electrical property of a secondary battery can be improved.
- the electrical characteristics can be improved, and the adhesion between the negative electrode mixture layer and the current collector can be secured.
- the binder composition for a secondary battery of the present invention can be used for a battery member of a secondary battery such as a positive electrode, a negative electrode, and a porous film provided on the positive electrode, the negative electrode, or a separator. Is used to form a negative electrode.
- the slurry composition for secondary battery electrodes of the present invention comprises the binder composition for secondary batteries of the present invention, and forms a positive or negative electrode of the secondary battery, preferably a negative electrode of the secondary battery. Used for formation.
- the negative electrode for secondary batteries of this invention can be manufactured using the slurry composition for secondary battery electrodes of this invention.
- the secondary battery of the present invention is characterized by using the negative electrode for a secondary battery of the present invention.
- the binder composition for a secondary battery of the present invention reacts with a water-soluble thickener (A) having a hydroxyl group or a carboxyl group, a crosslinking agent (B) having a carbodiimide group or an oxazoline group, and a crosslinking agent (B). And a particulate polymer (C) having a functional group and a specific main chain structure.
- the binder composition for secondary batteries of this invention contains 0.001 mass part or more and less than 100 mass parts of said crosslinking agent (B) per 100 mass parts of said water-soluble thickener (A), The said particle
- the binder composition for secondary batteries of this invention while obtaining favorable binding property, the electrical characteristic of the secondary battery using the battery member formed using this binder composition is improved. be able to.
- each component contained in the binder composition will be described by taking as an example a case where the binder composition is used for forming a negative electrode.
- Water-soluble thickener (A) adjusts the viscosity of the slurry composition containing the binder composition and the binder composition. It has a function as an agent.
- the water-soluble thickener (A) having a hydroxyl group or a carboxyl group may be any compound that has at least one of a hydroxyl group and a carboxyl group in its molecular structure and can be used as a water-soluble thickener. There is no particular limitation.
- the thickener is “water-soluble” means that the mixture obtained by adding 1 part by weight (corresponding to the solid content) of the thickener per 100 parts by weight of ion-exchanged water and stirring the temperature Adjust to at least one of the conditions within the range of 20 ° C. or higher and 70 ° C. or lower and within the range of pH 3 or higher and 12 or lower (NaOH aqueous solution and / or HCl aqueous solution is used for pH adjustment). It means that the mass of the solid content of the residue remaining on the screen without passing through the screen does not exceed 50 mass% with respect to the solid content of the added thickener when it passes through the screen.
- the thickener shall be water-soluble.
- water-soluble thickener (A) for example, carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethyl are used to improve workability when a slurry composition containing a binder composition is applied onto a current collector or the like.
- Methyl cellulose, polyvinyl alcohol, polycarboxylic acid, salts thereof, and the like can be used.
- the polycarboxylic acid include polyacrylic acid, polymethacrylic acid, and alginic acid.
- One of these water-soluble thickeners (A) may be used alone, or two or more thereof may be used in combination at any ratio.
- the water-soluble thickener (A) preferably contains carboxymethyl cellulose or a salt thereof (hereinafter sometimes abbreviated as “carboxymethyl cellulose (salt)”).
- carboxymethyl cellulose (salt) a salt thereof
- the workability when applying the slurry composition containing the binder composition onto a current collector or the like can be improved.
- the degree of etherification of the carboxymethyl cellulose (salt) to be used is preferably 0.4 or more, more preferably 0.7 or more, Preferably it is 1.5 or less, More preferably, it is 1.0 or less.
- carboxymethyl cellulose (salt) having a degree of etherification of 0.4 or more workability when a slurry composition containing a binder composition is applied onto a current collector or the like can be improved.
- the degree of etherification is less than 0.4, the water-soluble thickener (A) can be a gel-like substance because the hydrogen bonds within and between the molecules of carboxymethylcellulose (salt) are strong.
- carboxymethylcellulose having a degree of etherification of 1.5 or less the number of hydroxyl groups per molecule of carboxymethylcellulose (salt) is sufficient, and the reactivity with the crosslinking agent (B) described later is improved. Therefore, since carboxymethyl cellulose (salt) can form a good cross-linked structure via the cross-linking agent (B), the binding property of the binder composition of the present invention is improved by forming the cross-linked structure as will be described in detail later The cycle characteristics of the secondary battery can be made excellent.
- the degree of etherification of carboxymethylcellulose refers to the average value of the number of hydroxyl groups substituted with a substituent such as carboxymethyl group per unit of anhydrous glucose constituting carboxymethylcellulose (salt). It can take a value of less than 3. As the degree of etherification increases, the proportion of hydroxyl groups in one molecule of carboxymethylcellulose (salt) decreases (that is, the proportion of substituents increases), and as the degree of etherification decreases, the proportion of hydroxyl groups in one molecule of carboxymethylcellulose (salt) increases. This indicates that the proportion of hydroxyl groups increases (that is, the proportion of substituents decreases).
- This degree of etherification (degree of substitution) can be determined by the method described in JP2011-34962A.
- the viscosity of a 1% by mass aqueous solution of carboxymethylcellulose (salt) is preferably 500 mPa ⁇ s or more, more preferably 1000 mPa ⁇ s or more, preferably 10000 mPa ⁇ s or less, more preferably 9000 mPa ⁇ s or less.
- carboxymethylcellulose (salt) having a viscosity of 500 mPa ⁇ s or more when the aqueous solution is 1% by mass the slurry composition containing the binder composition can be given moderate viscosity. Therefore, the workability at the time of applying the slurry composition onto a current collector or the like can be improved.
- carboxymethylcellulose (salt) having a viscosity of 1 mass% aqueous solution of 10,000 mPa ⁇ s or less, the viscosity of the slurry composition containing the binder composition does not become too high, and the slurry composition is placed on a current collector or the like.
- the workability at the time of application can be improved, and the adhesion between the negative electrode mixture layer obtained by using the slurry composition containing the binder composition and the current collector can be improved.
- the viscosity of 1 mass% aqueous solution of carboxymethylcellulose (salt) is a value when it measures at 25 degreeC and rotation speed 60rpm using a B-type viscosity meter.
- the water-soluble thickener (A) further preferably contains carboxymethyl cellulose (salt) and polycarboxylic acid or a salt thereof (hereinafter sometimes abbreviated as “polycarboxylic acid (salt)”).
- carboxymethylcellulose (salt) and polycarboxylic acid (salt) in combination as the water-soluble thickener (A).
- Mechanical properties such as strength of the negative electrode mixture layer containing the water-soluble thickener (A) while improving the adhesion between the negative electrode mixture layer obtained using the slurry composition containing the product and the current collector Can be improved. Accordingly, the cycle characteristics and the like of the secondary battery using the negative electrode can be improved.
- Alginic acid and polyacrylic acid are less likely to swell excessively in the electrolyte solution of the secondary battery as compared with polymethacrylic acid, and thus carboxymethylcellulose (salt) and alginic acid (salt) or polyacrylic acid (salt) This is because the cycle characteristics of the secondary battery can be sufficiently improved by using together.
- polyacrylic acid (salt) reacts better with the crosslinking agent (B) than carboxymethylcellulose (salt)
- formation of a crosslinked structure via the crosslinking agent (B) This is because the reaction can be promoted.
- the blending amount of carboxymethyl cellulose (salt) and the polycarboxylic acid (salt) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more.
- the proportion of the polycarboxylic acid (salt) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more.
- it is 20 mass% or less, More preferably, it is 10 mass% or less, Most preferably, it is 5 mass% or less.
- the proportion of the blending amount of polycarboxylic acid (salt) is 0.1% by mass or more, so that carboxymethylcellulose ( Salt) and polycarboxylic acid (salt) can be sufficiently exerted, so that the binding property of the binder composition can be improved satisfactorily, and a slurry composition containing the binder composition is used.
- the adhesion between the negative electrode mixture layer and the current collector obtained can be improved satisfactorily.
- the ratio for which the compounding quantity of polycarboxylic acid (salt) accounts is 20 mass% or less, and a binder composition.
- the negative electrode mixture layer obtained by using the slurry composition containing the binder composition does not become too hard, and the binding property and ion conductivity of the binder composition can be ensured.
- the adhesiveness of the negative mix layer obtained using the slurry composition containing this binder composition and an electrical power collector can be improved favorably.
- crosslinking agent (B) having a carbodiimide group or an oxazoline group (hereinafter sometimes abbreviated as “crosslinking agent (B)”) is a water-soluble thickener (A) having the above hydroxyl group or carboxyl group, and will be described later.
- a crosslinked structure is formed with the particulate polymer (C) by heating or the like. That is, the crosslinking agent (B) is suitable for linking the water-soluble thickeners (A), the water-soluble thickener (A) and the particulate polymer (C), and the particulate polymers (C). It is presumed that a simple crosslinked structure is formed.
- the water-soluble thickener (A) and particles contained in the composition of the binder composition of the present invention and the slurry composition containing the binder composition of the present invention are subjected to a treatment such as heating.
- the polymer (C) forms a crosslinked structure via the crosslinking agent (B).
- the water-soluble thickener (A), the water-soluble thickener (A) and the particulate polymer (C), and the crosslinking between the particulate polymers (C), the elastic modulus and tensile strength at break can be obtained.
- this crosslinked structure also improves the wettability of the battery member formed using the binder composition and the electrolyte of the secondary battery.
- the water-soluble thickener (A) having a hydroxyl group or a carboxyl group is hard to be entangled with each other due to the formation of hydrogen bonds.
- the molecules of the crosslinking agent (B) enter into the molecular chain of the water-soluble thickener (A), and a physical space into which the electrolytic solution enters easily occurs.
- the formation of a crosslinked structure causes the negative electrode accompanying repeated charge / discharge. Swelling can be suppressed, and high adhesion between the negative electrode mixture layer and the current collector can be secured. Furthermore, using the water resistance (low solubility in water) obtained by forming a crosslinked structure, a porous film (for example, using alumina particles) on the negative electrode mixture layer using an aqueous slurry composition. It is also possible to form a formed heat-resistant porous film).
- the crosslinked structure derived from a crosslinking agent (B) improves the wettability with respect to electrolyte solution
- the battery member prepared using the binder composition of this invention and the slurry composition containing the binder composition of this invention is used. It is possible to improve the pouring property of the electrolytic solution when using it to form a secondary battery, and to improve output characteristics and the like.
- the cycle characteristics of the secondary battery can be improved, and an increase in resistance after cycling can be suppressed.
- the slurry composition containing a binder composition and a binder composition does not contain the water-soluble thickener (A) which has a hydroxyl group or a carboxyl group, that is, only a crosslinked structure of particulate polymers (C) only. If it is not formed, a crosslinked structure having sufficiently good mechanical properties such as elastic modulus, tensile strength at break and fatigue resistance cannot be obtained, and for example, swelling of the negative electrode cannot be suppressed.
- the slurry composition containing a binder composition and a binder composition does not contain the particulate polymer (C) described later, that is, when only a crosslinked structure between water-soluble thickeners (A) is formed. Since the resulting crosslinked structure becomes too rigid, for example, the flexibility of the electrode using the binder composition for a secondary battery of the present invention is reduced, the cycle characteristics may be deteriorated.
- the binder composition for a secondary battery of the present invention needs to contain 0.001 part by mass or more of the crosslinking agent (B) per 100 parts by mass of the water-soluble thickener (A), preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, particularly preferably 4 parts by mass or more, most preferably 5 parts by mass or more, and less than 100 parts by mass. It is necessary, preferably 60 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less.
- the binder composition for a secondary battery contains 0.001 part by mass or more of the crosslinking agent (B) per 100 parts by mass of the water-soluble thickener (A), a good crosslinked structure can be formed. Therefore, when the slurry composition containing the binder composition and the binder composition is used for forming a negative electrode, for example, the adhesion between the negative electrode mixture layer and the current collector can be secured, and in addition, the negative electrode In the production of a secondary battery having the above, the liquid injection property of the electrolytic solution becomes good.
- the binder composition for secondary batteries contains less than 100 parts by mass of the crosslinking agent (B) per 100 parts by mass of the water-soluble thickener (A), thereby suppressing unevenness in the crosslinked structure, and the negative electrode
- the adhesion between the composite material layer and the current collector can be secured, and in addition, the presence of a large amount of the (relatively flexible) crosslinking agent (B) reduces the strength of the negative electrode composite material layer. Can be suppressed.
- inhibition of the movement of charge carriers in the negative electrode mixture layer due to excessive crosslinking can also be suppressed.
- the electrochemical side reaction caused by the impurities derived from the crosslinking agent can be suppressed.
- the secondary battery binder composition contains the crosslinking agent in the above range per 100 parts by mass of the water-soluble thickener (A), thereby ensuring the cycle characteristics of the secondary battery, and after the cycle. The increase in resistance can be suppressed.
- the crosslinking agent (B) has in its molecule at least one of a carbodiimide group and an oxazoline group represented by the general formula (1): —N ⁇ C ⁇ N— (1), and is water-soluble.
- the carbodiimide compound which has a carbodiimide group as a group which can form a crosslinked structure and the oxazoline compound which has an oxazoline group as a group which can form a crosslinked structure are mentioned.
- a carbodiimide compound is preferable as the crosslinking agent (B).
- the carbodiimide compound is rarely lost due to reaction with water during the preparation of a binder composition or a slurry composition because of its excellent thermal stability, and the amount of the crosslinking agent (B) used is relatively small. Even in this case, it is possible to sufficiently enhance the adhesion between the obtained negative electrode mixture layer and the current collector and to secure the electrical characteristics of the secondary battery. Moreover, the water resistance of a negative electrode can be improved by using a carbodiimide compound.
- the carbodiimide compound and the oxazoline compound will be described in detail.
- Carbodiimide compound As the carbodiimide compound used as the crosslinking agent (B), a compound having two or more carbodiimide groups in the molecule, specifically, the general formula (2): —N ⁇ C ⁇ N—R 1 (2) (In general formula (2), R 1 represents a divalent organic group.) Preferred examples include polycarbodiimides and / or modified polycarbodiimides having a repeating unit represented by formula (2). In addition, in this specification, a modified polycarbodiimide means resin obtained by making the reactive compound mentioned later react with polycarbodiimide.
- the method for synthesizing the polycarbodiimide is not particularly limited.
- the organic polyisocyanate is reacted in the presence of a catalyst for promoting the carbodiimidization reaction of the isocyanate group (hereinafter referred to as “carbodiimidization catalyst”).
- Carbodiimidization catalyst a catalyst for promoting the carbodiimidization reaction of the isocyanate group
- Polycarbodiimide can be synthesized.
- the polycarbodiimide having a repeating unit represented by the general formula (2) is a copolymer of an oligomer obtained by reacting an organic polyisocyanate (carbodiimide oligomer) and a monomer copolymerizable with the oligomer. Can also be synthesized.
- combination of this polycarbodiimide organic diisocyanate is preferable.
- Examples of the organic diisocyanate used for the synthesis of polycarbodiimide include those described in JP-A-2005-49370. Among these, 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate are particularly preferable from the viewpoint of storage stability of a binder composition or a slurry composition containing polycarbodiimide as the crosslinking agent (B).
- An organic diisocyanate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- organic polyisocyanates having three or more isocyanate groups (trifunctional or higher functional organic polyisocyanates), and stoichiometric excesses of trifunctional or higher organic polyisocyanates and difunctional or higher polyfunctionality.
- Terminal isocyanate prepolymer obtained by reaction with a reactive active hydrogen-containing compound (hereinafter, the trifunctional or higher functional organic polyisocyanate and the terminal isocyanate prepolymer are collectively referred to as “trifunctional or higher functional organic polyisocyanates”). May be used.
- trifunctional or higher functional organic polyisocyanates include those described in JP-A-2005-49370.
- Trifunctional or higher functional organic polyisocyanates may be used alone or in combination of two or more at any ratio.
- the amount of the tri- or higher functional organic polyisocyanate used in the polycarbodiimide synthesis reaction is usually 40 parts by mass or less, preferably 20 parts by mass or less, per 100 parts by mass of the organic diisocyanate.
- an organic monoisocyanate can be added as necessary.
- an organic monoisocyanate when the organic polyisocyanate contains organic polyisocyanates having a functionality of 3 or more, the molecular weight of the resulting polycarbodiimide can be appropriately regulated, and the organic diisocyanate is used in combination with the organic monoisocyanate. By doing so, a polycarbodiimide having a relatively small molecular weight can be obtained.
- organic monoisocyanates include those described in JP-A-2005-49370.
- An organic monoisocyanate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the amount of the organic monoisocyanate used in the synthesis reaction of the polycarbodiimide depends on the molecular weight required for the obtained polycarbodiimide and the presence or absence of the use of trifunctional or higher functional organic polyisocyanates. It is usually 40 parts by mass or less, preferably 20 parts by mass or less per 100 parts by mass of the organic polyisocyanate having a functionality or higher) component.
- examples of the carbodiimidization catalyst include phospholene compounds, metal carbonyl complexes, metal acetylacetone complexes, and phosphate esters. Specific examples of these are disclosed in, for example, JP-A-2005-49370.
- a carbodiimidization catalyst may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the amount of the carbodiimidization catalyst used is usually 0.001 part by mass or more, preferably 0.01 part by mass per 100 parts by mass of the total organic isocyanate (organic monoisocyanate, organic diisocyanate, and trifunctional or higher functional organic polyisocyanate) component. Part or more, usually 30 parts by weight or less, preferably 10 parts by weight or less.
- the carbodiimidization reaction of organic polyisocyanate can be carried out in the absence of a solvent or in a suitable solvent.
- the solvent for carrying out the synthesis reaction in the solvent is not particularly limited as long as it can dissolve the polycarbodiimide or carbodiimide oligomer generated by heating during the synthesis reaction, and is a halogenated hydrocarbon solvent, ether solvent. , Ketone solvents, aromatic hydrocarbon solvents, amide solvents, aprotic polar solvents, and acetate solvents. Specific examples of these are disclosed in, for example, JP-A-2005-49370. These solvents may be used alone or in combination of two or more at any ratio.
- the amount of the solvent used in the synthesis reaction of the polycarbodiimide is such that the concentration of the total organic isocyanate component is usually 0.5% by mass or more, preferably 5% by mass or more, usually 60% by mass or less, preferably 50% by mass or less. It is. If the concentration of the total organic isocyanate component in the solvent is too high, the polycarbodiimide or carbodiimide oligomer produced may gel during the synthesis reaction, and if the concentration of the total organic isocyanate component in the solvent is too low, the reaction will occur. The speed is slow and productivity is reduced.
- the temperature of the carbodiimidization reaction of the organic polyisocyanate is appropriately selected according to the type of the organic isocyanate component and the carbodiimidization catalyst, but is usually 20 ° C. or higher and 200 ° C. or lower.
- the organic isocyanate component may be added in the whole amount before the reaction, or a part or the whole thereof may be added continuously or stepwise during the reaction.
- a compound capable of reacting with an isocyanate group is added at an appropriate reaction stage from the initial stage to the late stage of the carbodiimidization reaction of the organic polyisocyanate, and the terminal isocyanate group of the polycarbodiimide is sealed.
- the molecular weight of the polycarbodiimide can also be adjusted. Further, the molecular weight of the resulting polycarbodiimide can be regulated to a predetermined value by adding in the latter stage of the carbodiimidization reaction of the organic polyisocyanate.
- a compound capable of reacting with an isocyanate group include alcohols such as methanol, ethanol, i-propanol and cyclohexanol; and amines such as dimethylamine, diethylamine and benzylamine.
- a hydric alcohol, polyalkylene oxide, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, polyethylene glycol monoacrylate, or polypropylene glycol monoacrylate is preferred.
- polycarbodiimide having a polycarbodiimide group and a monomer unit derived from a divalent alcohol is synthesized by copolymerizing a divalent alcohol having a hydroxyl group at both ends of the molecular chain with a carbodiimide oligomer by a known method. can do.
- the polycarbodiimide as the crosslinking agent (B) has a divalent or higher alcohol-derived monomer unit, preferably a divalent alcohol-derived monomer unit, the binder composition containing the polycarbodiimide.
- the wettability of the battery member (for example, the negative electrode) formed from the electrolyte solution to the electrolyte solution can be improved, and the injection property of the electrolyte solution in the production of the secondary battery including the battery member can be improved.
- the water solubility of the polycarbodiimide can be increased, and the polycarbodiimide is self-micelleized in water (the hydrophobic carbodiimide group is covered with a hydrophilic ethylene glycol chain). Therefore, chemical stability can be improved.
- the above-described polycarbodiimide is used for preparing the binder composition or slurry composition of the present invention as a solution or as a solid separated from the solution.
- a method for separating polycarbodiimide from a solution for example, a polycarbodiimide solution is added to a non-solvent inert to the polycarbodiimide, and the resulting precipitate or oil is separated and collected by filtration or decantation.
- a method of separating and collecting by spray drying a method of separating and collecting by using a change in solubility with respect to the temperature of the solvent used in the synthesis of the obtained polycarbodiimide, that is, immediately after the synthesis, the solvent is dissolved in the solvent
- a method of separating and collecting from the turbid liquid by filtration or the like can be exemplified, and further, these separation and collecting methods can be appropriately combined.
- the number average molecular weight in terms of polystyrene (hereinafter referred to as “Mn”) determined by gel permeation chromatography (GPC) of polycarbodiimide in the present invention is usually 400 or more, preferably 1,000 or more, particularly preferably 2,000.
- the above is usually 500,000 or less, preferably 200,000 or less, particularly preferably 100,000 or less.
- the modified polycarbodiimide is prepared by adding at least one reactive compound to at least one polycarbodiimide having a repeating unit represented by the general formula (2) at an appropriate temperature in the presence or absence of a suitable catalyst. It can be synthesized by reaction (hereinafter referred to as “denaturation reaction”).
- the reactive compound used for the synthesis of the modified polycarbodiimide has one group having reactivity with the polycarbodiimide (hereinafter, simply referred to as “reactive group”) in the molecule, and another functional group.
- This reactive compound can be an aromatic compound, an aliphatic compound or an alicyclic compound, and the ring structure in the aromatic compound and the alicyclic compound may be a carbocyclic ring or a heterocyclic ring.
- the reactive group in the reactive compound may be a group having active hydrogen, and examples thereof include a carboxyl group or a primary or secondary amino group.
- a reactive compound has another functional group in addition to one reactive group in the molecule
- Other functional groups include groups having an action of accelerating the crosslinking reaction of polycarbodiimide and / or modified polycarbodiimide, and the second and subsequent groups in one molecule of the reactive compound (that is, different from the above-mentioned reactive group).
- the above-mentioned groups having active hydrogen are also included.
- carboxylic acid anhydride groups and tertiary amino groups carboxyl groups exemplified as groups having active hydrogen and primary or secondary amino groups Groups and the like.
- two or more identical or different groups may exist in one molecule of the reactive compound.
- Examples of the reactive compound include those described in JP-A-2005-49370. Of these, trimellitic anhydride and nicotinic acid are preferable.
- a reactive compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the amount of the reactive compound used in the modification reaction for synthesizing the modified polycarbodiimide is appropriately adjusted according to the type of polycarbodiimide and reactive compound, the physical properties required of the resulting modified polycarbodiimide, etc.
- the ratio of the reactive group in the reactive compound to 1 mol of the repeating unit represented by the general formula (2) is preferably 0.01 mol or more, more preferably 0.02 mol or more, preferably 1 mol or less. More preferably, the amount is 0.8 mol or less.
- the reaction between the reactive group in the reactive compound and the repeating unit represented by the general formula (2) of the polycarbodiimide proceeds quantitatively, and the functionality corresponding to the amount of the reactive compound used.
- Groups are introduced into the modified polycarbodiimide.
- the modification reaction can be carried out in the absence of a solvent, but is preferably carried out in a suitable solvent.
- a solvent is not particularly limited as long as it is inactive with respect to polycarbodiimide and a reactive compound and can dissolve them. Examples thereof are used for the synthesis of the above-mentioned polycarbodiimide.
- ether solvents, amide solvents, ketone solvents, aromatic hydrocarbon solvents, aprotic polar solvents, and the like are used for the synthesis of the above-mentioned polycarbodiimide.
- the amount of the solvent used in the modification reaction is usually 10 parts by mass or more, preferably 50 parts by mass or more, and usually 10,000 parts by mass or less, preferably 5,000 parts by mass or less, per 100 parts by mass of the reaction raw materials. is there.
- the temperature of the modification reaction is appropriately selected according to the type of polycarbodiimide or reactive compound, but is usually ⁇ 10 ° C. or higher, usually 100 ° C. or lower, preferably 80 ° C. or lower.
- the Mn of the modified polycarbodiimide in the present invention is usually 500 or more, preferably 1,000 or more, more preferably 2,000 or more, and usually 1,000,000 or less, preferably 400,000 or less, more preferably 200. , 000 or less.
- NCN equivalent The chemical formula amount (NCN equivalent) per mole of the carbodiimide group (—N ⁇ C ⁇ N—) of the carbodiimide compound used as the crosslinking agent (B) is preferably 300 or more, more preferably 400 or more, preferably 600 or less, more preferably 500 or less.
- NCN equivalent of the carbodiimide compound is 300 or more, the storage stability of the binder composition or slurry composition of the present invention can be sufficiently secured, and when it is 600 or less, the crosslinking reaction is good as a crosslinking agent. Can proceed to.
- the NCN equivalent of the carbodiimide compound is obtained, for example, by obtaining the polystyrene-equivalent number average molecular weight of the carbodiimide compound using GPC (gel permeation chromatography), and carbodiimide per molecule of the carbodiimide compound using IR (infrared spectroscopy).
- the number of groups can be quantitatively analyzed and calculated using the following formula.
- NCN equivalent (Number average molecular weight in terms of polystyrene of carbodiimide compound) / (Number of carbodiimide groups per molecule of carbodiimide compound)
- oxazoline compound used as the crosslinking agent (B) include compounds having two or more oxazoline groups in the molecule.
- some or all of the hydrogen atoms of the oxazoline group may be substituted with other groups.
- the compound having two or more oxazoline groups in the molecule include, for example, a compound having two oxazoline groups in the molecule (a divalent oxazoline compound), a polymer containing an oxazoline group (an oxazoline group-containing polymer) ).
- divalent oxazoline compounds examples include 2,2′-bis (2-oxazoline), 2,2′-bis (4-methyl-2-oxazoline), and 2,2′-bis (4,4-dimethyl).
- 2,2′-bis (2-oxazoline) is preferable from the viewpoint of forming a more rigid crosslinked structure.
- the oxazoline group-containing polymer is not particularly limited as long as it is a polymer containing an oxazoline group. In the present specification, the above-mentioned divalent oxazoline compound is not included in the oxazoline group-containing polymer.
- the oxazoline group-containing polymer can be synthesized, for example, by copolymerizing an oxazoline group-containing monomer represented by the following general formula (3) with another monomer.
- R 1 , R 2 , R 3 and R 4 each independently have a hydrogen atom, a halogen atom, an alkyl group, an aryl group which may have a substituent, or a substituent.
- An aralkyl group that may be present, and R 5 represents an acyclic organic group having an addition-polymerizable unsaturated bond
- examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a fluorine atom and a chlorine atom are preferable.
- examples of the alkyl group include an alkyl group having 1 to 8 carbon atoms. Among these, an alkyl group having 1 to 4 carbon atoms is preferable.
- examples of the aryl group which may have a substituent include an aryl group which may have a substituent such as a halogen atom.
- examples of the aryl group include aryl groups having 6 to 18 carbon atoms such as phenyl group, tolyl group, xylyl group, biphenyl group, naphthyl group, anthryl group, and phenanthryl group.
- a C6-C12 aryl group which may have a substituent is preferable.
- examples of the aralkyl group which may have a substituent include an aralkyl group which may have a substituent such as a halogen atom.
- examples of the aralkyl group include aralkyl groups having 7 to 18 carbon atoms such as a benzyl group, a phenylethyl group, a methylbenzyl group, and a naphthylmethyl group.
- the C7-C12 aralkyl group which may have a substituent is preferable.
- examples of the acyclic organic group having an addition-polymerizable unsaturated bond include alkenyl groups having 2 to 8 carbon atoms such as vinyl group, allyl group, and isopropenyl group. Of these, vinyl group, allyl group and isopropenyl group are preferable.
- Examples of the oxazoline group-containing monomer represented by the general formula (3) include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-4-ethyl-2- Oxazoline, 2-vinyl-4-propyl-2-oxazoline, 2-vinyl-4-butyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-vinyl-5-ethyl-2-oxazoline, 2-vinyl-5-propyl-2-oxazoline, 2-vinyl-5-butyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl -4-ethyl-2-oxazoline, 2-isopropenyl-4-propyl-2-oxazoline, 2-isopropenyl-4-butyl-2-oxy Zolin, 2-isopropenyl-5-
- the other monomer that can be used for the synthesis of the oxazoline group-containing polymer is not particularly limited as long as it is a known copolymerizable monomer.
- a (meth) acrylic acid monomer, (meta ) Acrylic acid ester monomers and aromatic monomers are preferred.
- (meth) acryl means acryl and / or methacryl.
- Examples of (meth) acrylic acid monomers that can be used in the synthesis of oxazoline group-containing polymers include acrylic acid, methacrylic acid, and acrylic acid salts such as sodium acrylate and ammonium acrylate, sodium methacrylate, and ammonium methacrylate.
- Methacrylic acid salts of These (meth) acrylic acid monomers may be used alone or in combination of two or more at any ratio.
- Examples of (meth) acrylic acid ester monomers that can be used for the synthesis of oxazoline group-containing polymers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, and perfluoroalkylethyl acrylate.
- Acrylates such as phenyl acrylate, 2-hydroxyethyl acrylate, 2-aminoethyl acrylate and salts thereof, methoxypolyethylene glycol acrylate, monoesters of acrylic acid and polyethylene glycol; methyl methacrylate, methacrylic acid Butyl, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, methoxypolyethylene glycol methacrylate, monoesterified product of methacrylic acid and polyethylene glycol, 2-methacrylic acid 2- Such Minoechiru and methacrylic acid esters, such as salts thereof.
- These (meth) acrylic acid ester monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- aromatic monomer examples include styrene compounds such as styrene, ⁇ -methylstyrene, and sodium styrenesulfonate. These aromatic monomers may be used alone or in combination of two or more at any ratio.
- An oxazoline group-containing polymer is synthesized by polymerizing these monomers at the usage ratio described in, for example, JP2013-72002A, JP2644161A, etc. Can do.
- the oxazoline group-containing polymer may be synthesized, for example, by polymerizing a polymer that does not have an oxazoline group, and then substituting part or all of the functional groups in the polymer with the oxazoline group.
- the glass transition temperature (Tg) of the oxazoline group-containing polymer is preferably ⁇ 50 ° C. or higher, more preferably ⁇ 20 ° C. or higher, preferably 60 ° C. or lower, more preferably 30 ° C. or lower.
- the "glass transition temperature" of an oxazoline group containing polymer can be measured based on the method used with the particulate polymer (C) as described in the Example of this specification.
- the chemical formula amount (oxazoline equivalent) per mole of the oxazoline group of the oxazoline compound used as the crosslinking agent (B) is preferably 70 or more, more preferably 100 or more, still more preferably 300 or more, preferably 600. Below, more preferably 500 or less.
- This oxazoline equivalent is also called an oxazoline value (mass per mole of oxazoline group (g-solid / eq.)).
- the oxazoline equivalent of the oxazoline compound is 70 or more, the storage stability of the binder composition or slurry composition of the present invention can be sufficiently secured, and when it is 600 or less, the crosslinking reaction is good as a crosslinking agent.
- the oxazoline equivalent of the oxazoline compound can be calculated using the following formula.
- Oxazoline equivalent (molecular weight of oxazoline compound) / (number of oxazoline groups per molecule of oxazoline compound)
- the molecular weight of the oxazoline compound can be, for example, a polystyrene-equivalent number average molecular weight measured using GPC (gel permeation chromatography).
- the number of oxazoline groups per molecule can be quantified using, for example, IR (infrared spectroscopy).
- the viscosity of the 1% by mass aqueous solution of the crosslinking agent (B) is preferably 5000 mPa ⁇ s or less, more preferably 700 mPa ⁇ s or less, and particularly preferably 150 mPa ⁇ s or less.
- the viscosity of the 1 mass% aqueous solution of a crosslinking agent (B) can be measured by the method similar to the viscosity of the 1 mass% aqueous solution of the above-mentioned carboxymethylcellulose (salt).
- the crosslinking agent (B) is preferably water-soluble. Since the crosslinking agent (B) is water-soluble, the crosslinking agent (B) is prevented from being unevenly distributed in the aqueous slurry composition containing the binder composition, and the obtained negative electrode mixture layer forms a suitable crosslinked structure. Can do. Accordingly, it is possible to secure the adhesion strength between the negative electrode mixture layer and the current collector in the obtained secondary battery, improve the cycle characteristics, and suppress the increase in resistance after the cycle. Furthermore, the water resistance of the negative electrode can be improved.
- crosslinking agent is “water-soluble” means that 1 part by mass of the crosslinking agent (corresponding to the solid content) is added per 100 parts by mass of ion-exchanged water, and the mixture obtained by stirring is adjusted to a temperature.
- pH adjustment uses NaOH aqueous solution and / or HCl aqueous solution.
- the crosslinking agent shall be water-soluble.
- the mixture of the crosslinking agent and water is separated into two phases from the viewpoint of improving the cross-linking structure formation reaction and improving the adhesion strength and cycle characteristics between the negative electrode mixture layer and the current collector. More preferably, it is in a one-phase water-soluble state, that is, the crosslinking agent is one-phase water-soluble.
- ⁇ Particulate polymer (C)> A particulate polymer (C) having a functional group that reacts with the crosslinking agent (B) and containing an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit (hereinafter referred to as “particulate polymer (C ) "May be abbreviated as”"when the electrode member (for example, the negative electrode) is formed using the slurry composition containing the binder composition for a secondary battery of the present invention. It is a component which can hold
- the electrode member is a negative electrode and the negative electrode mixture layer is formed using the slurry composition
- the particulate polymer in the negative electrode mixture layer is immersed in the electrolytic solution, While maintaining the particulate shape while absorbing and swelling the electrolytic solution, the negative electrode active materials are bound together, and the negative electrode active material is prevented from falling off the current collector.
- the particulate polymer also binds particles other than the negative electrode active material contained in the negative electrode mixture layer, and also plays a role of maintaining the strength of the negative electrode mixture layer.
- “including a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.
- the particulate polymer (C) used in the present invention has a functional group that the crosslinking agent (B) has, for example, a functional group that reacts with a carbodiimide group or an oxazoline group, and an aliphatic conjugated diene monomer unit and an aromatic group. Group vinyl monomer units. Since the particulate polymer (C) has a functional group that reacts with the crosslinking agent (B), the particulate polymers (C) and the water-soluble thickener ( Crosslinking between A) and the particulate polymer (C) becomes possible.
- the particulate polymer (C) is a low-rigidity and flexible repeating unit, an aliphatic conjugated diene monomer unit capable of enhancing the binding property, and the solubility of the polymer in the electrolytic solution.
- the binder composition for secondary batteries of the present invention needs to contain 10 parts by mass or more of the particulate polymer (C) per 100 parts by mass of the water-soluble thickener (A), preferably 50 parts by mass or more, more preferably 60 parts by mass or more, particularly preferably 80 parts by mass or more, most preferably 100 parts by mass or more, and less than 500 parts by mass, preferably 300 parts by mass or less, More preferably, it is 270 mass parts or less, Most preferably, it is 250 mass parts or less, Most preferably, it contains 150 mass parts or less.
- the binder composition for secondary batteries contains 10 parts by mass or more of the particulate polymer (C) per 100 parts by mass of the water-soluble thickener (A), the cross-linked structure is well formed and the binding property is increased. Can be secured. Therefore, for example, the strength of the negative electrode mixture layer obtained using the binder composition can be ensured, and swelling of the negative electrode can be sufficiently suppressed. And the adhesiveness of a negative electrode compound-material layer and an electrical power collector can be ensured. Moreover, the binder composition for secondary batteries contains less than 500 parts by mass of the particulate polymer (C) per 100 parts by mass of the water-soluble thickener (A), so that the injection property of the electrolytic solution and the water resistance of the negative electrode are reduced. Can be secured. Moreover, it can suppress that impurities, such as an emulsifier which remain
- impurities such as an
- the “particulate polymer” is a polymer that can be dispersed in an aqueous medium such as water, and exists in a particulate form in the aqueous medium.
- the particulate polymer has an insoluble content of 90% by mass or more when 0.5 g of the particulate polymer is dissolved in 100 g of water at 25 ° C.
- examples of the functional group that reacts with the crosslinking agent (B) in the particulate polymer (C) include a carboxyl group, a hydroxyl group, a glycidyl ether group, and a thiol group.
- the particulate polymer (C) is any one of a carboxyl group, a hydroxyl group, and a thiol group.
- it has at least one of a carboxyl group and a hydroxyl group.
- the particulate polymer (C) particularly preferably has both a carboxyl group and a hydroxyl group from the viewpoints of both cycle characteristics and suppression of swelling of the negative electrode accompanying charge / discharge.
- the aliphatic conjugated diene monomer that can form the aliphatic conjugated diene monomer unit of the particulate polymer (C) is not particularly limited, and 1,3-butadiene, 2-methyl-1,3 -Butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, among others, 1,3-butadiene Is preferred.
- an aliphatic conjugated diene monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- the content of the aliphatic conjugated diene monomer unit is preferably 20% by mass or more, more preferably 30% by mass or more, preferably 70% by mass or less, more preferably 60%. It is at most 55% by mass, particularly preferably at most 55% by mass.
- the content ratio of the aliphatic conjugated diene monomer unit is 20% by mass or more, the flexibility of the negative electrode can be increased, and when the content is 70% by mass or less, the negative electrode mixture layer and the current collector In addition, the electrolyte solution resistance of the negative electrode obtained using the secondary battery binder composition of the present invention can be improved.
- the aromatic vinyl monomer that can form the aromatic vinyl monomer unit of the particulate polymer (C) is not particularly limited, and includes styrene, ⁇ -methylstyrene, vinyl toluene, divinylbenzene, and the like. Among them, styrene 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.
- the content ratio of the aromatic vinyl monomer unit is preferably 30% by mass or more, more preferably 35% by mass or more, preferably 79.5% by mass or less, more preferably. It is 69 mass% or less.
- the content of the aromatic vinyl monomer unit is 30% by mass or more, the electrolytic solution resistance of the negative electrode obtained using the binder composition for a secondary battery of the present invention can be improved, 79.
- the adhesiveness of a negative electrode compound material layer and a collector can be made favorable.
- the particulate polymer (C) contains 1,3-butadiene units as aliphatic conjugated diene monomer units and styrene units as aromatic vinyl monomer units (that is, styrene-butadiene copolymer). It is preferable that
- the particulate polymer (C) needs to have a functional group that reacts with the crosslinking agent (B). That is, the particulate polymer (C) needs to have a monomer unit containing a functional group that reacts with the crosslinking agent (B).
- the monomer unit containing a functional group that reacts with the crosslinking agent (B) include an ethylenically unsaturated carboxylic acid monomer unit, an unsaturated monomer unit having a hydroxyl group, and an unsaturated monomer having a glycidyl ether group. Examples thereof include a unit and a monomer unit having a thiol group.
- Examples of the ethylenically unsaturated carboxylic acid monomer that can be used in the production of the particulate polymer (C) having a carboxylic acid group as a functional group that reacts with the crosslinking agent (B) include acrylic acid, methacrylic acid, crotonic acid, Examples thereof include monocarboxylic and dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, and anhydrides thereof.
- acrylic acid, methacrylic acid and itaconic acid are preferable as the ethylenically unsaturated carboxylic acid monomer from the viewpoint of the stability of the slurry composition containing the binder composition of the present invention.
- these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- Examples of unsaturated monomers having a hydroxyl group that can be used in the production of the particulate polymer (C) having a hydroxyl group as a functional group that reacts with the crosslinking agent (B) include 2-hydroxyethyl acrylate and 2-hydroxyethyl.
- 2-hydroxyethyl acrylate is preferred.
- these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- Examples of unsaturated monomers having a glycidyl ether group that can be used in the production of the particulate polymer (C) having a glycidyl ether group as a functional group that reacts with the crosslinking agent (B) include glycidyl acrylate and glycidyl. And methacrylate. Of these, glycidyl methacrylate is preferred. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- Examples of the monomer unit having a thiol group that can be used in the production of the particulate polymer (C) having a thiol group as a functional group that reacts with the crosslinking agent (B) include pentaerythritol tetrakis (3-mercaptobutyrate). ), Trimethylolpropane-tris (3-mercaptobutyrate), trimethylolethane-tris (3-mercaptobutyrate), and the like. Among these, pentaerythritol tetrakis (3-mercaptobutyrate) is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- the functional group that reacts with the crosslinking agent (B) in the particulate polymer (C) is introduced by using a monomer containing a functional group that reacts with the crosslinking agent (B) as described above for polymerization. For example, after polymerizing a particulate polymer that does not have a functional group that reacts with the crosslinking agent (B), the functional group in the particulate polymer is converted into a functional group that reacts with the crosslinking agent (B).
- Particulate polymer (C) may be prepared by introducing by partial or complete substitution.
- repeating unit in the granular polymer (C) having the “functional group that reacts with the crosslinking agent (B)” introduced in this way is also a “single quantity including a functional group that reacts with the crosslinking agent (B)”. It shall be included in “body unit”.
- the content rate of the monomer unit containing the functional group which reacts with a crosslinking agent (B) in a particulate polymer (C) is not specifically limited, 10 mass% or less is preferable and an upper limit is 8 mass% or less. More preferably, 5% by mass or less is particularly preferable, while the lower limit is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more. If the content rate of the said monomer is the said range, it will be excellent in the mechanical stability and chemical stability of the particulate polymer (C) obtained.
- the particulate polymer (C) may contain any repeating unit 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, and an unsaturated carboxylic acid amide monomer.
- these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- vinyl cyanide monomer examples include acrylonitrile, methacrylonitrile, ⁇ -chloroacrylonitrile, ⁇ -ethylacrylonitrile and the like. Of these, acrylonitrile and methacrylonitrile are preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl Examples thereof include fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. Of these, methyl methacrylate is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- 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. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- the particulate polymer (C) may be produced using monomers used in usual emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, and the like. . In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
- the upper limit is preferably 10% by mass or less, more preferably 8% by mass or less, particularly preferably 5% by mass or less, while the lower limit is preferably 0.5% by mass or more. 1.0 mass% or more is more preferable, and 1.5 mass% or more is especially preferable.
- a particulate polymer (C) is manufactured by superposing
- the content ratio of each monomer in the monomer composition is usually the same as the content ratio of the repeating unit in the desired particulate polymer (C).
- the aqueous solvent is not particularly limited as long as the particulate polymer (C) is dispersible in a particle state, and usually has a boiling point at normal pressure of usually 80 ° C. or higher, preferably 100 ° C. or higher. It is selected from aqueous solvents at 350 ° C. or lower, preferably 300 ° C. or lower.
- examples of the aqueous solvent include water; ketones such as diacetone alcohol and ⁇ -butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol, and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, and ethyl cellosolve.
- Glycol ethers such as ethylene glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; 1,3 -Ethers such as dioxolane, 1,4-dioxolane and tetrahydrofuran;
- water is particularly preferable from the viewpoint that it is not flammable and a dispersion of particles of the particulate polymer (C) can be easily obtained.
- 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.
- the binder composition of the present invention or the slurry composition of the present invention is used as it is. From the viewpoint of production efficiency, such as being capable of being used for production, the emulsion polymerization method is particularly preferred.
- the emulsion polymerization can be performed according to a conventional method.
- seed polymerization may be performed using seed particles.
- the polymerization conditions can also be arbitrarily selected depending on the polymerization method and the type of polymerization initiator.
- the aqueous dispersion of particulate polymer (C) particles obtained by the above-described polymerization method is, for example, alkali metal (for example, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium.
- alkali metal for example, Li, Na, K, Rb, Cs
- ammonia inorganic ammonium.
- a basic aqueous solution containing a compound for example, NH 4 Cl
- an organic amine compound for example, ethanolamine, diethylamine
- the particulate polymer (C) is water-insoluble. Therefore, the particulate polymer (C) is usually in the form of particles in the aqueous binder composition and the aqueous slurry composition, and is contained in, for example, the negative electrode for a secondary battery while maintaining the particle shape. .
- the particulate polymer (C) has a number average particle size of preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, more preferably 400 nm or less. When the number average particle size is in the above range, the strength and flexibility of the obtained negative electrode can be improved.
- the number average particle diameter can be easily measured by transmission electron microscopy, Coulter counter, laser diffraction scattering method, or the like.
- the gel content of the particulate polymer (C) is preferably 50% by mass or more, more preferably 80% by mass or more, preferably 98% by mass or less, more preferably 95% by mass or less.
- the gel content of the particulate polymer (C) is less than 50% by mass, the cohesive force of the particulate polymer (C) may be reduced, and the adhesion to the current collector or the like may be insufficient.
- the gel content of the particulate polymer (C) is more than 98% by mass, the particulate polymer (C) loses toughness and becomes brittle, and as a result, the adhesion may be insufficient.
- the "gel content" of a particulate polymer (C) can be measured using the measuring method as described in the Example of this specification.
- the glass transition temperature (T g ) of the particulate polymer (C) is preferably ⁇ 30 ° C. or higher, more preferably ⁇ 20 ° C. or higher, preferably 80 ° C. or lower, more preferably 30 ° C. or lower.
- T g glass transition temperature
- the glass transition temperature of the particulate polymer (C) is ⁇ 30 ° C. or higher, the blended components in the slurry composition containing the binder composition for a secondary battery of the present invention are prevented from aggregating and settling, The stability of the slurry composition can be ensured. Furthermore, swelling of the negative electrode can be suitably suppressed. Moreover, workability at the time of apply
- the glass transition temperature of a particulate polymer (C) is 80 degrees C or less. Can be good.
- the “glass transition temperature” of the particulate polymer (C) can be measured using the measuring method described in the examples of the present specification.
- the glass transition temperature and gel content of particulate polymer (C) are suitably adjusted by changing the preparation conditions (for example, the monomer to be used, polymerization conditions, etc.) of particulate polymer (C). be able to.
- the glass transition temperature can be adjusted by changing the type and amount of the monomer used. For example, the use of a monomer such as styrene or acrylonitrile can increase the glass transition temperature. When a monomer such as butadiene is used, the glass transition temperature can be lowered.
- the gel content can be adjusted by changing the polymerization temperature, the type of polymerization initiator, the type and amount of molecular weight regulator, the conversion rate when the reaction is stopped, for example, by reducing the chain transfer agent
- the gel content can be increased, and the gel content can be decreased by increasing the chain transfer agent.
- the binder composition of the present invention comprises a water-soluble thickener (A), a crosslinking agent (B), and an invention for an aqueous dispersion of the particulate polymer (C) obtained by polymerizing the monomer composition. It can be prepared by adding any other components within a range not impairing the effect.
- the slurry composition for secondary battery electrodes of the present invention comprises a water-soluble thickener (A) having a hydroxyl group or a carboxyl group, a crosslinking agent (B) having a carbodiimide group or an oxazoline group, and a particulate polymer (C).
- the particulate polymer (C) has a functional group that reacts with the crosslinking agent (B), and has an aliphatic conjugated diene monomer unit and an aromatic group. Contains vinyl monomer units.
- the slurry composition for secondary battery electrodes of the present invention contains 0.001 part by mass or more and less than 100 parts by mass of the crosslinking agent (B) per 100 parts by mass of the water-soluble thickener (A),
- the particulate styrene butadiene copolymer (C) is contained in an amount of 10 parts by mass or more and less than 500 parts by mass.
- an electrode mixture layer that has excellent adhesion to the current collector and can improve the electrical characteristics of the secondary battery is formed. be able to.
- the water-soluble thickener (A), the cross-linking agent (B), and the particulate polymer (C) contained in the slurry composition for secondary battery electrodes of the present invention are each the above-described secondary battery of the present invention.
- the thing similar to what was described in the term of the binder composition for can be used in the same compounding ratio.
- the electrode active material is a substance that transfers electrons in the electrodes (positive electrode and negative electrode) of the secondary battery.
- the electrode active material (negative electrode active material) used in the negative electrode of the lithium ion secondary battery will be described as an example.
- a material that can occlude and release lithium As a negative electrode active material of a lithium ion secondary battery, a material that can occlude and release lithium is usually used.
- the material that can occlude and release lithium include a carbon-based negative electrode active material, a metal-based negative electrode active material, and a negative electrode active material obtained by combining these materials.
- the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”).
- examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials. Is mentioned.
- the carbonaceous material is a material having a low degree of graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000 ° C. or lower.
- the minimum of the heat processing temperature at the time of carbonizing is not specifically limited, For example, it can be 500 degreeC or more.
- the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon.
- the graphitizable carbon for example, a carbon material using tar pitch obtained from petroleum or coal as a raw material can be mentioned.
- examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.
- the graphite material is a material having high crystallinity close to that of graphite obtained by heat-treating graphitizable carbon at 2000 ° C. or higher.
- the upper limit of heat processing temperature is not specifically limited, For example, it can be 5000 degrees C or less.
- the graphite material include natural graphite and artificial graphite.
- the artificial graphite for example, artificial graphite obtained by heat-treating carbon containing graphitizable carbon mainly at 2800 ° C. or higher, graphitized MCMB heat-treated at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. Examples thereof include graphitized mesophase pitch-based carbon fibers that have been heat-treated.
- the carbon-based negative electrode active material it is preferable to use natural graphite (amorphous coated natural graphite) having at least a part of its surface coated with amorphous carbon.
- amorphous coated natural graphite By using amorphous coated natural graphite, the density of the obtained negative electrode mixture layer can be improved, and the adhesion between the current collector and the negative electrode mixture layer and the cycle characteristics of the secondary battery can be ensured.
- a mixture of amorphous coated natural graphite and artificial graphite may be used as the negative electrode active material.
- artificial graphite is bulky as compared with amorphous coated natural graphite, but it tends to collapse as particles, and when the electrode is pressed, the particles tend to be oriented.
- the amorphous coated natural graphite is mixed in the total amount of amorphous coated natural graphite and artificial graphite.
- the proportion of the amount is preferably 30% by mass or more, more preferably 60% by mass or more, and particularly preferably 80% by mass or more.
- the amorphous coated natural graphite is not particularly limited and can be produced using a known method.
- Examples of the method for producing amorphous coated natural graphite include a method in which the surface of natural graphite is covered with a pitch using petroleum residue as a raw material and heated at about 1000 ° C.
- the metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more.
- the metal active material include lithium metal and a single metal capable of forming a lithium alloy (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn). , Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof.
- active materials containing silicon are preferable. This is because the capacity of the lithium ion secondary battery can be increased by using the silicon-based negative electrode active material.
- silicon-based negative electrode active material examples include silicon (Si), an alloy containing silicon, SiO, SiO x , a mixture of a Si-containing material and a carbon material, and Si formed by coating or combining a Si-containing material with conductive carbon. Examples thereof include composites of the contained material and conductive carbon.
- the alloy containing silicon examples include an alloy containing silicon, aluminum, and iron, and further containing a rare earth element such as tin and yttrium. Such an alloy can be prepared, for example, by melt spinning. Examples of such an alloy include those described in JP2013-65569A.
- SiO x is a compound containing at least one of SiO and SiO 2 and Si, and x is usually 0.01 or more and less than 2. Then, SiO x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or steam after grinding and mixing SiO and optionally a polymer.
- SiO x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or steam
- Si-containing materials such as silicon and SiO x and carbon materials such as carbonaceous materials and graphite materials are optionally pulverized and mixed in the presence of a polymer such as polyvinyl alcohol. The thing which was done is mentioned.
- a carbonaceous material and a graphite material the material which can be used as a carbon-type negative electrode active material can be used.
- a composite of Si-containing material and conductive carbon for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam.
- an organic gas and / or steam can be mentioned.
- the negative electrode active material when a carbon-based negative electrode active material or a metal-based negative electrode active material is used as the negative electrode active material, these negative electrode active materials expand and contract with charge / discharge. Therefore, when these negative electrode active materials are used, normally, the negative electrode gradually expands due to repeated expansion and contraction of the negative electrode active material, the secondary battery is deformed, and electrical characteristics such as cycle characteristics are obtained. May be reduced.
- the negative electrode formed using the binder composition of the present invention the negative electrode has a cross-linked structure formed by the water-soluble thickener (A), the cross-linking agent (B), and the particulate polymer (C). Swelling of the negative electrode due to expansion and contraction of the active material can be suppressed, and cycle characteristics can be improved.
- capacitance of a lithium ion secondary battery can be increased if the said silicon-type negative electrode active material is used, generally a silicon-type negative electrode active material expand
- a mixture of a carbon-based negative electrode active material and a silicon-based negative electrode active material is used as the negative electrode active material, from the viewpoint of sufficiently increasing the capacity of the lithium ion secondary battery while sufficiently suppressing the occurrence of swelling of the negative electrode.
- artificial graphite as a carbon-based negative electrode active material, Si as a silicon-based negative electrode active material, an alloy containing silicon, SiO x , a mixture of a Si-containing material and a carbon material, and a Si-containing material and a conductive material.
- the silicon-based negative electrode active material at least one of an alloy containing silicon and a composite of Si-containing material and conductive carbon is used. More preferably be used, an alloy containing silicon, and a composite compound of SiO x is dispersed in a matrix of conductive carbon (Si-SiO x It is particularly preferred to use at least one of the C complex). While these negative electrode active materials can occlude and release a relatively large amount of lithium, the volume change when lithium is occluded and released is relatively small.
- the capacity of the battery can be sufficiently increased.
- an alloy containing silicon is used, the capacity of the lithium ion secondary battery can be sufficiently increased, and the initial coulomb efficiency and cycle characteristics can be improved.
- the negative electrode active material preferably contains more than 0 parts by mass and 100 parts by mass or less of silicon-based negative electrode active material per 100 parts by mass of the carbon-based negative electrode active material, more preferably 10 parts by mass or more and 70 parts by mass or less. It is particularly preferable that the content is at least 50 parts by mass.
- the lithium ion secondary battery is sufficiently The capacity can be increased. Moreover, the generation
- the particle size and specific surface area of the negative electrode active material are not particularly limited, and can be the same as those of conventionally used negative electrode active materials.
- the slurry composition for secondary battery electrodes of the present invention preferably contains 5000 parts by mass or more, more preferably 8000 parts by mass or more of the negative electrode active material per 100 parts by mass of the water-soluble thickener (A). 15000 parts by mass or less, more preferably 12000 parts by mass or less.
- the secondary battery electrode slurry composition contains the negative electrode active material, preferably 5000 parts by mass or more per 100 parts by mass of the water-soluble thickener (A), whereby the secondary battery obtained using the slurry composition Electron transfer at the negative electrode is sufficient, and it functions well as a secondary battery.
- the slurry composition contains 15000 parts by mass or less of the negative electrode active material per 100 parts by mass of the water-soluble thickener, the swelling of the negative electrode is suppressed, and the slurry composition is applied to the current collector. The workability at the time can be ensured.
- the slurry composition for a secondary battery electrode of the present invention may contain components such as a conductive material, a reinforcing material, a leveling agent, and an electrolytic solution additive in addition to the above components. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Moreover, the binder composition for secondary batteries of this invention may contain these other components.
- the slurry composition for a secondary battery electrode of the present invention may be prepared by arbitrarily premixing each of the above components and then dispersing it in an aqueous medium as a dispersion medium, or a water-soluble thickener ( After preparing the binder composition of this invention containing A), a crosslinking agent (B), and a particulate polymer (C), this binder composition and an electrode active material are put into an aqueous medium as a dispersion medium. It may be prepared by dispersing.
- the water-soluble thickener (A) and the crosslinking agent (B) are dispersed by dispersing each component in an aqueous medium as a dispersion medium. It is preferable to prepare a slurry composition containing the particulate polymer (C) (that is, including the binder composition of the present invention). Specifically, the above components and the aqueous medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or a fill mix.
- a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, or a fill mix.
- a slurry composition water is usually used as the aqueous medium, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used.
- the solid content concentration of the slurry composition is a concentration at which each component can be uniformly dispersed, for example, 30% by mass to 90% by mass, and more preferably 40% by mass to 80% by mass. Can do.
- the mixing of each of the above components and the aqueous medium can usually be carried out in the range of room temperature to 80 ° C. for 10 minutes to several hours.
- the negative electrode for secondary batteries of this invention can be manufactured using the slurry composition for secondary battery electrodes of this invention. And the negative electrode for secondary batteries of this invention is equipped with the electrical power collector and the negative electrode composite material layer formed on the electrical power collector, and the negative electrode composite material layer is this invention whose electrode active material is a negative electrode active material. Obtained from the slurry composition for secondary battery electrodes. According to the secondary battery negative electrode of the present invention, the adhesion between the current collector and the negative electrode mixture layer can be improved, and the electrical characteristics of the secondary battery can be improved.
- the negative electrode for a secondary battery of the present invention includes, for example, a step of applying the slurry composition for a secondary battery electrode described above on a current collector (application step), and a secondary battery applied on the current collector. It is manufactured through a step of drying the electrode slurry composition to form a negative electrode mixture layer on the current collector (drying step) and, optionally, a step of further heating the negative electrode mixture layer (heating step). .
- drying step drying the cross-linking reaction via the cross-linking agent (B) proceeds by heat applied in the drying step or heat applied in the heating step.
- the water-soluble thickener (A), the water-soluble thickener (A) and the particulate polymer (C), and the particulate polymer (C) are the crosslinking agent (B).
- a cross-linked structure is formed through cross-linking, and this cross-linked structure can suppress swelling associated with charging and discharging, improve adhesion between the current collector and the negative electrode mixture layer, further improve cycle characteristics, and Thus, the electrical characteristics of the secondary battery can be improved, for example, by suppressing an increase in resistance after cycling.
- this crosslinked structure makes it difficult for the water-soluble thickener (A), the crosslinking agent (B), and the particulate polymer (C) incorporated in the crosslinked structure to dissolve and disperse in water. Water resistance is improved.
- a porous film is provided on an electrode plate having an electrode mixture layer obtained from an aqueous slurry composition for the purpose of improving strength and heat resistance, an aqueous one is used as the porous membrane slurry composition.
- the slurry composition for a porous film is applied on the electrode mixture layer, water-soluble components such as a water-soluble thickener contained in the electrode mixture layer are eluted in the slurry composition for the porous film. There is a problem that the characteristics of the battery are impaired.
- the secondary battery negative electrode formed from the slurry composition of the present invention has improved water resistance as described above, the porous film made of the water-based porous film slurry composition is placed on the negative electrode mixture layer. Even if provided, sufficient battery characteristics can be ensured. Furthermore, the formation of this cross-linked structure unwinds the molecular chain entangled with the water-soluble thickener (A), improves the wettability with respect to the electrolyte, and injects the electrolyte during the production of the secondary battery. Can be improved.
- a method for applying the slurry composition for a secondary battery electrode on the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector or may be applied to both sides. The thickness of the slurry film on the current collector after coating and before drying can be appropriately set according to the thickness of the negative electrode mixture layer obtained by drying.
- an electrically conductive and electrochemically durable material is used as the current collector to which the slurry composition is applied.
- a current collector for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used.
- a copper foil is particularly preferable as the current collector used for the negative electrode.
- the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
- a method for drying the slurry composition on the current collector is not particularly limited, and a known method can be used. For example, drying with warm air, hot air, low-humidity air, vacuum drying, irradiation with infrared rays, electron beams, or the like. A drying method is mentioned.
- a negative electrode mixture layer can be formed on the current collector to obtain a negative electrode for a secondary battery comprising the current collector and the negative electrode mixture layer. it can.
- the crosslinking reaction through a crosslinking agent (B) advances with the applied heat.
- the negative electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the negative electrode mixture layer and the current collector can be improved.
- a heating process is performed to advance the crosslinking reaction so that the crosslinked structure is further sufficient. The heating step is preferably performed at 80 ° C. to 160 ° C. for about 1 hour to 20 hours.
- the secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and uses the negative electrode for a secondary battery of the present invention as the negative electrode. And since the secondary battery of this invention uses the negative electrode for secondary batteries of this invention, while being able to improve an electrical property, the adhesiveness of a negative mix layer and a collector is ensured. be able to.
- the secondary battery of the present invention can be suitably used for, for example, mobile phones such as smartphones, tablets, personal computers, electric vehicles, stationary emergency storage batteries, and the like.
- a known positive electrode used as a positive electrode for a lithium ion secondary battery can be used.
- the positive electrode for example, a positive electrode formed by forming a positive electrode mixture layer on a current collector can be used.
- the current collector one made of a metal material such as aluminum can be used.
- the layer containing a known positive electrode active material, a electrically conductive material, and a binder can be used, and the binder composition for secondary batteries of this invention may be used as a binder. .
- an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.
- the solvent an organic solvent capable of dissolving the electrolyte can be used.
- the solvent include alkyl carbonate solvents such as ethylene carbonate, propylene carbonate, and ⁇ -butyrolactone, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane. , Dioxolane, methyl propionate, methyl formate and the like can be used.
- a lithium salt can be used as the electrolyte.
- the lithium salt for example, those described in JP 2012-204303 A can be used.
- these lithium salts LiPF 6 , LiClO 4 , and CF 3 SO 3 Li are preferable as the electrolyte because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation.
- the electrolytic solution may be a polymer and a gel electrolyte containing the electrolytic solution, or may be an intrinsic polymer electrolyte.
- ⁇ Separator> As the separator, for example, those described in JP 2012-204303 A can be used. Among them, the thickness of the entire separator can be reduced, and thereby the ratio of the electrode active material in the secondary battery can be increased to increase the capacity per volume. A microporous film made of polyethylene, polypropylene, polybutene, or polyvinyl chloride is preferred. Moreover, you may use the separator provided with the porous film formed by binding nonelectroconductive particle with the binder composition for secondary batteries of this invention as a separator.
- the secondary battery of the present invention includes, for example, a positive electrode and a negative electrode that are stacked with a separator interposed between them, wound as necessary according to the shape of the battery, folded into a battery container, and electrolyzed in the battery container. It can be manufactured by injecting and sealing the liquid.
- an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary.
- the shape of the secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, and a flat shape.
- ⁇ Glass transition temperature of particulate polymer (C)> The aqueous dispersion containing the particulate polymer (C) was dried for 3 days in an environment of 50% humidity and 23 ° C. to 25 ° C. to obtain a film having a thickness of 1 ⁇ 0.3 mm. The film was dried in a 120 ° C. hot air oven for 1 hour. Thereafter, the dried film was used as a sample in accordance with JIS K 7121 under the conditions of a measurement temperature of ⁇ 100 ° C. to 180 ° C. and a heating rate of 5 ° C./min. DSC6220SII (differential scanning calorimeter, manufactured by Nanotechnology Inc.) ) was used to measure the glass transition temperature (° C.).
- ⁇ Gel content of particulate polymer (C)> The aqueous dispersion containing the particulate polymer (C) was dried in an environment of 50% humidity and 23 ° C. to 25 ° C. to obtain a film having a thickness of 3 ⁇ 0.3 mm. This film was cut into 1 mm square, and about 1 g was precisely weighed. The mass of the film piece obtained by cutting is defined as w0. This piece of film was immersed in 10 g of tetrahydrofuran (THF) in an environment of 25 ° C. ⁇ 1 ° C. for 24 hours. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass w1 of insoluble matter was measured.
- THF tetrahydrofuran
- Gel content (mass%) (w1 / w0) ⁇ 100 ⁇ Tensile breaking strength of binder film>
- the prepared binder composition for a secondary battery is dried for 3 days in an environment of 50% humidity and 23 ° C. to 25 ° C., and further dried in a hot air oven at 120 ° C. for 1 hour to obtain a thickness of 0.5 ⁇ 0.02 mm.
- the binder film was obtained.
- a tensile test was performed at a tensile rate of 50 mm / min in an environment of a temperature of 25 ⁇ 1 ° C. and a dew point of ⁇ 60 ⁇ 5 ° C.
- the prepared binder composition for a secondary battery was applied to an electrolytic copper foil (NC-WS (registered trademark) manufactured by Furukawa Electric) using a table coater, 20 minutes at 50 ° C., 20 minutes at 120 ° C., hot air It dried with the drier and obtained the binder film of thickness 5 +/- 2micrometer.
- NC-WS registered trademark
- the contact angle was measured by the ⁇ / 2 method using a contact angle meter (manufactured by Kyowa Interface Science) using propylene carbonate (manufactured by Kishida Chemical Co., Ltd., reagent) as a solvent used in the electrolytic solution. It was evaluated according to the criteria. Note that the contact angle is a small desired characteristic, and the smaller this value, the better the wettability with respect to the electrolytic solution.
- the prepared binder composition for a secondary battery is dried for 3 days in an environment of 50% humidity and 23 ° C. to 25 ° C., and further dried in a hot air oven at 120 ° C. for 1 hour to obtain a thickness of 0.5 ⁇ 0.02 mm.
- the binder film was obtained.
- the binder film was cut into 0.5 mm square, and about 1 g was precisely weighed. Let the mass of the film piece obtained by cutting be w f 0.
- Insoluble amount is 95% or more
- the produced laminate cell type lithium ion secondary battery was allowed to stand for 5 hours after injecting the electrolyte, charged to a cell voltage of 3.65 V by a constant current method of 0.2 C, and then aged at 60 ° C. for 12 hours. Treatment was performed, and discharging was performed to a cell voltage of 3.00 V by a constant current method of 0.2C. The lithium ion secondary battery was charged to a cell voltage of 3.82 V at 25 ° C.
- ⁇ C is 85% or more
- the cell voltage was discharged to 3.00 V by a constant current method at 25 ° C. and 0.05 C. Thereafter, the cell voltage was charged to 3.82 V at 25 ° C. by a constant current method of 0.1 C, and left as it was for 5 hours to measure the voltage V 0 ′. Further, a discharge operation of 0.5 C was performed in an environment of ⁇ 10 ° C., and the voltage V 20 ′ 20 seconds after the start of discharge was measured.
- the rate of increase in resistance was defined as ⁇ V fin / ⁇ V ini and evaluated according to the following criteria. The smaller this resistance increase rate ⁇ V fin / ⁇ V ini , the better the resistance increase due to the cycle.
- the produced negative electrode for a secondary battery was cut into a circle having a diameter of 16 mm, and 1 ⁇ L of propylene carbonate (made by Kishida Chemical, reagent) was dropped on the surface having the negative electrode mixture layer. The time until the droplets penetrate into the negative electrode mixture layer (penetration time) was measured visually and evaluated according to the following criteria.
- the produced negative electrode for a secondary battery was cut into a rectangular shape having a length of 100 mm and a width of 10 mm to obtain a test piece.
- Mass change ratio by soaking and heat treatment to the ion exchange water (mass%) defined in [(w a 1-w a 2) / w a 1] ⁇ 100, were evaluated by the following criteria. It shows that a negative electrode is excellent in water resistance, so that this mass change rate is small.
- Mass change rate is 20% or more
- the reaction was stopped by cooling.
- a 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the polymer thus obtained to adjust the pH to 8.
- the unreacted monomer was removed by heating under reduced pressure. Furthermore, it cooled to 30 degrees C or less after that, and obtained the aqueous dispersion liquid of the particulate polymer C1.
- the gel content and the glass transition temperature of the particulate polymer C1 were measured by the method described above. As a result of the measurement, the gel content was 92% and the glass transition temperature (Tg) was 10 ° C.
- Example 1 ⁇ Preparation of secondary battery binder composition> This mixture was prepared by mixing 2 parts of a crosslinking agent B1 corresponding to the solid content as the crosslinking agent (B) and 150 parts of the particulate polymer C1 corresponding to the solid content as the particulate polymer (C) in an environment of 25 ° C. Is added to 100 parts by mass (corresponding to the solid part) of the water-soluble thickener (A) consisting of 2 parts by mass of PAA1 corresponding to the solid part as well as 98 parts by mass of CMC1 corresponding to the solid part.
- a binder composition for a secondary battery was prepared. Using the prepared binder composition for a secondary battery, a binder film was prepared by the method described above, and the tensile strength at break, the wettability with respect to the electrolytic solution, and the water resistance were evaluated. The results are shown in Table 1.
- ⁇ Preparation of slurry composition for secondary battery negative electrode> As a planetary mixer, 10000 parts of natural graphite (amorphous coated natural graphite, BET specific surface area: 3.0 m 2 / g, average particle size: 13 ⁇ m) as a carbon-based active material, water-soluble thickener (A) 98 parts of 1% aqueous solution of CMC1 corresponding to solid content, 2 parts of 1% aqueous solution of PAA1 (pH adjusted to 8 with NaOH) corresponding to solid content, and crosslinker B1 as solid content corresponding to solid content 2 parts, and the aqueous dispersion of the particulate polymer C1 as the particulate polymer (C) is added in an amount of 150 parts corresponding to the solid content, and ion-exchanged water is added and mixed so that the solid content concentration becomes 52%.
- a secondary battery negative electrode slurry composition containing a secondary battery binder composition comprising CMC1, PAA1, cross-linking agent B1, and
- the above-mentioned secondary battery negative electrode slurry composition, a comma coater, the amount with the coating is 8.8 mg / cm 2 or more 9.2 mg / cm 2 or less on the thickness 20 ⁇ m copper foil (collector) It was applied as follows. By transporting the copper foil coated with the secondary battery negative electrode slurry composition at a rate of 0.3 m / min in an oven at 80 ° C. for 2 minutes and further in an oven at 120 ° C. over 2 minutes, The slurry composition on the copper foil was dried to obtain a negative electrode raw material.
- the obtained negative electrode raw material is pressed by a roll press machine so that the composite layer density is 1.45 g / cm 2 or more and 1.55 g / cm 3 or less, and further, the purpose is to further remove moisture and further promote crosslinking.
- the obtained negative electrode raw material was placed in an environment of 120 ° C. under vacuum conditions for 10 hours to obtain a negative electrode formed by forming a negative electrode mixture layer on the current collector.
- the adhesion between the negative electrode mixture layer and the current collector, the pouring property of the electrolytic solution, and the water resistance of the negative electrode were evaluated. The results are shown in Table 1.
- ⁇ Manufacture of positive electrode> 100 parts of LiCoO 2 as a positive electrode active material, 2 parts of acetylene black as a conductive material (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride, “KF manufactured by Kureha Chemical Co., Ltd.) ⁇ 1100 ”) and 2 parts, and N-methylpyrrolidone was added and mixed so that the total solid concentration was 67% to prepare a slurry composition for a secondary battery positive electrode.
- the obtained slurry composition for secondary battery positive electrode was applied onto an aluminum foil having a thickness of 20 ⁇ m with a comma coater 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. Obtained positive electrode raw fabric was pressed to mixture layer density after the pressing by a roll press machine is below 3.40 g / cm 3 or more 3.50 g / cm 3, as further purpose of removing moisture, vacuum A positive electrode formed by forming a positive electrode mixture layer on a current collector for 3 hours in an environment of 120 ° C. under conditions was obtained.
- a single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 ⁇ m; manufactured by a dry method; porosity 55%) was prepared, and cut into a 5 cm ⁇ 5 cm square shape.
- the aluminum packaging material exterior was prepared as a battery exterior.
- the produced positive electrode was cut into a rectangular shape of 3.8 cm ⁇ 2.8 cm, and arranged so that the surface on the current collector side was in contact with the aluminum packaging exterior.
- the above-described square separator was disposed on the surface of the positive electrode mixture layer of the positive electrode.
- Example 2 (Examples 2, 3, 9, 10, 16-19)
- the amount of the crosslinking agent B1 was 5 parts, 10 parts, 20 parts, 50 parts, 0.01 parts, 0.6 parts, 1 part, and 80 parts, respectively, corresponding to the solid content.
- a secondary battery binder composition, a secondary battery negative electrode slurry composition, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 1.
- FIG. The results are shown in Tables 1 and 2.
- Example 4 A secondary battery binder composition, a secondary battery negative electrode slurry composition, a negative electrode, a positive electrode, lithium, and the like, except that the crosslinking agent B2 and the crosslinking agent B3 were used in place of the crosslinking agent B1.
- An ion secondary battery was manufactured. And it evaluated similarly to Example 1.
- FIG. The results are shown in Table 1.
- Example 6 As the water-soluble thickener (A), 100 parts of CMC1 only, 99.5 parts of CMC1 and 0.5 parts of PAA1, and 90 parts of CMC1 and 10 parts of PAA1 were used corresponding to the solid content (all A secondary battery binder composition, a secondary battery negative electrode slurry composition, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 2 except for the solid content). And it evaluated similarly to Example 1. FIG. The results are shown in Table 1.
- Example 11 to 15 The binder composition for a secondary battery, two in the same manner as in Example 2, except that the blending amount of the particulate polymer C1 was 15 parts, 60 parts, 100 parts, 270 parts, and 400 parts, respectively, corresponding to the solid content.
- a slurry composition for a secondary battery negative electrode, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 1. FIG. The results are shown in Table 2.
- Example 20 The binder composition for a secondary battery and the secondary battery negative electrode were the same as in Example 2 except that artificial graphite (BET specific surface area: 3.7 m 2 / g, average particle size: 23 ⁇ m) was used as the negative electrode active material.
- a slurry composition, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 1.
- FIG. The results are shown in Table 2.
- Example 21 As in the case of Example 2, except that the mixture of natural graphite used in Example 1 and artificial graphite used in Example 20 (ratio of natural graphite in the mixture: 50% by mass) was used as the negative electrode active material.
- the secondary battery binder composition, secondary battery negative electrode slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were manufactured. And it evaluated similarly to Example 1.
- FIG. The results are shown in Table 2.
- Example 2 The binder composition for the secondary battery, the slurry composition for the secondary battery negative electrode, the negative electrode, the positive electrode, and the lithium ion secondary battery were the same as in Example 1 except that the blending amount of the crosslinking agent B1 was 110 parts corresponding to the solid content. A secondary battery was manufactured. And it evaluated similarly to Example 1. FIG. The results are shown in Table 3.
- Examples 1 to 21 using the predetermined water-soluble thickener (A), the oxazoline compound as the crosslinking agent (B), and the particulate polymer (C) in specific ratios were used as negative electrode composites. It can be seen that the adhesion between the layer and the current collector and the electrolyte pouring property can be ensured, and the electrical characteristics of the lithium ion secondary battery can be improved. Moreover, it turns out that the water resistance of the negative electrode is also improved. On the other hand, Comparative Examples 1, 5, and 6 that do not contain the crosslinking agent (B) cannot ensure the adhesion between the negative electrode composite material layer and the current collector and the liquid injection property of the electrolyte solution.
- Comparative Examples 1, 5, and 6 the water resistance of the negative electrode is also low.
- Comparative Example 2 in which the blending amount of the cross-linking agent (B) is larger than a predetermined amount cannot ensure the adhesion between the negative electrode composite material layer and the current collector, and the electrical properties of the lithium ion secondary battery It can be seen that the characteristics cannot be improved.
- the comparative example 3 with more compounding quantity of a particulate polymer (C) cannot ensure the pouring property of electrolyte solution, but improves the electrical property of a lithium ion secondary battery. I can't understand.
- Comparative Example 4 containing the particulate polymer (C) but having a blending amount less than the predetermined amount is the adhesion between the negative electrode mixture layer and the current collector and the electrical characteristics of the lithium ion secondary battery. It can be seen that both cannot be improved in a balanced manner.
- the crosslinking agent (B) is one-phase water-soluble, so that the adhesion between the negative electrode composite material layer and the current collector, the injection property of the electrolyte, and the lithium ion secondary battery It can be seen that the electrical characteristics and the water resistance of the negative electrode can be aligned in a high dimension. From Examples 2 and 6 to 8, adhesiveness between the negative electrode mixture layer and the current collector was obtained by using carboxymethyl cellulose and polyacrylic acid in combination as the water-soluble thickener (A) and adjusting the blending ratio thereof. It can be seen that the liquid injection property of the electrolyte, the electrical characteristics of the lithium ion secondary battery, and the water resistance of the negative electrode can be aligned in a high dimension.
- Crosslinking agent B4 Polycarbodiimide (manufactured by Nisshinbo Chemical Co., Ltd., product name: Carbodilite (registered trademark) SV-02, NCN equivalent 429, one-phase water-soluble)
- Crosslinking agent B5 Polycarbodiimide (manufactured by Nisshinbo Chemical Co., Ltd., product name: Carbodilite (registered trademark) V-02, NCN equivalent 600, single-phase water-soluble)
- Cross-linking agent B6 Polycarbodiimide (product name: Carbodilite (registered trademark) E-02 NCN equivalent 445 emulsion manufactured by Nisshinbo Chemical Co., Ltd.)
- Example 22 ⁇ Preparation of secondary battery binder composition> After mixing 2 parts of crosslinking agent B4 corresponding to the solid content as the crosslinking agent (B) and 150 parts of particulate polymer C1 corresponding to the solid content as the particulate polymer (C) in an environment of 25 ° C., this mixture Is added to 100 parts by mass of the water-soluble thickener (A) consisting of 2 parts by mass of PAA1 corresponding to the solids as well as 98 parts by mass of CMC1 corresponding to the solids, and the binder composition for the secondary battery of Example 22 A product was prepared. Using the prepared binder composition for a secondary battery, a binder film was prepared by the method described above, and the tensile strength at break, the wettability with respect to the electrolytic solution, and the water resistance were evaluated. The results are shown in Table 4.
- slurry composition for secondary battery negative electrode As a planetary mixer, 10000 parts of natural graphite (amorphous coated natural graphite, BET specific surface area: 3.0 m 2 / g, average particle size: 13 ⁇ m) as a carbon-based active material, water-soluble thickener (A) 98 parts of 1% aqueous solution of CMC1 corresponding to solid content, 2 parts of 1% aqueous solution of PAA1 (pH adjusted to 8 with NaOH) corresponding to solid content, and crosslinker B1 as solid content corresponding to solid content 2 parts, and the aqueous dispersion of the particulate polymer C1 as the particulate polymer (C) is added in an amount of 150 parts corresponding to the solid content, and ion-exchanged water is added and mixed so that the solid content concentration becomes 52%.
- a secondary battery negative electrode slurry composition containing a secondary battery binder composition comprising CMC1, PAA1, cross-linking agent B4, and particulate
- the above-mentioned secondary battery negative electrode slurry composition, a comma coater, the amount with the coating is 8.8 mg / cm 2 or more 9.2 mg / cm 2 or less on the thickness 20 ⁇ m copper foil (collector) It was applied as follows. By transporting the copper foil coated with the secondary battery negative electrode slurry composition at a rate of 0.3 m / min in an oven at 80 ° C. for 2 minutes and further in an oven at 120 ° C. over 2 minutes, The slurry composition on the copper foil was dried to obtain a negative electrode raw material.
- the obtained negative electrode raw material is pressed by a roll press machine so that the composite layer density is 1.45 g / cm 2 or more and 1.55 g / cm 3 or less, and further, the purpose is to further remove moisture and further promote crosslinking.
- the obtained negative electrode raw material was placed in an environment of 120 ° C. under vacuum conditions for 10 hours to obtain a negative electrode formed by forming a negative electrode mixture layer on the current collector.
- the adhesion between the negative electrode mixture layer and the current collector, the pouring property of the electrolytic solution, and the water resistance of the negative electrode were evaluated. The results are shown in Table 4.
- ⁇ Manufacture of positive electrode> 100 parts of LiCoO 2 as a positive electrode active material, 2 parts of acetylene black as a conductive material (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride, “KF manufactured by Kureha Chemical Co., Ltd.) ⁇ 1100 ”) and 2 parts, and N-methylpyrrolidone was added and mixed so that the total solid concentration was 67% to prepare a slurry composition for a secondary battery positive electrode.
- the obtained slurry composition for secondary battery positive electrode was applied onto an aluminum foil having a thickness of 20 ⁇ m with a comma coater 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. After drying the obtained positive electrode raw and pressed as mixture layer density after pressing is less than 3.40 g / cm 3 or more 3.50 g / cm 3 by a roll press machine, further purpose of removing moisture As above, a positive electrode formed by forming a positive electrode mixture layer on a current collector by placing in a 120 ° C. environment under vacuum conditions for 3 hours was obtained.
- a single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 ⁇ m; manufactured by a dry method; porosity 55%) was prepared, and cut into a 5 cm ⁇ 5 cm square shape.
- the aluminum packaging material exterior was prepared as a battery exterior.
- the produced positive electrode was cut into a rectangular shape of 3.8 cm ⁇ 2.8 cm, and arranged so that the surface on the current collector side was in contact with the aluminum packaging exterior.
- the above-described square separator was disposed on the surface of the positive electrode mixture layer of the positive electrode.
- Example 23 (Examples 23, 24, 30, 31, 37 to 40)
- the amount of the crosslinking agent B4 was 5 parts, 10 parts, 20 parts, 50 parts, 0.01 parts, 0.6 parts, 1 part, and 80 parts in equivalent to the solid content, respectively, as in Example 22.
- a secondary battery binder composition, a secondary battery negative electrode slurry composition, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 22.
- FIG. The results are shown in Tables 4 and 5.
- Example 25 A binder composition for a secondary battery, a slurry composition for a secondary battery negative electrode, a negative electrode, a positive electrode, lithium, and the like, except that the crosslinking agent B5 and the crosslinking agent B6 were used in place of the crosslinking agent B4, respectively.
- An ion secondary battery was manufactured. And it evaluated similarly to Example 22. FIG. The results are shown in Table 4.
- Example 27 As the water-soluble thickener (A), 100 parts of CMC1 only, 99.5 parts of CMC1 and 0.5 parts of PAA1, and 90 parts of CMC1 and 10 parts of PAA1 were used corresponding to the solid content (all Except for the solid content), a secondary battery binder composition, a secondary battery negative electrode slurry composition, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced in the same manner as in Example 23. And it evaluated similarly to Example 22. FIG. The results are shown in Table 4.
- Examples 32 to 36 The binder composition for a secondary battery, two in the same manner as in Example 23, except that the blending amount of the particulate polymer C1 was 15 parts, 60 parts, 100 parts, 270 parts, and 400 parts, respectively, corresponding to the solid content.
- a slurry composition for a secondary battery negative electrode, a negative electrode, a positive electrode, and a lithium ion secondary battery were produced. And it evaluated similarly to Example 22. FIG. The results are shown in Table 5.
- Example 41 A binder composition for a secondary battery and a secondary battery negative electrode were obtained in the same manner as in Example 23 except that artificial graphite (BET specific surface area: 3.7 m 2 / g, average particle size: 23 ⁇ m) was used as the negative electrode active material.
- FIG. The results are shown in Table 5.
- Example 42 The negative electrode active material was the same as in Example 23, except that a mixture of natural graphite used in Example 22 and artificial graphite used in Example 41 (ratio of natural graphite in the mixture: 50% by mass) was used.
- the secondary battery binder composition, secondary battery negative electrode slurry composition, negative electrode, positive electrode, and lithium ion secondary battery were manufactured. And it evaluated similarly to Example 22. FIG. The results are shown in Table 5.
- Examples 22 to 42 using the predetermined water-soluble thickener (A), the carbodiimide compound as the cross-linking agent (B), and the particulate polymer (C) in specific ratios were used as negative electrode composites. It can be seen that the adhesion between the layer and the current collector and the electrolyte pouring property can be ensured, and the electrical characteristics of the lithium ion secondary battery can be improved. Moreover, it turns out that the water resistance of the negative electrode is also improved.
- Comparative Examples 7, 11, and 12 that do not contain the crosslinking agent (B) cannot ensure the adhesion between the negative electrode composite material layer and the current collector and the injection property of the electrolytic solution, and the lithium ion secondary It can be seen that the electrical characteristics of the battery cannot be improved. Moreover, Comparative Examples 7, 11, and 12 have low water resistance of the negative electrode.
- Comparative Example 8 in which the blending amount of the cross-linking agent (B) is larger than a predetermined amount cannot ensure the adhesion between the negative electrode composite material layer and the current collector, and the electrical properties of the lithium ion secondary battery It can be seen that the characteristics cannot be improved.
- the comparative example 9 with more compounding quantity of a particulate polymer (C) cannot ensure the pouring property of electrolyte solution, and improves the electrical property of a lithium ion secondary battery. I can't understand. Furthermore, although the particulate polymer (C) is contained, the amount of the compounded comparative example 10 is less than a predetermined amount, the adhesion between the negative electrode composite material layer and the current collector and the electrical characteristics of the lithium ion secondary battery. It can be seen that the balance cannot be improved.
- the crosslinking agent (B) is one-phase water-soluble so that the adhesion between the negative electrode composite material layer and the current collector, the injection property of the electrolyte, and the lithium ion secondary battery It can be seen that the electrical characteristics and the water resistance of the negative electrode can be aligned in a high dimension. From Examples 23 and 27 to 29, carboxymethyl cellulose and polyacrylic acid were used in combination as the water-soluble thickener (A), and the blending ratio was adjusted to adjust the adhesion between the negative electrode mixture layer and the current collector. It can be seen that the liquid injection property of the electrolyte, the electrical characteristics of the lithium ion secondary battery, and the water resistance of the negative electrode can be aligned in a high dimension.
- the binder composition for a secondary battery of the present invention good binding properties can be obtained, and the electrical characteristics of a secondary battery using a battery member formed using the binder composition can be improved. it can.
- the slurry composition for secondary battery electrodes of the present invention an electrode mixture layer that has excellent adhesion to the current collector and can improve the electrical characteristics of the secondary battery is formed. be able to.
- the negative electrode for secondary batteries of this invention while improving the adhesiveness of a collector and a negative mix layer, the electrical property of a secondary battery can be improved.
- the electrical characteristics can be improved, and the adhesion between the negative electrode mixture layer and the current collector can be secured.
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Abstract
Description
そこで、近年では、二次電池の更なる性能向上を達成すべく、これら電池部材の形成に用いられるバインダー組成物や電極用スラリー組成物の改良が試みられている。
そして、本発明は、集電体と負極合材層との密着性に優れ、かつ、二次電池の電気的特性を向上させることができる二次電池用負極を提供することを目的とする。
更に、本発明は、集電体と負極合材層との密着性が優れており、かつ、電気的特性に優れる二次電池を提供することを目的とする。
そして、本発明の二次電池用負極によれば、集電体と負極合材層との密着性を向上させると共に、二次電池の電気的特性を向上させることができる。
更に、本発明の二次電池によれば、電気的特性を向上させることができると共に、負極合材層と集電体との密着性を確保できる。
ここで、本発明の二次電池用バインダー組成物は、正極、負極、並びに、正極や負極またはセパレータの上に設けられる多孔膜、などの二次電池の電池部材に用いることができるが、好適には、負極の形成に用いる。そして、本発明の二次電池電極用スラリー組成物は、本発明の二次電池用バインダー組成物を含んで構成され、二次電池の正極又は負極の形成、好適には二次電池の負極の形成に用いる。また、本発明の二次電池用負極は、本発明の二次電池電極用スラリー組成物を用いて製造することができる。更に、本発明の二次電池は、本発明の二次電池用負極を用いたことを特徴とする。
本発明の二次電池用バインダー組成物は、水酸基又はカルボキシル基を有する水溶性増粘剤(A)と、カルボジイミド基又はオキサゾリン基を有する架橋剤(B)と、架橋剤(B)と反応する官能基および特定の主鎖構造を有する粒子状重合体(C)とを含む。そして、本発明の二次電池用バインダー組成物は、前記水溶性増粘剤(A)100質量部当たり、前記架橋剤(B)を0.001質量部以上100質量部未満含有し、前記粒子状重合体(C)を10質量部以上500質量部未満含有する。そして、本発明の二次電池用バインダー組成物によれば、良好な結着性が得られると共に、該バインダー組成物を用いて形成した電池部材を使用した二次電池の電気的特性を向上させることができる。
以下、上記バインダー組成物に含まれる各成分について、特に該バインダー組成物を負極の形成に用いた場合を例に挙げて説明する。
水酸基又はカルボキシル基を有する水溶性増粘剤(A)(以下「水溶性増粘剤(A)」と略記することがある)は、バインダー組成物及びバインダー組成物を含むスラリー組成物の粘度調整剤としての機能を有するものである。水酸基又はカルボキシル基を有する水溶性増粘剤(A)としては、その分子構造中に水酸基とカルボキシル基との少なくとも一方を有し、且つ、水溶性の増粘剤として使用されうる化合物であれば特に限定されない。
ここで本明細書において、増粘剤が「水溶性」であるとは、イオン交換水100質量部当たり増粘剤1質量部(固形分相当)を添加し攪拌して得られる混合物を、温度20℃以上70℃以下の範囲内で、かつ、pH3以上12以下(pH調整にはNaOH水溶液及び/又はHCl水溶液を使用)の範囲内である条件のうち少なくとも一条件に調整し、250メッシュのスクリーンを通過させた際に、スクリーンを通過せずにスクリーン上に残る残渣の固形分の質量が、添加した増粘剤の固形分に対して50質量%を超えないことをいう。なお、上記増粘剤と水との混合物が、静置した場合に二相に分離するエマルジョン状態であっても、上記定義を満たせば、その増粘剤は水溶性であるとする。
そして、水溶性増粘剤(A)は、カルボキシメチルセルロースまたはその塩(以下「カルボキシメチルセルロース(塩)」と略記することがある)を含むことが好ましい。水溶性増粘剤(A)がカルボキシメチルセルロース(塩)を含むことで、バインダー組成物を含むスラリー組成物を集電体上などに塗布する際の作業性をより良好とすることができる。
カルボジイミド基又はオキサゾリン基を有する架橋剤(B)(以下「架橋剤(B)」と略記することがある)は、上述の水酸基又はカルボキシル基を有する水溶性増粘剤(A)、そして後述する粒子状重合体(C)と、加熱などにより架橋構造を形成する。即ち、架橋剤(B)は、水溶性増粘剤(A)同士、水溶性増粘剤(A)と粒子状重合体(C)、そして、粒子状重合体(C)同士、を繋ぐ好適な架橋構造を形成すると推察される。
即ち、本発明のバインダー組成物や、本発明のバインダー組成物を含むスラリー組成物は、加熱などの処理を施すことにより、組成物中に含まれている水溶性増粘剤(A)および粒子状重合体(C)が架橋剤(B)を介して架橋構造を形成する。その結果、水溶性増粘剤(A)同士、水溶性増粘剤(A)と粒子状重合体(C)、および、粒子状重合体(C)同士の架橋により、弾性率、引っ張り破断強度、耐疲労性などの機械的特性や、接着性に優れ、且つ、水への溶解度が小さい(即ち耐水性に優れる)架橋構造が得られる。加えてこの架橋構造の形成は、バインダー組成物を用いて形成した電池部材と、二次電池の電解液に対する濡れ性も向上させる。これは、水酸基又はカルボキシル基を有する水溶性増粘剤(A)は水素結合の形成などにより分子鎖同士が硬く絡み合い易いところ、架橋反応の際、硬く絡まった水溶性増粘剤(A)中に架橋剤(B)分子が入りこむことで、水溶性増粘剤(A)の分子鎖がほどかれ、電解液の入り込む物理的な空間が生じ易くなるからであると推察される。
そしてそれらの結果、二次電池用バインダー組成物が水溶性増粘剤(A)100質量部当たり、架橋剤を上記の範囲で含有することで、二次電池のサイクル特性を確保し、サイクル後の抵抗上昇を抑制することができる。
架橋剤(B)は、その分子中に、一般式(1):-N=C=N-・・・(1)で表されるカルボジイミド基およびオキサゾリン基の少なくとも一方を有し、かつ、水溶性増粘剤(A)間、水溶性増粘剤(A)と粒子状重合体(C)との間、および、粒子状重合体(C)間に架橋構造を形成し得る架橋性化合物であれば特に限定されない。
そして、架橋剤(B)としては、架橋構造を形成し得る基としてカルボジイミド基を有するカルボジイミド化合物、架橋構造を形成し得る基としてオキサゾリン基を有するオキサゾリン化合物が挙げられる。これらの中でも、架橋剤(B)としてはカルボジイミド化合物が好ましい。カルボジイミド化合物は、その優れた熱安定性のため、バインダー組成物やスラリー組成物の調製の際などに水と反応して失われることも少なく、特に架橋剤(B)の使用量が比較的少量である場合にも、得られる負極合材層と集電体の密着性を十分に高め、二次電池の電気的特性を確保することができる。また、カルボジイミド化合物を用いることで、負極の耐水性を高めることができる。
以下、カルボジイミド化合物、オキサゾリン化合物について詳述する。
架橋剤(B)として用いられるカルボジイミド化合物としては、分子中にカルボジイミド基を2つ以上有する化合物、具体的には、一般式(2):-N=C=N-R1・・・(2)(一般式(2)中、R1は2価の有機基を示す。)で表される繰返し単位を有するポリカルボジイミドおよび/または変性ポリカルボジイミドが好適に挙げられる。なお、本明細書において変性ポリカルボジイミドとは、ポリカルボジイミドに対して、後述する反応性化合物を反応させることによって得られる樹脂をいう。
ポリカルボジイミドの合成法は特に限定されるものではないが、例えば、有機ポリイソシアネートを、イソシアネート基のカルボジイミド化反応を促進する触媒(以下「カルボジイミド化触媒」という。)の存在下で反応させることにより、ポリカルボジイミドを合成することができる。また、一般式(2)で表される繰り返し単位を有するポリカルボジイミドは、有機ポリイソシアネートを反応させて得たオリゴマー(カルボジイミドオリゴマー)と、当該オリゴマーと共重合可能な単量体とを共重合させることによっても合成することができる。
なお、このポリカルボジイミドの合成に用いられる有機ポリイソシアネートとしては、有機ジイソシアネートが好ましい。
例えば分子鎖の両末端に水酸基を有する2価のアルコールをカルボジイミドオリゴマーと既知の方法で共重合させることにより、ポリカルボジイミド基と、2価のアルコール由来の単量体単位とを有するポリカルボジイミドを合成することができる。このように、架橋剤(B)としてのポリカルボジイミドが2価以上のアルコール由来の単量体単位、好ましくは2価のアルコール由来の単量体単位を有する場合、該ポリカルボジイミドを含むバインダー組成物から形成される電池部材(例えば負極)の電解液に対する濡れ性が向上し、該電池部材を備える二次電池の製造における、電解液の注液性を向上させることができる。また、上述したアルコールを共重合させると、ポリカルボジイミドの水溶性を増加させることができるとともに、水中でポリカルボジイミドが自己ミセル化する(疎水性のカルボジイミド基の周りが親水性のエチレングリコール鎖で覆われる構造をとる)ため、化学的安定性を向上させることができる。
次に、変性ポリカルボジイミドの合成法について説明する。変性ポリカルボジイミドは、一般式(2)で表される繰返し単位を有するポリカルボジイミドの少なくとも1種に、反応性化合物の少なくとも1種を、適当な触媒の存在下あるいは不存在下で、適宜温度で反応(以下、「変性反応」という。)させることによって合成することができる。
架橋剤(B)として用いられるカルボジイミド化合物の、カルボジイミド基(-N=C=N-)1モル当たりの化学式量(NCN当量)は、好ましくは300以上、より好ましくは400以上であり、好ましくは600以下、より好ましくは500以下である。カルボジイミド化合物のNCN当量が300以上であることで、本発明のバインダー組成物やスラリー組成物の保存安定性を十分に確保することができ、600以下であることで、架橋剤として架橋反応を良好に進行させることができる。
なお、カルボジイミド化合物のNCN当量は、例えば、GPC(ゲル浸透クロマトグラフィー)を用いてカルボジイミド化合物のポリスチレン換算数平均分子量を求めると共に、IR(赤外分光法)を用いてカルボジイミド化合物1分子当たりのカルボジイミド基の数を定量分析し、下記式を用いて算出することができる。
NCN当量=(カルボジイミド化合物のポリスチレン換算数平均分子量)/(カルボジイミド化合物1分子当たりのカルボジイミド基の数)
架橋剤(B)として用いられるオキサゾリン化合物としては、分子中にオキサゾリン基を2つ以上有する化合物が好適に挙げられる。なお、オキサゾリン基の水素原子の一部又は全部は、他の基により置換されていてもよい。このような分子中にオキサゾリン基を2つ以上有する化合物としては、例えば、分子中にオキサゾリン基を2つ有する化合物(2価のオキサゾリン化合物)、オキサゾリン基を含有する重合体(オキサゾリン基含有重合体)が挙げられる。
2価のオキサゾリン化合物としては、例えば、2,2'-ビス(2-オキサゾリン)、2,2'-ビス(4-メチル-2-オキサゾリン)、2,2'-ビス(4,4-ジメチル-2-オキサゾリン)、2,2'-ビス(4-エチル-2-オキサゾリン)、2,2'-ビス(4,4'-ジエチル-2-オキサゾリン)、2,2'-ビス(4-プロピル-2-オキサゾリン)、2,2'-ビス(4-ブチル-2-オキサゾリン)、2,2'-ビス(4-ヘキシル-2-オキサゾリン)、2,2'-ビス(4-フェニル-2-オキサゾリン)、2,2'-ビス(4-シクロヘキシル-2-オキサゾリン)、2,2'-ビス(4-ベンジル-2-オキサゾリン)などが挙げられる。中でも、より剛直な架橋構造体を形成する観点から、2,2'-ビス(2-オキサゾリン)が好ましい。
オキサゾリン基含有重合体は、オキサゾリン基を含有する重合体であれば特に限定されない。なお本明細書において、オキサゾリン基含有重合体には上述の2価のオキサゾリン化合物は含まれない。
そして、オキサゾリン基含有重合体は、例えば、以下の一般式(3)で表されるオキサゾリン基含有単量体と、他の単量体とを共重合することにより合成することができる。
なお、本発明において、オキサゾリン基含有重合体の「ガラス転移温度」は、本明細書の実施例に記載の粒子状重合体(C)で用いた方法に準拠して測定することができる。
架橋剤(B)として用いられるオキサゾリン化合物の、オキサゾリン基1モル当たりの化学式量(オキサゾリン当量)は、好ましくは70以上、より好ましくは100以上であり、更に好ましくは300以上であり、好ましくは600以下、より好ましくは500以下である。このオキサゾリン当量は、オキサゾリン価(オキサゾリン基1モル当たりの質量(g-solid/eq.))とも呼ばれる。オキサゾリン化合物のオキサゾリン当量が70以上であることで、本発明のバインダー組成物やスラリー組成物の保存安定性を十分に確保することができ、600以下であることで、架橋剤として架橋反応を良好に進行させることができる。
なお、オキサゾリン化合物のオキサゾリン当量は、下記式を用いて算出することができる。
オキサゾリン当量=(オキサゾリン化合物の分子量)/(オキサゾリン化合物1分子当たりのオキサゾリン基の数)
ここで、オキサゾリン化合物がオキサゾリン基含有重合体の場合には、オキサゾリン化合物の分子量は、例えば、GPC(ゲル浸透クロマトグラフィー)を用いて測定したポリスチレン換算数平均分子量とすることができ、オキサゾリン化合物1分子当たりのオキサゾリン基の数は、例えば、IR(赤外分光法)を用いて定量することができる。
架橋剤(B)の1質量%水溶液の粘度は、好ましくは5000mPa・s以下、より好ましくは700mPa・s以下、特に好ましくは150mPa・s以下である。1質量%水溶液の粘度が上記範囲内である架橋剤を用いることで、負極合材層と集電体との密着性を優れたものとすることができる。なお、架橋剤(B)の1質量%水溶液の粘度は、上述のカルボキシメチルセルロース(塩)の1質量%水溶液の粘度と同様の方法で測定することができる。
架橋剤(B)と反応する官能基を有し、かつ、脂肪族共役ジエン単量体単位および芳香族ビニル単量体単位を含む粒子状重合体(C)(以下「粒子状重合体(C)」と略記することがある)は、本発明の二次電池用バインダー組成物を含むスラリー組成物を用いて電極部材(例えば負極)を形成した際に、製造した電極部材において、電極部材に含まれる成分(例えば、電極活物質)が電極部材から脱離しないように保持しうる成分である。ここで、電極部材が負極であり、スラリー組成物を用いて負極合材層を形成する場合には、一般的に、負極合材層における粒子状重合体は、電解液に浸漬された際に、電解液を吸収して膨潤しながらも粒子状の形状を維持し、負極活物質同士を結着させ、負極活物質が集電体から脱落するのを防ぐ。また、粒子状重合体は、負極合材層に含まれる負極活物質以外の粒子をも結着し、負極合材層の強度を維持する役割も果たしている。
なお、本明細書において「単量体単位を含む」とは、「その単量体を用いて得た重合体中に単量体由来の構造単位が含まれている」ことを意味する。
粒子状重合体(C)の脂肪族共役ジエン単量体単位を形成し得る脂肪族共役ジエン単量体としては、特に限定されることなく、1,3-ブタジエン、2-メチル-1,3-ブタジエン、2,3-ジメチル-1,3-ブタジエン、2-クロロ-1,3-ブタジエン、置換直鎖共役ペンタジエン類、置換および側鎖共役ヘキサジエン類などが挙げられ、中でも1,3-ブタジエンが好ましい。なお、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。
そして、粒子状重合体(C)は、例えば、上述した単量体を含む単量体組成物を水系溶媒中で重合することにより製造される。
ここで、単量体組成物中の各単量体の含有割合は、通常、所望の粒子状重合体(C)における繰り返し単位の含有割合と同様にする。
具体的には、水系溶媒としては、例えば、水;ダイアセトンアルコール、γ-ブチロラクトンなどのケトン類;エチルアルコール、イソプロピルアルコール、ノルマルプロピルアルコールなどのアルコール類;プロピレングリコールモノメチルエーテル、メチルセロソルブ、エチルセロソルブ、エチレングリコールターシャリーブチルエーテル、ブチルセロソルブ、3-メトキシ-3メチル-1-ブタノール、エチレングリコールモノプロピルエーテル、ジエチレングリコールモノブチルエーテル、トリエチレングリコールモノブチルエーテル、ジプロピレングリコールモノメチルエーテルなどのグリコールエーテル類;1,3-ジオキソラン、1,4-ジオキソラン、テトラヒドロフランなどのエーテル類;などが挙げられる。中でも水は可燃性がなく、粒子状重合体(C)の粒子の分散体が容易に得られやすいという観点から特に好ましい。なお、主溶媒として水を使用して、粒子状重合体(C)の粒子の分散状態が確保可能な範囲において上記の水以外の水系溶媒を混合して用いてもよい。
通常、粒子状重合体(C)は、非水溶性である。したがって、通常、粒子状重合体(C)は、水系のバインダー組成物、および水系のスラリー組成物において粒子状となっており、その粒子形状を維持したまま、例えば二次電池用負極に含まれる。
そして、本発明のバインダー組成物、スラリー組成物では、粒子状重合体(C)は、個数平均粒径が、好ましくは50nm以上、より好ましくは70nm以上であり、好ましくは500nm以下、より好ましくは400nm以下である。個数平均粒径が上記範囲にあることで、得られる負極の強度および柔軟性を良好にできる。なお、個数平均粒径は、透過型電子顕微鏡法やコールターカウンター、レーザー回折散乱法などによって容易に測定することができる。
なお、本発明において、粒子状重合体(C)の「ゲル含有量」は、本明細書の実施例に記載の測定方法を用いて測定することができる。
なお、本発明において、粒子状重合体(C)の「ガラス転移温度」は、本明細書の実施例に記載の測定方法を用いて測定することができる。
ガラス転移温度は、使用する単量体の種類および量を変更することにより調整することができ、例えば、スチレン、アクリロニトリルなどの単量体を使用するとガラス転移温度を高めることができ、ブチルアクリレート、ブタジエンなどの単量体を使用するとガラス転移温度を低下させることができる。
また、ゲル含有量は、重合温度、重合開始剤の種類、分子量調整剤の種類、量、反応停止時の転化率などを変更することにより調整することができ、例えば、連鎖移動剤を少なくするとゲル含有量を高めることができ、連鎖移動剤を多くするとゲル含有量を低下させることができる。
本発明のバインダー組成物は、単量体組成物を重合して得た粒子状重合体(C)の水分散液に対し、水溶性増粘剤(A)、架橋剤(B)、そして発明の効果を損ねない範囲で任意のその他の成分を添加して調製することができる。
本発明の二次電池電極用スラリー組成物は、水酸基又はカルボキシル基を有する水溶性増粘剤(A)と、カルボジイミド基又はオキサゾリン基を有する架橋剤(B)と、粒子状重合体(C)と、電極活物質と、水とを含み、前記粒子状重合体(C)は、前記架橋剤(B)と反応する官能基を有し、かつ、脂肪族共役ジエン単量体単位および芳香族ビニル単量体単位を含む。そして、本発明の二次電池電極用スラリー組成物は、前記水溶性増粘剤(A)100質量部当たり、前記架橋剤(B)を0.001質量部以上100質量部未満含有し、前記粒子状スチレンブタジエン共重合体(C)を10質量部以上500質量部未満含有する。そして、本発明の二次電池電極用スラリー組成物によれば、集電体との密着性に優れ、かつ、二次電池の電気的特性を向上させることが可能な電極合材層を形成することができる。
ここで、本発明の二次電池電極用スラリー組成物に含まれる水溶性増粘剤(A)、架橋剤(B)、粒子状重合体(C)はそれぞれ、上述の本発明の二次電池用バインダー組成物の項で記載したものと同様のものを、同様の配合割合で使用することができる。
電極活物質は、二次電池の電極(正極、負極)において電子の受け渡しをする物質である。以下、リチウムイオン二次電池の負極において使用する電極活物質(負極活物質)を例に挙げて説明する。
そして、炭素質材料としては、例えば、熱処理温度によって炭素の構造を容易に変える易黒鉛性炭素や、ガラス状炭素に代表される非晶質構造に近い構造を持つ難黒鉛性炭素などが挙げられる。
ここで、易黒鉛性炭素としては、例えば、石油または石炭から得られるタールピッチを原料とした炭素材料が挙げられる。具体例を挙げると、コークス、メソカーボンマイクロビーズ(MCMB)、メソフェーズピッチ系炭素繊維、熱分解気相成長炭素繊維などが挙げられる。
また、難黒鉛性炭素としては、例えば、フェノール樹脂焼成体、ポリアクリロニトリル系炭素繊維、擬等方性炭素、フルフリルアルコール樹脂焼成体(PFA)、ハードカーボンなどが挙げられる。
そして、黒鉛質材料としては、例えば、天然黒鉛、人造黒鉛などが挙げられる。
ここで、人造黒鉛としては、例えば、易黒鉛性炭素を含んだ炭素を主に2800℃以上で熱処理した人造黒鉛、MCMBを2000℃以上で熱処理した黒鉛化MCMB、メソフェーズピッチ系炭素繊維を2000℃以上で熱処理した黒鉛化メソフェーズピッチ系炭素繊維などが挙げられる。
なお、負極活物質として、非晶質コート天然黒鉛と人造黒鉛の混合物を用いてもよい。ここで、人造黒鉛は、非晶質コート天然黒鉛に比してかさ高い一方、粒子としてはつぶれやすく、電極をプレスすると、粒子が配向しやすい傾向にある。そのため、電極表面に配向した粒子がならび、電解液が侵入しにくくなる虞がある。そのような観点から、負極活物質として非晶質コート天然黒鉛と人造黒鉛との混合物を用いる場合、非晶質コート天然黒鉛と人造黒鉛の配合量の合計中に非晶質コート天然黒鉛の配合量が占める割合は、好ましくは30質量%以上、より好ましくは60質量%以上、特に好ましくは80質量%以上である。
二次電池電極用スラリー組成物が、水溶性増粘剤(A)100質量部当たり、負極活物質を好ましくは5000質量部以上含有することにより、該スラリー組成物を用いて得られる二次電池の負極における電子の受け渡しが十分となり、二次電池として良好に機能する。また、スラリー組成物が、水溶性増粘剤100質量部当たり、負極活物質を15000質量部以下含有することで、負極の膨れが抑制され、また、該スラリー組成物を集電体に塗布する際の作業性を確保することができる。
本発明の二次電池電極用スラリー組成物は、上記成分の他に、導電材、補強材、レベリング剤、電解液添加剤などの成分を含有していてもよい。これらは、電池反応に影響を及ぼさないものであれば特に限られず、公知のもの、例えば国際公開第2012/115096号に記載のものを使用することができる。これらの成分は、1種類を単独で用いてもよく、2種類以上を任意の比率で組み合わせて用いてもよい。また、本発明の二次電池用バインダー組成物が、これらのその他の成分を含有してもよい。
本発明の二次電池電極用スラリー組成物は、上記各成分を任意に一部予混合した後に分散媒としての水系媒体中に分散させることにより調製してもよいし、水溶性増粘剤(A)と、架橋剤(B)と、粒子状重合体(C)とを含む本発明のバインダー組成物を調製した後、該バインダー組成物と電極活物質とを分散媒としての水系媒体中に分散させることにより調製してもよい。なお、スラリー組成物中の各成分の分散性の観点からは、上記各成分を分散媒としての水系媒体中に分散させることにより、水溶性増粘剤(A)と、架橋剤(B)と、粒子状重合体(C)とを含有する(即ち、本発明のバインダー組成物を含む)スラリー組成物を調製することが好ましい。具体的には、ボールミル、サンドミル、ビーズミル、顔料分散機、らい潰機、超音波分散機、ホモジナイザー、プラネタリーミキサー、フィルミックスなどの混合機を用いて上記各成分と水系媒体とを混合することにより、スラリー組成物を調製することが好ましい。
ここで、水系媒体としては、通常は水を用いるが、任意の化合物の水溶液や、少量の有機媒体と水との混合溶液などを用いてもよい。また、スラリー組成物の固形分濃度は、各成分を均一に分散させることができる濃度、例えば、30質量%以上90質量%以下であり、より好ましくは40質量%以上80質量%以下とすることができる。更に、上記各成分と水系媒体との混合は、通常、室温以上80℃以下の範囲で、10分以上数時間以下行うことができる。
本発明の二次電池用負極は、本発明の二次電池電極用スラリー組成物を使用して製造することができる。
そして、本発明の二次電池用負極は、集電体と、集電体上に形成された負極合材層とを備え、負極合材層は、電極活物質が負極活物質である本発明の二次電池電極用スラリー組成物から得られる。本発明の二次電池用負極によれば、集電体と負極合材層との密着性を向上させると共に、二次電池の電気的特性を向上させることができる。
上記二次電池電極用スラリー組成物を集電体上に塗布する方法としては、特に限定されず公知の方法を用いることができる。具体的には、塗布方法としては、ドクターブレード法、ディップ法、リバースロール法、ダイレクトロール法、グラビア法、エクストルージョン法、ハケ塗り法などを用いることができる。この際、スラリー組成物を集電体の片面だけに塗布してもよいし、両面に塗布してもよい。塗布後乾燥前の集電体上のスラリー膜の厚みは、乾燥して得られる負極合材層の厚みに応じて適宜に設定しうる。
集電体上のスラリー組成物を乾燥する方法としては、特に限定されず公知の方法を用いることができ、例えば温風、熱風、低湿風による乾燥、真空乾燥、赤外線や電子線などの照射による乾燥法が挙げられる。このように集電体上のスラリー組成物を乾燥することで、集電体上に負極合材層を形成し、集電体と負極合材層とを備える二次電池用負極を得ることができる。なお、スラリー組成物を乾燥する際には、加えられた熱により、架橋剤(B)を介した架橋反応が進行する。
また、負極合材層の形成後に、加熱工程を実施して架橋反応を進行させ、架橋構造をさらに十分なものとすることが好ましい。該加熱工程は、80℃以上160℃以下で、1時間以上20時間以下程度行うことが好ましい。
本発明の二次電池は、正極と、負極と、電解液と、セパレータとを備え、負極として、本発明の二次電池用負極を用いたものである。そして、本発明の二次電池は、本発明の二次電池用負極を用いているので、電気的特性を向上させることができると共に、負極合材層と集電体との密着性を確保することができる。本発明の二次電池は、例えば、スマートフォン等の携帯電話、タブレット、パソコン、電気自動車、定置型非常用蓄電池などに好適に用いることができる。
二次電池の正極としては、例えば二次電池がリチウムイオン二次電池である場合、リチウムイオン二次電池用正極として用いられる既知の正極を用いることができる。具体的には、正極としては、例えば、正極合材層を集電体上に形成してなる正極を用いることができる。
なお、集電体としては、アルミニウムなどの金属材料からなるものを用いることができる。また、正極合材層としては、既知の正極活物質と、導電材と、バインダーとを含む層を用いることができ、バインダーとしては本発明の二次電池用バインダー組成物を使用してもよい。
電解液としては、溶媒に電解質を溶解した電解液を用いることができる。
ここで、溶媒としては、電解質を溶解可能な有機溶媒を用いることができる。具体的には、溶媒としては、エチレンカーボネート、プロピレンカーボネート、γ-ブチロラクトンなどのアルキルカーボネート系溶媒に、2,5-ジメチルテトラヒドロフラン、テトラヒドロフラン、ジエチルカーボネート、エチルメチルカーボネート、ジメチルカーボネート、酢酸メチル、ジメトキシエタン、ジオキソラン、プロピオン酸メチル、ギ酸メチルなどの粘度調整溶媒を添加したものを用いることができる。
電解質としては、リチウム塩を用いることができる。リチウム塩としては、例えば、特開2012-204303号公報に記載のものを用いることができる。これらのリチウム塩の中でも、有機溶媒に溶解しやすく、高い解離度を示すという点より、電解質としてはLiPF6、LiClO4、CF3SO3Liが好ましい。
また、電解液は、ポリマーおよび上記電解液を含有するゲル電解質であってもよく、さらには真性ポリマー電解質であってもよい。
セパレータとしては、例えば、特開2012-204303号公報に記載のものを用いることができる。中でも、セパレータ全体の膜厚を薄くすることができ、これにより、二次電池内の電極活物質の比率を高くして体積あたりの容量を高くすることができるという点より、ポリオレフィン系の樹脂(ポリエチレン、ポリプロピレン、ポリブテン、ポリ塩化ビニル)からなる微多孔膜が好ましい。また、セパレータとして、非導電性粒子を本発明の二次電池用バインダー組成物で結着してなる多孔膜を備えるセパレータを使用してもよい。
本発明の二次電池は、例えば、正極と、負極とを、セパレータを介して重ね合わせ、これを必要に応じて電池形状に応じて巻く、折るなどして電池容器に入れ、電池容器に電解液を注入して封口することにより製造することができる。リチウムイオン二次電池の内部の圧力上昇、過充放電などの発生を防止するために、必要に応じて、ヒューズ、PTC素子などの過電流防止素子、エキスパンドメタル、リード板などを設けてもよい。二次電池の形状は、例えば、コイン型、ボタン型、シート型、円筒型、角形、扁平型など、何れであってもよい。
実施例および比較例において、粒子状重合体(C)のガラス転移温度およびゲル含有量、バインダーフィルムの引っ張り破断強度、電解液に対する濡れ性、および耐水性、二次電池のサイクル特性およびサイクル後の抵抗上昇抑制、電解液の注液性、並びに、負極合材層と集電体との密着性および負極の耐水性は、それぞれ以下の方法を使用して評価した。
粒子状重合体(C)を含む水分散液を50%湿度、23℃以上25℃以下の環境下で3日間乾燥させて、厚み1±0.3mmのフィルムを得た。このフィルムを、120℃の熱風オーブンで1時間乾燥させた。その後、乾燥させたフィルムをサンプルとして、JIS K 7121に準じて、測定温度-100℃以上180℃以下、昇温速度5℃/分の条件下、DSC6220SII(示差走査熱量分析計、ナノテクノロジー社製)を用いてガラス転移温度(℃)を測定した。
<粒子状重合体(C)のゲル含有量>
粒子状重合体(C)を含む水分散液を50%湿度、23℃以上25℃以下の環境下で乾燥させて、厚み3±0.3mmのフィルムを得た。このフィルムを1mm角に裁断し、約1gを精秤した。
裁断により得られたフィルム片の質量をw0とする。このフィルム片を、10gのテトラヒドロフラン(THF)に25℃±1℃の環境の下、24時間浸漬した。その後、THFから引き揚げたフィルム片を105℃で3時間真空乾燥して、不溶分の質量w1を計測した。
そして、下記式にしたがってゲル含有量(質量%)を算出した。
ゲル含有量(質量%)=(w1/w0)×100
<バインダーフィルムの引っ張り破断強度>
調製した二次電池用バインダー組成物を50%湿度、23℃以上25℃以下の環境下で3日間乾燥後、さらに120℃の熱風オーブンで1時間乾燥させて、厚み0.5±0.02mmのバインダーフィルムを得た。
該バインダーフィルムを使用し、JIS K 6251に準じて、温度25±1℃、露点-60±5℃の環境下、引っ張り速度50mm/minで引っ張り試験を行い、バインダーフィルムの引っ張り破断強度を算出した。引っ張り破断強度の値が大きいほど、引っ張りに対する耐性が高く、機械的特性に優れることを示す。
A:引っ張り破断強度が50MPa以上
B:引っ張り破断強度が45MPa以上50MPa未満
C:引っ張り破断強度が40MPa以上45MPa未満
D:引っ張り破断強度が40MPa未満
<バインダーフィルムの電解液に対する濡れ性>
調製した二次電池用バインダー組成物を、電解銅箔(古河電工製NC-WS(登録商標))に対してテーブルコーターを用いて塗布し、50℃で20分、120℃で20分、熱風乾燥器で乾燥させ、厚さ5±2μmのバインダーフィルムを得た。
該バインダーフィルムについて、電解液に用いる溶媒としてのプロピレンカーボネート(キシダ化学製、試薬)を用いて、接触角計(協和界面科学製)を使用してθ/2法によって接触角を測定し、以下の基準により評価した。なお接触角は望小特性であり、この値が小さいほど、電解液に対する濡れ性に優れることを示す。
A:接触角が35度未満
B:接触角が45度未満35度以上
C:接触角が55度未満45度以上
D:接触角が55度以上
<バインダーフィルムの耐水性>
調製した二次電池用バインダー組成物を50%湿度、23℃以上25℃以下の環境下で3日間乾燥後、さらに120℃の熱風オーブンで1時間乾燥させて、厚み0.5±0.02mmのバインダーフィルムを得た。
該バインダーフィルムを0.5mm角に裁断し、約1gを精秤した。裁断により得られたフィルム片の質量をwf0とする。このフィルム片を、100gのイオン交換水(25±1℃)に一晩浸漬し、その後超音波洗浄機を用いて超音波を10分間照射した。その後、100メッシュにて濾過を実施し、イオン交換水およびアセトンで洗浄し、固形分を得た。該固形分を120℃の熱風オーブンにて5時間乾燥させて質量wf1を測定し、下記式にしたがって不溶解量(質量%)を算出した。
不溶解量(質量%)=(wf1/wf0)×100
得られた不溶解量を、以下の基準により評価した。不溶解量の値が大きいほど耐水性に優れることを示す。
A:不溶解量が95%以上
B:不溶解量が85%以上95%未満
C:不溶解量が70%以上85%未満
D:不溶解量が70%未満
<二次電池のサイクル特性>
作製したラミネートセル型のリチウムイオン二次電池を、電解液注液後、5時間静置させ、0.2Cの定電流法によって、セル電圧3.65Vまで充電し、その後60℃で12時間エージング処理を行い、0.2Cの定電流法によってセル電圧3.00Vまで放電を行った。上記リチウムイオン二次電池を、25℃で、0.1Cの定電流法にて、セル電圧3.82Vまで充電し、そのまま5時間放置して電圧V0を測定した。その後、-10℃の環境下で、0.5Cの放電の操作を行い、放電開始20秒後の電圧V20を測定した。そして、ΔVini=V0-V20で示す電圧変化で定義される初期抵抗を算出した。なお、この初期抵抗は、後述するサイクル後の抵抗上昇抑制の評価に用いる。
上記初期抵抗測定後のリチウムイオン二次電池を用いて、25℃雰囲気下で0.2Cの定電流法によって、セル電圧3.65Vまで充電し、その後60℃に昇温し、12時間エージング処理を行い、25℃雰囲気下で0.2Cの定電流法によってセル電圧3.00Vまで放電を行った。
さらに、45℃環境下で4.2V、1.0Cの充放電レートにて100サイクル充放電の操作を行った。そのとき1サイクル目の容量、すなわち初期放電容量X1、および100サイクル目の放電容量X2を測定し、ΔC=(X2/X1)×100(%)で示す容量変化率を求め、以下の基準により評価した。この容量変化率ΔCの値が高いほど、サイクル特性に優れることを示す。
A:ΔCが85%以上
B:ΔCが83%以上85%未満
C:ΔCが80%以上83%未満
D:ΔCが80%未満
<サイクル後の抵抗上昇抑制>
上記サイクル特性測定後のリチウムイオン二次電池を用いて、25℃、0.05Cの定電流法にて、セル電圧3.00Vまで放電させた。その後、25℃で、0.1Cの定電流法にて、セル電圧3.82Vまで充電し、そのまま5時間放置して電圧V0´を測定した。さらに、-10℃の環境下で、0.5Cの放電の操作を行い、放電開始20秒後の電圧V20´を測定した。そして、ΔVfin=V0´-V20´で示す電圧変化で定義されるサイクル後の抵抗を算出した。
抵抗上昇率をΔVfin/ΔViniで定義し、以下の基準により評価した。この抵抗上昇率ΔVfin/ΔViniの値が小さいほど、サイクルによる抵抗上昇の抑制に優れることを示す。
A:ΔVfin/ΔViniが110%以下
B:ΔVfin/ΔViniが110%超120%以下
C:ΔVfin/ΔViniが120%超130%以下
D:ΔVfin/ΔViniが130%超
<電解液の注液性>
作製した二次電池用負極を直径16mmの円形に切り出し、負極合材層を有する面にプロピレンカーボネート(キシダ化学製、試薬)を1μL滴下して、滴下してから、その負極上のプロピレンカーボネートの液滴が負極合材層内に浸透するまでの時間(浸透時間)を目視で測定し、以下の基準により評価した。この浸透時間が短いほど、一般的な電解液に含まれるプロピレンカーボネートと負極との親和性が良好であり、即ち、二次電池の製造における、電解液の注液性に優れることを示す。
A:浸透時間が80秒未満
B:浸透時間が80秒以上100秒未満
C:浸透時間が100秒以上150秒未満
D:浸透時間が150秒以上
<負極合材層と集電体との密着性>
作製した二次電池用負極を長さ100mm、幅10mmの長方形状に切り出して試験片とし、負極合材層を有する面を下にし、負極合材層表面にセロハンテープ(JIS Z1522に規定されるもの)を貼り付け、集電体の一端を垂直方向に引張り速度50mm/分で引っ張って剥がしたときの応力を測定した(なお、セロハンテープは試験台に固定されている)。測定を3回行い、その平均値を求めてこれを剥離ピール強度とし、以下の基準により評価した。剥離ピール強度の値が大きいほど、負極合材層と集電体との密着性に優れることを示す。
A:剥離ピール強度が20N/m以上
B:剥離ピール強度が15N/m以上20N/m未満
C:剥離ピール強度が10N/m以上15N/m未満
D:剥離ピール強度が10N/m未満
<負極の耐水性>
作製した二次電池用負極を直径16mmの円形に切り出し、質量を測定して、該質量から、集電体の質量を差し引き、負極合材層の質量(wa1)を算出した。該円形の負極を、サンプル瓶に入れ、イオン交換水50mLを注ぎ、60℃で72時間、熱処理を行った。その後、該円形の負極を取り出し、イオン交換水で洗浄した後に、120℃で1時間乾燥させ、質量を測定し、該質量から、集電体の質量を差し引き、負極合材層の質量(wa2)を算出した。上記イオン交換水への浸漬および加熱処理による質量変化率(質量%)を[(wa1-wa2)/wa1]×100で定義し、以下の基準により評価した。この質量変化率が小さいほど、負極が耐水性に優れることを示す。
A:質量変化率が5%未満
B:質量変化率が5%以上10%未満
C:質量変化率が10%以上20%未満
D:質量変化率が20%以上
まず、実施例1~21および比較例1~6において、架橋剤(B)としてオキサゾリン化合物を用いて、二次電池用バインダー組成物、二次電池負極用スラリー組成物、二次電池用負極、二次電池を作製して評価を行った。
以下の水溶性増粘剤(A)、架橋剤(B)、粒子状重合体(C)を使用した。
[水溶性増粘剤(A)]
CMC1:カルボキシメチルセルロースのナトリウム塩(日本製紙ケミカル社製、製品名:MAC350HC、エーテル化度0.8 1%水溶液の粘度3500mPa・s)
PAA1:ポリアクリル酸(アルドリッチ社製、重量平均分子量45万)
[架橋剤(B)]
架橋剤B1:2,2'-ビス(2-オキサゾリン)(東京化成工業社製 オキサゾリン当量70 一相水溶性)
架橋剤B2:オキサゾリン基含有重合体(日本触媒社製 製品名:エポクロス(登録商標)WS-700 オキサゾリン当量220 一相水溶性)
架橋剤B3:オキサゾリン基含有重合体(日本触媒社製 製品名:エポクロス(登録商標)K-2020E オキサゾリン当量550 エマルジョン)
[粒子状重合体(C)]
以下のように、粒子状重合体C1(カルボキシル基+水酸基を有する重合体)を調製した。
攪拌機付き5MPa耐圧容器に、芳香族ビニル単量体としてスチレン65部、脂肪族共役ジエン単量体として1,3-ブタジエン35部、エチレン性不飽和カルボン酸単量体としてイタコン酸4部、水酸基含有単量体として2-ヒドロキシエチルアクリレート1部、分子量調整剤としてt-ドデシルメルカプタン0.3部、乳化剤としてドデシルベンゼンスルホン酸ナトリウム5部、溶媒としてイオン交換水150部、及び重合開始剤として過硫酸カリウム1部を入れ、十分に攪拌した後、55℃に加温して重合を開始した。
モノマー消費量が95.0%になった時点で冷却し、反応を停止した。こうして得られた重合体を含んだ水分散体に、5%水酸化ナトリウム水溶液を添加して、pH8に調整した。その後、加熱減圧蒸留によって未反応単量体の除去を行った。さらにその後、30℃以下まで冷却し、粒子状重合体C1の水分散液を得た。得られた粒子状重合体C1の水分散液を用いて、上述した方法により、粒子状重合体C1のゲル含有量、及び、ガラス転移温度を測定した。測定の結果、ゲル含有量は92%、ガラス転移温度(Tg)は10℃であった。
<二次電池用バインダー組成物の調製>
架橋剤(B)として固形分相当で2部の架橋剤B1と、粒子状重合体(C)として固形分相当で150部の粒子状重合体C1とを25℃環境下混合したのち、この混合物を、固形分相当で98質量部のCMC1と同じく固形分相当で2質量部のPAA1とからなる水溶性増粘剤(A)100質量部(固形部相当)に加えて、実施例1の二次電池用バインダー組成物を調製した。
調製した二次電池用バインダー組成物を用いて、上述した方法により、バインダーフィルムを作成し、引っ張り破断強度、電解液に対する濡れ性、耐水性を評価した。結果を表1に示す。
プラネタリーミキサーに、炭素系活物質である天然黒鉛(非晶質コート天然黒鉛、BET比表面積:3.0m2/g、平均粒径:13μm)10000部、水溶性増粘剤(A)としてCMC1の1%水溶液を固形分相当で98部、およびPAA1の1%水溶液(NaOHでpHを8に調整済み)を固形分相当で2部、架橋剤(B)として架橋剤B1を固形分相当で2部、粒子状重合体(C)として粒子状重合体C1の水分散液を固形分相当で150部投入し、さらに固形分濃度が52%となるようにイオン交換水を加えて混合し、CMC1、PAA1、架橋剤B1、および粒子状重合体C1を含んでなる二次電池用バインダー組成物を含有する二次電池負極用スラリー組成物を調製した。
上述の二次電池負極用スラリー組成物を、コンマコーターで、厚さ20μmの銅箔(集電体)の上に塗付量が8.8mg/cm2以上9.2mg/cm2以下となるように塗布した。この二次電池負極用スラリー組成物が塗布された銅箔を、0.3m/分の速度で80℃のオーブン内を2分間、さらに120℃のオーブン内を2分間かけて搬送することにより、銅箔上のスラリー組成物を乾燥させ、負極原反を得た。
そして得られた負極原反をロールプレス機にて合材層密度が1.45g/cm2以上1.55g/cm3以下となるようプレスし、さらに、水分の除去および架橋のさらなる促進を目的として、真空条件下120℃の環境に10時間置き、集電体上に負極合材層を形成してなる負極を得た。
作製した負極を用いて、負極合材層と集電体との密着性、電解液の注液性、負極の耐水性を評価した。結果を表1に示す。
プラネタリーミキサーに、正極活物質としてLiCoO2100部、導電材としてアセチレンブラック2部(電気化学工業(株)製「HS-100」)、PVDF(ポリフッ化ビニリデン、(株)クレハ化学製「KF-1100」)2部、さらに全固形分濃度が67%となるようにN-メチルピロリドンを加えて混合し、二次電池正極用スラリー組成物を調製した。
得られた二次電池正極用スラリー組成物をコンマコーターで、厚さ20μmのアルミ箔の上に塗布し、乾燥した。なお、この乾燥は、アルミ箔を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分間加熱処理して正極原反を得た。
得られた正極原反をロールプレス機にてプレス後の合材層密度が3.40g/cm3以上3.50g/cm3以下になるようにプレスし、さらに水分の除去を目的として、真空条件下120℃の環境に3時間置き、集電体上に正極合材層を形成してなる正極を得た。
単層のポリプロピレン製セパレータ(幅65mm、長さ500mm、厚さ25μm;乾式法により製造;気孔率55%)を用意し、5cm×5cmの正方形状に切り抜いた。また、電池の外装として、アルミ包材外装を用意した。
そして作製した正極を、3.8cm×2.8cmの長方形状に切り出し、集電体側の表面がアルミ包材外装に接するように配置した。次に、正極の正極合材層の面上に、上記の正方形状のセパレータを配置した。さらに、作製した負極を、4.0cm×3.0cmの長方形状に切り出し、これをセパレータ上に、負極合材層側の表面がセパレータに向かい合うよう配置した。その後、電解液として濃度1.0MのLiPF6溶液(溶媒はエチレンカーボネート(EC)/エチルメチルカーボネート(EMC)=1/2(体積比)の混合溶媒、添加剤としてビニレンカーボネート2体積%(溶媒比)含有)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、ラミネートセル型のリチウムイオン二次電池を製造した。
作製したリチウムイオン二次電池について、サイクル特性、サイクル後の抵抗上昇抑制を評価した。結果を表1に示す。
架橋剤B1の配合量を、それぞれ固形分相当で5部、10部、20部、50部、0.01部、0.6部、1部、80部とした以外は、実施例1と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表1、2に示す。
架橋剤B1に替えて、それぞれ架橋剤B2、架橋剤B3を使用した以外は、実施例2と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表1に示す。
水溶性増粘剤(A)として、それぞれ固形分相当で、CMC1のみを100部、CMC1を99.5部およびPAA1を0.5部、CMC1を90部およびPAA1を10部、使用した(全て固形分相当)以外は、実施例2と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表1に示す。
粒子状重合体C1の配合量を、それぞれ固形分相当で15部、60部、100部、270部、400部とした以外は、実施例2と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表2に示す。
負極活物質として人造黒鉛(BET比表面積:3.7m2/g、平均粒径:23μm)を使用した以外は、実施例2と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表2に示す。
負極活物質として、実施例1で使用した天然黒鉛と実施例20で使用した人造黒鉛の混合物(混合物中に天然黒鉛が占める割合:50質量%)を使用した以外は、実施例2と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表2に示す。
架橋剤B1を使用しない以外は、それぞれ実施例1,20,21と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表3に示す。
架橋剤B1の配合量を、固形分相当で110部とした以外は、実施例1と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表3に示す。
粒子状重合体C1の配合量を、それぞれ固形分相当で510部、3部とした以外は、実施例2と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表3に示す。
一方、架橋剤(B)を含まない比較例1,5,6は、負極合材層と集電体との密着性および電解液の注液性を確保することができず、リチウムイオン二次電池の電気的特性を向上させることができないことが分かる。また、比較例1,5,6は、負極の耐水性も低い。
ここで、架橋剤(B)の配合量が所定量よりも多い比較例2は、負極合材層と集電体との密着性を確保することができず、リチウムイオン二次電池の電気的特性を向上させることができないことが分かる。
そして、粒子状重合体(C)の配合量が所定量よりも多い比較例3は、電解液の注液性を確保することができず、リチウムイオン二次電池の電気的特性を向上させることができないことが分かる。
更に、粒子状重合体(C)を含むが、その配合量が所定量よりも少ない比較例4は、負極合材層と集電体との密着性とリチウムイオン二次電池の電気的特性の双方をバランスよく向上させることができないことが分かる。
実施例2,4より、架橋剤(B)のオキサゾリン当量を変更することで、電解液の注液性、リチウムイオン二次電池の電気的特性を高い次元で並立し得ることが分かる。
実施例2,4,5より、架橋剤(B)が一相水溶性であることで、負極合材層と集電体との密着性、電解液の注液性、リチウムイオン二次電池の電気的特性、および、負極の耐水性を高い次元で並立し得ることが分かる。
実施例2,6~8より、水溶性増粘剤(A)としてカルボキシメチルセルロースとポリアクリル酸を併用し、それらの配合比率を調整することで、負極合材層と集電体との密着性、電解液の注液性、リチウムイオン二次電池の電気的特性、および、負極の耐水性を高い次元で並立し得ることが分かる。
実施例2,11~15より、粒子状重合体(C)の水溶性増粘剤(A)に対する配合比率を調整することで、負極合材層と集電体との密着性、電解液の注液性、リチウムイオン二次電池の電気的特性、および、負極の耐水性を高い次元で並立し得ることが分かる。
実施例2,20,21より、負極活物質として用いる黒鉛の種類を変更することで、負極合材層と集電体との密着性、電解液の注液性、および、リチウムイオン二次電池の電気的特性を高い次元で並立し得ることが分かる。
水溶性増粘(A)としては上述したCMC1,PAA1を使用し、粒子状重合体(C)としては上述した粒子状重合体C1を使用した。そして、以下の架橋剤(B)を使用した。
[架橋剤(B)]
架橋剤B4:ポリカルボジイミド(日清紡ケミカル社製 製品名:カルボジライト(登録商標)SV-02 NCN当量429 一相水溶性)
架橋剤B5:ポリカルボジイミド(日清紡ケミカル社製 製品名:カルボジライト(登録商標)V-02 NCN当量600 一相水溶性)
架橋剤B6:ポリカルボジイミド(日清紡ケミカル社製 製品名:カルボジライト(登録商標)E-02 NCN当量445 エマルジョン)
<二次電池用バインダー組成物の調製>
架橋剤(B)として固形分相当で2部の架橋剤B4と、粒子状重合体(C)として固形分相当で150部の粒子状重合体C1とを25℃環境下混合したのち、この混合物を、固形分相当で98質量部のCMC1と同じく固形分相当で2質量部のPAA1とからなる水溶性増粘剤(A)100質量部に加えて、実施例22の二次電池用バインダー組成物を調製した。
調製した二次電池用バインダー組成物を用いて、上述した方法により、バインダーフィルムを作成し、引っ張り破断強度、電解液に対する濡れ性、耐水性を評価した。結果を表4に示す。
プラネタリーミキサーに、炭素系活物質である天然黒鉛(非晶質コート天然黒鉛、BET比表面積:3.0m2/g、平均粒径:13μm)10000部、水溶性増粘剤(A)としてCMC1の1%水溶液を固形分相当で98部、およびPAA1の1%水溶液(NaOHでpHを8に調整済み)を固形分相当で2部、架橋剤(B)として架橋剤B1を固形分相当で2部、粒子状重合体(C)として粒子状重合体C1の水分散液を固形分相当で150部投入し、さらに固形分濃度が52%となるようにイオン交換水を加えて混合し、CMC1、PAA1、架橋剤B4、および粒子状重合体C1を含んでなる二次電池用バインダー組成物を含有する二次電池負極用スラリー組成物を調製した。
上述の二次電池負極用スラリー組成物を、コンマコーターで、厚さ20μmの銅箔(集電体)の上に塗付量が8.8mg/cm2以上9.2mg/cm2以下となるように塗布した。この二次電池負極用スラリー組成物が塗布された銅箔を、0.3m/分の速度で80℃のオーブン内を2分間、さらに120℃のオーブン内を2分間かけて搬送することにより、銅箔上のスラリー組成物を乾燥させ、負極原反を得た。
そして得られた負極原反をロールプレス機にて合材層密度が1.45g/cm2以上1.55g/cm3以下となるようプレスし、さらに、水分の除去および架橋のさらなる促進を目的として、真空条件下120℃の環境に10時間置き、集電体上に負極合材層を形成してなる負極を得た。
作製した負極を用いて、負極合材層と集電体との密着性、電解液の注液性、負極の耐水性を評価した。結果を表4に示す。
プラネタリーミキサーに、正極活物質としてLiCoO2100部、導電材としてアセチレンブラック2部(電気化学工業(株)製「HS-100」)、PVDF(ポリフッ化ビニリデン、(株)クレハ化学製「KF-1100」)2部、さらに全固形分濃度が67%となるようにN-メチルピロリドンを加えて混合し、二次電池正極用スラリー組成物を調製した。
得られた二次電池正極用スラリー組成物をコンマコーターで、厚さ20μmのアルミ箔の上に塗布し、乾燥した。なお、この乾燥は、アルミ箔を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分間加熱処理して正極原反を得た。
得られた正極原反を乾燥後、ロールプレス機にてプレス後の合材層密度が3.40g/cm3以上3.50g/cm3以下になるようにプレスし、さらに水分の除去を目的として、真空条件下120℃の環境に3時間置き、集電体上に正極合材層を形成してなる正極を得た。
単層のポリプロピレン製セパレータ(幅65mm、長さ500mm、厚さ25μm;乾式法により製造;気孔率55%)を用意し、5cm×5cmの正方形状に切り抜いた。また、電池の外装として、アルミ包材外装を用意した。
そして作製した正極を、3.8cm×2.8cmの長方形状に切り出し、集電体側の表面がアルミ包材外装に接するように配置した。次に、正極の正極合材層の面上に、上記の正方形状のセパレータを配置した。さらに、作製した負極を、4.0cm×3.0cmの長方形状に切り出し、これをセパレータ上に、負極合材層側の表面がセパレータに向かい合うよう配置した。その後、電解液として濃度1.0MのLiPF6溶液(溶媒はエチレンカーボネート(EC)/エチルメチルカーボネート(EMC)=1/2(体積比)の混合溶媒、添加剤としてビニレンカーボネート2体積%(溶媒比)含有)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、ラミネートセル型のリチウムイオン二次電池を製造した。
作製したリチウムイオン二次電池について、サイクル特性、サイクル後の抵抗上昇抑制を評価した。結果を表4に示す。
架橋剤B4の配合量を、それぞれ固形分相当で5部、10部、20部、50部、0.01部、0.6部、1部、80部とした以外は、実施例22と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表4、5に示す。
架橋剤B4に替えて、それぞれ架橋剤B5、架橋剤B6を使用した以外は、実施例23と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表4に示す。
水溶性増粘剤(A)として、それぞれ固形分相当で、CMC1のみを100部、CMC1を99.5部およびPAA1を0.5部、CMC1を90部およびPAA1を10部、使用した(全て固形分相当)以外は、実施例23と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表4に示す。
粒子状重合体C1の配合量を、それぞれ固形分相当で15部、60部、100部、270部、400部とした以外は、実施例23と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表5に示す。
負極活物質として人造黒鉛(BET比表面積:3.7m2/g、平均粒径:23μm)を使用した以外は、実施例23と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表5に示す。
負極活物質として、実施例22で使用した天然黒鉛と実施例41で使用した人造黒鉛の混合物(混合物中に天然黒鉛が占める割合:50質量%)を使用した以外は、実施例23と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表5に示す。
架橋剤B4を使用しない以外は、それぞれ実施例22、41、42と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表6に示す。
架橋剤B4の配合量を、固形分相当で110部とした以外は、実施例22と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例22と同様にして評価した。結果を表6に示す。
粒子状重合体C1の配合量を、それぞれ固形分相当で510部、3部とした以外は、実施例23と同様にして二次電池用バインダー組成物、二次電池負極用スラリー組成物、負極、正極、リチウムイオン二次電池を製造した。そして、実施例1と同様にして評価した。結果を表6に示す。
一方、架橋剤(B)を含まない比較例7,11,12は、負極合材層と集電体との密着性および電解液の注液性を確保することができず、リチウムイオン二次電池の電気的特性を向上させることができないことが分かる。また、比較例7,11,12は、負極の耐水性も低い。
ここで、架橋剤(B)の配合量が所定量よりも多い比較例8は、負極合材層と集電体との密着性を確保することができず、リチウムイオン二次電池の電気的特性を向上させることができないことが分かる。
そして、粒子状重合体(C)の配合量が所定量よりも多い比較例9は、電解液の注液性を確保することができず、リチウムイオン二次電池の電気的特性を向上させることができないことが分かる。
更に、粒子状重合体(C)を含むが、その配合量が所定量よりも少ない比較例10は、負極合材層と集電体との密着性とリチウムイオン二次電池の電気的特性をバランスよく向上させることができないことが分かる。
実施例23,25より、架橋剤(B)のNCN当量を変更することで、電解液の注液性、リチウムイオン二次電池の電気的特性を高い次元で並立し得ることが分かる。
実施例23,25,26より、架橋剤(B)が一相水溶性であることで、負極合材層と集電体との密着性、電解液の注液性、リチウムイオン二次電池の電気的特性、および、負極の耐水性を高い次元で並立し得ることが分かる。
実施例23,27~29より、水溶性増粘剤(A)としてカルボキシメチルセルロースとポリアクリル酸を併用し、それらの配合比率を調整することで、負極合材層と集電体との密着性、電解液の注液性、リチウムイオン二次電池の電気的特性、および、負極の耐水性を高い次元で並立し得ることが分かる。
実施例23,32~36より、粒子状重合体(C)の水溶性増粘剤(A)に対する配合比率を調整することで、負極合材層と集電体との密着性、電解液の注液性、リチウムイオン二次電池の電気的特性、および、負極の耐水性を高い次元で並立し得ることが分かる。
実施例23,41,42より、負極活物質として用いる黒鉛の種類を変更することで、負極合材層と集電体との密着性、電解液の注液性、および、リチウムイオン二次電池の電気的特性を高い次元で並立し得ることが分かる。
そして、本発明の二次電池用負極によれば、集電体と負極合材層との密着性を向上させると共に、二次電池の電気的特性を向上させることができる。
更に、本発明の二次電池によれば、電気的特性を向上させることができると共に、負極合材層と集電体との密着性を確保できる。
Claims (7)
- 水酸基又はカルボキシル基を有する水溶性増粘剤(A)と、カルボジイミド基又はオキサゾリン基を有する架橋剤(B)と、粒子状重合体(C)とを含み、
前記粒子状重合体(C)は、前記架橋剤(B)と反応する官能基を有し、かつ、脂肪族共役ジエン単量体単位および芳香族ビニル単量体単位を含み、
前記水溶性増粘剤(A)100質量部当たり、前記架橋剤(B)を0.001質量部以上100質量部未満含有し、前記粒子状重合体(C)を10質量部以上500質量部未満含有する、二次電池用バインダー組成物。 - 前記水溶性増粘剤(A)が、カルボキシメチルセルロース、メチルセルロース、ヒドロキシプロピルメチルセルロース、ヒドロキシエチルメチルセルロース、ポリビニルアルコール、ポリカルボン酸、および、これらの塩、からなる群から選択される少なくとも1種である、請求項1に記載の二次電池用バインダー組成物。
- 前記粒子状重合体(C)中の前記架橋剤(B)と反応する官能基が、カルボキシル基、水酸基、グリシジルエーテル基、および、チオール基からなる群から選択される少なくとも1種である、請求項1または2に記載の二次電池用バインダー組成物。
- 水酸基又はカルボキシル基を有する水溶性増粘剤(A)と、カルボジイミド基又はオキサゾリン基を有する架橋剤(B)と、粒子状重合体(C)と、電極活物質と、水とを含み、
前記粒子状重合体(C)は、前記架橋剤(B)と反応する官能基を有し、かつ、脂肪族共役ジエン単量体単位および芳香族ビニル単量体単位を含み、
前記水溶性増粘剤(A)100質量部当たり、前記架橋剤(B)を0.001質量部以上100質量部未満含有し、前記粒子状重合体(C)を10質量部以上500質量部未満含有する、二次電池電極用スラリー組成物。 - 前記電極活物質が負極活物質である請求項4に記載の二次電池電極用スラリー組成物から得られる負極合材層を有する、二次電池用負極。
- 前記負極合材層は、前記水溶性増粘剤(A)、前記架橋剤(B)、および、前記粒子状重合体(C)から形成される架橋構造を有する、請求項5に記載の二次電池用負極。
- 請求項5又は6に記載の二次電池用負極と、正極と、電解液と、セパレータとを備える、二次電池。
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US10811687B2 (en) | 2015-11-23 | 2020-10-20 | Lg Chem, Ltd. | Electrode with improved adhesion property for lithium secondary battery, and manufacturing method thereof |
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CN115960280B (zh) * | 2021-10-12 | 2023-12-26 | 宁德时代新能源科技股份有限公司 | 一种粘结剂化合物及其制备方法 |
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Also Published As
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KR20160012141A (ko) | 2016-02-02 |
JPWO2014188724A1 (ja) | 2017-02-23 |
CN105229832A (zh) | 2016-01-06 |
JP6481609B2 (ja) | 2019-03-13 |
US20160204439A1 (en) | 2016-07-14 |
KR102369488B1 (ko) | 2022-03-02 |
CN105229832B (zh) | 2017-09-01 |
KR20210100219A (ko) | 2021-08-13 |
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