Binder composition for all-solid-state secondary battery, slurry composition for all-solid-state secondary battery, functional layer for all-solid-state secondary battery, and all-solid-state secondary battery

Abstract

The purpose of the present invention is to provide a binder composition for an all-solid-state secondary battery capable of giving excellent adhesive properties to a functional layer for an all-solid-state secondary battery while reducing internal resistance of the all-solid-state secondary battery. The present invention is a binder composition for an all-solid-state secondary battery comprising a copolymer that contains a nitrile group-containing monomer unit and a solvent. In the binder composition for an all-solid-state secondary battery, the solvent contains an ester solvent of C6 or higher, the content ratio of the nitrile group-containing monomer unit in the copolymer is 10-22 mass% inclusive when all repeating units in the copolymer are 100 mass%, and when the copolymer is dissolved in the solvent so that the tetrahydrofuran insoluble fraction of the copolymer is 0.5-3 mass% inclusive and the copolymer concentration is 8 mass%, the haze of the obtained copolymer solution is 30-80% inclusive.

Description

Binder composition for all-solid-state secondary battery, slurry composition for all-solid-state secondary battery, functional layer for all-solid-state secondary battery, and all-solid-state secondary battery

[0001] The present invention relates to a binder composition for an all-solid-state secondary battery, a slurry composition for an all-solid-state secondary battery, a functional layer for an all-solid-state secondary battery, and an all-solid-state secondary battery.

[0002] In recent years, demand for secondary batteries such as lithium-ion batteries has been increasing for a variety of applications, including portable terminals such as personal digital assistants and portable electronic devices, as well as small-sized home power storage devices, electric motorcycles, electric vehicles, and hybrid electric vehicles.

[0003] With the expansion of applications, further improvements in the safety of secondary batteries are required. To ensure the safety of secondary batteries, for example, a method of preventing leakage of an organic electrolyte solution obtained by dissolving an electrolyte in an organic solvent is effective. Meanwhile, techniques for producing secondary batteries (all-solid-state secondary batteries) in which all components are solid, including a solid electrolyte layer instead of a flammable organic electrolyte solution, have also been studied.

[0004] Specifically, all-solid-state secondary batteries typically have a solid electrolyte layer between a positive electrode and a negative electrode. A binder is typically used in the production of all-solid-state secondary batteries. The binder is used, for example, in the solid electrolyte layer or in the electrode mixture layer of an electrode formed by providing the electrode mixture layer on a current collector (hereinafter, the solid electrolyte layer and the electrode mixture layer may be collectively referred to as "all-solid-state secondary battery functional layers") to bind functional particles such as solid electrolyte particles and electrode active material particles together and prevent the functional particles from detaching from battery materials such as the solid electrolyte layer and the electrode. For example, Patent Document 1 describes an all-solid-state secondary battery having a positive electrode having a positive electrode active material layer (positive electrode composite layer), a negative electrode having a negative electrode active material layer (negative electrode composite layer), and a solid electrolyte layer located between the positive electrode active material layer and the negative electrode active material layer. It also describes forming the positive electrode active material layer, the negative electrode active material layer, or the solid electrolyte layer using a slurry composition containing functional particles, a predetermined polymer as a binder, and an organic solvent. Patent Document 2 also describes forming a cathode for an all-solid-state lithium-ion battery by applying a slurry containing an active material, a conductive material, a sulfide-based solid electrolyte, a predetermined binder, and a solvent to a substrate. It also describes an all-solid-state lithium-ion battery including this cathode. The slurry compositions in Patent Documents 1 and 2 use a nitrile-based polymer as a binder and xylene, cyclopentyl methyl ether (CPME), or the like as a solvent.

[0005] Patent No. 5768815 Publication Special Publication No. 2020-525992

[0006] Here, in an all-solid-state secondary battery, it is desirable that the functional layer for the all-solid-state secondary battery has excellent adhesion to a battery material (e.g., a current collector) that comes into contact with the functional layer for the all-solid-state secondary battery, but conventional binder compositions have room for further improvement in terms of imparting excellent adhesion to the functional layer for the all-solid-state secondary battery.Furthermore, it is desirable that the internal resistance of an all-solid-state secondary battery is low, but conventional binder compositions have room for further improvement in terms of reducing the internal resistance of the all-solid-state secondary battery.

[0007] Therefore, an object of the present invention is to provide a binder composition for an all-solid-state secondary battery that can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. Another object of the present invention is to provide a slurry composition for an all-solid-state secondary battery that can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. Another object of the present invention is to provide a functional layer for an all-solid-state secondary battery that can exhibit excellent adhesion while reducing the internal resistance of the all-solid-state secondary battery. Another object of the present invention is to provide an all-solid-state secondary battery in which battery materials are firmly bonded together while the internal resistance is reduced.

[0008] The present inventors have conducted extensive research with the aim of solving the above-mentioned problems, and have found that the above-mentioned problems can be solved by using a binder composition for an all-solid-state secondary battery that contains a predetermined copolymer and a predetermined solvent, and that when the copolymer is dissolved in the solvent to a concentration of 8 mass %, the haze of the resulting copolymer solution is within a predetermined range, thereby completing the present invention.

[0009]

[0010] The present invention aims to advantageously solve the above-mentioned problems. [1] The present invention provides a binder composition for an all-solid-state secondary battery, comprising a copolymer containing a nitrile group-containing monomer unit and a solvent, wherein the solvent contains an ester solvent having 6 or more carbon atoms, the content of the nitrile group-containing monomer unit in the copolymer is 10% by mass to 22% by mass, where the total mass of all repeating units in the copolymer is 100% by mass, the copolymer has a tetrahydrofuran-insoluble fraction of 0.5% by mass to 3% by mass, and when the copolymer is dissolved in the solvent to a copolymer concentration of 8% by mass, the resulting copolymer solution has a haze of 30% to 80%. The binder composition for an all-solid-state secondary battery can impart excellent adhesion to a functional layer for the all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. In this specification, the "monomer unit" of a (co)polymer means "a repeating unit derived from the monomer contained in a polymer obtained using the monomer." In this specification, the content ratio of various repeating units (monomer units and structural units) in a copolymer is expressed as follows: １ It can be measured using a nuclear magnetic resonance (NMR) method such as H-NMR. Herein, the tetrahydrofuran insoluble content can be measured according to the method described in the Examples of the present specification. Herein, the haze of a copolymer solution can be measured according to the method described in the Examples of the present specification.

[0010] [2] In the binder composition for an all-solid-state secondary battery described in [1] above, the iodine value of the copolymer is preferably 0.5 mg / 100 mg or more and 30 mg / 100 mg or less. If the iodine value of the copolymer is equal to or greater than the lower limit, the deterioration of the cycle characteristics of the all-solid-state secondary battery can be effectively suppressed. On the other hand, if the iodine value of the copolymer is equal to or less than the upper limit, the cycle characteristics of the all-solid-state secondary battery can be further improved. In this specification, the iodine value of the copolymer can be measured according to the method described in the examples of this specification.

[0011] [3] In the binder composition for an all-solid-state secondary battery according to [1] or [2] above, it is preferable that the copolymer further contains an alkylene structural unit, the alkylene structural unit being a 1,3-butadiene hydride unit, and the nitrile group-containing monomer unit being an acrylonitrile unit. When the copolymer contains the above-mentioned monomer unit, it is possible to impart superior adhesiveness to the functional layer for an all-solid-state secondary battery. Furthermore, when the copolymer contains the above-mentioned monomer unit, it is possible to further improve the dispersibility of functional particles in a slurry composition for an all-solid-state secondary battery prepared using the binder composition for an all-solid-state secondary battery.

[0012] [4] In the binder composition for an all-solid-state secondary battery according to any one of the above [1] to [3], the copolymer preferably contains a (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms. If the copolymer contains a (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms, the internal resistance of the all-solid-state secondary battery can be further reduced.

[0013] [5] In the binder composition for an all-solid-state secondary battery according to [4] above, the content of the (meth)acrylic acid ester monomer units having an alkyl group containing 4 to 9 carbon atoms in the copolymer is preferably 25% by mass or more and 45% by mass or less, when the total mass of all repeating units in the copolymer is 100% by mass. If the content of the (meth)acrylic acid ester monomer units having an alkyl group containing 4 to 9 carbon atoms in the copolymer is equal to or greater than the lower limit, when the total mass of all repeating units in the copolymer is 100% by mass, the internal resistance of the all-solid-state secondary battery can be further reduced. On the other hand, if the content of the (meth)acrylic acid ester monomer units having an alkyl group containing 4 to 9 carbon atoms in the copolymer is equal to or less than the upper limit, when the total mass of all repeating units in the copolymer is 100% by mass, the internal resistance of the all-solid-state secondary battery can be further reduced. Furthermore, the cycle characteristics of the all-solid-state secondary battery can be further improved.

[0014] [6] In the binder composition for an all-solid-state secondary battery according to any one of [1] to [5] above, the copolymer preferably has a hydrophilic group. If the copolymer has a hydrophilic group, better adhesion can be imparted to the functional layer for an all-solid-state secondary battery.

[0015] Another object of the present invention is to advantageously solve the above-mentioned problems, and [7] the present invention is a slurry composition for an all-solid-state secondary battery, comprising functional particles and the binder composition for an all-solid-state secondary battery according to any one of [1] to [6]. The above-mentioned slurry composition for an all-solid-state secondary battery can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery.

[0016] [8] In the slurry composition for a solid secondary battery according to the above item [7], the functional particles are preferably at least one of solid electrolyte particles and electrode active material particles. When the functional particles are at least one of solid electrolyte particles and electrode active material particles, the functional layer for an all-solid-state secondary battery can be endowed with the function of a solid electrolyte layer and / or an electrode mixture layer.

[0017] Another object of the present invention is to advantageously solve the above-mentioned problems, and [9] the present invention is a functional layer for an all-solid-state secondary battery formed using the slurry composition for an all-solid-state secondary battery according to [7] or [8] above. The functional layer for an all-solid-state secondary battery can exhibit excellent adhesion while reducing the internal resistance of the all-solid-state secondary battery.

[0018] Another object of the present invention is to advantageously solve the above-mentioned problems, and

[10] the present invention is an all-solid-state secondary battery including the all-solid-state secondary battery functional layer according to [9]. The all-solid-state secondary battery can be an all-solid-state secondary battery in which the internal resistance is reduced and the battery materials are firmly bonded to each other.

[0019] According to the present invention, it is possible to provide a binder composition for an all-solid-state secondary battery that can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. Furthermore, according to the present invention, it is possible to provide a slurry composition for an all-solid-state secondary battery that can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. Furthermore, according to the present invention, it is possible to provide a functional layer for an all-solid-state secondary battery that can exhibit excellent adhesion while reducing the internal resistance of the all-solid-state secondary battery. Furthermore, according to the present invention, it is possible to provide an all-solid-state secondary battery in which battery materials are firmly bonded together while the internal resistance is reduced.

[0020] Hereinafter, embodiments of the present invention will be described in detail. Hereinafter, the binder composition for an all-solid-state secondary battery of the present invention (hereinafter, sometimes simply referred to as the "binder composition") can be used to prepare the slurry composition for an all-solid-state secondary battery of the present invention (hereinafter, sometimes simply referred to as the "slurry composition"). In addition, the slurry composition of the present invention can be used to form a functional layer for an all-solid-state secondary battery (hereinafter, sometimes simply referred to as the "functional layer"), such as a solid electrolyte layer or an electrode mixture layer. The all-solid-state secondary battery of the present invention includes the functional layer of the present invention formed using the slurry composition of the present invention.

[0021] (Binder Composition for All-Solid-State Secondary Battery) The binder composition for all-solid-state secondary batteries of the present invention comprises a predetermined copolymer and a predetermined solvent. The solvent contains an ester solvent having 6 or more carbon atoms. The copolymer also contains a nitrile group-containing monomer unit. The content of the nitrile group-containing monomer unit in the copolymer is 10% by mass to 22% by mass, where the total repeating units in the copolymer is 100% by mass. The copolymer has a tetrahydrofuran-insoluble content (hereinafter sometimes referred to as "THF-insoluble content") of 0.5% by mass to 3% by mass. When the copolymer and the solvent are dissolved in the solvent to a copolymer concentration of 8% by mass, the resulting copolymer solution has a haze of 30% to 80%. The binder composition of the present invention may further contain other optional components in addition to the predetermined copolymer and solvent. Examples of other components include surfactants, dispersants, and antioxidants. The binder composition can reduce the internal resistance of the all-solid-state secondary battery while imparting excellent adhesion to the functional layer, and can also improve the cycle characteristics of the all-solid-state secondary battery.

[0022] <Copolymer> The copolymer is a component that can prevent functional particles contained in the functional layer from detaching from the functional layer. Here, the copolymer has the predetermined composition and properties described above, but preferably has a hydrophilic group, since this can impart better adhesiveness to the functional layer. Examples of hydrophilic groups include a carboxyl group, a sulfonic acid group, a phosphate group, and a hydroxyl group. Among these, a carboxyl group and a hydroxyl group are preferred, since they can impart even better adhesiveness to the functional layer, and a hydroxyl group is more preferred. The copolymer may have only one type of these hydrophilic groups, or two or more types.

[0023] The method for introducing hydrophilic groups into a copolymer is not particularly limited. A copolymer containing hydrophilic group-containing monomer units may be obtained by preparing a copolymer using a monomer composition containing a hydrophilic group-containing monomer described below, or a copolymer having a predetermined composition may be modified (e.g., terminally modified) to obtain a copolymer having the above-mentioned hydrophilic group, but the former is preferred.

[0024] <<Composition of Copolymer>> The copolymer contains a nitrile group-containing monomer unit, and optionally contains a conjugated diene monomer unit, an alkylene structural unit, a hydrophilic group-containing monomer unit, a (meth)acrylic acid ester monomer unit having an alkyl group having from 4 to 9 carbon atoms, and an aromatic vinyl monomer unit. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0025] [Nitrile Group-Containing Monomer Unit] The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Examples of nitrile group-containing monomers that can form the nitrile group-containing monomer unit include α,β-ethylenically unsaturated nitrile monomers. The α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, but examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferred as the nitrile group-containing monomer, as they can impart superior adhesiveness to the functional layer, and acrylonitrile is more preferred. These can be used alone or in combination of two or more.

[0026] In the binder composition of the present invention, the content of the nitrile group-containing monomer units in the copolymer is 10% by mass or more and 22% by mass or less, when the total amount of all repeating units in the copolymer is 100% by mass. The content of the nitrile group-containing monomer units in the copolymer is preferably 12% by mass or more, more preferably 14% by mass or more, and preferably 20.5% by mass or less, and more preferably 19% by mass or less, when the total amount of all repeating units in the copolymer is 100% by mass. If the content of the nitrile group-containing monomer units in the copolymer is 10% by mass or more, when the total amount of all repeating units in the copolymer is 100% by mass, the adhesive properties of the copolymer itself are improved, and excellent adhesiveness can be imparted to the functional layer. On the other hand, if the content of the nitrile group-containing monomer units in the copolymer is 22% by mass or less, when the total amount of all repeating units in the copolymer is 100% by mass, excellent adhesiveness can be imparted to the functional layer. The reason for this is presumably that the solubility of the copolymer in the solvent is improved, making it possible to obtain a slurry composition in which the functional particles and the like are well dispersed, and when such a slurry composition is used to form a functional layer, a functional layer is formed in which the functional particles and the like are well dispersed. Furthermore, because the functional particles and the like can be well dispersed in the functional layer, the internal resistance of the all-solid-state secondary battery can be reduced, and further, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0027] [Conjugated diene monomer unit] The conjugated diene monomer unit is a repeating unit derived from a conjugated diene monomer. Examples of conjugated diene monomers that can form the conjugated diene monomer unit include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Of these, 1,3-butadiene is preferred. These can be used alone or in combination of two or more.

[0028] The content of the conjugated diene monomer units in the copolymer is preferably 10% by mass or less, and more preferably 5% by mass or less, when all repeating units in the copolymer are taken as 100% by mass. On the other hand, the content of the conjugated diene monomer units in the copolymer is, for example, 0.5% by mass or more, and may be 1% by mass or more, when all repeating units in the copolymer are taken as 100% by mass.

[0029] [Alkylene structural unit] The alkylene structural unit is represented by the general formula: -C ｎ H ２ｎ - [where n is an integer of 2 or greater]. When the copolymer contains the alkylene structural unit, the dispersibility of the functional particles in a slurry composition prepared using the binder composition can be improved.

[0030] The alkylene structural unit may be linear or branched, but from the viewpoint of further improving the dispersibility of the functional particles in the slurry composition, the alkylene structural unit is preferably linear, i.e., a linear alkylene structural unit. The alkylene structural unit has 4 or more carbon atoms (i.e., the alkylene structural unit represented by the general formula -C ｎ H ２ｎ -n is an integer of 4 or more).

[0031] The method for introducing alkylene structural units into a copolymer is not particularly limited, and examples thereof include the following methods (1) and (2): (1) a method in which a copolymer is prepared from a monomer composition containing the above-mentioned conjugated diene monomer, and the copolymer is hydrogenated (hydrogenated) to convert the conjugated diene monomer units into alkylene structural units; and (2) a method in which a copolymer is prepared from a monomer composition containing a 1-olefin monomer. Among these, method (1) is preferred because it allows the copolymer to be easily produced.

[0032] Conjugated diene monomers that can be used in the above method (1) include, for example, conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among these, 1,3-butadiene is preferred. These can be used alone or in combination of two or more. The alkylene structural unit is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating (hydrogenating) a conjugated diene monomer unit. Furthermore, the alkylene structural unit is more preferably a structural unit (1,3-butadiene hydride unit) obtained by hydrogenating a 1,3-butadiene unit, since this can further improve the dispersibility of functional particles in a slurry composition prepared using the binder composition. Hydrogenation can be carried out using known methods such as those described below. On the other hand, 1-olefin monomers that can be used in the above method (2) include, for example, 1-butene and 1-hexene. These conjugated diene monomers and 1-olefin monomers can be used alone or in combination of two or more.

[0033] When an alkylene structural unit is introduced into a copolymer via the above method (1), if the conjugated diene monomer unit is not completely hydrogenated, the conjugated diene monomer unit may remain in the copolymer.

[0034] The total content of the alkylene structural units and the conjugated diene monomer units in the copolymer is preferably 30% by mass or more, more preferably 40% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, when the total repeating units in the copolymer (the sum of the structural units and the monomer units) is taken as 100% by mass. If the total content of the alkylene structural units and the conjugated diene monomer units in the copolymer is within the above range, when the total repeating units in the copolymer is taken as 100% by mass, the dispersibility of the functional particles in a slurry composition prepared using the binder composition can be further improved.

[0035] In addition, when the copolymer does not contain conjugated diene monomer units, for example, when the conjugated diene monomer units are completely hydrogenated by the above method (1), or when the copolymer is produced by the above method (2), the content of alkylene structural units in the copolymer is preferably 30% by mass or more, more preferably 40% by mass or more, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, when the total repeating units in the copolymer (the total of structural units and monomer units) is taken as 100% by mass. If the content of alkylene structural units in the copolymer is within the above range, when the total repeating units in the copolymer is taken as 100% by mass, the dispersibility of functional particles in a slurry composition prepared using the binder composition can be further improved.

[0036] [Hydrophilic Group-Containing Monomer Unit] The hydrophilic group-containing monomer unit is a repeating unit derived from a hydrophilic group-containing monomer. By containing the hydrophilic group-containing monomer unit in the copolymer, it is possible to impart superior adhesiveness to the functional layer. Examples of hydrophilic group-containing monomers that can form the hydrophilic group-containing monomer unit include monomers having a carboxylic acid group, monomers having a sulfonic acid group, monomers having a phosphoric acid group, and monomers having a hydroxyl group. These can be used alone or in combination of two or more.

[0037] Examples of monomers having a carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, as a monomer having a carboxylic acid group, an acid anhydride that generates a carboxyl group upon hydrolysis can also be used. Other examples include monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate. Among the above, monocarboxylic acids are preferred, and methacrylic acid is more preferred.

[0038] Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In this specification, "(meth)allyl" means allyl and / or methallyl.

[0039] Examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, vinylphosphonic acid, dimethyl vinylphosphonate, etc. In this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0040] Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 1,4-cyclohexanedimethanol monoacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and compounds of the general formula: CH ２ =CR １ -COO-(C ｎ H ２ｎ O) ｍ -H (wherein m is an integer from 2 to 9, n is an integer from 2 to 4, R １represents hydrogen or a methyl group); mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; acrylic ethers such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether. mono(meth)allyl ethers of alkylene glycols; polyoxyalkylene glycol mono(meth)allyl ethers such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether; mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol and halogen-substituted products thereof; (meth)allyl thioethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; etc. Among the above, alkanol esters of ethylenically unsaturated carboxylic acids are preferred, and 1,4-cyclohexanedimethanol monoacrylate and 2-hydroxyethyl methacrylate are more preferred.

[0041] From the viewpoint of further improving the dispersibility of the functional particles in the slurry composition prepared using the binder composition, it is preferable to use, as the hydrophilic group-containing monomer, a monomer having a carboxylic acid group (carboxylic acid group-containing monomer) and / or a monomer having a hydroxyl group (hydroxyl group-containing monomer unit), and it is more preferable to use a hydroxyl group-containing monomer unit.

[0042] The content of the hydrophilic group-containing monomer units in the copolymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less, when the total repeating units in the copolymer is taken as 100% by mass. If the content of the hydrophilic group-containing monomer units in the copolymer is equal to or greater than the lower limit above, when the total repeating units in the copolymer is taken as 100% by mass, the adhesive ability of the copolymer itself is further improved, and better adhesiveness can be imparted to the functional layer. On the other hand, if the content of the hydrophilic group-containing monomer units in the copolymer is equal to or less than the upper limit above, when the total repeating units in the copolymer is taken as 100% by mass, better adhesiveness can be imparted to the functional layer. The reason for this is presumably that the solubility of the copolymer in a solvent is further improved, resulting in a slurry composition in which functional particles and the like are better dispersed. When such a slurry composition is used to form a functional layer, a functional layer in which functional particles and the like are better dispersed is formed. Furthermore, since the functional particles and the like can be dispersed more satisfactorily in the functional layer, the internal resistance of the all-solid-state secondary battery can be further reduced, and further, the cycle characteristics of the all-solid-state secondary battery can be further improved.

[0043] [(Meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms] The (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms is a repeating unit derived from a (meth)acrylic acid ester monomer having 4 to 9 carbon atoms. By including a (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms in a copolymer, the dispersibility of functional particles in a slurry composition prepared using the binder composition can be further improved, thereby further reducing the internal resistance of an all-solid-state secondary battery. Here, "having an alkyl group having 4 to 9 carbon atoms" means that an alkyl group having 4 to 9 carbon atoms is bonded to a non-carbonyl oxygen atom of the (meth)acrylic acid ester monomer. The alkyl group having 4 to 9 carbon atoms may be linear, branched, or cyclic, but is preferably linear because it facilitates the preparation of the copolymer. Note that the (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms does not include the hydrophilic group-containing monomer unit described above. That is, for example, a unit in which a hydroxyl group is bonded to an alkyl group having 4 to 9 carbon atoms is not included in the (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms.

[0044] In the (meth)acrylic acid ester monomer units having an alkyl group having from 4 to 9 carbon atoms, the number of carbon atoms in the alkyl group is preferably 8 or less, and more preferably 6 or less. When the number of carbon atoms in the alkyl group is the above-mentioned upper limit or less, the copolymer can be easily prepared.

[0045] Here, examples of C4-C9 (meth)acrylic acid ester monomers capable of forming units of a (meth)acrylic acid ester monomer having an alkyl group having from 4 to 9 carbon atoms (hereinafter, sometimes referred to as a "C4-C9 (meth)acrylic acid ester monomer") include alkyl acrylate esters such as n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, and nonyl acrylate; and alkyl methacrylate esters such as n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, and nonyl methacrylate. Of these, n-butyl acrylate is preferred. These may be used alone or in combination of two or more.

[0046] The content of the C4-C9 (meth)acrylic acid ester monomer units in the copolymer is preferably 25% by mass or more, more preferably 27.5% by mass or more, and even more preferably 30% by mass or more, and preferably 45% by mass or less, more preferably 42.5% by mass or less, and even more preferably 40% by mass or less, when the total repeating units in the copolymer is taken as 100% by mass. If the content of the C4-C9 (meth)acrylic acid ester monomer units in the copolymer is equal to or greater than the above lower limit, the dispersibility of functional particles in a slurry composition prepared using the binder composition can be further improved, and as a result, the internal resistance of the all-solid-state secondary battery can be further reduced. On the other hand, when the content of the C4-C9 (meth)acrylic acid ester monomer units in the copolymer is equal to or less than the upper limit above, assuming that the total mass of all repeating units in the copolymer is 100%, the flexibility of the functional layer is further improved, and the adhesion between the functional layer and the layer adjacent to it is further improved, thereby further reducing the internal resistance of the all-solid-state secondary battery.In addition, the adhesion between the functional layer and the layer adjacent to it can be further improved, thereby further improving the cycle characteristics of the all-solid-state secondary battery.

[0047] [Aromatic vinyl monomer unit] The aromatic vinyl monomer unit is a repeating unit derived from an aromatic vinyl monomer. Examples of aromatic vinyl monomers that can form the aromatic vinyl monomer unit include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. These can be used alone or in combination of two or more.

[0048] The content of aromatic vinyl monomer units in the copolymer is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 12% by mass or less, when all repeating units in the copolymer are taken as 100% by mass.

[0049] [Other Monomer Units] The copolymer may contain, as repeating units, monomer units other than the above-mentioned nitrile group-containing monomer units, conjugated diene monomer units, alkylene structural units, hydrophilic group-containing monomer units, C4-C9 (meth)acrylic acid ester monomer units, and aromatic vinyl monomer units (hereinafter, these may be referred to as "other monomer units").

[0050] Examples of other monomer units include (meth)acrylic acid ester monomer units having an alkyl group other than an alkyl group having from 4 to 9 carbon atoms, i.e., (meth)acrylic acid ester monomer units having an alkyl group having 3 or less carbon atoms, and (meth)acrylic acid ester monomer units having an alkyl group having 10 or more carbon atoms. Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units having an alkyl group having 3 or less carbon atoms include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and isopropyl methacrylate. Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units having an alkyl group having 10 or more carbon atoms include decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate.

[0051] The content of other monomer units in the copolymer is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, even more preferably 2% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0% by mass, when all repeating units in the copolymer are taken as 100% by mass. That is, it is particularly preferable that the copolymer does not contain other monomer units.

[0052] <<Method for Preparing Copolymer>> The method for preparing the copolymer described above is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. Among these, emulsion polymerization is preferred. Furthermore, addition polymerization such as ionic polymerization, radical polymerization, or living radical polymerization can be used as the polymerization method. Furthermore, known polymerization initiators can be used as the polymerization initiator.

[0053] Examples of the polymerization initiator include inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; organic peroxides such as t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, dibenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and t-butylperoxyisobutyrate; and azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate. These polymerization initiators can be used alone or in combination of two or more. Inorganic or organic peroxides are preferred as the polymerization initiator.

[0054] When a peroxide is used as a polymerization initiator, it can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite or ferrous sulfate. Here, when the above method (1) is used, that is, when a method of converting conjugated diene monomer units into alkylene structural units by hydrogenation (hydrogenation) is used, it is preferable to use radical polymerization using a redox polymerization initiator containing an iron-based compound as a polymerization method for the copolymer before hydrogenation (i.e., pre-hydrogenated copolymer).

[0055] In the polymerization, it is preferable to use a molecular weight modifier having a sulfur-containing group such as a mercapto group. Examples of compounds having a mercapto group as a molecular weight regulator include compounds having a mercapto group having 8 to 12 carbon atoms, such as octyl mercaptan, 2,2,4,6,6-pentamethyl-4-heptanethiol, 2,4,4,6,6-pentamethyl-2-heptanethiol, 2,3,4,6,6-pentamethyl-2-heptanethiol, 2,3,4,6,6-pentamethyl-3-heptanethiol, t-dodecyl mercaptan, and n-dodecyl mercaptan; and compounds having a mercapto group, such as 2,2,4,6,6-pentamethyl-4-octanethiol, 2,2,4,6,6,8,8-heptamethyl-4-nonanethiol, bis(2-mercaptoethyl)sulfide, methyl 3-mercaptopropionate, and 1-butanethiol. Among these, compounds having a mercapto group having 8 to 12 carbon atoms are preferred, and t-dodecyl mercaptan is more preferred.

[0056] The polymerization temperature is preferably 7° C. or higher, more preferably 8° C. or higher, and even more preferably 9° C. or higher, and is preferably 18° C. or lower, more preferably 15° C. or lower, and even more preferably 12° C. or lower. When the polymerization temperature is within the above range, the THF-insoluble content and weight-average molecular weight of the copolymer can be easily adjusted.

[0057] Here, for example, when the above method (1) is used after emulsion polymerization, it is preferable to add a coagulant such as aluminum sulfate to the obtained aqueous dispersion of the pre-hydrogenated copolymer to coagulate it, recover the pre-hydrogenated copolymer, and then hydrogenate the recovered material (or the filtrate if recovered by filtration) (optionally after carrying out the "metathesis reaction" described below). At this time, the recovered material (the filtrate, etc.) may be washed with water or the like before hydrogenation. Note that an antioxidant such as alkylated phenol may be added to the aqueous dispersion before adding the coagulant.

[0058] The hydrogenation of the pre-hydrogenated copolymer can be carried out using a known hydrogenation method such as oil phase hydrogenation or aqueous phase hydrogenation. The catalyst used for hydrogenation can be any known selective hydrogenation catalyst, including palladium-based catalysts and rhodium-based catalysts. Two or more of these catalysts may be used in combination. The amount of the hydrogenation catalyst used may be determined appropriately, but is preferably 50 ppm by mass or more, more preferably 200 ppm by mass or more, and even more preferably 300 ppm by mass or more, and preferably 4000 ppm by mass or less, more preferably 2000 ppm by mass or less, and even more preferably 1000 ppm by mass or less, calculated as the metal amount of the hydrogenation catalyst relative to the amount of the pre-hydrogenated copolymer to be hydrogenated. When the amount of the hydrogenation catalyst used is within the above range, the iodine value of the copolymer can be easily adjusted.

[0059] The hydrogenation of the pre-hydrogenated copolymer may be carried out using, for example, the method described in Japanese Patent No. 4509792. Specifically, the hydrogenation of the pre-hydrogenated copolymer may be carried out after carrying out a metathesis reaction of the copolymer in the presence of a catalyst and a co-olefin. Here, known ruthenium-based catalysts can be used as the catalyst for the metathesis reaction. Among them, it is preferable to use a Grubbs catalyst such as bis(tricyclohexylphosphine)benzylidene ruthenium dichloride or 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinylidene)(dichlorophenylmethylene)(tricyclohexylphosphine)ruthenium as the catalyst for the metathesis reaction. Furthermore, olefins having 2 to 16 carbon atoms such as ethylene, isobutane, and 1-hexane can be used as the co-olefin. Furthermore, as the hydrogenation catalyst for carrying out hydrogenation after the metathesis reaction, for example, a Wilkinson catalyst (PPh ３ ) ３ Known homogeneous hydrogenation catalysts such as RhCl can be used.

[0060] <<Properties of the Copolymer>> [THF-Insoluble Content Ratio] In the binder composition of the present invention, the THF-insoluble content ratio of the copolymer is 0.5% by mass or more and 3% by mass or less. The THF-insoluble content ratio of the copolymer is preferably 0.75% by mass or more, more preferably 1.0% by mass or more, and preferably 2.5% by mass or less, and more preferably 2.0% by mass or less. When the THF-insoluble content ratio of the copolymer is 0.5% by mass or more, the copolymer itself has adequate strength, thereby imparting excellent adhesiveness to the functional layer. On the other hand, when the THF-insoluble content ratio of the copolymer is 3% by mass or less, the flexibility of the functional layer is improved, improving the adhesion between the functional layer and the layer adjacent to it, thereby reducing the internal resistance of the all-solid-state secondary battery. Furthermore, the improved adhesion between the functional layer and the layer adjacent to it can improve the cycle characteristics of the all-solid-state secondary battery. The THF-insoluble content of the copolymer can be adjusted by the composition (content ratio of various repeating units) and weight average molecular weight of the copolymer, as well as the conditions of the copolymer preparation method (e.g., polymerization temperature).

[0061] [Iodine Value] The iodine value of the copolymer is preferably 0.5 mg / 100 mg or more, more preferably 1.0 mg / 100 mg or more, even more preferably 2.0 mg / 100 mg or more, and preferably 30 mg / 100 mg or less, more preferably 15 mg / 100 mg or less, and even more preferably 10 mg / 100 mg or less. Here, in order to make the iodine value of the copolymer less than the above-mentioned lower limit, a large amount of catalyst must be used for hydrogenation. However, using such a large amount of catalyst increases the amount of impurities (residual metals, etc.) mixed into the binder composition, which may result in a deterioration in the cycle characteristics of the all-solid-state secondary battery. Therefore, if the iodine value of the copolymer is equal to or greater than the above-mentioned lower limit, the deterioration of the cycle characteristics of the all-solid-state secondary battery can be effectively suppressed. On the other hand, if the iodine value of the copolymer is equal to or less than the above-mentioned upper limit, the occurrence of side reactions between the copolymer and the functional particles is suppressed, thereby further improving the cycle characteristics of the all-solid-state secondary battery. The iodine value of the copolymer can be adjusted, for example, by the amount of hydrogenation catalyst used when hydrogenating the copolymer.

[0062] [Weight-average molecular weight (Mw)] The weight-average molecular weight of the copolymer is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 30,000 or more, even more preferably 40,000 or more, and preferably 3,000,000 or less, more preferably 2,000,000 or less, even more preferably 1,000,000 or less, even more preferably 80,000 or less, and even more preferably 60,000 or less. If the weight-average molecular weight is above the above lower limit, the functional layer can be imparted with better adhesiveness. In addition, the cycle characteristics of the all-solid-state secondary battery can be further improved. On the other hand, if the weight-average molecular weight of the copolymer is below the above upper limit, the functional layer can be imparted with better adhesiveness. The reason for this is presumably that the solubility of the copolymer in the solvent is further improved, resulting in a slurry composition in which the functional particles and the like are more well dispersed. When such a slurry composition is used to form a functional layer, a functional layer in which the functional particles and the like are more well dispersed is formed. Furthermore, since the functional particles and the like can be dispersed more satisfactorily in the functional layer, the internal resistance of the all-solid-state secondary battery can be further reduced, and further, the cycle characteristics of the all-solid-state secondary battery can be further improved. In this specification, the "weight average molecular weight" can be measured using the method described in the Examples.

[0063] [Molecular Weight Distribution] The molecular weight distribution of the copolymer is preferably 1.5 or more, more preferably 1.8 or more, even more preferably 2.0 or more, and preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less. When the molecular weight distribution of the copolymer is within the above range, superior adhesion can be imparted to the functional layer. This is presumably because the solubility of the copolymer in a solvent is improved, resulting in a slurry composition in which functional particles and the like are better dispersed. When such a slurry composition is used to form a functional layer, a functional layer in which functional particles and the like are better dispersed is formed. Furthermore, because functional particles and the like can be better dispersed in the functional layer, the internal resistance of the all-solid-state secondary battery can be further reduced, and the cycle characteristics of the all-solid-state secondary battery can be further improved. In this specification, "molecular weight distribution" can be determined by calculating the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight). Furthermore, "number average molecular weight" can be measured using gel permeation chromatography as a standard polystyrene equivalent value. The weight-average molecular weight and number-average molecular weight of the copolymer can be controlled, for example, by the composition of the copolymer (the content ratio of various repeating units), the amount of a molecular weight modifier added during polymerization, and the conditions of the copolymer preparation method (e.g., polymerization temperature).

[0064] <<Copolymer Content>> The copolymer content in the binder composition is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, when the total of all components (including the solvent) in the binder composition is 100% by mass.

[0065] <Solvent> The solvent used in the binder composition of the present invention contains an ester solvent having 6 or more carbon atoms, and optionally further contains other solvents (hereinafter, sometimes referred to as "other solvents") that are compatible with the ester solvent having 6 or more carbon atoms. Examples of other solvents include ester solvents having 5 or less carbon atoms, ketone solvents, and alcohol solvents. By using a solvent containing an ester solvent having 6 or more carbon atoms, the haze of the copolymer solution can be maintained in a good state. Furthermore, by using a solvent containing an ester solvent having 6 or more carbon atoms, the occurrence of side reactions between the solvent and the functional particles can be suppressed, and as a result, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0066] Here, an ester solvent having 6 or more carbon atoms means that the total number of carbon atoms in the ester, excluding the carbon atom of the carbonyl group, is 6 or more. That is, it means that the total number of carbon atoms in the organic group bonded to the carbon atom of the carbonyl group (hereinafter sometimes referred to as "organic group A") and the total number of carbon atoms in the organic group bonded to the non-carbonyl oxygen atom (hereinafter sometimes referred to as "organic group B") is 6 or more. For example, isobutyl isobutyrate is an ester solvent having 7 carbon atoms, since organic group A has 3 carbon atoms and organic group B has 4 carbon atoms. Organic group A and / or organic group B are preferably hydrocarbon groups without substituents, and more preferably alkyl groups. The number of carbon atoms in the ester solvent is not particularly limited as long as the haze of the copolymer solution is within a predetermined range, but it may be, for example, 12 or less, or 10 or less.

[0067] Examples of ester solvents having 6 or more carbon atoms include ethyl butyrate, butyl butyrate, isobutyl isobutyrate, pentyl acetate, isopentyl acetate, ethyl caproate, octyl acetate, pentyl valerate, etc. Among these, butyl butyrate, isobutyl isobutyrate, and octyl acetate are preferred, and butyl butyrate and isobutyl isobutyrate are more preferred.

[0068] The content of the ester solvent in the solvent is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, still more preferably 99% by mass or more, and particularly preferably 100%. That is, it is particularly preferable that the solvent does not contain any other solvents.

[0069] <Haze> In the binder composition of the present invention, when the copolymer is dissolved in a solvent so that the copolymer concentration is 8% by mass, the haze of the resulting copolymer solution is 30% or more and 80% or less. The haze of the copolymer solution is preferably 40% or more, more preferably 50% or more, and preferably 75% or less, and more preferably 70% or less. A copolymer solution with a haze of 30% or more can reduce the internal resistance of an all-solid-state secondary battery while imparting excellent adhesion to the functional layer. The reason for this is unclear, but is presumed to be as follows. First, a copolymer solution with a haze of less than 30% can mean that most of the copolymer is dissolved in the solvent. However, when a binder composition containing such a copolymer and solvent is used, most of the surfaces of the functional particles are covered with the copolymer, and in the formed functional layer, the functional particles come into indirect contact with each other via the copolymer, which can result in an increase in the internal resistance of the all-solid-state secondary battery. On the other hand, when the haze of the copolymer solution is 30% or more, as in the binder composition of the present invention, the surfaces of the functional particles are adequately covered with the copolymer, and the areas in which the functional particles directly contact each other in the formed functional layer are increased. As a result, it is presumed that the internal resistance of the all-solid-state secondary battery is reduced. Furthermore, in the functional layer, the areas in which the functional particles indirectly contact each other via the copolymer and the areas in which the functional particles directly contact each other are well balanced, and as a result, it is presumed that the excellent adhesiveness of the functional layer is maintained. On the other hand, when the haze of the copolymer solution is 80% or less, the functional layer can be imparted with excellent adhesiveness. This is presumed to be because the solubility of the copolymer in the solvent is improved, resulting in a slurry composition in which the functional particles and the like are well dispersed. When such a slurry composition is used to form the functional layer, a functional layer in which the functional particles and the like are well dispersed is formed. Furthermore, because the functional particles and the like can be well dispersed in the functional layer, the internal resistance of the all-solid-state secondary battery can be reduced, and the cycle characteristics of the all-solid-state secondary battery can be improved. The haze of the copolymer solution can be adjusted by the composition of the copolymer (the content ratio of various repeating units), the type of solvent, the weight average molecular weight, and the conditions of the copolymer preparation method.

[0070] Furthermore, since the binder composition of the present invention can easily satisfy the above-mentioned predetermined haze, a combination of a copolymer (hereinafter sometimes referred to as "Copolymer A") containing nitrile group-containing monomer units, conjugated diene monomer units, alkylene structural units, and C4-C9 (meth)acrylic acid ester monomer units, where the content of the nitrile group-containing monomer units is 10% by mass or more and 22% by mass or less, when the total repeating units in the copolymer is 100% by mass, and a solvent (hereinafter sometimes referred to as "Solvent A") consisting of any one of butyl butyrate, isobutyl isobutyrate, and octyl acetate is particularly preferred. Furthermore, if the copolymer and solvent are a combination of Copolymer A and Solvent A, in addition to being able to easily satisfy the above-mentioned predetermined haze, it can particularly reduce the internal resistance of the all-solid-state secondary battery and impart particularly excellent adhesion to the functional layer for the all-solid-state secondary battery.

[0071] <Method for Preparing Binder Composition for All-Solid-State Secondary Battery> The binder composition can be prepared by dissolving or dispersing the above-described copolymer in a solvent containing an ester solvent having 6 or more carbon atoms. Specifically, the binder composition can be prepared by mixing the above-described copolymer and the solvent using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, or Filmix. Note that when the copolymer is prepared as a dispersion liquid containing only another solvent, it is preferable to obtain the binder composition of the present invention by solvent exchange. Here, the solvent exchange can be performed by a known method.

[0072] (Slurry Composition for All-Solid-State Secondary Battery) The slurry composition for an all-solid-state secondary battery of the present invention comprises functional particles and the binder composition of the present invention, and optionally further comprises a conductive material and other additives. That is, the slurry composition of the present invention comprises at least functional particles, the copolymer described above, and a solvent containing an ester solvent having 6 or more carbon atoms. The solvent contained in the slurry composition may be entirely derived from the binder composition, or may be newly added to the slurry composition separately from the solvent derived from the binder composition. The binder composition of the present invention can impart excellent adhesion to the functional layer while reducing the internal resistance of the all-solid-state secondary battery. Therefore, a slurry composition containing this binder composition can also impart excellent adhesion to the functional layer while reducing the internal resistance of the all-solid-state secondary battery.

[0073] <Functional Particles> Functional particles are particles that can impart a predetermined function to a layer formed using a slurry composition. Here, the functional particles are preferably at least one of solid electrolyte particles and electrode active material particles. If the functional particles are at least one of solid electrolyte particles and electrode active material particles, the functional layer can be imparted with the functions of a solid electrolyte layer and / or an electrode mixture layer. Here, a slurry composition that can be used to form a solid electrolyte layer (hereinafter sometimes referred to as a "slurry composition for a solid electrolyte layer") contains solid electrolyte particles but usually does not contain electrode active material particles, and preferably does not contain a conductive material. Furthermore, a slurry composition that can be used to form an electrode mixture layer (hereinafter sometimes referred to as a "slurry composition for an electrode mixture layer") contains electrode active material particles (positive electrode active material particles, negative electrode active material particles) and optionally further contains solid electrolyte particles and a conductive material. More specifically, the slurry composition that can be used to form the positive electrode composite layer (hereinafter, may be referred to as the "slurry composition for a positive electrode composite layer") contains positive electrode active material particles, and the slurry composition that can be used to form the negative electrode composite layer (hereinafter, may be referred to as the "slurry composition for a negative electrode composite layer") contains negative electrode active material particles, and these slurry compositions optionally further contain solid electrolyte particles and a conductive material.

[0074] <<Solid Electrolyte Particles>> Solid electrolyte particles are usually particulate because they have been subjected to a pulverization process, but they are irregularly shaped rather than perfectly spherical. The size of fine particles is generally measured by a method in which a particle is irradiated with laser light and the scattered light is measured, but the particle diameter in this case is a value assuming that each particle has a spherical shape. When multiple particles are measured together, the proportion of particles with a corresponding particle diameter can be expressed as a particle size distribution. The solid electrolyte particles that form the solid electrolyte layer are often expressed as an average particle diameter, measured using this method.

[0075] The average particle diameter of the solid electrolyte particles is preferably 0.3 μm or more and 5.0 μm or less from the viewpoint of ion conduction resistance in the functional layer. The average particle diameter of the solid electrolyte particles is a volume-average particle diameter, and refers to the particle diameter (D50) at which the cumulative volume calculated from the smallest diameter side in the particle size distribution (volume basis) measured by laser diffraction method becomes 50%.

[0076] In the case of an all-solid-state lithium secondary battery, the solid electrolyte particles are not particularly limited as long as they have lithium ion conductivity, but preferably contain a crystalline inorganic lithium ion conductor or an amorphous inorganic lithium ion conductor.

[0077] As the crystalline inorganic lithium ion conductor, Li ３ N, LISICON (Li １４ Zn(GeO ４ ) ４ ), perovskite-type Li ０．５ La ０．５ TiO ３ , LIPON (Li ３＋ｙ P.O. ４－ｘ N ｘ ), Thio-LISICON (Li ３．２５ Ge ０．２５ P ０．７５ S ４ ) etc.

[0078] Examples of amorphous inorganic lithium ion conductors include those containing S (sulfur atoms) and having ion conductivity (sulfide solid electrolyte materials). When the all-solid-state secondary battery obtained using the slurry composition of the present invention is an all-solid-state lithium secondary battery, the sulfide solid electrolyte material used may be Li ２ Examples of such a method include a method using a raw material composition containing S and a sulfide of an element of Groups 13 to 15. A method for synthesizing a sulfide solid electrolyte material using such a raw material composition includes, for example, an amorphization method. Examples of the amorphization method include a mechanical milling method and a melt quenching method, and among these, the mechanical milling method is preferred. This is because the mechanical milling method enables processing at room temperature, thereby simplifying the manufacturing process.

[0079] Examples of the elements of Groups 13 to 15 include Al, Si, Ge, P, As, and Sb. Specific examples of sulfides of elements of Groups 13 to 15 include Al, ２ S ３ , SiS ２ , GeS ２ , P ２ S ３ , P ２ S ５ , As ２ S ３ , Sb ２ S ３ Among them, sulfides of Group 14 or 15 are preferably used. In particular, Li ２ The sulfide solid electrolyte material obtained by using a raw material composition containing S and sulfides of elements of Groups 13 to 15 is Li ２ S-P ２ S ５ Material, Li ２ S-SiS ２ Material, Li ２ S-GeS ２ Material or Li ２ S-Al ２ S ３ Preferably, the material is Li ２ S-P ２ S ５It is more preferable that the material is a SiO 2 SiO 3 SiO 4 ...

[0080] Furthermore, the sulfide solid electrolyte material preferably has bridging sulfur, because the presence of bridging sulfur increases ionic conductivity. Note that "having bridging sulfur" can also be determined by taking into consideration, for example, measurement results by Raman spectroscopy, raw material composition ratios, measurement results by NMR, etc.

[0081] Li ２ S-P ２ S ５ Material or Li ２ S-Al ２ S ３ Li in materials ２ From the viewpoint of more reliably obtaining a sulfide solid electrolyte material having bridging sulfur, the molar fraction of S is preferably, for example, in the range of 50% or more and 74% or less, and particularly in the range of 60% or more and 74% or less.

[0082] The sulfide solid electrolyte material may be sulfide glass, or may be crystallized sulfide glass obtained by heat-treating the sulfide glass. The sulfide glass can be obtained, for example, by the amorphization method described above. The crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass.

[0083] In particular, the sulfide solid electrolyte material is Li ７ P ３ S １１ It is preferable that the crystallized sulfide glass be represented by the formula: ７ P ３ S １１ As a method for synthesizing Li ２ S and P ２ S ５ The sulfide glass was synthesized by mixing these in a molar ratio of 70:30 and amorphizing it in a ball mill. The obtained sulfide glass was then heat-treated at 150°C or higher and 360°C or lower to obtain Li. ７ P ３ S １１ can be synthesized.

[0084] In addition, as the amorphous inorganic lithium ion conductor, a material containing O (oxygen atom) and having ion conductivity (oxide solid electrolyte material) can also be used. ３ N, LISICON (Li １４ Zn(GeO ４ ) ４ ), perovskite type (e.g., Li ０．５ La ０．５ TiO ３ ), garnet type (e.g., Li ７ La ３ Zr ２ O １２ ), LIPON (Li ３ +yPO ４ -xNx), Thio-LISICON (Li ３．２５ Ge ０．２５ P ０．７５ S ４ ) etc.

[0085] <<Electrode Active Material Particles>> Examples of electrode active material particles include positive electrode active material particles and negative electrode active material particles. Here, the positive electrode active material particles can be used in a slurry composition for a positive electrode composite layer, and the negative electrode active material particles can be used in a slurry composition for a negative electrode composite layer.

[0086] [Positive electrode active material particles] The positive electrode active material particles are particles made of a positive electrode active material. In the case of an all-solid-state lithium secondary battery, the positive electrode active material is a compound capable of absorbing and releasing lithium ions. Positive electrode active materials are broadly classified into those made of inorganic compounds and those made of organic compounds.

[0087] Examples of inorganic compounds include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metals include Fe, Co, Ni, and Mn. Specific examples of inorganic compounds include LiCoO ２ , LiNiO ２ , LiMnO ２ , LiMn ２ O ４ , LiFePO ４ , LiFeVO ４ Lithium-containing composite metal oxides such as TiS ２, TiS ３ , amorphous MoS ２ transition metal sulfides such as Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３ , V ２ O ５ , V ６ O １３ These compounds may be partially element-substituted.

[0088] Examples of the organic compound include polyaniline, polypyrrole, polyacene, disulfide-based compounds, polysulfide-based compounds, N-fluoropyridinium salts, etc. The positive electrode active material may be a mixture of the above inorganic compounds and organic compounds.

[0089] The average particle size of the positive electrode active material particles is usually 0.1 μm to 50 μm, preferably 1 μm to 20 μm, from the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, obtaining an all-solid electrolyte secondary battery with large charge / discharge capacity, and facilitating handling of the slurry composition and handling during production of the positive electrode. The average particle size can be determined by measuring the particle size distribution by laser diffraction.

[0090] [Negative Electrode Active Material Particles] The negative electrode active material particles are particles made of a negative electrode active material. Examples of negative electrode active materials include carbon allotropes such as graphite and coke. The negative electrode active material made of the carbon allotrope can also be used in the form of a mixture or coating with a metal, metal salt, oxide, etc. In addition, examples of the negative electrode active material that can be used include oxides and sulfates of silicon, tin, zinc, manganese, iron, nickel, etc., metallic lithium, lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd, lithium transition metal nitrides, and silicon. In the case of metal materials, metal foils or metal plates can be used as electrodes as they are, but particles may also be used.

[0091] The average particle size of the negative electrode active material particles is usually 1 μm or more and 50 μm or less, preferably 15 μm or more and 30 μm or less, from the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics.

[0092] <Conductive Material> The conductive material is usually a component that can be blended to promote electrical contact between functional particles in the electrode mixture layer. Examples of the conductive material include conductive carbon materials such as carbon nanotubes, carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite, carbon fibers other than carbon nanotubes, and carbon flakes; and fibers and foils of various metals. These can be used alone or in combination of two or more.

[0093] <Other Additives> Other additives that can be contained in the slurry composition include reinforcing materials, etc. As the reinforcing materials, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used.

[0094] <Solid content concentration of slurry composition> The solid content concentration of the slurry composition for an all-solid-state secondary battery is preferably 30% by mass or more, more preferably 40% by mass or more, and is preferably 80% by mass or less, and more preferably 70% by mass or less. When the solid content concentration of the slurry composition for an all-solid-state secondary battery is within the above range, it is possible to effectively suppress the detachment of functional particles from the functional layer without inhibiting the battery reaction.

[0095] The solid content concentration of the slurry composition for a solid electrolyte layer is preferably 30% by mass or more, more preferably 40% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. When the solid content concentration of the slurry composition for a solid electrolyte layer is within the above range, the detachment of solid electrolyte particles from the solid electrolyte layer can be effectively suppressed without inhibiting the battery reaction.

[0096] The solids concentration of the slurry composition for the positive electrode composite layer is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and is preferably 80% by mass or less, and more preferably 70% by mass or less. If the solids concentration of the slurry composition for the positive electrode composite layer is within the above range, the positive electrode active material particles and solid electrolyte particles can be effectively prevented from falling off from the positive electrode composite layer without inhibiting the battery reaction.

[0097] The solids concentration of the slurry composition for the negative electrode composite layer is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and is preferably 80% by mass or less, and more preferably 70% by mass or less. If the solids concentration of the slurry composition for the negative electrode composite layer is within the above range, the negative electrode active material particles and solid electrolyte particles can be effectively prevented from falling off from the negative electrode composite layer without inhibiting the battery reaction.

[0098] <Content and Mass Ratio of Each Component> The content of the copolymer in the slurry composition for an all-solid-state secondary battery is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, when the total solid content of the slurry composition for an all-solid-state secondary battery is 100 parts by mass. If the content of the copolymer in the slurry composition for an all-solid-state secondary battery is within the above range, when the total solid content of the slurry composition for an all-solid-state secondary battery is 100 parts by mass, it is possible to effectively suppress detachment of functional particles from the functional layer without inhibiting the battery reaction.

[0099] The content of the copolymer in the slurry composition for a solid electrolyte layer is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1.5 parts by mass or less, when the total solid content of the slurry composition for a solid electrolyte layer is 100 parts by mass. If the content of the copolymer in the slurry composition for a solid electrolyte layer is within the above range, when the total solid content of the slurry composition for a solid electrolyte layer is 100 parts by mass, the battery reaction is not inhibited and detachment of solid electrolyte particles from the solid electrolyte layer can be effectively suppressed.

[0100] The content of the copolymer in the slurry composition for the positive electrode composite layer is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1.5 parts by mass or less, when the total solid content of the slurry composition for the positive electrode composite layer is 100 parts by mass. If the content of the copolymer in the slurry composition for the positive electrode composite layer is within the above range, when the total solid content of the slurry composition for the positive electrode composite layer is 100 parts by mass, the battery reaction is not inhibited and detachment of the positive electrode active material particles and the solid electrolyte particles from the positive electrode composite layer can be effectively suppressed.

[0101] The content of the copolymer in the slurry composition for the negative electrode composite layer is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, when the total solid content of the slurry composition for the negative electrode composite layer is 100 parts by mass. If the content of the copolymer in the slurry composition for the negative electrode composite layer is within the above range, when the total solid content of the slurry composition for the negative electrode composite layer is 100 parts by mass, the battery reaction is not inhibited and detachment of the negative electrode active material particles and the solid electrolyte particles from the negative electrode composite layer can be effectively suppressed.

[0102] The content of all functional particles in the slurry composition for an all-solid-state secondary battery is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more, and is preferably 99.5 parts by mass or less, and more preferably 99 parts by mass or less, when the total solid content in the slurry composition for an all-solid-state secondary battery is 100 parts by mass.

[0103] The content of the solid electrolyte particles in the slurry composition for a solid electrolyte layer is preferably 80 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 97 parts by mass or more, and is preferably 99.5 parts by mass or less, and more preferably 99 parts by mass or less, when the total solid content in the slurry composition for a solid electrolyte layer is 100 parts by mass.

[0104] The content of the positive electrode active material particles and the solid electrolyte particles in the positive electrode composite layer slurry composition is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more, and is preferably 99.5 parts by mass or less, and more preferably 98 parts by mass or less, when the total solid content in the positive electrode composite layer slurry composition is 100 parts by mass.

[0105] The mass ratio of the positive electrode active material particles to the solid electrolyte particles is preferably 90:10 to 50:50 (positive electrode active material particles:solid electrolyte particles), more preferably 60:40 to 80:20 (positive electrode active material particles:solid electrolyte particles). When the mass ratio of the positive electrode active material particles is within the above range, it is possible to prevent a phenomenon in which the mass of the positive electrode active material particles in a battery is reduced due to a too small mass ratio of the positive electrode active material particles, resulting in a decrease in the capacity of the battery. It is also possible to prevent a phenomenon in which the mass ratio of the solid electrolyte particles is too small, resulting in insufficient conductivity and ineffective utilization of the positive electrode active material particles, resulting in a decrease in the capacity of the battery.

[0106] The content of the negative electrode active material particles and the solid electrolyte particles in the negative electrode composite layer slurry composition is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more, and is preferably 99.5 parts by mass or less, and more preferably 98 parts by mass or less, when the total solid content in the negative electrode composite layer slurry composition is 100 parts by mass.

[0107] The mass ratio of the negative electrode active material particles to the solid electrolyte particles is preferably 90:10 to 50:50 (negative electrode active material particles:solid electrolyte particles), more preferably 60:40 to 80:20 (negative electrode active material particles:solid electrolyte particles). When the mass ratio of the negative electrode active material particles is within the above range, it is possible to prevent a phenomenon in which the mass ratio of the negative electrode active material particles is too low, resulting in a reduction in the mass of the negative electrode active material particles in the battery and a decrease in the capacity of the battery. It is also possible to prevent a phenomenon in which the mass ratio of the solid electrolyte particles is too low, resulting in insufficient conductivity and an inability to effectively utilize the negative electrode active material particles, resulting in a decrease in the capacity of the battery.

[0108] The content of the conductive material in the slurry composition for an all-solid-state secondary battery is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 1.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2.5 parts by mass or less, when the total solid content in the slurry composition for an all-solid-state secondary battery is 100 parts by mass.

[0109] <Method for preparing slurry composition for all-solid-state secondary battery> The above-mentioned slurry composition can be prepared by dissolving or dispersing each of the above-mentioned components in a solvent containing an ester solvent having 6 or more carbon atoms. For example, it is preferable to prepare a slurry composition by adding functional particles, and optionally a solvent containing an additional ester solvent having 6 or more carbon atoms, a conductive material, other additives, etc. to the above-mentioned binder composition and mixing them by the known method described above.

[0110] (Functional Layer for All-Solid-State Secondary Battery) The functional layer for an all-solid-state secondary battery of the present invention is a layer formed using the slurry composition for a secondary battery of the present invention. That is, the functional layer for an all-solid-state secondary battery contains at least a copolymer and functional particles. Note that the components contained in the functional layer are those (solid contents) contained in the above-mentioned slurry composition, and the preferred abundance ratio of each of these components is the same as the preferred abundance ratio of each component (each solid content) in the slurry composition. The slurry composition of the present invention can impart excellent adhesion to the functional layer while reducing the internal resistance of the all-solid-state secondary battery, and therefore the functional layer formed using this slurry composition can exhibit excellent adhesion while reducing the internal resistance of the all-solid-state secondary battery.

[0111] When the functional layer is a solid electrolyte layer, the solid electrolyte layer contains a copolymer and solid electrolyte particles, but typically does not contain electrode active material particles, and preferably does not contain a conductive material. When the functional layer is a positive electrode mixture layer, the positive electrode mixture layer contains a copolymer and positive electrode active material particles, and optionally further contains solid electrolyte particles and a conductive material. When the functional layer is a negative electrode mixture layer, the negative electrode mixture layer contains a copolymer and negative electrode active material particles, and optionally further contains solid electrolyte particles and a conductive material.

[0112] The thickness of the functional layer is not particularly limited, but is preferably 20 μm or more, more preferably 40 μm or more, and even more preferably 70 μm or more, and is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0113] When the functional layer is a solid electrolyte layer, the thickness of the solid electrolyte layer is not particularly limited, but is preferably 20 μm or more, more preferably 40 μm or more, even more preferably 70 μm or more, and is preferably 200 μm or less.

[0114] When the functional layer is a positive electrode composite layer, the thickness of the positive electrode composite layer is not particularly limited, but is preferably 20 μm or more, more preferably 40 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less.

[0115] When the functional layer is a negative electrode composite layer, the thickness of the negative electrode composite layer is not particularly limited, but is preferably 20 μm or more, more preferably 40 μm or more, and even more preferably 70 μm or more, and is preferably 200 μm or less, and more preferably 150 μm or less.

[0116] <Method for Forming Functional Layer for All-Solid State Secondary Battery> The functional layer can be formed on, for example, a substrate using the slurry composition of the present invention. Examples of the substrate include a current collector and an electrode.

[0117] Here, the method for forming a functional layer on a substrate using a slurry composition is not particularly limited, and examples thereof include: (A) a method in which the slurry composition is applied to the surface of a substrate and then dried; (B) a method in which the slurry composition is applied to a release substrate and dried to form a functional layer, and the resulting functional layer is transferred onto a substrate. Here, the release substrate is not particularly limited, and a known release substrate such as an imide film can be used.

[0118] The method for applying the slurry composition to the substrate or release substrate is not particularly limited, and examples thereof include the doctor blade method, reverse roll method, direct roll method, gravure method, extrusion method, and brush coating method.

[0119] The method for drying the slurry composition on the substrate or the release substrate is not particularly limited and any known method can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 50 to 150°C, and the drying time is preferably 1 to 90 minutes.

[0120] (All-solid-state secondary battery) The all-solid-state secondary battery of the present invention comprises the functional layer for an all-solid-state secondary battery of the present invention. Specifically, the all-solid-state secondary battery of the present invention comprises a positive electrode having a positive electrode composite layer on a current collector, a negative electrode having a negative electrode composite layer on a current collector, and a solid electrolyte layer located between the positive electrode composite layer and the negative electrode composite layer, and at least one layer of the positive electrode composite layer, the negative electrode composite layer, and the solid electrolyte layer, preferably all layers, is the functional layer of the present invention. With the above all-solid-state secondary battery, it is possible to obtain an all-solid-state secondary battery in which the internal resistance is reduced and the battery materials are firmly bonded to each other.

[0121] <Solid electrolyte layer> The composition of the solid electrolyte layer has been explained in the section "Functional layer for all-solid-state secondary battery", and therefore will not be explained here. When the slurry composition of the present invention is used to form the positive electrode mixture layer and / or the negative electrode mixture layer, a known solid electrolyte layer may be used as the solid electrolyte layer.

[0122] <Positive electrode mixture layer> The composition of the positive electrode mixture layer has been explained in the section "Functional layer for all-solid-state secondary battery", and therefore will not be explained here. When the slurry composition of the present invention is used to form the solid electrolyte layer and / or the negative electrode mixture layer, a known positive electrode mixture layer may be used as the positive electrode mixture layer.

[0123] <Negative electrode mixture layer> The composition of the negative electrode mixture layer has been explained in the section "Functional layer for all-solid-state secondary battery", and therefore will not be explained here. When the slurry composition of the present invention is used to form the solid electrolyte layer and / or the positive electrode mixture layer, a known negative electrode mixture layer may be used as the negative electrode mixture layer.

[0124] <Current Collector> The current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material. However, from the viewpoint of heat resistance, metal materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum are preferred. Among these, aluminum is particularly preferred for the positive electrode, and copper is particularly preferred for the negative electrode. The shape of the current collector is not particularly limited, but a sheet-like current collector having a thickness of approximately 0.001 to 0.5 mm is preferred. The current collector is preferably roughened before use to increase the adhesive strength with the positive and negative electrode composite layers described above. Examples of surface roughening methods include mechanical polishing, electrolytic polishing, and chemical polishing. In mechanical polishing, abrasive cloths with abrasive particles attached, grinding stones, emery buffs, wire brushes equipped with steel wires, etc., are used.

[0125] <Thickness of each layer> The thickness of the functional layer in the all-solid-state secondary battery is not particularly limited, but is preferably 16 μm or more, more preferably 32 μm or more, and even more preferably 56 μm or more, and is preferably 160 μm or less, more preferably 120 μm or less, and even more preferably 80 μm or less.

[0126] The thickness of the solid electrolyte layer in the all-solid-state secondary battery is not particularly limited, but is preferably 16 μm or more, more preferably 32 μm or more, even more preferably 56 μm or more, and is preferably 160 μm or less.

[0127] The thickness of the positive electrode composite layer in the all-solid-state secondary battery is not particularly limited, but is preferably 16 μm or more, more preferably 32 μm or more, and is preferably 160 μm or less, more preferably 80 μm or less.

[0128] The thickness of the negative electrode composite layer in the all-solid-state secondary battery is not particularly limited, but is preferably 16 μm or more, more preferably 32 μm or more, and even more preferably 56 μm or more, and is preferably 160 μm or less, and more preferably 120 μm or less.

[0129] <Method for Manufacturing All-Solid-State Secondary Battery> All-solid-state batteries can be manufactured by fabricating a positive electrode, a negative electrode, and a solid electrolyte layer in any desired method and order, without any particular limitations. Specifically, all-solid-state batteries can be manufactured, for example, by any of the following methods (a) to (d): (a) a method of fabricating a laminate consisting of a positive electrode composite layer, a solid electrolyte layer, and a negative electrode composite layer in this order, and then bonding current collectors to both sides of this laminate; (b) a method of bonding individually fabricated positive electrodes, negative electrodes, and solid electrolyte layers; (c) a method of forming a solid electrolyte layer on one electrode to fabricate an electrode with a solid electrolyte layer, and then bonding the other electrode; or (d) a method of fabricating a laminate consisting of a positive electrode composite layer, a solid electrolyte layer, and a negative electrode composite layer in this order on one current collector, and then bonding the other current collector. Note that in methods (a) to (d), press processing may be performed in the fabrication of the laminate, the fabrication of the electrode with a solid electrolyte layer, and the bonding of each layer to the current collector. The pressure during the press treatment is preferably 100 MPa or more, more preferably 200 MPa or more, and even more preferably 300 MPa or more, and is preferably 700 MPa or less, more preferably 600 MPa or less, and even more preferably 500 MPa or less.

[0130] The all-solid-state secondary battery element obtained as described above is then placed in a battery container either as is or after being rolled or folded depending on the shape of the battery, and the container is sealed to obtain an all-solid-state secondary battery. If necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, etc. may be placed in the battery container to prevent pressure buildup within the battery and overcharging and discharging. The shape of the battery may be any of a coin type, button type, sheet type, cylindrical type, prismatic type, flat type, etc.

[0131] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, the terms "%" and "parts" used to represent amounts are based on mass unless otherwise specified. In a copolymer produced by copolymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the copolymer usually corresponds to the ratio (feed ratio) of the certain monomer to all monomers used in the polymerization of the copolymer, unless otherwise specified. In a copolymer produced by hydrogenating a copolymer containing conjugated diene monomer units, the total content of unhydrogenated conjugated diene monomer units and alkylene structural units as hydrogenated conjugated diene monomer units in the hydrogenated copolymer corresponds to the ratio (feed ratio) of the conjugated diene monomer to all monomers used in the polymerization of the copolymer. In the examples and comparative examples, various measurements and evaluations were carried out using the following methods.

[0132] <Composition of Copolymer> 100 g of the copolymer solution (binder composition) obtained in the examples and comparative examples was solidified with 1 L of methanol, and then vacuum dried at a temperature of 60° C. for 12 hours. 1 The copolymer was analyzed by H-NMR. Based on the analytical values ​​obtained, the content (mass%) of each monomer unit and structural unit contained in the copolymer was calculated.

[0133] <Weight-average molecular weight and molecular weight distribution of copolymer> The weight-average molecular weight (Mw) of the copolymer was measured by gel permeation chromatography (GPC) using a 10 mM LiBr-DMF solution under the following measurement conditions. The number-average molecular weight (Mn) of the copolymer was also measured by the same method, and the molecular weight distribution (Mw / Mn) was calculated. Separation column: Shodex KD-806M (manufactured by Showa Denko K.K.) Detector: Differential refractometer detector RID-10A (manufactured by Shimadzu Corporation) Eluent flow rate: 0.3 mL / min Column temperature: 40°C Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0134] <THF-insoluble content of copolymer> The copolymer solutions (binder compositions) obtained in the examples and comparative examples were dried in an environment of 50% humidity and 23°C to 25°C to prepare films with a thickness of 3±0.3 mm. Next, the prepared films were cut into 5 mm squares to prepare film pieces. Approximately 1 g of these film pieces was precisely weighed, and the weight of the precisely weighed film pieces was designated as W0. The precisely weighed film pieces were then immersed in 100 g of THF (temperature 25°C) of the binder composition for 24 hours. After immersion for 24 hours, the film pieces were removed from the THF and vacuum-dried at 105°C for 3 hours, and their weight (weight of the insoluble content) W1 was precisely weighed. The THF-insoluble content (%) was then calculated according to the following formula: THF-insoluble content (%) = W1 / W0 × 100

[0135] <Iodine Value of Copolymer> 100 g of the copolymer solution (binder composition) obtained in each of the Examples and Comparative Examples was coagulated with 1 L of methanol and then vacuum dried for 12 hours at a temperature of 60° C. The iodine value of the obtained dried copolymer was measured in accordance with JIS K6235 (2006).

[0136] <Haze of Copolymer Solution (Binder Composition)> The solvent used in preparing the copolymer solution (solvent for the binder composition) was further added to the copolymer solution (binder composition) obtained in the Examples and Comparative Examples to adjust the copolymer concentration to 8% by mass. If the copolymer concentration in the copolymer solution is less than 8% by mass, the copolymer concentration is adjusted by, for example, evaporating the solvent. If the solvent used in preparing the copolymer is different from the solvent for the binder composition, solvent exchange or the like is performed. Using a haze meter (product name "NDH7000SP", manufactured by Nippon Denshoku Industries Co., Ltd., an apparatus conforming to JIS K 7136:2000) at 25°C, the solvent used in preparing the copolymer solution was placed in a glass cell for liquid measurement and standard calibration was performed. The 8% by mass copolymer solution obtained above was then placed in the glass cell, and the haze of this copolymer solution was measured.

[0137] <Adhesion of Positive Electrode Composite Layer> The positive electrodes obtained in the examples and comparative examples were cut into rectangles measuring 1.0 cm wide x 10 cm long to prepare test specimens. Cellophane tape (as specified in JIS Z1522) was attached to the surface of the positive electrode composite layer of each test specimen, and the stress was measured when the cellophane tape was peeled from one end of the specimen in a 180° direction at a rate of 50 mm / min. The measurement was performed three times, and the average value was calculated as the peel strength (N / m) and evaluated according to the following criteria. A higher peel strength indicates better adhesion of the positive electrode composite layer and stronger adhesion to the current collector. A+: Peel strength of 3 N / m or more A: Peel strength of 2 N / m or more but less than 3 N / m B: Peel strength of 1.5 N / m or more but less than 2 N / m C: Peel strength of 1.5 N / m or more but less than 1 N / m D: Peel strength of less than 1 N / m

[0138] <Adhesion of Negative Electrode Composite Layer> The negative electrodes obtained in the examples and comparative examples were cut into rectangles measuring 1.0 cm wide x 10 cm long to prepare test specimens. Cellophane tape (as specified in JIS Z1522) was attached to the surface of the negative electrode composite layer of each test specimen, and the stress was measured when the cellophane tape was peeled from one end of the specimen in a 180° direction at a rate of 50 mm / min. The measurement was performed three times, and the average value was calculated as the peel strength (N / m) and evaluated according to the following criteria. A higher peel strength indicates better adhesion of the negative electrode composite layer and stronger adhesion to the current collector. A+: Peel strength of 5 N / m or more A: Peel strength of 4 N / m or more but less than 5 N / m B: Peel strength of 3 N / m or more but less than 4 N / m C: Peel strength of 2 N / m or more but less than 3 N / m D: Peel strength of less than 2 N / m

[0139] <IV Resistance of All-Solid-State Secondary Battery> The all-solid-state secondary batteries obtained in the examples and comparative examples were charged to 50% SOC (State Of Charge: depth of charge) at 1 C (C is a value expressed as rated capacity (mA) / 1 h (hours)) in an atmosphere of 25°C. Next, the batteries were charged for 30 seconds and discharged for 30 seconds at 0.1 C, 0.2 C, 0.5 C, 1 C, and 2 C, centered around 50% SOC. The battery voltage after 10 seconds on the discharge side was plotted against the current value, and the slope was calculated as the IV resistance (Ω) (IV resistance during discharge). The obtained IV resistance values ​​(Ω) were evaluated according to the following criteria. The smaller the IV resistance value, the lower the internal resistance of the all-solid-state secondary battery. A: IV resistance is 80Ω or less B: IV resistance is more than 80Ω and less than 90Ω C: IV resistance is more than 90Ω and less than 100Ω D: IV resistance is more than 100Ω

[0140] <Cycle characteristics of all-solid-state secondary battery> The all-solid-state secondary batteries obtained in the examples and comparative examples were charged from 3 V to 4.2 V at 0.2 C at 25°C, and then discharged from 4.2 V to 3 V at 0.2 C, and this charge-discharge cycle was repeated 50 times. The ratio of the 0.2 C discharge capacity at the 50th cycle to the 0.2 C discharge capacity at the first cycle was calculated as a percentage, which was taken as the capacity retention rate and evaluated according to the following criteria. A larger capacity retention rate indicates less discharge capacity loss and more excellent cycle characteristics of the all-solid-state secondary battery. A: Capacity retention rate is 90% or more B: Capacity retention rate is 80% or more but less than 90% C: Capacity retention rate is 70% or more but less than 80% D: Capacity retention rate is less than 70%

[0141] Example 1 Preparation of Copolymer Solution (Binder Composition) A reactor was charged with 200 parts of ion-exchanged water, 2.5 parts of sodium dodecyl diphenyl ether sulfonate as an emulsifier, a monomer composition containing 18 parts of acrylonitrile (a nitrile group-containing monomer), 42 parts of 1,3-butadiene (a conjugated diene monomer), 35 parts of n-butyl acrylate (a C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (a hydrophilic group-containing monomer), and 0.2 parts of t-dodecyl mercaptan as a molecular weight modifier. Subsequently, 0.06 parts of cumene hydroperoxide and 0.025 parts of ferrous sulfate were added as redox polymerization initiators containing an iron compound, and emulsion polymerization of the monomer composition was initiated at 10°C. When the polymerization conversion rate reached 80%, 0.2 parts of hydroxylamine sulfate was added per 100 parts of the monomer composition to terminate the polymerization. After termination of the polymerization, the resulting product was heated and subjected to steam distillation under reduced pressure at 80°C to remove unreacted monomers. Two parts of alkylated phenol were added as an antioxidant to the remaining liquid to obtain a copolymer latex (aqueous dispersion of particulate pre-hydrogenated copolymer). Then, 0.6 parts of a 10% aqueous solution of aluminum sulfate (coagulant) was added to 100 parts of the copolymer solids in the resulting aqueous dispersion with stirring to coagulate the copolymer in the aqueous dispersion. The resulting mixture was then filtered, and the resulting residue was washed with 50 times the amount of ion-exchanged water to obtain a pre-hydrogenated copolymer. Next, the oil phase hydrogenation method was used as the hydrogenation method, and the pre-hydrogenated copolymer was hydrogenated. Specifically, the pre-hydrogenated copolymer was first dissolved in acetone to a concentration of 10%, to obtain an acetone solution of the hydrogenation target (pre-hydrogenated copolymer). This solution was placed in an autoclave, and 500 ppm by mass of palladium-silica catalyst was added to this solution relative to 100% of the material to be hydrogenated. The contents (solution) of the autoclave were then heated to 50°C while pressurized with hydrogen gas to 3 MPa. This temperature was maintained for 6 hours to carry out a hydrogenation reaction of the pre-hydrogenated copolymer, thereby obtaining a hydrogenated product. After completion of the hydrogenation reaction, the palladium-silica catalyst was filtered off, and the target copolymer (acetone solution) was obtained. An appropriate amount of isobutyl isobutyrate was then added to the acetone solution of the obtained copolymer to obtain a mixture.Then, acetone and excess isobutyl isobutyrate were removed from the mixture by vacuum distillation at 80°C, and solvent exchange was performed from acetone to isobutyl isobutyrate to obtain a copolymer solution (binder composition) with a solids concentration of 10%. The copolymer solution (binder composition) was used to measure the copolymer composition, weight average molecular weight and molecular weight distribution, THF insoluble fraction, iodine value, and haze of the copolymer solution. The results are shown in Table 1.

[0142] <Preparation of Slurry Composition for Positive Electrode Mixture Layer> 72 parts of lithium cobalt oxide (number average particle diameter: 11.5 μm) as positive electrode active material particles and 10 parts of Li as inorganic solid electrolyte particles were mixed. ２ S and P ２ S ５ and sulfide glass (Li ２ S / P ２ S ５ 24.9 parts of acetylene black (70 mol% / 30 mol%, number average particle diameter: 0.9 μm), 2.5 parts of acetylene black as a conductive material, and 0.6 parts (solid content equivalent) of the binder composition obtained as described above were mixed, and isobutyl isobutyrate was further added as a solvent to adjust the solid content to 80%, followed by mixing for 60 minutes with a planetary mixer. Thereafter, isobutyl isobutyrate was further added to adjust the solid content to 60%, followed by mixing for 10 minutes to prepare a slurry composition for a positive electrode composite layer.

[0143] <Preparation of Slurry Composition for Negative Electrode Mixture Layer> A slurry composition for a negative electrode mixture layer was prepared by dissolving 65 parts of graphite (number average particle diameter: 20 μm) as negative electrode active material particles and 65 parts of Li as inorganic solid electrolyte particles. ２ S and P ２ S ５ and sulfide glass (Li ２ S / P ２ S ５32 parts of a cellulose acetate copolymer (polymer of 1,2-dimethylaminopropyl cellulose, 1.5 parts of acetylene black as a conductive material, 1.5 parts of the binder composition obtained above (corresponding to the solid content) were mixed, and isobutyl isobutyrate was further added as a solvent to adjust the solid content to 65%, followed by mixing for 60 minutes with a planetary mixer. Thereafter, isobutyl isobutyrate was further added to adjust the solid content to 60%, followed by mixing with a planetary mixer to prepare a slurry composition for a negative electrode composite layer.

[0144] <Preparation of Slurry Composition for Solid Electrolyte Layer> In a glove box under an argon gas atmosphere (water concentration: 0.6 ppm, oxygen concentration: 1.8 ppm), Li as inorganic solid electrolyte particles was mixed. ２ S and P ２ S ５ and sulfide glass (Li ２ S / P ２ S ５ 99.0 parts of a cellulose acetate copolymer (polymer of cellulose acetate and cellulose acetate copolymer, ...

[0145] <Preparation of Positive Electrode> The above-described slurry composition for the positive electrode composite layer was applied to the surface of a current collector (aluminum foil, thickness: 20 μm) and dried (temperature: 120° C., 60 minutes) to form a positive electrode composite layer with a thickness of 75 μm, thereby obtaining a positive electrode. The adhesiveness of the positive electrode composite layer was evaluated using the obtained positive electrode. The results are shown in Table 1.

[0146] <Preparation of Negative Electrode> The above-described negative electrode composite layer slurry composition was applied to the surface of a current collector (copper foil, thickness: 15 μm) and dried (temperature: 120° C., 60 minutes) to form a negative electrode composite layer with a thickness of 90 μm, thereby obtaining a negative electrode. The adhesiveness of the negative electrode composite layer was evaluated using the obtained negative electrode. The results are shown in Table 1.

[0147] <Production of All-Solid-State Secondary Battery> The solid electrolyte layer slurry composition was applied to an imide film (thickness: 25 μm) and dried (at 120° C. for 60 minutes) to form a solid electrolyte layer with a thickness of 150 μm. The solid electrolyte layer on the imide film and a positive electrode were bonded together so that the solid electrolyte layer and the positive electrode composite layer were in contact with each other, and a press treatment was performed under a pressure (press pressure) of 400 MPa. The solid electrolyte layer was transferred from the imide film to the positive electrode composite layer, thereby obtaining a positive electrode with a solid electrolyte layer. The positive electrode with a solid electrolyte layer and a negative electrode were bonded together so that the solid electrolyte layer of the positive electrode with a solid electrolyte layer was in contact with the negative electrode composite layer of the negative electrode, and a press treatment was performed under a pressure (press pressure) of 400 MPa was applied to the solid electrolyte layer of the positive electrode with a solid electrolyte layer, thereby obtaining an all-solid-state secondary battery (stacking order: aluminum foil / positive electrode composite layer / solid electrolyte layer / negative electrode composite layer / copper foil). The thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 120 μm. The IV resistance and cycle characteristics of this all-solid-state secondary battery were evaluated. The results are shown in Table 1.

[0148] Example 2 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 18 parts of acrylonitrile (nitrile group-containing monomer), 44 parts of 1,3-butadiene (conjugated diene monomer), 35 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 3 parts of 2-hydroxyethyl methacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0149] Example 3 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 15 parts of acrylonitrile (nitrile group-containing monomer), 40 parts of 1,3-butadiene (conjugated diene monomer), 30 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer), and 10 parts of styrene (aromatic vinyl monomer) was used as the monomer composition. The results are shown in Table 1.

[0150] (Example 4) Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that butyl butyrate was used instead of isobutyl isobutyrate in the preparation of the copolymer solution (binder composition), the preparation of the slurry composition for the positive electrode composite layer, the preparation of the slurry composition for the negative electrode composite layer, and the preparation of the slurry composition for the solid electrolyte layer. The results are shown in Table 1.

[0151] Example 5 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 13 parts of acrylonitrile (nitrile group-containing monomer), 47 parts of 1,3-butadiene (conjugated diene monomer), 35 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0152] Example 6 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 21 parts of acrylonitrile (nitrile group-containing monomer), 39 parts of 1,3-butadiene (conjugated diene monomer), 35 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0153] (Example 7) In preparing the copolymer solution (binder composition), the polymerization temperature of the emulsion polymerization was changed from 10° C. to 8° C., and the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0154] (Example 8) In preparing the copolymer solution (binder composition), the polymerization temperature of the emulsion polymerization was changed from 10° C. to 15° C., and the same operations, measurements, and evaluations were carried out as in Example 1. The results are shown in Table 1.

[0155] (Example 9) Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that octyl acetate was used instead of isobutyl isobutyrate in the preparation of the copolymer solution (binder composition), the preparation of the slurry composition for the positive electrode composite layer, the preparation of the slurry composition for the negative electrode composite layer, and the preparation of the slurry composition for the solid electrolyte layer. The results are shown in Table 1.

[0156] Example 10 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 18 parts of acrylonitrile (nitrile group-containing monomer), 32 parts of 1,3-butadiene (conjugated diene monomer), 45 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0157] Example 11 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 18 parts of acrylonitrile (nitrile group-containing monomer), 52 parts of 1,3-butadiene (conjugated diene monomer), 25 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0158] (Example 12) In preparing the copolymer solution (binder composition), the amount of the palladium-silica catalyst used was changed from 500 ppm by mass to 200 ppm by mass, except that various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0159] (Example 13) In preparing the copolymer solution (binder composition), the amount of the palladium-silica catalyst used was changed from 500 ppm by mass to 2000 ppm by mass, except that various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0160] (Example 14) Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 17 parts of acrylonitrile (a nitrile group-containing monomer), 48 parts of 1,3-butadiene (a conjugated diene monomer), and 35 parts of n-butyl acrylate (a C4-C9 (meth)acrylic acid ester monomer) was used as the monomer composition. The results are shown in Table 1.

[0161] Example 15 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 15 parts of acrylonitrile (nitrile group-containing monomer), 49 parts of 1,3-butadiene (conjugated diene monomer), 30 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), 4 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer), and 2 parts of methacrylic acid (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0162] Comparative Example 1 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 8 parts of acrylonitrile (nitrile group-containing monomer), 52 parts of 1,3-butadiene (conjugated diene monomer), 35 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0163] Comparative Example 2 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing a copolymer solution (binder composition), a composition containing 28 parts of acrylonitrile (nitrile group-containing monomer), 32 parts of 1,3-butadiene (conjugated diene monomer), 35 parts of n-butyl acrylate (C4-C9 (meth)acrylic acid ester monomer), and 5 parts of 1,4-cyclohexanedimethanol monoacrylate (hydrophilic group-containing monomer) was used as the monomer composition. The results are shown in Table 1.

[0164] (Comparative Example 3) In the preparation of the copolymer solution (binder composition), various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the polymerization temperature for emulsion polymerization was changed from 10° C. to 6° C. The results are shown in Table 1.

[0165] Comparative Example 4 Various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in preparing the copolymer solution (binder composition), the polymerization temperature for emulsion polymerization was changed from 10° C. to 20° C. The results are shown in Table 1.

[0166] Comparative Example 5 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that xylene was used instead of isobutyl isobutyrate in the preparation of the copolymer solution (binder composition), the preparation of the slurry composition for the positive electrode composite layer, the preparation of the slurry composition for the negative electrode composite layer, and the preparation of the slurry composition for the solid electrolyte layer. The results are shown in Table 1.

[0167] Comparative Example 6 Various operations, measurements, and evaluations were performed in the same manner as in Example 1, except that cyclopentyl methyl ether was used instead of isobutyl isobutyrate in the preparation of the copolymer solution (binder composition), the preparation of the slurry composition for the positive electrode composite layer, the preparation of the slurry composition for the negative electrode composite layer, and the preparation of the slurry composition for the solid electrolyte layer. The results are shown in Table 1.

[0168] In Table 1, "C4-C9 (meth)acrylic acid ester monomer unit" refers to a (meth)acrylic acid ester monomer unit having an alkyl group having 4 to 9 carbon atoms, "AN" refers to an acrylonitrile unit, "BD" refers to a 1,3-butadiene unit, "H-BD" refers to a 1,3-butadiene hydride unit, "BA" refers to an n-butyl acrylate unit, "CHDMMA" refers to a 1,4-cyclohexanedimethanol monoacrylate unit, "HEMA" refers to a 2-hydroxyethyl methacrylate unit, "MAA" refers to a methacrylic acid unit, "St" refers to a styrene unit, and "CPME" refers to cyclopentyl methyl ether.

[0169]

[0170] As is clear from Table 1, in Examples 1 to 15, the internal resistance of the all-solid-state secondary battery was reduced, and the functional layer for the all-solid-state secondary battery had excellent adhesiveness.

[0171] According to the present invention, it is possible to provide a binder composition for an all-solid-state secondary battery that can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. Furthermore, according to the present invention, it is possible to provide a slurry composition for an all-solid-state secondary battery that can impart excellent adhesion to a functional layer for an all-solid-state secondary battery while reducing the internal resistance of the all-solid-state secondary battery. Furthermore, according to the present invention, it is possible to provide a functional layer for an all-solid-state secondary battery that can exhibit excellent adhesion while reducing the internal resistance of the all-solid-state secondary battery. Furthermore, according to the present invention, it is possible to provide an all-solid-state secondary battery in which battery materials are firmly bonded together while the internal resistance is reduced.

Claims

1. A binder composition for all-solid-state secondary batteries comprising a copolymer containing nitrile group-containing monomer units and a solvent, The solvent contains an ester solvent having 6 or more carbon atoms. The content ratio of the nitrile group-containing monomer units in the copolymer is 10% by mass or more and 22% by mass or less, when the total repeating units in the copolymer are considered to be 100% by mass. The tetrahydrofuran insoluble fraction of the copolymer is 0.5% by mass or more and 3% by mass or less. A binder composition for all-solid-state secondary batteries, wherein when the copolymer is dissolved in the solvent at a concentration of 8% by mass of the copolymer, the resulting copolymer solution has a haze of 30% or more and 80% or less.

2. The binder composition for all-solid-state secondary batteries according to claim 1, wherein the iodine value of the copolymer is 0.5 mg / 100 mg or more and 30 mg / 100 mg or less.

3. The copolymer further contains alkylene structural units, The alkylene structural unit is a 1,3-butadiene hydride unit. The binder composition for all-solid-state secondary batteries according to claim 1, wherein the nitrile group-containing monomer unit is an acrylonitrile unit.

4. The binder composition for all-solid-state secondary batteries according to claim 1, wherein the copolymer contains (meth)acrylic acid ester monomer units having an alkyl group with 4 to 9 carbon atoms.

5. The binder composition for all-solid-state secondary batteries according to claim 4, wherein the content of the (meth)acrylic acid ester monomer units having an alkyl group having 4 to 9 carbon atoms in the copolymer is 25% by mass or more and 45% by mass or less, when the total repeating units in the copolymer are considered to be 100% by mass.

6. The binder composition for all-solid-state secondary batteries according to claim 1, wherein the copolymer has hydrophilic groups.

7. A slurry composition for an all-solid-state secondary battery, comprising functional particles and a binder composition for an all-solid-state secondary battery according to any one of claims 1 to 6.

8. The slurry composition for an all-solid-state secondary battery according to claim 7, wherein the functional particles are at least one of solid electrolyte particles and electrode active material particles.

9. A functional layer for an all-solid-state secondary battery, formed using the slurry composition for all-solid-state secondary batteries described in claim 7.

10. An all-solid-state secondary battery comprising the functional layer for all-solid-state secondary batteries described in claim 9.