Binder for power storage devices, binder solution for power storage devices, power storage device electrode slurry, power storage device electrode, and power storage device

Abstract

Provided is a binder for power storage devices, that provides an excellent peel strength when used in an electrode and that is favorable for obtaining a low-resistance electrode. Also provided are a binder solution for power storage devices, a power storage device electrode slurry, a power storage device electrode, and a power storage device. The binder for power storage devices contains a modified vinyl alcohol polymer that has a 0.05-10 mol% content of structural units deriving from (A) ethylenically unsaturated dicarboxylic acid derivatives and that has a degree of saponification of 70.0-99.9 mol%. The amount of insoluble component in the modified vinyl alcohol polymer, considered for the aqueous solution prepared with a 5 mass% concentration thereof and residing at 90°C, is from 0.1 ppm to less than 2,000 ppm.

Description

Binder for electricity storage device, binder solution for electricity storage device, electricity storage device electrode slurry, electricity storage device electrode, and electricity storage device

[0001] The present disclosure relates to a binder for an electricity storage device, a binder solution for an electricity storage device, an electricity storage device electrode slurry, an electricity storage device electrode, and an electricity storage device.

[0002] In recent years, the popularity of mobile terminals such as mobile phones, notebook computers, and pad-type information terminal devices has been remarkable. As mobile terminals are required to be more portable and are rapidly becoming smaller, thinner, lighter, and more powerful, batteries used in mobile terminals are also required to be smaller, thinner, lighter, and more powerful. Lithium-ion secondary batteries are widely used as power storage devices for such mobile terminals. Lithium-ion secondary batteries and other power storage devices have a positive electrode and a negative electrode sandwiched between a separator, and are typically made of LiPF ６ , LiBF ４ The battery has a structure in which a lithium salt such as LiTFSI (lithium (bistrifluoromethylsulfonylimide)) or LiFSI (lithium bis(fluorosulfonyl)imide) is housed in a container together with an electrolyte solution prepared by dissolving the lithium salt in an organic liquid such as ethylene carbonate.

[0003] The negative electrode and positive electrode that constitute the electricity storage device are usually formed by dissolving or dispersing a binder and a thickener in water or a solvent, mixing this with an active material, a conductive assistant (conductivity imparting agent), etc. to obtain an electrode slurry, applying the slurry to a current collector, and then drying the water or solvent to bind the resulting mixture into a mixed layer.

[0004] From the viewpoints of reducing environmental impact and simplifying manufacturing equipment, there has been a rapid shift to electrode slurries using aqueous media, particularly in the production of negative electrodes. Known binders for such aqueous media include vinyl alcohol-based polymers, acrylic polymers such as acrylic acid, and amide / imide polymer binders (e.g., Patent Documents 1 and 2).

[0005] On the other hand, in the production of positive electrodes, electrode slurries using solvents are generally used. Examples of such solvents include organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, N,N-dimethylacetamide, N,N-dimethylmethanesulfonamide, and hexamethylphosphoric triamide. Examples of binders that can be used for such organic solvents include vinylidene fluoride polymers, tetrafluoroethylene polymers, and fluororubbers (see, for example, Patent Documents 3 and 4).

[0006] JP 11-250915 A JP 2017-59527 A JP 2017-107827 A JP 2013-37955 A

[0007] To meet the demand for further miniaturization, thinning, and weight reduction of power storage devices, improvements in energy density are required for both negative and positive electrodes. This has led to an increasing demand for electrodes with reduced binder content and increased active material content, and there is a need for electrodes with high peel strength that can suppress powder falling off when the electrode is cut, even when the binder content is low.

[0008] Furthermore, due to the demand for shorter charging times, there is a demand for batteries that can suppress capacity loss during high-speed charging compared to low-speed charging. The capacity loss during high-speed charging is thought to be mainly due to energy loss associated with internal resistance, and therefore electrodes with low resistance are required.

[0009] In view of the above-mentioned problems, the present disclosure aims to provide a binder for an electricity storage device that is suitable for obtaining an electrode having excellent peel strength and low resistance when used in an electrode, and also aims to provide a binder solution for an electricity storage device, an electricity storage device electrode slurry, an electricity storage device electrode, and an electricity storage device.

[0010] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by using a binder for an electricity storage device containing a specified modified vinyl alcohol polymer.

[0011] That is, the present invention encompasses the following inventions: [1] A binder for an electrical storage device, comprising a modified vinyl alcohol-based polymer having a content of structural units derived from an ethylenically unsaturated dicarboxylic acid derivative (A) of 0.05 mol % or more and 10 mol % or less and a degree of saponification of 70.0 mol % or more and 99.9 mol % or less, wherein the amount of insoluble components when an aqueous solution of the modified vinyl alcohol-based polymer is prepared at 90°C in a concentration of 5% by mass is 0.1 ppm or more and less than 2000 ppm. [2] The binder for an electrical storage device according to [1], wherein the derivative (A) of the ethylenically unsaturated dicarboxylic acid is at least one selected from the group consisting of a monoester of an ethylenically unsaturated dicarboxylic acid, a diester of an ethylenically unsaturated dicarboxylic acid, and an anhydride of an ethylenically unsaturated dicarboxylic acid. [3] The binder for an electrical storage device according to [1] or [2] above, wherein the derivative (A) of the ethylenically unsaturated dicarboxylic acid comprises at least one selected from the group consisting of a monoalkyl maleate, a dialkyl maleate, maleic anhydride, a monoalkyl fumarate, and a dialkyl fumarate. [4] The binder for an electrical storage device according to any of [1] to [3] above, wherein at least a portion of the structural units derived from the derivative (A) of the ethylenically unsaturated dicarboxylic acid constitute a portion of a structural unit represented by the following formula (I), and the modified vinyl alcohol-based polymer satisfies the following formula (Q): (In formula (I), R １ is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms. ２ is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms. (In formula (Q), X is the content (mol %) of the structural unit derived from the derivative (A) of the ethylenically unsaturated dicarboxylic acid. Y is the content (mol %) of the structural unit represented by formula (I).) [5] The binder for an electricity storage device according to any of [1] to [4], wherein the modified vinyl alcohol-based polymer is in a powder form, and the amount passing through a sieve having an opening of 1.00 mm is 95% by mass or more of the entire modified vinyl alcohol-based polymer. [6] The binder for an electricity storage device according to any of [1] to [5], wherein the modified vinyl alcohol-based polymer is in a powder form, and the amount passing through a sieve having an opening of 500 μm is 30% by mass or more of the entire modified vinyl alcohol-based polymer. [7] The binder for an electricity storage device according to any of [1] to [6], wherein the modified vinyl alcohol-based polymer is a modified vinyl alcohol-based polymer having a crosslinked structure. [8] The binder for an electricity storage device according to any one of [1] to [7] above, further comprising a water-soluble Li salt, wherein the mass ratio of the modified vinyl alcohol-based polymer to the water-soluble Li salt is 70:30 to 95:5. [9] The binder for an electricity storage device according to [8] above, wherein the solubility of the water-soluble Li salt in water at 20°C is 10 g / 100 mL or more.

[10] The binder for an electricity storage device according to [8] or [9] above, wherein the molecular weight of the water-soluble Li salt is 1,000 or less.

[11] The binder for an electricity storage device according to any one of [8] to

[10] above, wherein the water-soluble Li salt is at least one selected from the group consisting of lithium chloride, lithium acetate, lithium formate, lithium hydroxide, lithium sulfate, lithium carbonate, lithium maleate, lithium oxalate, lithium citrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[12] A binder solution for an electricity storage device, comprising the binder for an electricity storage device according to any one of [1] to

[11] above and a solvent.

[13] An electrode slurry for an electricity storage device, comprising the binder solution for an electricity storage device according to

[12] above and an active material.

[14] The electrode slurry for an electricity storage device according to

[13] above, in which the content of the binder for an electricity storage device is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the active material.

[15] An electricity storage device electrode, comprising a cured product of the electricity storage device electrode slurry according to

[13] above and a current collector.

[16] An electricity storage device comprising the electricity storage device electrode according to

[15] above.

[0012] The binder for an electricity storage device, the binder solution for an electricity storage device, the electricity storage device electrode slurry, the electricity storage device electrode, and the electricity storage device according to the present disclosure have excellent peel strength and excellent resistance characteristics.

[0013] Hereinafter, embodiments of the present invention will be described in detail. However, it is not intended that the present invention be limited to the following embodiments. In this specification, upper and lower limit values ​​of numerical ranges (contents of each component, values ​​calculated from each component, and each physical property, etc.) can be combined as appropriate. Furthermore, numerical ranges expressed with "to" include the upper and lower limit values. In other words, "A to B" means "A or more and B or less."

[0014] <Binder for Electricity Storage Device> The binder for an electricity storage device (hereinafter also simply referred to as "binder") of the present disclosure is a binder for an electricity storage device comprising a modified vinyl alcohol-based polymer having a content of structural units derived from an ethylenically unsaturated dicarboxylic acid derivative (A) of 0.05 mol % or more and 10 mol % or less and a degree of saponification of 70.0 mol % or more and 99.9 mol % or less, the modified vinyl alcohol-based polymer having an amount of insoluble components of 0.1 ppm or more and less than 2000 ppm when an aqueous solution of the modified vinyl alcohol-based polymer having a concentration of 5% by mass at 90° C. Furthermore, a preferred embodiment of the binder for an electricity storage device of the present disclosure is a binder for an electrode of an electricity storage device.

[0015] A vinyl alcohol polymer (also referred to herein as "polyvinyl alcohol" or "PVA") is a polymer having vinyl alcohol units as monomer units. PVA is obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer, which is a raw material monomer for PVA. The saponified PVA may contain vinyl ester units in addition to vinyl alcohol units.

[0016] Furthermore, PVA can be produced by saponifying a copolymer obtained by copolymerizing a vinyl ester monomer, which is a raw material monomer, with other monomers to produce a PVA containing monomer units other than vinyl alcohol units and vinyl ester units. In the present disclosure, such a PVA is referred to as a "modified vinyl alcohol polymer (modified PVA)," and monomers other than vinyl ester monomers among the raw material monomers of the modified PVA may be referred to as "modified species." Furthermore, a polymer of (modified) PVA before saponification may be referred to as a (modified) vinyl ester polymer. The term "modified vinyl ester polymer" refers to a vinyl ester polymer containing monomer units other than vinyl ester units.

[0017] The modified PVA of the present disclosure has good affinity for active materials used in electricity storage devices, such as carbon materials, metals, and metal oxides, and therefore, when used as a binder, an electrode with high peel strength and low resistance can be obtained.

[0018] The saponification degree of the modified PVA of the present disclosure is 70.0 mol% or more and 99.9 mol% or less. The saponification degree is preferably 82.0 mol% or more and 99.0 mol% or less, and more preferably 85.0 mol% or more and 95.0 mol% or less. If the saponification degree is less than 70.0 mol%, the resulting electrode may have insufficient practical physical properties such as peel strength and resistance characteristics, and it may be difficult to reduce the amount of insoluble components to less than 2000 ppm when an aqueous solution of 5% by mass at 90°C is prepared. The saponification degree of the modified PVA can be measured according to the method described in JIS K 6726 (1994).

[0019] The viscosity average degree of polymerization (hereinafter also simply referred to as "degree of polymerization") of the modified PVA of the present disclosure is not particularly limited, but is preferably 100 to 5000, more preferably 150 to 4500, and in some cases even more preferably 200 to 4000. The lower limit of the degree of polymerization may be 300 or 500. The degree of polymerization of the modified PVA can be measured according to the method described in JIS K 6726 (1994).

[0020] In the modified PVA of the present disclosure, when a 5% by mass aqueous solution is prepared at 90°C, the amount of insoluble components is 0.1 ppm or more and less than 2000 ppm. In other words, in a 5% by mass aqueous solution of the modified PVA of the present disclosure at 90°C, the amount of insoluble components (modified PVA) is 0.1 ppm or more and less than 2000 ppm. When a 5% by mass aqueous solution is prepared at 90°C, the amount of insoluble components is preferably 0.1 ppm or more and less than 1000 ppm, and more preferably 0.1 ppm or more and less than 500 ppm. If the amount of insoluble components is 2000 ppm or more when the specific aqueous solution is prepared, the peel strength of the resulting electrode may decrease or the resistance may increase when the PVA is used as a binder. In this specification, ppm means ppm by mass.

[0021] The amount of insoluble components when a 5% by mass aqueous solution is prepared at 90°C is determined by the following method. A 500 mL flask equipped with a stirrer and reflux condenser is placed in a water bath set to 20°C. 285 g of distilled water is added to the flask and stirring is initiated at 300 rpm. 15 g of modified PVA is weighed and gradually added to the flask. After the entire amount (15 g) of modified PVA is added, the temperature of the water bath is increased to 90°C over approximately 30 minutes to dissolve the modified PVA, yielding a modified PVA solution. After the water bath temperature reaches 90°C, dissolution is continued for an additional 60 minutes while stirring at 300 rpm. The modified PVA solution is then used to filter out remaining undissolved modified PVA particles (hereinafter also referred to as "undissolved particles") through a metal filter with a 63 μm mesh. The filter is then thoroughly washed with warm water at 90°C to remove the modified PVA solution adhering to the filter, leaving only undissolved particles on the filter, and then dried in a heated dryer at 120°C for 1 hour. The mass of the filter after drying is compared with the mass of the filter before use for filtration to calculate the mass of undissolved particles. The mass ppm of undissolved particles relative to the total amount of modified PVA used to prepare the modified PVA aqueous solution is defined as the amount of insoluble components when a 5% by mass aqueous solution is prepared at 90°C. In this specification, the amount of insoluble components when a 5% by mass aqueous solution is prepared at 90°C is sometimes referred to as the "water-insoluble content."

[0022] The modified PVA of the present disclosure has structural units derived from a derivative (A) of an ethylenically unsaturated dicarboxylic acid.

[0023] The content (X) of structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) in the modified PVA is 0.05 mol% or more and 10 mol% or less. The content (X) is preferably 0.1 mol% or more and 5.0 mol% or less, and sometimes more preferably 0.2 mol% or more and 2.0 mol% or less. If the content (X) of structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) is less than 0.05 mol%, the amount of carboxylic acid introduced into the modified PVA is low, which may result in a decrease in the peel strength of the resulting electrode when used as a binder. Furthermore, if the content (X) exceeds 10 mol%, problems with handling may occur, such as the modified PVA powder adhering to each other due to moisture in the air to form blocks, or the generation of water-insoluble components due to crosslinking during production may increase, making it difficult to control the amount of insoluble components to less than 2000 ppm. In this specification, the content (X) of structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) in the modified PVA may also be referred to as the "modification amount (X)." The modification amount (X) means the ratio of the number of moles of structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) to the total number of moles of monomer units constituting the main chain of the modified PVA. The modification amount (X) is the ratio of the number of moles of the modified vinyl ester polymer (C) before the modified PVA is saponified. １ It can be calculated by H-NMR analysis.

[0024] The ethylenically unsaturated dicarboxylic acid derivative (A) used in the present disclosure is not particularly limited as long as it does not impair the effects of the present disclosure. As the ethylenically unsaturated dicarboxylic acid derivative (A), a monoester of an ethylenically unsaturated dicarboxylic acid, a diester of an ethylenically unsaturated dicarboxylic acid, or an anhydride of an ethylenically unsaturated dicarboxylic acid is preferred as a monomer. Specific examples of the ethylenically unsaturated dicarboxylic acid derivative (A) include monoalkyl unsaturated dicarboxylic acid esters such as monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl citraconate, monoethyl citraconate, monomethyl mesaconic acid, monoethyl mesaconic acid, monomethyl itaconate, and monoethyl itaconate; dialkyl unsaturated dicarboxylic acid esters such as dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl citraconic acid, diethyl citraconic acid, dimethyl mesaconic acid, diethyl mesaconic acid, dimethyl itaconate, and diethyl itaconate; and unsaturated dicarboxylic acid anhydrides such as maleic anhydride and citraconic anhydride. From the viewpoint of industrial availability and reactivity with vinyl ester monomers, monoalkyl maleates, dialkyl maleates, maleic anhydride, monoalkyl fumarate esters, or dialkyl fumarate esters are preferred, and monomethyl maleate or maleic anhydride may be more preferred. The modified PVA of the present disclosure may have structural units derived from at least one of the ethylenically unsaturated dicarboxylic acid derivatives (A), and may have structural units derived from two or more of the ethylenically unsaturated dicarboxylic acid derivatives (A).

[0025] In the modified PVA of the present disclosure, it is preferable that at least a portion of the structural units derived from the derivative (A) of the ethylenically unsaturated dicarboxylic acid constitute a portion of the structural units represented by the following formula (I) and that the modified PVA satisfies the following formula (Q), in terms of further reducing the water-insoluble content. In formula (I), R １ is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms. ２ is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms. In formula (Q), X is the content (X) (mol %) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid derivative (A). Y is the content (Y) (mol %) of the structural unit represented by formula (I). That is, X is the modification amount (X) described above. The content (Y) of the structural unit represented by formula (I) may also be referred to as the "modification amount (Y)."

[0026] When Y / X satisfies the range represented by formula (Q), modified PVA with a reduced water-insoluble content can be more easily produced industrially. The lower limit of Y / X may more preferably be 0.06, 0.07, or 0.10. Meanwhile, the upper limit of Y / X may more preferably be 0.80, even more preferably 0.60, and particularly preferably 0.40. The content (Y) of the structural unit represented by formula (I) is the ratio of the number of moles of the structural unit of formula (I) to the total number of moles of the monomer units constituting the main chain of the modified PVA.

[0027] R １ and R ２Examples of the linear or branched alkyl group having 1 to 8 carbon atoms in the formula (I) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a 2-methylpropyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentyl group, a neopentyl group, a tert-pentyl group, a 1-ethylpropyl group, a 1,1-dimethylpropyl group, a 1,2-dimethylpropyl group, an n-hexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 5-methylpentyl group, a 6-methylpentyl group, a 7-methylpentyl group, a 8-methylpentyl group, a 9-methylpentyl group, a 10-methylpentyl group, a 11-methylpentyl group, a 12-methylpentyl group, a 13-methylpentyl group, a 14-methylpentyl group, a 15-methylpentyl group, a 16-methylpentyl group, a 17-methylpentyl group, a 18-methylpentyl group, a 19-methylpentyl group, a 20-methylpentyl group, a 21-methylpentyl group, a 22-methylpentyl group, a 23-methylpentyl group, a 24-methylpentyl group, a 25-methylpentyl group, a 26-methylpentyl group, a 27-methylpentyl group, a 28-methylpentyl group, a 29-methylpentyl group, a 30-methylpentyl group, a 31-methylpentyl group, a 32-methylpentyl group, a 33-methylpentyl group, a 34-methylpentyl group, a 35-methylpentyl group, a 36-methylpentyl group, a 37-methylpent Examples of the alkyl group include an n-butyl group (isohexyl group), 1-ethylbutyl group, 2-ethylbutyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 1,4-dimethylbutyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, 3,3-dimethylbutyl group, 1-ethyl-2-methylpropyl group, 1,1,2-trimethylpropyl group, n-heptyl group, 2-methylhexyl group, n-octyl group, isooctyl group, tert-octyl group, 2-ethylhexyl group, and 3-methylheptyl group. The number of carbon atoms in the alkyl group is preferably 1 to 6, more preferably 1 to 4, and in some cases 1 to 3 is even more preferable.

[0028] R ２ In the formula (I), examples of the metal atom include alkali metals such as lithium, sodium, potassium, rubidium, and cesium; and alkaline earth metals such as calcium, barium, strontium, and radium. Among these, alkali metals are preferred, and in some cases lithium or sodium is more preferred.

[0029] When a modified PVA is produced using the ethylenically unsaturated dicarboxylic acid derivative (A), a portion of the structural units derived from the introduced ethylenically unsaturated dicarboxylic acid derivative (A) may react with adjacent vinyl alcohol units after saponification to form a six-membered lactone ring structure represented by formula (I). The six-membered lactone structure represented by formula (I) may undergo ring-opening upon heating and subsequently form a crosslinked product through an intermolecular esterification reaction, which may increase the amount of water-insoluble content in the modified PVA. In other words, if the content (Y) of the structural unit represented by formula (I) is higher than the content (X) of the structural unit derived from the introduced ethylenically unsaturated dicarboxylic acid derivative (A), this means that the crosslinking reaction is suppressed. The six-membered lactone structure represented by formula (I) was measured in a deuterated dimethyl sulfoxide solvent. １ It is believed that the structural unit represented by formula (I) is detected at 6.8 to 7.2 ppm in the H-NMR spectrum. In the modified PVA of the present disclosure, from the viewpoint of making it easier to reduce the water-insoluble content to less than 2000 ppm, it is preferable that the content (Y) of the structural unit represented by formula (I) satisfies the above formula (Q) relative to the content (X) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid derivative (A) obtained from the modified vinyl ester polymer (C) before saponification. In formula (Q), when Y / X is 0.50, this means that half of all the structural units derived from the introduced ethylenically unsaturated dicarboxylic acid derivative (A) form the structural unit represented by formula (I).

[0030] The shape of the modified PVA of the present disclosure is not particularly limited, but a powdery modified PVA powder is preferred. The particle size of the particles constituting the powder is not particularly limited, but it is preferred that 95% by mass or more of the entire modified PVA powder pass through a sieve with a mesh size of 1.00 mm, and it may be more preferred that 95% by mass or more of the entire modified PVA powder pass through a sieve with a mesh size of 710 μm. Here, the phrase "95% by mass or more of the entire modified PVA powder" refers to an integrated particle size distribution in which, for example, 95% by mass or more of the particles pass through a sieve with a mesh size of 1.00 mm. Having 95% by mass or more of the particles pass through a sieve with a mesh size of 1.00 mm makes it possible to further suppress drying unevenness and to more easily control the amount of water-insoluble content. Furthermore, the particle size of the particles constituting the modified PVA powder of the present disclosure is preferably such that the amount passing through a sieve with a mesh size of 500 μm of the entire modified PVA powder is 30% by mass or more, more preferably 35% by mass or more, even more preferably 45% by mass or more, and particularly preferably 56% by mass or more. Furthermore, the particle size of the particles constituting the modified PVA powder is preferably such that 99% by mass or more of the modified PVA powder passes through a sieve with a mesh size of 1.00 mm, and more preferably 99% by mass or more of the modified PVA powder passes through a sieve with a mesh size of 1.00 mm and 56% by mass or more passes through a sieve with a mesh size of 500 μm. The mesh size of the sieve conforms to the nominal mesh size W of JIS Z 8801-1 (2006).

[0031] In the binder for an electricity storage device of the present disclosure, the modified PVA may preferably have a crosslinked structure. The crosslinked structure may be a structure in which structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) in the modified PVA are crosslinked intermolecularly. Furthermore, the crosslinked structure of the modified PVA may be formed in the binder solution for an electricity storage device, the electricity storage device electrode slurry, the electricity storage device electrode, and / or the electricity storage device, which will be described later.

[0032] [Method for producing modified PVA] The method for producing the modified PVA of the present disclosure will be described in detail below. Note that the method for producing the modified PVA of the present disclosure is not limited to the embodiment described below.

[0033] The modified PVA of the present disclosure is produced, for example, by a production method including a step of copolymerizing an ethylenically unsaturated dicarboxylic acid derivative (A) with a vinyl ester monomer (B) to obtain a modified vinyl ester polymer (C), a saponification step of saponifying the obtained modified vinyl ester polymer (C) in an alcohol solution using an alkali catalyst or an acid catalyst, a washing step, and a drying step.

[0034] Examples of the vinyl ester monomer (B) include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate, with vinyl acetate being preferred.

[0035] Methods for copolymerizing the ethylenically unsaturated dicarboxylic acid derivative (A) and the vinyl ester monomer (B) include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these methods, bulk polymerization carried out without a solvent or solution polymerization carried out using a solvent such as alcohol is usually used. In terms of enhancing the effects of the present disclosure, solution polymerization in which polymerization is carried out together with a lower alcohol such as methanol is preferred. When carrying out the polymerization reaction by bulk polymerization or solution polymerization, either a batch or continuous reaction system can be used.

[0036] The initiator used in the polymerization reaction is not particularly limited as long as it does not impair the effects of the present disclosure, and examples include known initiators such as azo initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and organic peroxide initiators such as benzoyl peroxide and n-propyl peroxycarbonate. The polymerization temperature when carrying out the polymerization reaction is not particularly limited, and may be in the range of 5 to 200°C or 30 to 150°C.

[0037] When copolymerizing the ethylenically unsaturated dicarboxylic acid derivative (A) and the vinyl ester-based monomer (B), another copolymerizable monomer (D) other than the ethylenically unsaturated dicarboxylic acid derivative (A) and the vinyl ester-based monomer (B) may be further copolymerized as necessary, as long as the effects of the present disclosure are not impaired. Examples of such monomer (D) include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylamide-based monomers such as acrylamide, N-methylacrylamide, and N-ethylacrylamide; methacrylamide-based monomers such as methacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide; vinyl ether-based monomers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; hydroxy group-containing vinyl ether-based monomers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol vinyl ether; allyl ether-based monomers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; Monomers having an oxyalkylene group; hydroxy group-containing α-olefins such as isopropenyl acetate, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, and 3-methyl-3-buten-1-ol; monomers having a silyl group such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamide-propyltrimethoxysilane, and 3-(meth)acrylamide-propyltriethoxysilane; and N-vinylamide monomers such as N-vinylformamide, N-vinylacetamide, N-vinyl-2-pyrrolidone, and N-vinyl-2-caprolactam. The amount of these monomers (D) used varies depending on the purpose of use, etc., but is usually 10 mol % or less, preferably 5.0 mol % or less, more preferably 3.0 mol % or less, and even more preferably 2.0 mol % or less, based on the total amount of all monomers used in the copolymerization.

[0038] The modified vinyl ester polymer (C) obtained in the copolymerization step is subjected to a step of saponifying in an alcohol solvent, a step of washing, and a step of drying to obtain a modified PVA. Although there are no particular limitations on the saponification conditions and drying conditions for obtaining the modified PVA of the present disclosure, it is preferable to set the water content of the saponification raw material solution, the temperature of the PVA resin during drying, or the drying time within a specific range in order to reduce the amount of water-insoluble matter present in the modified PVA.

[0039] A saponification raw solution can be prepared by further adding a small amount of water to the solution containing the modified vinyl ester polymer (C) and the solvent obtained in the copolymerization step. The amount of water added is preferably adjusted so that the water content of the resulting saponification raw solution (also referred to as the "system water content") is greater than 1.0% by mass and less than 5.0% by mass. In some cases, the water content is more preferably 1.5 to 4.0% by mass. By keeping the water content within this range, the alkali catalyst can be more effectively prevented from acting as a crosslinking catalyst, the content of water-insoluble components can be more easily controlled during drying, and the saponification reaction rate can be improved.

[0040] Examples of solvents that can be used in the saponification reaction include methanol, ethanol, and isopropyl alcohol. These may be used alone or in combination of two or more. Furthermore, a mixed solvent containing an ester such as methyl acetate may also be used, provided that it does not interfere with the saponification reaction step. Among these solvents, methanol or a mixed solvent of methanol and methyl acetate is preferably used.

[0041] An alkali catalyst is usually used as a catalyst for the saponification reaction of the modified vinyl ester polymer (C). Examples of alkali catalysts include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, and sodium hydroxide; and alkali metal alkoxides such as sodium methoxide, with sodium hydroxide being preferred. The amount of catalyst used, expressed as a molar ratio relative to the vinyl ester monomer units of the modified vinyl ester polymer (C), is preferably 0.005 to 0.50, more preferably 0.008 to 0.40, and in some cases even more preferably 0.01 to 0.30. The catalyst may be added all at once at the beginning of the saponification reaction, or a portion may be added at the beginning of the saponification reaction and the remainder added as additional material during the saponification reaction.

[0042] The temperature of the saponification reaction is preferably in the range of 5 to 80°C, and more preferably in the range of 20 to 70°C in some cases. The time of the saponification reaction is preferably 5 minutes to 10 hours, and more preferably 10 minutes to 5 hours in some cases. The saponification reaction may be carried out as either a batch method or a continuous method. When the saponification reaction is carried out using an alkaline catalyst, the remaining catalyst may be neutralized by adding an acid such as acetic acid or lactic acid to terminate the saponification reaction, as necessary. However, since the remaining acid after neutralization facilitates the intermolecular crosslinking reaction of the modified PVA during drying, it is preferable not to carry out neutralization by adding such an acid from the viewpoint of reducing and controlling the water-insoluble content to less than 2000 ppm.

[0043] The saponification reaction method is not particularly limited as long as it is a known method. Examples include: (1) a method in which a solution of the modified vinyl ester polymer (C) prepared to a concentration of more than 20% by mass is mixed with a catalyst, and the resulting semi-solid (gel-like substance) or solid is pulverized with a pulverizer to obtain a modified PVA powder; (2) a method in which the concentration of the modified vinyl ester polymer (C) dissolved in a solvent containing alcohol (preferably methanol) is controlled to less than 10% by mass, thereby preventing the entire reaction solution from becoming a gel-like substance with no fluidity, and the modified PVA is precipitated in the solvent to obtain fine particles dispersed in methanol; and (3) a method in which the modified vinyl ester polymer (C) is saponified in an emulsion or suspension phase by adding a saturated hydrocarbon solvent to obtain a modified PVA. In the above method (1), the pulverizer is not particularly limited, and known pulverizers and crushers can be used. From a manufacturing standpoint, the method (1) or method (2) that does not require a saturated hydrocarbon solvent is preferred. The method (2) is preferable from the viewpoint of industrial advantage, since it can reduce the amount of water-insoluble matter to a very small amount even when the subsequent washing step and drying step are carried out at lower temperatures than in the past.

[0044] In order to reduce the amount of water-insoluble matter in the resulting modified PVA, it is preferable to provide a step of washing the modified PVA as needed after the saponification step. As the washing liquid, a solution containing a lower alcohol such as methanol as the main component and further containing water and / or an ester such as methyl acetate can be used. As the washing liquid, a solution containing methanol as the main component and methyl acetate is preferred. Using methanol, which is preferably used in the copolymerization step of the modified vinyl ester polymer (C), and methyl acetate produced in the saponification step as washing liquids allows for in-process recycling, eliminates the need to prepare another solvent as a washing liquid, and is therefore economically and process-wise preferable. To reduce the amount of water-insoluble matter in the resulting modified PVA, the methyl acetate content is preferably 50% by volume or more, more preferably 60% by volume or more, and in some cases even more preferably 70% by volume or more.

[0045] After the saponification step or the washing step, the polymer can be dried to obtain a powdery modified PVA. Specifically, hot air drying using a cylindrical dryer is preferred, and the temperature of the modified PVA during drying is preferably greater than 80°C and less than 120°C, and in some cases, more preferably 90°C or higher and less than 110°C. The drying time is preferably 2 to 10 hours, and in some cases, more preferably 3 to 8 hours. By setting the drying conditions within the above range, the amount of water-insoluble content present in the resulting modified PVA can be more easily reduced to less than 2000 ppm.

[0046] In one embodiment of the present disclosure, the binder for an electrical storage device may contain two or more types of PVA. For example, the binder for an electrical storage device may contain the modified PVA and another PVA (E). In this case, the content of PVA (E) relative to the total amount of the modified PVA and PVA (E) may be 0% by mass or more and 70% by mass or less. The content of PVA (E) is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, even more preferably 20% by mass or less, and even more preferably 10% by mass or less. Alternatively, the content of PVA (E) may be 0% by mass. All PVAs in the binder for an electrical storage device may be a single modified PVA. The viscosity-average degree of polymerization of PVA (E) is not particularly limited and may be, for example, 100 to 5,000, preferably 200 to 3,000, and more preferably 400 to 2,000. The viscosity-average degree of polymerization of the PVA (E) is preferably equal to or less than the viscosity-average degree of polymerization of the modified PVA. The viscosity-average degree of polymerization of the PVA (E) can be measured according to the method described in JIS K 6726 (1994). The saponification degree of the PVA (E) may be 80.0 mol% or more and 99.9 mol% or less. The saponification degree of the PVA (E) can be measured according to the method described in JIS K 6726 (1994). The PVA (E) may be modified. The PVA (E) may be a modified PVA having a content (X) of structural units derived from the ethylenically unsaturated dicarboxylic acid derivative (A) of 0.05 mol % or more and 10 mol % or less, a degree of saponification of 70.0 mol % or more and 99.9 mol % or less, and a potential for an amount of insoluble components of 0.1 ppm or more and less than 2000 ppm when an aqueous solution of the PVA (E) is prepared at 90° C. and a concentration of 5% by mass, or a PVA that does not satisfy any or all of these characteristics. Furthermore, the amount of water-insoluble components in all PVAs, including the modified PVA, contained in the binder for an electrical storage device (the amount of water-insoluble components based on all PVAs) is preferably 0.1 ppm or more and less than 2000 ppm, more preferably 0.1 ppm or more and less than 1000 ppm, and even more preferably 0.1 ppm or more and less than 500 ppm.

[0047] The modified PVA of the present disclosure is preferably soluble in N-methyl-2-pyrrolidone to a solids concentration of 7.5% by mass or more under heating and stirring conditions at 90°C for 2 hours, because this increases affinity with carbon materials such as graphite and improves adhesiveness and coatability. In some cases, it is preferable that the PVA be soluble in N-methyl-2-pyrrolidone to a solids concentration of more preferably 8.0% by mass or more, and even more preferably 8.5% by mass or more.

[0048] The binder for an electrical storage device according to the present disclosure further contains a water-soluble Li salt (water-soluble lithium salt) in addition to the modified PVA, which facilitates improving the ionic conductivity of the electrode. In this specification, Li salt refers to a compound composed of lithium ions and anions, including LiOH. The mass ratio of the modified PVA to the water-soluble Li salt is preferably 70:30 to 95:5, more preferably 78:12 to 94:6, and even more preferably 80:20 to 92:8 in some cases. This range tends to further improve ionic conductivity, lower resistance, and enhance adhesion, making chipping less likely to occur when the electrode is cut. Furthermore, when the binder for an electrical storage device contains two or more types of PVA, the mass ratio of the water-soluble Li salt to the total amount of PVA, including the modified PVA, may be 70:30 to 98:2, preferably 80:20 to 95:5, and more preferably 85:15 to 94:6 in some cases.

[0049] The solubility of the water-soluble Li salt in water at 20° C. is preferably 10 g / 100 mL or more. When the solubility in water is within this range, the water-soluble Li salt is more uniformly present in the modified PVA in the binder for an electricity storage device, and the effect of reducing resistance is greater.

[0050] The molecular weight of the water-soluble Li salt may be preferably 1,000 or less, more preferably 700 or less, and even more preferably 500 or less. By keeping the molecular weight below the specified upper limit, the water-soluble Li salt is more uniformly present in the modified PVA, thereby enhancing the effect of reducing resistance. Furthermore, excessive viscosity increase is less likely to occur when the resulting slurry is prepared, making it easier to obtain a more uniform electrode.

[0051] Examples of water-soluble Li salts include lithium chloride, lithium acetate, lithium formate, lithium hydroxide, lithium sulfate, lithium carbonate, lithium maleate, lithium oxalate, lithium citrate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. Preferred water-soluble Li salts include lithium chloride, lithium acetate, lithium formate, lithium hydroxide, lithium sulfate, lithium maleate, lithium oxalate, lithium citrate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide. Preferred water-soluble Li salts include lithium acetate, lithium formate, lithium hydroxide, lithium sulfate, lithium carbonate, lithium maleate, lithium oxalate, lithium citrate, and lithium bis(fluorosulfonyl)imide. These water-soluble Li salts can be used alone or in combination of two or more.

[0052] The method of adding the water-soluble Li salt includes adding it as a powder, adding it in a state where it is mixed with other substances such as an active material, adding it as a solution of the water-soluble Li salt, adding it in a state where the water-soluble Li salt is coexistent with the binder solution, etc. These addition methods are not particularly limited, but from the viewpoint of dispersing the water-soluble Li salt in the polyvinyl alcohol-based resin, adding it in a state where the water-soluble Li salt is coexistent with the binder solution is preferred.

[0053] The binder of the present disclosure may further contain a material that adjusts the viscosity of the binder in an aqueous solution or N-methyl-2-pyrrolidone (NMP) solution, etc. Examples of viscosity-adjusting materials include polybasic acids such as citric acid, tartaric acid, and aspartic acid, salts thereof, and condensates thereof, as well as inorganic substances such as fumed silica and alumina. The amount of these added is not particularly limited, but is typically preferably 0.01 to 10 parts by mass, more preferably 0.02 to 8 parts by mass, and even more preferably 0.05 to 5 parts by mass, per 100 parts by mass of all PVA, including the modified PVA of the present disclosure. The more such viscosity-adjusting material is added, the more the viscosity of the binder in a solution state of the present disclosure can be increased, making it easier to adjust the viscosity within a predetermined range. The smaller the particle size of the inorganic substance added, the more easily the viscosity of the binder in an aqueous solution or NMP solution state, etc., can be increased.

[0054] The binder for an electricity storage device of the present disclosure or the binder solution for an electricity storage device described below may further contain additives to the extent that the effects of the present disclosure are not impaired. Examples of additives include light stabilizers, ultraviolet absorbers, freezing stabilizers, thickeners, leveling agents, rheology stabilizers, thixotropic agents, antifoaming agents, plasticizers, lubricants, preservatives, rust inhibitors, antistatic agents, antistatic agents, antiyellowing agents, pH adjusters, film-forming aids, curing catalysts, crosslinking reaction catalysts, crosslinking agents (glyoxal, urea resins, melamine resins, polyvalent metal salts, polyvalent isocyanates, polyamide epichlorohydrin, etc.), dispersants, etc. The additives can be selected or combined according to the respective purposes. The content of the additives may be, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, based on the total amount of the binder for an electricity storage device or the binder solution for an electricity storage device.

[0055] The binder for an electricity storage device according to the present disclosure may be obtained by dissolving the modified PVA and optional components other than the modified PVA in a solvent (e.g., water or NMP) to form a solution, and then removing the solvent. Alternatively, the resulting solution may be used as a binder solution for an electricity storage device, as described below, in the subsequent preparation of an electricity storage device electrode slurry. The binder according to the present disclosure is contained in a cured product of the electricity storage device electrode slurry in a mixed state with components such as the active material.

[0056] <Binder Solution for Electrical Storage Device> A binder solution for an electrical storage device (hereinafter also simply referred to as "binder solution") is obtained by dissolving the binder for an electrical storage device of the present disclosure in at least one solvent. The solvent is not particularly limited, but water or NMP is preferred. Water is preferred as the solvent from the viewpoint of reducing the environmental load and simplifying the equipment. On the other hand, NMP is preferred as the solvent because it is less likely to deteriorate the active material in the slurry, particularly when used as a slurry for a positive electrode.

[0057] In addition to the binder of the present disclosure, the binder solution may contain an additive (referred to as additive (F)) that can be dissolved in a solvent, as long as the effects of the present disclosure are not impaired. Examples of additive (F) include polyethylene glycol, polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, and polyethyleneimine. The content of additive (F) may be, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, based on the total amount of the binder solution. In some cases, it may be preferable not to include additive (F).

[0058] The binder solution is obtained by mixing the binder of the present disclosure, a solvent (water, NMP, etc.), and components other than the binder, such as the additives described above, which are optionally included as needed, by a known method, for example, stirring. The mixing temperature and mixing time can be adjusted appropriately depending on the type of solvent. In the binder solution, the mass of the binder dissolved in the solvent is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 99% by mass or more, and in some cases particularly preferably 100% by mass, relative to the total mass (100% by mass) of the binder used in the binder solution.

[0059] The binder content in the binder solution of the present disclosure is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less, based on the total amount of the binder solution. When the binder content is 1% by mass or more, the adhesion of the active material to the current collector when forming an electrode is more likely to be improved. When the binder content is 30% by mass or less, rapid aggregation of the active material when forming an electrode can be more effectively suppressed.

[0060] <Electricity Storage Device Electrode Slurry> The electricity storage device electrode slurry of the present disclosure contains the above-described binder solution for an electricity storage device of the present disclosure and an active material.

[0061] The electricity storage device electrode slurry of the present disclosure may be used for either a positive electrode or a negative electrode. It may also be used for both a positive electrode and a negative electrode. Therefore, the active material may be either a positive electrode active material or a negative electrode active material. When the binder solution of the present disclosure contains water (when the solvent is water), the electricity storage device electrode slurry preferably contains a negative electrode active material and is used as a negative electrode slurry. When the binder solution of the present disclosure contains NMP (when the solvent is NMP), the electricity storage device electrode slurry preferably contains a positive electrode active material and is used as a positive electrode slurry.

[0062] The negative electrode active material can be, for example, a material that has been conventionally used as a negative electrode active material for power storage devices. Examples of such materials include carbonaceous materials such as amorphous carbon, artificial graphite, natural graphite (graphite), mesocarbon microbeads (MCMB), pitch-based carbon fiber, carbon black, activated carbon, carbon fiber, hard carbon, soft carbon, mesoporous carbon, and conductive polymers such as polyacene; SiO ｘ , SnO ｘ and LiTiO ｘ other metal oxides, lithium metals such as lithium alloys, TiS ２ and LiTiS ２ and composite materials of metal oxides and carbonaceous materials. Among these, from the viewpoints of economy and battery capacity, graphite is preferred, and spherical natural graphite may be more preferred. These negative electrode active materials can be used alone or in combination of two or more.

[0063] The positive electrode active material can be, for example, a material that has been conventionally used as a positive electrode active material in power storage devices. ２ , TiS ３ , amorphous MoS ３ , Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３ , V ２ O ５ and V ６ O １３ transition metal oxides such as LiCoO ２ , LiNiO ２ , LiMnO ２ , LiMn ２ O ４ These positive electrode active materials may be used alone or in combination of two or more.

[0064] The electricity storage device electrode slurry may contain a conductive additive (conductivity imparting agent). The conductive additive is used to increase the output of the electricity storage device and can be appropriately selected depending on whether it is used for a positive electrode or a negative electrode. Examples of conductive additives include graphite, acetylene black, carbon black, ketjen black, and vapor-grown carbon fiber. Among these, acetylene black is preferred because it facilitates achieving a higher output of the resulting electricity storage device.

[0065] When the electrical storage device electrode slurry contains a conductive additive, the content of the conductive additive is preferably 0.1 parts by mass or more and 15 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less, and even more preferably 3 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the active material. When the content of the conductive additive is within this range, a decrease in the capacity of the electrical storage device to which the slurry is applied can be suppressed, and a more excellent conductive additive effect can be obtained.

[0066] The binder content in the electrical storage device electrode slurry is preferably 0.1 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the active material. A content of 0.1 parts by mass or more improves the adhesion of the active material to the current collector, which is advantageous from the viewpoint of maintaining the durability of the applied battery. Furthermore, a content of 20 parts by mass or less is more likely to improve the discharge capacity. From this viewpoint, the content range is more preferably 0.2 parts by mass or more and 18 parts by mass or less, even more preferably 0.5 parts by mass or more and 16 parts by mass or less, and even more preferably 1 part by mass or more and 12 parts by mass or less. From the viewpoint of increasing the energy density of the electrode, the upper limit of the content may be 10 parts by mass, 8 parts by mass, 6 parts by mass, 4 parts by mass, or 2 parts by mass.

[0067] In addition to the binder, active material, conductive aid, and solvent, the electricity storage device electrode slurry may contain additives such as a flame retardant aid, a thickener, an antifoaming agent, a leveling agent, and an adhesion promoter, as needed. Examples of thickeners include polysaccharides such as carboxymethyl cellulose (CMC) and salts thereof. When these additives are contained, the content of the additives is preferably 0.1% by mass or more and 10% by mass or less based on the total amount of the slurry.

[0068] The electricity storage device electrode slurry can be obtained by mixing a binder, an active material, and, if necessary, a conductive aid, a solvent, and an additive by a conventional method, for example, using a mixer such as a planetary stirrer, a ball mill, a blender mill, or a three-roll mill.

[0069] The electric storage device electrode of the present disclosure includes a current collector and a cured product of the electric storage device electrode slurry. The cured product of the electric storage device electrode slurry is a cured product obtained by removing the solvent in the electric storage device electrode slurry by drying or the like.

[0070] The power storage device electrode of the present disclosure may be either a positive electrode or a negative electrode. The electrode of the present disclosure has excellent adhesion of the active material to the current collector. Therefore, the peel strength of the electrode (peel strength of the cured product of the power storage device electrode slurry) before immersion in the electrolyte may be preferably 300 N / m or more, more preferably 350 N / m or more, even more preferably 400 N / m or more, and even more preferably 450 N / m or more. The upper limit of the electrode peel strength may be 1000 N / m. When the electrode peel strength is within the above range, the active material is less likely to peel from the current collector, thereby suppressing precipitation of lithium and the like and short-circuiting during charging and discharging of the electrode. Furthermore, when the peel strength is within the above range, the active material is less likely to peel from the current collector when the electrode is punched or cut, which is preferable.

[0071] The electricity storage device electrode of the present disclosure can be obtained by applying the electricity storage device electrode slurry of the present disclosure to a current collector and removing the solvent by drying, etc. Alternatively, the electrode may be subjected to a rolling treatment after drying.

[0072] The current collector is not particularly limited as long as it is made of a conductive material. Examples include metal materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. These current collectors can be used alone or in combination. Among current collectors, copper is preferred for the negative electrode current collector and aluminum is preferred for the positive electrode current collector from the viewpoints of adhesion of the active material and discharge capacity.

[0073] The method for applying the slurry to the current collector is not particularly limited, and examples thereof include an extrusion coater, a reverse roller, a doctor blade, an applicator, etc. The amount of the slurry to be applied is appropriately selected depending on the desired thickness of the cured body derived from the electricity storage device electrode slurry.

[0074] Examples of the rolling method for the electricity storage device electrode of the present disclosure include die pressing, roll pressing, etc. The pressing pressure is preferably 1 MPa or more and 40 MPa or less, from the viewpoint of easily increasing the capacity of the electricity storage device.

[0075] In the electricity storage device electrode of the present disclosure, the thickness of the current collector may be preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less. The thickness of the cured product of the electricity storage device electrode slurry may be preferably 10 μm or more and 400 μm or less, more preferably 20 μm or more and 300 μm. The thickness of the electricity storage device electrode of the present disclosure is preferably 20 μm or more and 200 μm.

[0076] <Electricity Storage Device> The electricity storage device of the present disclosure includes the electricity storage device electrode described above. The electricity storage device electrode in the electricity storage device may be either a negative electrode or a positive electrode, or may be both a negative electrode and a positive electrode.

[0077] The power storage device may be a battery, such as a lithium ion secondary battery, a sodium ion battery, a lithium sulfur battery, an all-solid-state battery, a lithium ion capacitor, a lithium battery, a nickel-metal hydride battery, or an alkaline dry battery.

[0078] The electricity storage device may contain an electrolyte solution. Here, the electrolyte solution is a solution in which an electrolyte is dissolved in a solvent. The electrolyte may be liquid or gel, as long as it is used in a typical electricity storage device, and may be appropriately selected from those that exhibit the function of a battery depending on the types of negative electrode active material and positive electrode active material. Specific examples of the electrolyte include known lithium salts, such as LiClO ４ , LiBF ６ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２ and lithium N and lower aliphatic carboxylates.

[0079] The solvent contained in the electrolytic solution is not particularly limited. Specific examples thereof include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and vinylene carbonate, lactones such as γ-butyl lactone, ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran, sulfoxides such as dimethyl sulfoxide, 1,3-dioxolane, and 4-methyl-1, Examples of suitable electrolytes include oxolanes such as 3-dioxolane, nitrogen-containing compounds such as acetonitrile and nitromethane, organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate, inorganic acid esters such as triethyl phosphate, dimethyl carbonate, and diethyl carbonate, diglymes, triglymes, sulfolanes, oxazolidinones such as 3-methyl-2-oxazolidinone, and sultones such as 1,3-propane sultone, 1,4-butane sultone, and naphthasultone. These may be used alone or in combination. When a gelled electrolyte solution is used, a gelling agent such as a nitrile polymer, an acrylic polymer, a fluorine-based polymer, or an alkylene oxide polymer may be added.

[0080] In an electricity storage device, when the above-described electricity storage device electrode is used as either the positive electrode or the negative electrode, a conventional electrode can be used for the electrode that does not use the electricity storage device electrode of the present disclosure (i.e., the electrode that does not contain the above-described binder for an electricity storage device).

[0081] In one preferred embodiment, the electricity storage device according to the present disclosure includes the electricity storage device electrode according to the present disclosure as a negative electrode and a conventional electrode as a positive electrode. That is, in one preferred embodiment of the present disclosure, the electricity storage device includes a negative electrode containing the above-described binder for an electricity storage device and a positive electrode not containing the above-described binder for an electricity storage device. In this case, the positive electrode is not particularly limited as long as it is a positive electrode normally used in electricity storage devices.

[0082] Alternatively, in another preferred embodiment, the electricity storage device according to the present disclosure includes the electricity storage device electrode according to the present disclosure as a positive electrode and a conventional electrode as a negative electrode. That is, in one preferred embodiment of the present disclosure, the electricity storage device includes a positive electrode containing the aforementioned binder for an electricity storage device and a negative electrode not containing the aforementioned binder for an electricity storage device. The negative electrode is not particularly limited as long as it is a negative electrode typically used in electricity storage devices. In this case, it is preferable that the binder solution contained in the electricity storage device electrode slurry used to form the positive electrode is a binder solution containing the binder according to the present disclosure and N-methyl-2-pyrrolidone (NMP). This is because the use of NMP as the solvent in the electricity storage device electrode slurry suppresses deterioration of the positive electrode active material in the electricity storage device electrode slurry, and the properties of the aforementioned modified PVA contained in the binder enhance the peel strength of the positive electrode.

[0083] In addition, both the positive electrode and the negative electrode may be the electricity storage device electrodes of the present disclosure. That is, in one preferred embodiment of the present disclosure, the electricity storage device includes a positive electrode containing the above-mentioned binder for an electricity storage device, and a negative electrode containing the above-mentioned binder for an electricity storage device.

[0084] The method for manufacturing the electricity storage device of the present disclosure is not particularly limited, but for example, when the electricity storage device is a battery, it can be manufactured as follows. That is, the negative electrode and the positive electrode may be stacked with a separator such as a porous polypropylene film interposed therebetween, and the stack may be rolled and / or folded depending on the shape of the battery, placed in a battery container, and the electrolyte solution may be poured in and sealed. The shape of the battery may be any of the known types such as a coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0085] The power storage device according to the present disclosure is useful for a variety of applications. For example, it is useful as a battery for use in portable terminals that require small size, thinness, light weight, and high performance. It can also be suitably used as a battery for devices that require flexibility, such as wound dry batteries and laminated batteries.

[0086] Examples of the present invention will be described below, but the present invention is not limited to these. % in the examples refers to mass unless otherwise specified. First, the measurement methods and evaluation methods are shown below. Note that the physical property values ​​(or evaluation values) described in this specification are based on values ​​determined by the following methods.

[0087] The physical properties of each PVA used in each of the examples and comparative examples described below, evaluation in electrode application, and evaluation in battery application were measured according to the following methods.

[0088] [Viscosity-average degree of polymerization of PVA] The viscosity-average degree of polymerization of modified PVA and PVA(E) was measured in accordance with JIS K 6726 (1994). Specifically, when the degree of saponification of the modified PVA was less than 99.5 mol%, it was saponified until the degree of saponification reached 99.5 mol% or more, and the viscosity-average degree of polymerization (P) of the resulting modified PVA or PVA(E) was calculated by the following formula using the intrinsic viscosity [η] (liters / g) measured in water at 30°C. P = ([η] x 10 ４ / 8.29) （１／０．６２）

[0089] [Degree of Saponification of PVA] The degrees of saponification of the modified PVA and PVA (E) were determined by the method described in JIS K 6726 (1994).

[0090] [Modification Amount (X)] The content (X) of the structural unit derived from the derivative (A) of the ethylenically unsaturated dicarboxylic acid in the modified PVA (modification amount (X)) is １ The amount of modification (X) of PVA (E) was calculated from the spectrum of the modified species by H-NMR spectrum analysis.

[0091] [Modification Amount (Y)] The content (Y) of the structural unit represented by formula (I) in the modified PVA (modification amount (Y)) was measured using dimethyl sulfoxide as a solvent. １ The amount of modification was calculated from the spectrum detected at 6.8 to 7.2 ppm in H-NMR spectrum analysis. In addition, the ratio of the amount of modification (Y) to the amount of modification (X), Y / X, was calculated.

[0092] [Amount of Insoluble Components (Water-Insoluble Content) When a 5% by Weight Aqueous Solution Was Prepared at 90°C] A 500 mL flask equipped with a stirrer and reflux condenser was placed in a water bath set to 20°C. 285 g of distilled water was added to the flask, and stirring at 300 rpm was initiated. 15 g of modified PVA powder was weighed and gradually added to the flask. After the entire amount (15 g) of modified PVA powder was added, the temperature of the water bath was immediately raised to 90°C over approximately 30 minutes to dissolve the modified PVA powder, thereby obtaining a modified PVA solution. After the water bath temperature reached 90°C, dissolution was continued for an additional 60 minutes while stirring at 300 rpm. The modified PVA solution was then used to filter out undissolved particles (undissolved particles) using a metal filter with a 63 μm mesh. The filter was then thoroughly washed with warm water at 90°C to remove the solution adhering to the filter, leaving only undissolved particles on the filter. The filter was then dried for 1 hour in a heated dryer at 120°C. The mass of the filter after drying was compared with the mass of the filter before use for filtration, and the mass of the undissolved particles was calculated. The mass ratio of the undissolved particles to the total amount of modified PVA used to prepare the modified PVA solution was taken as the amount of insoluble components (water-insoluble content) when a 5% by mass aqueous solution was prepared at 90°C.

[0093] [Particle Size Distribution] The particle size distribution of the modified PVA powder was measured by the dry sieving method described in JIS Z 8815 (1994). The modified PVA powder was passed through a sieve (filter) with a mesh size of 1.00 mm, and the mass of the modified PVA powder that passed through the sieve was measured. The proportion (mass%) of the modified PVA particles that passed through the sieve was calculated from the mass of the modified PVA powder before passing through the sieve. Similarly, independently of the 1.00 mm mesh size sieve, the modified PVA powder was passed through a 500 μm mesh size sieve (filter). The mass of the modified PVA powder that passed through the sieve was measured, and the proportion (mass%) of the modified PVA particles that passed through the sieve was calculated from the mass of the modified PVA powder before passing through the sieve. The mesh size conforms to the nominal mesh size W of JIS Z 8801-1 (2006).

[0094] <Evaluation of Peel Strength (N / m)> For the negative electrodes for lithium secondary batteries produced in each of the Examples and Comparative Examples described below, the strength was measured when the cured body (the portion derived from the negative electrode slurry prepared in each of the Examples and Comparative Examples) was peeled from the copper foil current collector. Specifically, the negative electrode slurry-coated surface of the obtained negative electrode for lithium ion secondary batteries was attached to a stainless steel plate using double-sided tape (double-sided tape manufactured by Nichiban), and the 180° peel strength (peel width 10 mm, peel rate 100 mm / min) was measured using a 50 N load cell (manufactured by Imada Co., Ltd.).

[0095] Evaluation of Initial Charge-Discharge Efficiency (%) and DC Resistance (Ω) The lithium-ion secondary batteries (coin batteries) prepared in each of the Examples and Comparative Examples described below were tested using a commercially available charge-discharge tester (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.). The resistance value measured when a 0.1 mA current was applied for 3 seconds after initial charging was defined as the DC resistance. Charging consisted of constant-current charging at 0.2 C (1-1.2 mA) up to 0.01 V relative to the lithium potential, followed by constant-voltage charging at 0.01 V relative to the lithium potential until the current reached 0.02 mA. Discharging consisted of constant-current discharging at 0.2 C (1-1.2 mA) up to 1.5 V relative to the lithium potential. The lithium-ion secondary batteries were placed in a thermostatic chamber at 25°C and subjected to initial charging and discharging under the conditions described above. The charge specific capacity (mAh / g), discharge specific capacity (mAh / g), and DC resistance (Ω) were measured. The initial charge-discharge efficiency (%) was calculated by the formula: (specific discharge capacity) / (specific charge capacity)×100.

[0096] <Evaluation of 0.5C Charge Capacity Retention Rate> For the lithium ion secondary batteries (coin batteries) prepared in each of the Examples and Comparative Examples described below, a rate test was conducted following the initial charge and discharge using a commercially available charge / discharge tester (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.). For charging, a constant current of 0.5C (2.5 to 3.0 mA) was charged to 0 V relative to the lithium potential. For discharging, a constant current of 0.2C (1 to 1.2 mA) was discharged to 1.5 V relative to the lithium potential. The lithium ion secondary batteries were placed in a thermostatic chamber at 25°C and charged and discharged under the above-mentioned conditions. The cell charge capacity (mAh) at this time was measured. The 0.5C charge capacity retention rate (%) was calculated by (specific charge capacity at 0.5C (mAh / g)) / (specific charge capacity at 0.2C (mAh / g))×100.

[0097] <Evaluation of the number of chips (pieces)> For the negative electrodes for lithium ion secondary batteries produced in each of the examples and comparative examples described below, 10 electrodes were punched out using a punching machine with a diameter of 14 mm, and the number of electrodes in which the active material had peeled off from the current collector was counted.

[0098] - Preparation of Modified PVA [Production Example 1] (PVA-1) A reactor equipped with a stirrer, reflux condenser, nitrogen inlet, comonomer dropping port, and polymerization initiator addition port was charged with 970 parts by mass of vinyl acetate and 30 parts by mass of methanol, and the system was purged with nitrogen for 30 minutes while bubbling with nitrogen. Monomethyl maleate was selected as the ethylenically unsaturated dicarboxylic acid derivative (A) used as the modified species, and a methanol solution of monomethyl maleate (2% concentration) was purged with nitrogen by bubbling with nitrogen gas. The reactor was heated, and when the internal temperature reached 60°C, 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The methanol solution of monomethyl maleate was added dropwise to the reactor, and polymerization was carried out at 60°C for 2 hours while maintaining a constant monomer composition ratio in the polymerization solution. The polymerization was then terminated by cooling. The total amount of ethylenically unsaturated dicarboxylic acid derivative (A) added up to the termination of polymerization was 1.4 parts by mass, and the polymerization rate at the time of termination was 20%. Subsequently, unreacted monomers were removed at 30°C under reduced pressure with occasional addition of methanol to obtain a methanol solution of vinyl ester polymer (concentration 30%). Next, 666.7 parts by mass of a methanol solution of vinyl ester polymer (200.0 parts by mass of the polymer in the solution) was prepared by further adding methanol to this methanol solution. 14.8 parts by mass of a 10% methanol solution of sodium hydroxide was added to the methanol solution, and saponification was carried out at 40°C. The polymer concentration of the saponification solution was 15%, and the molar ratio of sodium hydroxide to vinyl acetate units in the polymer was 0.016. After the addition of the methanol solution of sodium hydroxide, a gel-like substance was formed in about 20 minutes. This was crushed in a crusher and left to stand at 40°C for 1 hour to allow saponification to proceed. Subsequently, 500 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the mixture was filtered to obtain a white solid. 2,000 parts by mass of a mixed solution of methanol and methyl acetate (volume ratio: 20:80) was added to the white solid, which was then left at room temperature for 3 hours and washed. This washing procedure was repeated three times, and the resulting white solid was centrifuged for dewatering. The resulting white solid was then dried by heat treatment at 95°C for 4 hours in a dryer, and the resulting modified PVA powder (PVA-1) was used as a binder for electricity storage devices.The various manufacturing materials for PVA-1 and their physical properties are summarized in Table 1.

[0099] [Production Examples 2 to 9] (PVA-2 to PVA-9) Various modified PVAs (PVA-2 to PVA-9), which are binders for electricity storage devices, were produced in the same manner as in the production method for PVA-1 (Production Example 1), except that the polymerization conditions, such as the amount of vinyl acetate and methanol charged, the type and amount of modified species (derivative (A) of ethylenically unsaturated dicarboxylic acid) used during polymerization, and the polymerization rate, as well as the saponification conditions, such as the molar ratio of sodium hydroxide, were changed as shown in Table 1. The physical properties of each modified PVA are summarized in Table 1.

[0100] - Production of PVA (E) [Production Examples 10 to 13] (PVA-10 to PVA-13) Various modified PVA (E) (PVA10 to PVA-13) were produced in the same manner as in the production method for PVA-1 (Production Example 1), except that the amounts of vinyl acetate and methanol charged, the type and amount of modified species (ethylenically unsaturated dicarboxylic acid derivative (A)) used during polymerization, polymerization conditions such as polymerization rate, and saponification conditions such as the molar ratio of sodium hydroxide were changed as shown in Table 2. The physical properties of each PVA (E) are summarized in Table 2.

[0101]

[0102]

[0103] Example 1 Hereinafter, an example will be shown in which an electricity storage device was manufactured using the PVA-1 manufactured above.

[0104] -Production of a binder for an electricity storage device PVA-1 was used as a binder.

[0105] Preparation of Binder Solution for Electrical Storage Device Water was added to the binder (PVA-1) and mixed under heating at 80° C. for 1 hour to obtain a binder solution with a solid content of approximately 10% by mass.

[0106] Preparation of Power Storage Device Electrode Slurry (Negative Electrode Slurry) The binder solution having a solid content concentration of 10% by mass described above, artificial graphite (FSN-1, manufactured by Shanghai Shanshan Co., Ltd.) as the negative electrode active material, Super-P (manufactured by Timcal) as a conductive additive (conductivity imparting agent), and CMC (CMC Daicel 2200, manufactured by Daicel Miraize Co., Ltd.) as a thickener were charged into a dedicated container and kneaded using a planetary stirrer (ARE-250, manufactured by Thinky Corporation) to prepare a negative electrode slurry. When charged, the ratio of each component in the negative electrode slurry was 96 parts by mass of artificial graphite, 1 part by mass of Super-P, 1.5 parts by mass of the solid content (i.e., binder) in the binder solution, and 1.5 parts by mass of CMC. That is, the composition ratio of the negative electrode active material, conductive additive, binder, and thickener in the negative electrode slurry was, in terms of solid content, negative electrode active material:conductive additive:binder:thickener=96:1:1.5:1.5 (mass ratio).

[0107] Fabrication of an Energy Storage Device Electrode (Lithium-Ion Secondary Battery Negative Electrode) The negative electrode slurry obtained as described above was applied to a current collector made of copper foil (CST8G, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). After primary drying in a hot air dryer at 80°C for 30 minutes, the resultant was rolled using a roll press (manufactured by Hosen Co., Ltd.). Subsequently, a battery electrode (φ14 mm) was punched out, and secondary drying was performed under reduced pressure at 140°C for 3 hours to fabricate a lithium-ion secondary battery negative electrode (coin battery negative electrode). Ten φ14 mm punched out electrodes were fabricated, and the number of chips was counted. Chip-free negative electrodes were selected for use in the lithium-ion secondary battery (coin battery) described below. The peel strength of the fabricated lithium-ion secondary battery negative electrodes was measured using the method described above. The results are summarized in Table 3.

[0108] Fabrication of an Electrical Storage Device (Lithium Ion Secondary Battery) The negative electrode for a lithium ion secondary battery obtained as described above was transferred to a glove box (manufactured by Miwa Manufacturing Co., Ltd.) under an argon gas atmosphere. Metallic lithium foil (thickness 0.2 mm, φ16 mm) was used as the counter electrode, a polypropylene separator (Celgard #2400, manufactured by Polypore Corporation) was used, and lithium hexafluorophosphate (LiPF ) in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was used as the electrolyte. ６ ) was added, followed by the addition of vinylene carbonate (VC) to the mixed solvent system (1M-LiPF ６ , EC / EMC = 3 / 7 vol%, VC = 2 mass%) (manufactured by Toyama Pharmaceutical Co., Ltd.) was used for injection. With this configuration, a coin battery (2032 type), which is a lithium-ion secondary battery, was fabricated. The fabricated coin battery was subjected to measurements of the initial charge / discharge efficiency at 0.2 C charge / discharge, DC resistance, and cell charge capacity at 0.5 C charge / discharge using the methods described above. The results are summarized in Table 3.

[0109] [Examples 2 to 6, Comparative Examples 1 to 3] Except for using PVA-2 to PVA-9 instead of PVA-1, the production of binders, the preparation of binder solutions, the preparation of negative electrode slurries, the production of negative electrodes for lithium ion secondary batteries, and the production of lithium ion secondary batteries were carried out in the same manner as in Example 1, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0110] Except for producing a binder using 1.0 part by mass of PVA-1 and 0.5 part by mass of PVA-10, the preparation of a binder solution, the preparation of a negative electrode slurry, the production of a lithium ion secondary battery negative electrode, and the production of a lithium ion secondary battery were carried out in the same manner as in Example 1, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0111] [Examples 8 to 10] Except for using 0.5 parts by mass of each of PVA-11 to PVA-13 instead of PVA-10, the preparation of a binder solution, the preparation of a negative electrode slurry, the production of a lithium ion secondary battery negative electrode, and the production of a lithium ion secondary battery were carried out in the same manner as in Example 7, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0112] [Example 11] PVA-1 was added with water and heated and mixed at 80 ° C. for 1 hour to prepare a solution with a solids concentration of approximately 10% by mass. Lithium acetate was added as a water-soluble Li salt, and the solution was stirred and dissolved to prepare a binder solution with a mass ratio of PVA-1: lithium acetate of 90:10. The solution was mixed to prepare a binder solution. Except for using this binder solution with a ratio of PVA-1: lithium acetate = 90:10, the same procedures as in Example 1 were used to prepare a negative electrode slurry, prepare a negative electrode for a lithium ion secondary battery, and prepare a lithium ion secondary battery. The same measurements and evaluations were carried out. In this case, the composition ratio of the components contained in the negative electrode slurry, the negative electrode active material, the conductive additive, the binder (a mixture of PVA-1 and a water-soluble Li salt), and the thickener was, as solids, negative electrode active material: conductive additive: PVA-1: water-soluble Li salt: thickener = 96: 1: 1.35: 0.15: 1.5 (mass ratio). The results are summarized in Table 3.

[0113] [Example 12] Except for preparing a binder solution containing PVA-1, lithium acetate, and PVA-10 in a ratio of 90:10:50, a negative electrode slurry was prepared, a lithium ion secondary battery negative electrode was fabricated, and a lithium ion secondary battery was fabricated in the same manner as in Example 11, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0114] [Example 13] Except for preparing a binder solution containing PVA-1, lithium acetate, and PVA-10 in a ratio of 80:20:50, a negative electrode slurry was prepared, a lithium ion secondary battery negative electrode was fabricated, and a lithium ion secondary battery was fabricated in the same manner as in Example 11, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0115] [Examples 14 to 26] Preparation of a binder solution for an electrical storage device, preparation of a slurry for a negative electrode, production of a negative electrode for a lithium ion secondary battery, and production of a lithium ion secondary battery were carried out in the same manner as in Example 11, except that the amounts of PVA-1 and various water-soluble Li salts used were changed as shown in Table 3. The same measurements and evaluations were carried out. The results are summarized in Table 3. In Table 3, LiOAc represents lithium acetate, LiOH represents lithium hydroxide, LiCl represents lithium chloride, and Li ２ SO ４ is lithium sulfate, LiFSI is lithium bis(fluorosulfonyl)imide, Li ２ CO ３ represents lithium carbonate.

[0116] [Example 27] Except for using 3 parts by mass of PVA-1 as the binder and not using CMC, a binder solution for an electricity storage device, a slurry for a negative electrode, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were prepared in the same manner as in Example 1, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0117] [Example 28] Water-soluble Li salt (lithium acetate), was added as a powder rather than as a binder solution, that is, the binder solution of Example 1, lithium acetate (powder), artificial graphite as a negative electrode active material (FSN-1, manufactured by Shanghai Shanshan), Super-P (manufactured by Timcal) as a conductive additive (conductivity imparting agent), and CMC as a thickener (CMC Daicel 2200, manufactured by Daicel Miraize Co., Ltd.) were charged into a dedicated container, and kneaded using a planetary stirrer (ARE-250, manufactured by Thinky Corporation), except that a negative electrode slurry was prepared, by the same method as in Example 11, the production of a lithium ion secondary battery negative electrode and the production of a lithium ion secondary battery were carried out, and the same measurements and evaluations were carried out. The results are summarized in Table 3.

[0118]

[0119] As shown in Table 3, the electrodes for electricity storage devices and electricity storage devices of the Examples were excellent in peel strength, initial charge / discharge efficiency, 0.5C charge capacity retention rate, DC resistance, and number of chips. Among the Examples that did not use a water-soluble Li salt, Example 8 had the highest peel strength, but a relatively high DC resistance. Furthermore, when Example 1 and Example 4, which differ only in the type of modified PVA, were compared, Example 4, which had a peel strength that was approximately 30% lower, had a lower DC resistance. It can be seen that high peel strength and low DC resistance are not necessarily correlated.

[0120] Furthermore, the water-insoluble content of each of PVA-10 to PVA-13 used in the examples was not measured. Here, compared to Example 1, which used only PVA-1, Examples 7 to 10, which used PVA-1 and any of PVA10 to PVA-13, had similarly good peel strength and DC resistance. Furthermore, PVA-10 to PVA-13 were produced using the same drying conditions as PVA-1, etc. Based on these performances and production procedures, it is highly likely that the water-insoluble content of PVA-10 to PVA-13 is 0.1 ppm or more and less than 2000 ppm.

Claims

1. A binder for an electrical storage device, comprising a modified vinyl alcohol-based polymer having a content of structural units derived from a derivative (A) of an ethylenically unsaturated dicarboxylic acid of 0.05 mol % or more and 10 mol % or less and a degree of saponification of 70.0 mol % or more and 99.9 mol % or less, wherein the amount of insoluble components when an aqueous solution of the modified vinyl alcohol-based polymer is prepared at 90°C and at a concentration of 5% by mass is 0.1 ppm or more and less than 2000 ppm.

2. 2. The binder for a storage battery device according to claim 1, wherein the derivative (A) of an ethylenically unsaturated dicarboxylic acid is at least one selected from the group consisting of a monoester of an ethylenically unsaturated dicarboxylic acid, a diester of an ethylenically unsaturated dicarboxylic acid, and an anhydride of an ethylenically unsaturated dicarboxylic acid.

3. 2. The binder for a storage battery device according to claim 1, wherein the derivative (A) of the ethylenically unsaturated dicarboxylic acid comprises at least one selected from the group consisting of a monoalkyl maleate, a dialkyl maleate, maleic anhydride, a monoalkyl fumarate, and a dialkyl fumarate.

4. 2. The binder for an electricity storage device according to claim 1, wherein at least a portion of the structural units derived from the derivative (A) of the ethylenically unsaturated dicarboxylic acid constitute a portion of a structural unit represented by the following formula (I), and the modified vinyl alcohol-based polymer satisfies the following formula (Q): 【number】 (In formula (I), R １ is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms. ２ is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms. [Equation 1] (In formula (Q), X represents the content (mol %) of the structural unit derived from the derivative (A) of the ethylenically unsaturated dicarboxylic acid. Y represents the content (mol %) of the structural unit represented by formula (I).)

5. 2. The binder for a storage battery device according to claim 1, wherein the modified vinyl alcohol-based polymer is in a powder form, and the amount passing through a sieve with an opening of 1.00 mm is 95% by mass or more of the entire modified vinyl alcohol-based polymer.

6. 2. The binder for a storage battery device according to claim 1, wherein the modified vinyl alcohol-based polymer is in a powder form, and the amount passing through a sieve with an opening of 500 μm is 30% by mass or more of the entire modified vinyl alcohol-based polymer.

7. 2. The binder for an electricity storage device according to claim 1, wherein the modified vinyl alcohol polymer has a crosslinked structure.

8. 2. The binder for an electricity storage device according to claim 1, further comprising a water-soluble Li salt, wherein the mass ratio of the modified vinyl alcohol polymer to the water-soluble Li salt is 70:30 to 95:

5.

9. The binder for an electricity storage device according to claim 8 , wherein the water-soluble Li salt has a solubility in water at 20° C. of 10 g / 100 mL or more.

10. The binder for an electricity storage device according to claim 8 , wherein the water-soluble Li salt has a molecular weight of 1,000 or less.

11. 9. The binder for an electricity storage device according to claim 8, wherein the water-soluble Li salt is at least one selected from the group consisting of lithium chloride, lithium acetate, lithium formate, lithium hydroxide, lithium sulfate, lithium carbonate, lithium maleate, lithium oxalate, lithium citrate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

12. A binder solution for an electrical storage device, comprising the binder for an electrical storage device according to any one of claims 1 to 11 and a solvent.

13. An electrode slurry for an electricity storage device, comprising the binder solution for an electricity storage device according to claim 12 and an active material.

14. The electricity storage device electrode slurry according to claim 13 , wherein the content of the electricity storage device binder is 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the active material.

15. An electricity storage device electrode comprising a current collector and a hardened body of the electricity storage device electrode slurry according to claim 13 .

16. An electricity storage device comprising the electricity storage device electrode according to claim 15 .

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