Power storage device-use binder, binder solution for power storage device, slurry for electrode of power storage device, electrode of power storage device, and power storage device

Abstract

Provided are: a power storage device-use binder, which exhibits excellent peel strength, resistance characteristics and foaming suppression when used in an electrode; a binder solution for a power storage device; a slurry for an electrode of power storage device; an electrode of a power storage device; and a power storage device. The power storage device-use binder contains a vinyl alcohol-based polymer and a compound represented by formula (1). In formula (1), R1 and R2 are each independently an alkyl group having 1-4 carbon atoms. m and n are each independently an integer between 0 and 25.

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 invention 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 and positive electrodes that constitute an electricity storage device are usually produced by the following procedure. First, a binder and a thickener are dissolved or dispersed in water or a solvent, and then an active material, a conductive additive (conductivity imparting agent), etc. are mixed with this to obtain an electrode slurry. The obtained electrode slurry is applied to a current collector and dried. This results in an electrode in which a mixed layer containing the active material, etc. is formed on the current collector.

[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. Known binders 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 electrodes with high peel strength even in compositions with a low binder content are required.

[0008] Furthermore, due to the demand for shorter charging times, there is a demand for batteries that can be charged at high speeds without losing capacity compared to slow 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] Furthermore, during the preparation process of electrode slurry, fine bubbles may be entrained in the slurry due to the mechanical stirring action of the mixer or due to powders of the active material, conductive additive, etc. If these bubbles remain, mechanical energy is not efficiently transmitted by mixing, resulting in insufficient particle dispersion. Furthermore, if the electrode slurry is applied while still containing bubbles, fine holes and streak-like defects may occur in the resulting mixed layer. Therefore, there is a need for an electrode material that can suppress foaming during the preparation of electrode slurry.

[0010] In view of the above-mentioned problems, the present disclosure aims to provide a binder for an electricity storage device that, when used in an electrode, has excellent peel strength, is suitable for obtaining an electrode with low resistance, and can suppress foaming, 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.

[0011] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using a binder for an electricity storage device having a predetermined composition.

[0012] That is, the present invention includes the following inventions: [1] A binder for an electricity storage device, comprising a vinyl alcohol polymer and a compound represented by the following formula (1): In formula (1), R １ and R ２ are each independently an alkyl group having 1 to 4 carbon atoms. m and n are each independently an integer of 0 to 25. [2] The binder for an electrical storage device according to [1], wherein the vinyl alcohol polymer contains structural units derived from an ethylenically unsaturated dicarboxylic acid monomer, the content of which is 0.01 mol % to 10 mol % based on all structural units constituting the vinyl alcohol polymer, and the degree of saponification of the vinyl alcohol polymer is 60.0 mol % to 99.9 mol %. [3] The binder for an electrical storage device according to [2], wherein the ethylenically unsaturated dicarboxylic acid monomer contains at least one selected from the group consisting of maleic acid, monoalkyl maleate, dialkyl maleate, maleic anhydride, monoalkyl fumarate, and dialkyl fumarate. [4] R of the compound １ is a methyl group, and R ２is an isobutyl group, and m and n are each less than 8. [5] A binder solution for an electricity storage device, comprising the binder for an electricity storage device of any of [1] to [4] and a solvent. [6] An electricity storage device electrode slurry, comprising the binder solution for an electricity storage device of [5] and an active material. [7] An electricity storage device electrode slurry of [6], in which the content of the electricity storage device binder is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the active material. [8] An electricity storage device electrode, comprising a current collector and a cured product of the electricity storage device electrode slurry of [6] or [7]. [9] An electricity storage device, comprising the electricity storage device electrode of [8].

[0013] In the present invention, 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 are excellent in peel strength, resistance characteristics, and foaming suppression.

[0014] 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."

[0015] <Binder for Electricity Storage Device> In the present invention, the binder for an electricity storage device (hereinafter also simply referred to as "binder") is a binder for an electricity storage device containing a vinyl alcohol-based polymer and a compound represented by the following formula (1): In addition, in the present invention, a preferred embodiment of the binder for an electricity storage device is a binder for an electrode of an electricity storage device.

[0016]

[0017] In formula (1), R １ and R ２ are each independently an alkyl group having 1 to 4 carbon atoms. m and n are each independently an integer of 0 to 25.

[0018] [Vinyl alcohol polymer] A vinyl alcohol polymer (also referred to as "PVA" in this specification) is a polymer having a vinyl alcohol unit as a structural unit. 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.

[0019] 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 structural 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 the (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 structural units other than vinyl ester units.

[0020] In the present invention, PVA has a good affinity with 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 can be obtained.

[0021] The saponification degree of the PVA is preferably 60.0 mol% or more and 99.9 mol% or less, more preferably 65.0 mol% or more and 99.9 mol% or less, even more preferably 82.0 mol% or more and 99.0 mol% or less, and particularly preferably 85.0 mol% or more and 95.0 mol% or less. When the saponification degree is within the above range, practical physical properties such as peel strength tend to be better, and the amount of water-insoluble components tends to be smaller. The saponification degree of the PVA can be measured according to the method described in JIS K 6726 (1994).

[0022] The viscosity average degree of polymerization (hereinafter sometimes abbreviated as "degree of polymerization") of the PVA 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 degree of polymerization of the PVA can be measured according to the method described in JIS K 6726 (1994).

[0023] When a PVA is prepared as an aqueous solution of 5% by mass at 90°C, the amount of insoluble components (hereinafter sometimes referred to as "water-insoluble content") is preferably 0.1 ppm or more and less than 3000 ppm. The water-insoluble content is more preferably 0.1 ppm or more and 2000 ppm or less, even more preferably 0.1 ppm or more and 1000 ppm or less, even more preferably 0.1 ppm or more and 500 ppm or less, and particularly preferably 0.1 ppm or more and 100 ppm or less. When the water-insoluble content is in the above range, the peel strength is superior when used as a binder. In this specification, ppm means ppm by mass.

[0024] The amount of insoluble components (water-insoluble content) 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 PVA is weighed and gradually added to the flask. After the entire amount (15 g) of PVA is added, the temperature of the water bath is increased to 90°C over approximately 30 minutes to dissolve the PVA, yielding a PVA solution. After the water bath temperature reaches 90°C, dissolution is continued for an additional 60 minutes while stirring at 300 rpm. The PVA solution is then used to filter the remaining undissolved 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 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 PVA used to prepare the PVA aqueous solution is defined as the amount of insoluble components when a 5% by mass aqueous solution is prepared at 90°C.

[0025] From the viewpoint of obtaining an electrode with lower resistance, the PVA is preferably a modified PVA having a structural unit derived from an ethylenically unsaturated dicarboxylic acid monomer.

[0026] The content (X) of structural units derived from ethylenically unsaturated dicarboxylic acid monomers in the modified PVA is preferably 0.01 mol% or more and 10 mol% or less, more preferably 0.1 mol% or more and 5.0 mol% or less, and even more preferably 0.2 mol% or more and 2.0 mol% or less. When the content (X) of structural units derived from ethylenically unsaturated dicarboxylic acid monomers is within the above range, the modified PVA exhibits improved peel strength when used as a binder, and is also inhibited from adhering to each other and forming blocks due to moisture in the air, improving handleability and further inhibiting the formation of water-insoluble components. In this specification, the content (X) of structural units derived from ethylenically unsaturated dicarboxylic acid monomers in the modified PVA is sometimes referred to as the "modification amount (X)." The modification amount (X) refers to the ratio of the number of moles of structural units derived from ethylenically unsaturated dicarboxylic acid monomers to the total number of moles of structural units constituting the main chain of the modified PVA. The modification amount (X) is the amount of the modified vinyl ester polymer before the modified PVA is saponified. １ It can be calculated by H-NMR analysis.

[0027] The ethylenically unsaturated dicarboxylic acid monomer is not particularly limited. In the present disclosure, the ethylenically unsaturated dicarboxylic acid monomer refers to an ethylenically unsaturated dicarboxylic acid and its derivatives. The ethylenically unsaturated dicarboxylic acid derivative is preferably 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. The ethylenically unsaturated dicarboxylic acid monomer is preferably 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.

[0028] The ethylenically unsaturated dicarboxylic acid monomer is preferably an ethylenically unsaturated dicarboxylic acid, 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. Specific examples of the ethylenically unsaturated dicarboxylic acid monomer include unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid; monoalkyl unsaturated dicarboxylic acid esters such as monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl citraconic acid, monoethyl citraconic acid, 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, maleic acid, monoalkyl maleate esters, dialkyl maleate esters, maleic anhydride, monoalkyl fumarate esters, or dialkyl fumarate esters are preferred, and monoalkyl maleate esters, dialkyl maleate esters, maleic anhydride, monoalkyl fumarate esters, or dialkyl fumarate esters are more preferred, and monomethyl maleate or maleic anhydride may be even more preferred. The modified PVA may have structural units derived from at least one of the ethylenically unsaturated dicarboxylic acid monomers, or may have structural units derived from two or more of the ethylenically unsaturated dicarboxylic acid monomers.

[0029] In the modified PVA having structural units derived from an ethylenically unsaturated dicarboxylic acid monomer, it is preferred that at least a portion of the structural units derived from the ethylenically unsaturated dicarboxylic acid monomer constitute a portion of the structural units represented by the following formula (2): Furthermore, it is more preferred that the ratio (molar ratio) of the content (Y) of the structural units represented by formula (2) (hereinafter also referred to as the modification amount (Y)) to the content (X) of the structural units derived from the ethylenically unsaturated dicarboxylic acid monomer satisfies the following formula (Q), in order to further suppress the amount of water-insoluble matter.

[0030]

[0031] 0.05≦(Y) / (X)<0.98 (Q)

[0032] In formula (2), R ３ is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms. ４ is a metal atom, a hydrogen atom, or a linear or branched alkyl group having 1 to 8 carbon atoms.

[0033] When (Y) / (X) satisfies the range represented by formula (Q), modified PVA with a reduced water-insoluble content can be industrially produced more easily. The lower limit of (Y) / (X) may be more preferably 0.06. Meanwhile, the upper limit of (Y) / (X) may be more preferably 0.80, even more preferably 0.60, and particularly preferably 0.40. The content (Y) of the structural unit represented by formula (2) is the ratio of the number of moles of the structural unit of formula (2) to the total number of moles of the structural units constituting the main chain of the modified PVA.

[0034] R ３ and R ４Examples 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.

[0035] R ４ In the formula, 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 lithium or sodium may be more preferred.

[0036] When a modified PVA is produced using the ethylenically unsaturated dicarboxylic acid monomer, some of the structural units derived from the introduced ethylenically unsaturated dicarboxylic acid monomer may form a six-membered lactone ring structure represented by formula (2) after saponification. The six-membered lactone structure represented by formula (2) 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 (2) is higher than the content (X) of the structural unit derived from the introduced ethylenically unsaturated dicarboxylic acid monomer, this means that the crosslinking reaction is suppressed. The six-membered lactone structure represented by formula (2) was measured in a deuterated dimethyl sulfoxide solvent. １ It is believed that the structural unit represented by formula (2) is detected at 6.8 to 7.2 ppm in the H-NMR spectrum. From the viewpoint of further reducing the water-insoluble content in the modified PVA, it is preferable that the content (Y) of the structural unit represented by formula (2) satisfies the above formula (Q) relative to the content (X) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid monomer obtained from the modified vinyl ester polymer 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 monomer form part of the structural unit represented by formula (2).

[0037] In one embodiment of the present invention, the shape of the PVA is not particularly limited, but a powdered PVA powder may be preferred. The particle size of the particles constituting the powder is not particularly limited, but it is preferable that 95% by mass or more of the entire PVA powder pass through a sieve with a mesh size of 1.00 mm, and more preferably 95% by mass or more of the entire PVA powder pass through a sieve with a mesh size of 710 μm. Here, "95% by mass or more of the entire PVA powder" refers to, for example, an integrated particle size distribution in which 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 uneven drying due to the small particles, and also makes it easier to control the amount of water-insoluble content. The particle size of the particles constituting the PVA powder is preferably such that the amount passing through a sieve with a mesh size of 500 μm of the total 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 PVA powder is preferably such that 99% by mass or more of the PVA powder passes through a sieve with a mesh size of 1.00 mm, and more preferably 99% by mass or more of the 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).

[0038] In the binder for an electricity storage device of the present invention, the PVA may preferably have a crosslinked structure. The crosslinked structure may be a structure in which structural units derived from an ethylenically unsaturated dicarboxylic acid monomer in the PVA are crosslinked intermolecularly. Furthermore, the crosslinked structure of the 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.

[0039] [PVA Manufacturing Method] Hereinafter, a method for manufacturing a PVA will be described, although the method for manufacturing a PVA is not limited to the method described below.

[0040] PVA is produced, for example, by a production method including a step of polymerizing a vinyl ester monomer to obtain a vinyl ester polymer, a saponification step of saponifying the obtained vinyl ester polymer in an alcohol solution using an alkali catalyst or an acid catalyst, a washing step, and a drying step.

[0041] Furthermore, when the PVA is a modified PVA containing a structural unit derived from an ethylenically unsaturated dicarboxylic acid monomer, it is produced by a production method including, for example, a step of copolymerizing an ethylenically unsaturated dicarboxylic acid monomer with a vinyl ester monomer to obtain a modified vinyl ester polymer, a saponification step of saponifying the obtained modified vinyl ester polymer in an alcohol solution using an alkali catalyst or an acid catalyst, a washing step, and a drying step.

[0042] Examples of the vinyl ester monomer 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.

[0043] Methods for polymerizing vinyl ester monomers 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 employed. From the viewpoint of enhancing the effects of the present invention, 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. Furthermore, the above-mentioned methods are also preferred when copolymerizing a vinyl ester monomer with a monomer other than the vinyl ester monomer, such as an ethylenically unsaturated dicarboxylic acid monomer.

[0044] The initiator used in the polymerization reaction is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof 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.

[0045] As long as the effects of the present invention are not impaired, other copolymerizable monomers other than the vinyl ester-based monomers may be further copolymerized as necessary. For example, as described above, an ethylenically unsaturated dicarboxylic acid monomer may be copolymerized with a vinyl ester-based monomer, or an ethylenically unsaturated dicarboxylic acid monomer may be copolymerized with other copolymerizable monomers other than the vinyl ester-based monomer. Examples of monomers that can be mentioned other than the ethylenically unsaturated dicarboxylic acid monomers and vinyl ester monomers include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylamide monomers such as acrylamide, N-methylacrylamide, and N-ethylacrylamide; methacrylamide monomers such as methacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide; vinyl ether 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 monomers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol vinyl ether; 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 the monomer other than the ethylenically unsaturated dicarboxylic acid monomer and the vinyl ester monomer to be used varies depending on the purpose and application of the monomer, but is usually 10 mol % or less, preferably 5.0 mol % or less, more preferably 3.0 mol % or less, and in some cases even more preferably 2.0 mol % or less, based on the total amount of all the monomers to be used in the copolymerization.

[0046] The vinyl ester polymer obtained in the polymerization step is subjected to a step of saponifying in an alcohol solvent, a step of washing, and a step of drying to obtain PVA. The saponification conditions and drying conditions for obtaining PVA are not particularly limited, but 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 suppress the amount of water-insoluble content of the PVA.

[0047] A saponification raw solution can be prepared by further adding a small amount of water to the solution containing the vinyl ester polymer and the solvent obtained in the polymerization 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.

[0048] 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.

[0049] An alkali catalyst is usually used as a catalyst for the saponification reaction of a vinyl ester polymer. 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 units of the vinyl ester polymer, 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.

[0050] 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 progression of a crosslinking reaction between PVA molecules during drying, it is preferable not to carry out neutralization by adding such an acid from the viewpoint of suppressing and controlling the amount of water-insoluble matter.

[0051] 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 a modified vinyl ester polymer 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 PVA powder; (2) a method in which the concentration of the modified vinyl ester polymer 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 PVA is precipitated in the solvent to obtain fine particles dispersed in methanol; and (3) a method in which a saturated hydrocarbon solvent is added to saponify the vinyl ester polymer in an emulsion or suspension phase to obtain a PVA. In the method (1), the pulverizer is not particularly limited, and known pulverizers and crushers can be used. From a manufacturing standpoint, method (1) or method (2) that does not require a saturated hydrocarbon solvent are preferred. Method (2) is also preferred because it can reduce the amount of water-insoluble matter to a minimum even when the subsequent washing and drying steps are performed at lower temperatures than conventional methods, making it industrially advantageous.

[0052] In order to reduce the amount of water-insoluble matter in the resulting PVA, it is preferable to provide a step of washing the PVA after the saponification step, as necessary. 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 a vinyl ester polymer, 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 preferable from an economic and process standpoint. In order to reduce the amount of water-insoluble matter in the resulting 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.

[0053] After the saponification step or the washing step, the polymer can be dried to obtain a powdered PVA. Specifically, hot air drying using a cylindrical dryer is preferred, and the temperature of the PVA during drying is preferably greater than 80°C and less than 120°C, and sometimes more preferably 90°C or higher and less than 110°C. The drying time is preferably 2 to 10 hours, and sometimes more preferably 3 to 8 hours. By setting the drying conditions within the above ranges, the amount of water-insoluble content in the resulting PVA can be more easily reduced.

[0054] In one embodiment of the present invention, 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 a modified PVA (A1) containing a structural unit derived from an ethylenically unsaturated dicarboxylic acid monomer and another PVA (A2). The content of the PVA (A2) relative to the total amount of the modified PVA (A1) and the PVA (A2) may be 0% by mass or more and 70% by mass or less. The upper limit of the content of the PVA (A2) is preferably 60% by mass, more preferably 50% by mass, even more preferably 40% by mass, even more preferably 20% by mass, and even more preferably 10% by mass. Alternatively, the content of the PVA (A2) may be 0% by mass, i.e., all of the PVA in the binder for an electrical storage device may be modified PVA (A1). The viscosity-average degree of polymerization of the PVA (A2) 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 (A2) is preferably equal to or lower than the viscosity-average degree of polymerization of the modified PVA (A1). The viscosity-average degree of polymerization of the PVA (A2) can be measured according to the method described in JIS K 6726 (1994). The saponification degree of the PVA (A2) may be 80.0 mol% to 99.9 mol%. The saponification degree of the PVA (A2) can be measured according to the method described in JIS K 6726 (1994). The PVA (A2) may be modified.

[0055] In the present invention, it is preferable that the PVA can be dissolved 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. In such cases, the affinity for carbon materials such as graphite is enhanced, resulting in good adhesiveness and coatability. Furthermore, in some cases, it may be preferable to be able to dissolve the PVA to a solids concentration of 8.0% by mass or more, and even 8.5% by mass or more.

[0056] [Compound Represented by Formula (1)] In the present invention, the binder for an electricity storage device contains, in addition to the PVA, a compound represented by the following formula (1) (hereinafter sometimes referred to as "compound (1)").

[0057]

[0058] In formula (1), R １ and R ２ are each independently an alkyl group having 1 to 4 carbon atoms. １ Similarly, two R ２ may be the same or different. However, two R １ It is preferable that the two R ２ It is preferable that R １ is preferably an alkyl group having 1 to 2 carbon atoms, more preferably a methyl group. ２ is preferably an alkyl group having 2 to 4 carbon atoms, more preferably an alkyl group having 3 to 4 carbon atoms, still more preferably an alkyl group having 4 carbon atoms, and particularly preferably an isobutyl group. m and n are each independently an integer of 0 to 25. It is preferable that at least one of m and n is 1 or greater.

[0059] The structure of compound (1) enhances the affinity between the PVA and the surface of the active material, allowing compound (1) to be uniformly present in the PVA, thereby reducing the resistance. Furthermore, when the compound (1) is made into a slurry, the active material can be dispersed together with the PVA, and foaming can be suppressed, resulting in a highly uniform electrode.

[0060] From this viewpoint, in formula (1), R １is a methyl group, and R ２ is an isobutyl group, and m and n are each an integer less than 8. Compound (1) may consist of only one type, or may be a mixture of two or more types. In compound (1) consisting of one type or two or more types, the average value of the sum of m and n (m+n) is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more. In addition, the average value of m+n is preferably 50 or less, more preferably 30 or less, and even more preferably 25 or less.

[0061] The mass ratio of PVA to compound (1) is preferably 60:40 to 99:1, more preferably 80:20 to 95:5, and even more preferably 85:15 to 90:10 in some cases. By being in this range, foaming of the slurry during slurry preparation can be suppressed, adhesion is improved, chipping during electrode cutting tends to be less likely to occur, and ionic conductivity is improved, resulting in lower resistance. Furthermore, when the binder for an electrical storage device contains a modified PVA (A1), the mass ratio of the modified PVA (A1) to compound (1) may be 60:40 to 99:1, preferably 80:20 to 95:5, and even more preferably 85:15 to 90:10 in some cases.

[0062] Examples of the method for adding compound (1) include adding it as a liquid, adding it in a state where it is mixed with other substances such as an active material, adding it as a solution of compound (1), adding it in a state where compound (1) is coexistent with the PVA or a solution thereof, etc. These addition methods are not particularly limited.

[0063] In the present invention, the binder may further contain a material that adjusts the viscosity of the binder in an aqueous solution or N-methyl-2-pyrrolidone (NMP) solution. 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 materials added is not particularly limited, but may be preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.02 parts by mass or more and 8 parts by mass or less, and even more preferably 0.05 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the total amount of PVA and compound (1). By adding such a viscosity-adjusting material in the above-mentioned range, the viscosity of the binder in a solution state can be further increased and can be more easily adjusted within a predetermined range. Furthermore, the smaller the particle size of the inorganic substance added, the more likely it is that the viscosity of the binder in an aqueous solution or NMP solution state will be increased.

[0064] In the present invention, the binder for an electrical storage device or the binder solution for an electrical storage device described below can further contain additives to the extent that the effects of the present invention 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 PVA and compound (1) or the total amount of the binder solution for an electrical storage device.

[0065] In one embodiment of the present invention, the binder for an electricity storage device may be a solid, specifically, a powder. In the case of a powder, it may be a mixture of powders of the respective components (PVA, compound (1), etc.), or a powder containing multiple components in a single particle. In the present invention, the binder for an electricity storage device may be obtained by dissolving the above-mentioned PVA and compound (1), as well as other components that may be included as needed, in a solvent to form a solution, and then removing the solvent. Here, water or NMP is preferred as the solvent. Furthermore, the solution may be used as is as the binder solution for an electricity storage device described below in the subsequent preparation of an electrode slurry for an electricity storage device. The components of the binder for an electricity storage device, PVA and compound (1), may be mixed in advance before preparing the electrode slurry for an electricity storage device. Furthermore, during the preparation of the electrode slurry for an electricity storage device, PVA and compound (1) may be added and mixed simultaneously or at different times, and the electrode slurry for an electricity storage device prepared in this manner contains the binder for an electricity storage device of the present invention. The binder of the present invention is contained in a hardened product of the electricity storage device electrode slurry in a mixed state with components such as the active material.

[0066] <Binder Solution for Electricity Storage Device> A binder solution for an electricity storage device (hereinafter also simply referred to as "binder solution") is obtained by dissolving the binder for an electricity storage device of the present invention in at least one solvent, and this is also one aspect of the present invention. The binder solution for an electricity storage device according to one embodiment of the present invention may contain the binder for an electricity storage device according to one embodiment of the present invention and a solvent. The solvent is not particularly limited, but water or NMP is preferred. When the solvent is water, this is preferable from the viewpoint of reducing the environmental load and simplifying the equipment. On the other hand, when the solvent is NMP, this is preferable because the active material in the slurry is less likely to deteriorate, particularly when used as a slurry for a positive electrode.

[0067] In addition to the binder of the present invention described above, 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 invention 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.

[0068] The binder solution is obtained by mixing the binder of the present invention, a solvent such as water or NMP, 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 appropriately adjusted 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, and even more preferably 99% by mass or more, relative to the total mass (100% by mass) of the binder used in the binder solution. 100% by mass, i.e., substantially all of the binder is dissolved, is particularly preferred.

[0069] In the present invention, the content of the binder in the binder solution may be 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 content of the binder 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 content of the binder is 30% by mass or less, rapid aggregation of the active material when forming an electrode can be more effectively suppressed. Furthermore, as a preferred embodiment, the total content of PVA and compound (1) in the binder solution may be within the above range, based on the total amount of the binder solution.

[0070] <Electricity Storage Device Electrode Slurry> The electricity storage device electrode slurry of the present invention contains the electricity storage device binder solution of the present invention and an active material.

[0071] The power storage device electrode slurry of the present invention 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. In a preferred embodiment, when the binder solution of the present invention contains water (when the solvent is water), it contains a negative electrode active material and is used as a negative electrode slurry. In a preferred embodiment, when the binder solution of the present invention contains NMP (when the solvent is NMP), it contains a positive electrode active material and is used as a positive electrode slurry.

[0072] 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 carbon 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; silicon (Si) and silicon compounds (SiO ｘ ), composite materials of silicon-based materials and carbon materials (Si / C or SiO ｘ / C), 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 carbon materials. Among these, carbon materials (such as graphite), silicon-based materials, and composite materials of silicon-based materials and carbon materials are preferred from the viewpoints of economy and battery capacity. These negative electrode active materials can be used alone or in combination of two or more.

[0073] 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 , TiS３ , 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 , LiNi ｘ Co ｙ Mo ｚ O ２ , and LiFePO ４ , LiMn １－ｘ Fe ｘ P.O. ４ Examples of the positive electrode active material include lithium-containing composite metal oxides such as those mentioned above, as well as sulfur compounds such as elemental sulfur, organic sulfur compounds, and mixtures thereof. These positive electrode active materials can be used alone or in combination. The above-mentioned x, y, and z represent the composition ratio.

[0074] 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, vapor-grown carbon fiber, etc. Among these, acetylene black is preferred from the viewpoint of facilitating the achievement of a higher output for the resulting electricity storage device.

[0075] When the electrical storage device electrode slurry contains a conductive additive, the content of the conductive additive may be preferably 0.1 parts by mass or more and 15 parts by mass or less, and more preferably 0.5 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 battery to which the slurry is applied can be further suppressed, and a more excellent conductive additive effect can be obtained.

[0076] The content of the binder in the electricity 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 battery to which it is applied. Furthermore, a content of 20 parts by mass or less is more likely to improve the discharge capacity. From this viewpoint, the content range may more preferably be 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. Furthermore, as a preferred embodiment, the total content of PVA and compound (1) in the electricity storage device electrode slurry may be within the above-mentioned range relative to 100 parts by mass of the active material.

[0077] 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 about 0.1% by mass or more and 10% by mass or less based on the total amount of the slurry.

[0078] In the electrical storage device electrode slurry, the PVA content relative to all polymer components is preferably 20% by mass or more, and more preferably 40% by mass or more. In such a case, the PVA function as a binder is more fully exhibited. The PVA content relative to all polymer components may be 100% by mass or less, 80% by mass or less, or 60% by mass or less.

[0079] In the electricity storage device electrode slurry, the content of the water-soluble polymer (e.g., PVA, CMC, etc.) relative to all polymer components is preferably 50% by mass or more, and more preferably 70% by mass or more. In this embodiment, it is preferable to contain water as a solvent. In such a case, the adhesion of the active material to the current collector is further improved. The content of the water-soluble polymer relative to all polymer components may be 100% by mass or less. In this embodiment, the electricity storage device electrode slurry may be a negative electrode slurry.

[0080] 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.

[0081] <Electricity storage device electrode> The electricity storage device electrode of the present invention includes a cured product of the above-described electricity storage device electrode slurry and a current collector. The cured product of the electricity storage device electrode slurry is a cured product obtained by removing the solvent in the electricity storage device electrode slurry by drying or the like. In other words, the cured product in this specification is not limited to one that has been cured by a chemical reaction such as a crosslinking reaction, but may be one from which the solvent has been removed by drying or the like. In other words, the cured product may be a dried product or a solid product.

[0082] The power storage device electrode of the present invention may be either a positive electrode or a negative electrode. The electrode of the present invention has excellent adhesion of the active material to the current collector. Therefore, the peel strength of the electrode (peel strength between the current collector and the cured body) before immersion in the electrolyte is preferably 200 N / m or more, more preferably 300 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 other elements and short circuits 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.

[0083] The electricity storage device electrode of the present invention can be obtained, for example, by applying the electricity storage device electrode slurry of the present invention to a current collector and removing the solvent by drying, etc. Alternatively, the electrode may be subjected to a rolling treatment after drying.

[0084] 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.

[0085] The method for applying the slurry to the current collector is not particularly limited, but 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 product derived from the slurry composition.

[0086] Examples of a method for rolling an electrode for a power storage device include die pressing, roll pressing, etc. The pressing pressure is preferably 1 MPa or more and 40 MPa or less, from the viewpoint of making it easier to increase the battery capacity.

[0087] In the electricity storage device electrode, the current collector may be a plate-shaped member. 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. In the electricity storage device electrode, the hardened product of the electricity storage device electrode slurry may be a layer laminated on the current collector directly or via another layer. The thickness of the hardened product of the electricity storage device electrode slurry may be preferably 10 μm or more and 400 μm, more preferably 20 μm or more and 300 μm. In the present invention, the thickness of the electricity storage device electrode is preferably 20 μm or more and 200 μm.

[0088] <Electricity Storage Device> The electricity storage device of the present invention 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] In the electricity storage device of the present invention, when the above-mentioned electricity storage device electrode is used as either the positive electrode or the negative electrode, a known or conventional electrode can be used for the electrode that does not use the electricity storage device electrode (i.e., the electrode that does not contain the above-mentioned binder for an electricity storage device).

[0093] In one preferred embodiment, the electricity storage device includes the above-described electricity storage device electrode as a negative electrode and a known or commonly used electrode as a positive electrode. That is, in one preferred embodiment of the present invention, 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.

[0094] Alternatively, in another preferred embodiment, an electricity storage device includes the electricity storage device electrode of the present invention as a positive electrode and a known or commonly used electrode as a negative electrode. That is, in one preferred embodiment, the electricity storage device includes a positive electrode containing the aforementioned electricity storage device binder and a negative electrode not containing the aforementioned electricity storage device binder. 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 of the present invention 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 PVA contained in the binder enable the peel strength of the positive electrode to be increased.

[0095] In addition, both the positive electrode and the negative electrode may be the electricity storage device electrodes of the present invention. That is, in one preferred embodiment of the present invention, 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.

[0096] The method for producing the electricity storage device is not particularly limited, but for example, when the electricity storage device is a battery, it can be produced 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 coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0097] The power storage device of the present invention is useful for various 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.

[0098] 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.

[0099] The physical properties of each PVA used in each of the examples and comparative examples described below, the evaluation of a binder aqueous solution and an NMP solution containing each PVA, the evaluation of electrode application, and the evaluation of battery application were measured according to the following methods.

[0100] [Viscosity-average degree of polymerization of PVA] The viscosity-average degree of polymerization of PVA was measured in accordance with JIS K 6726 (1994). Specifically, when the degree of saponification of PVA was less than 99.5 mol%, it was saponified until the degree of saponification reached 99.5 mol% or more. The viscosity-average degree of polymerization (P) of the obtained PVA 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）

[0101] [Degree of Saponification of PVA] The degree of saponification of PVA was determined by the method described in JIS K 6726 (1994).

[0102] [Modification Amount (X)] The content (X) of the structural unit derived from the ethylenically unsaturated dicarboxylic acid monomer in the modified PVA (modification amount (X)) is １ The values ​​were calculated from the spectrum of the modified species by H-NMR spectrum analysis.

[0103] [Content (Y) of structural unit represented by formula (2)] The content (Y) of the structural unit represented by formula (2) (modification amount (Y)) in the modified PVA was measured using dimethyl sulfoxide as a solvent. １ The amount of modification (Y) was calculated from the spectrum detected at 6.8 to 7.2 ppm in H-NMR spectrum analysis. The ratio (Y) / (X) was calculated from the ratio of the amount of modification (Y) to the amount of modification (X).

[0104] [Amount of Insoluble Components (Water-Insoluble Content) When a 5% by Mass Aqueous Solution at 90°C Was Prepared] 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 PVA powder was weighed and gradually added to the flask. After the entire amount (15 g) of PVA powder was added, the temperature of the water bath was immediately raised to 90°C over approximately 30 minutes to dissolve the PVA powder, thereby obtaining a PVA solution. After the water bath temperature reached 90°C, dissolution was continued for an additional 60 minutes while stirring at 300 rpm. The PVA solution was then used to filter out remaining 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 PVA used to prepare the 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.

[0105] [Particle Size Distribution] The particle size distribution of the PVA powder was measured by the dry sieving method described in JIS Z 8815 (1994). The PVA powder was passed through a sieve (filter) with a mesh size of 1.00 mm, and the mass of the PVA powder that passed through the sieve was measured. The proportion (mass%) of PVA particles that passed through the sieve was calculated from the mass of the PVA powder before passing through the sieve. Similarly, separately from the 1.00 mm mesh sieve, the PVA powder was passed through a sieve (filter) with a mesh size of 500 μm, and the mass of the PVA powder that passed through the sieve was measured. The proportion (mass%) of PVA particles that passed through the sieve was calculated from the mass of the PVA powder before passing through the sieve. The mesh size conforms to the nominal mesh size W of JIS Z 8801-1 (2006).

[0106] <Evaluation of Appearance of Coating Film (Foaming Suppression)> Immediately after the electricity storage device electrode slurry was applied to the current collector, the appearance of the electrode was visually evaluated. In a randomly selected 5 cm x 5 cm field of view, the number of coating defects (foaming marks, striations) with a diameter of 0.5 mm or more was counted, and this was used as an index of foaming suppression and evaluated according to the following criteria: A: 0 to 1 B: 2 to 4 C: 5 or more

[0107] <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.).

[0108] 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.

[0109] <Evaluation of 1C 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 performed 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 1.0 C (5.0 to 6.0 mA) was charged to 0 V relative to the lithium potential. For discharging, a constant current of 0.2 C (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 1C charge capacity retention rate (%) was calculated by (specific charge capacity at 1.0 C (mAh / g)) / (specific charge capacity at 0.2 C (mAh / g))×100.

[0110] - 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 nitrogen bubbling was performed. Monomethyl maleate was selected as the modified species (ethylenically unsaturated dicarboxylic acid monomer), and a methanol solution of monomethyl maleate (concentration: 2%) was purged with nitrogen by bubbling 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 monomer 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 while occasionally adding methanol, yielding 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) prepared by further adding methanol to this methanol solution was added to 14.8 parts by mass of a 10% methanol solution of sodium hydroxide, 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 in a volume ratio of 20:80 was added to the white solid, which was then left to stand at room temperature for 3 hours and washed. This washing procedure was repeated three times, and the resulting white solid was dewatered by centrifugation. The resulting white solid was then dried by heating at 95°C for 4 hours in a dryer to obtain a modified PVA powder (PVA-1). Various production materials for PVA-1 and their physical properties are summarized in Tables 1 and 2.

[0111] [Production Examples 2 to 9] (PVA-2 to PVA-9) Various modified PVAs (PVA-2 to PVA-9) 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 (ethylenically unsaturated dicarboxylic acid monomer) used during polymerization and polymerization rate, the saponification conditions, such as the molar ratio of sodium hydroxide, and the drying conditions, were changed as shown in Table 1. The physical properties of each modified PVA are summarized in Table 2.

[0112] Compound (1) The following acetylene glycol derivatives AG1 to AG4 were used as compound (1): AG1: 3,6-dimethyl-4-octyne-3,6-diol (in formula (1), R １ is a methyl group, and R ２ is an ethyl group, m=0, and n=0) AG2: 2,4,7,9-tetramethyl-5-decyne-4,7-diol (in formula (1), R １ is a methyl group, and R ２ is an isobutyl group, m=0, and n=0) AG3: an ethoxylated product of AG2 (in formula (1), R １ is a methyl group, and R ２ is an isobutyl group, and the average value of m+n is 7) AG4: an ethoxylated product of AG2 (in formula (1), R １ is a methyl group, and R ２ is an isobutyl group, and the average value of m+n is 20.

[0113]

[0114]

[0115] Example 1 Hereinafter, an example will be shown in which an electricity storage device was produced using the PVA-1 produced above.

[0116] Preparation of Power Storage Device Electrode Slurry (Negative Electrode Slurry) PVA-1 and water were mixed and heated at 80°C for 1 hour to obtain a solution with a solid content of about 10% by mass. １ is a methyl group, and R ２is an isobutyl group, and the average value of m + n is 7 compound (AG3), artificial graphite as a negative electrode active material (FSN-1, manufactured by Shanghai Shanshan Co., Ltd.), 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-310, manufactured by Thinky Corporation), and a negative electrode slurry containing a binder for an electricity storage device was prepared. At the time of charging, 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, the total amount of vinyl alcohol polymer and compound (1) (i.e., PVA-1 and AG3) was 1.50 parts by mass, and CMC was 1.5 parts by mass. That is, the composition ratio of the negative electrode active material, conductive additive, PVA-1, AG3, and thickener in the negative electrode slurry was, in terms of solid content, negative electrode active material:conductive additive:PVA-1:AG3:thickener=96:1:1.35:0.15:1.5 (mass ratio).

[0117] Preparation of an Electricity Storage Device Electrode (Lithium-Ion Secondary Battery Negative Electrode) The negative electrode slurry obtained as described above was applied to a copper foil (CST8G, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) current collector using an applicator, and the appearance of the coating film was evaluated. After primary drying at 80°C for 30 minutes in a hot air dryer, 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 120°C for 3 hours to prepare a lithium-ion secondary battery negative electrode (coin battery negative electrode). The peel strength of the prepared lithium-ion secondary battery negative electrode was measured using the method described above. The results are shown in Table 3.

[0118] 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 positive electrode (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 A lithium-ion secondary battery (2032 type) was fabricated using a lithium-ion secondary battery (EC / EMC = 3 / 7 vol ratio, VC = 2% by mass) (manufactured by Toyama Pharmaceutical Co., Ltd.). The resulting 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 1.0 C charge-discharge using the methods described above. The results are shown in Table 3.

[0119] [Examples 2 to 9] Except for using PVA-2 to PVA-9 instead of PVA-1, the preparation of an electrode slurry (slurry for a negative electrode), the production of a negative electrode for a lithium ion secondary battery, 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 shown in Table 3.

[0120] [Example 10] In place of AG3, R １ is a methyl group, and R ２ Except for using a compound (AG1) in which m is an ethyl group, m = 0, and n = 0, i.e., 3,6-dimethyl-4-octyne-3,6-diol, an electricity storage device electrode slurry (slurry for negative electrode) 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 1, and the same measurements and evaluations were carried out. The results are shown in Table 3.

[0121] Example 11: In place of AG3, R １ is a methyl group, and R ２ Except for using a compound (AG2) in which m=0, n=0, and n=1, i.e., 2,4,7,9-tetramethyl-5-decyne-4,7-diol, in which n=0 is an isobutyl group, an electricity storage device electrode slurry (slurry for negative electrode), a lithium ion secondary battery negative electrode, 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 shown in Table 3.

[0122] Example 12: In place of AG3, R １ is a methyl group, and R ２An electricity storage device electrode slurry (slurry for negative electrode), a lithium ion secondary battery negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that a compound (AG4) was used in which m was an isobutyl group and the average value of m+n was 20. The same measurements and evaluations were carried out. The results are shown in Table 3.

[0123] Except for not using AG3, the preparation of an electrode slurry (slurry for a negative electrode), the production of a negative electrode for a lithium ion secondary battery, 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 shown in Table 3.

[0124]

[0125] As shown in Table 3 above, the electrodes for electricity storage devices and electricity storage devices of the examples were excellent in peel strength, and also in initial charge / discharge efficiency, 1C charge capacity retention rate, DC resistance, and foaming suppression.

Claims

1. A binder for an electricity storage device, comprising a vinyl alcohol-based polymer and a compound represented by the following formula (1): 【Chemistry 1】 (In formula (1), R １ and R ２ are each independently an alkyl group having 1 to 4 carbon atoms; m and n are each independently an integer of 0 to 25.

2. 2. The binder for an electrical storage device according to claim 1, wherein the vinyl alcohol-based polymer contains a structural unit derived from an ethylenically unsaturated dicarboxylic acid-based monomer, the content of which is 0.01 mol % or more and 10 mol % or less based on all structural units constituting the vinyl alcohol-based polymer, and the degree of saponification of the vinyl alcohol-based polymer is 60.0 mol % or more and 99.9 mol % or less.

3. 3. The binder for an electrical storage device according to claim 2, wherein the ethylenically unsaturated dicarboxylic acid monomer comprises at least one selected from the group consisting of maleic acid, a maleic acid monoalkyl ester, a maleic acid dialkyl ester, maleic anhydride, a fumaric acid monoalkyl ester, and a fumaric acid dialkyl ester.

4. R of the compound １ is a methyl group, R ２ The binder for an electrical storage device according to claim 1 , wherein: is an isobutyl group; and m and n are each less than 8.

5. A binder solution for an electricity storage device, comprising the binder for an electricity storage device according to any one of claims 1 to 4 and a solvent.

6. An electrode slurry for an electricity storage device, comprising the binder solution for an electricity storage device according to claim 5 and an active material.

7. The electricity storage device electrode slurry according to claim 6 , wherein a 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.

8. An electricity storage device electrode comprising a hardened body of the electricity storage device electrode slurry according to claim 6 and a current collector.

9. An electricity storage device comprising the electricity storage device electrode according to claim 8 .

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