Resin composition for power storage device, slurry for power storage device electrode, power storage device electrode, and power storage device

Abstract

A resin composition for a power storage device, comprising a polymer and a liquid medium, wherein the polymer contains 1-90 mass% of a structural unit derived from an unsaturated carboxylic acid, 1-90 mass% of a structural unit derived from an unsaturated carboxylic acid ester having a number average molecular weight of less than 1,300, and 1-30 mass% of a structural unit derived from an unsaturated carboxylic acid ester having a number average molecular weight of 1,300 to 36,000.

Description

Resin composition for energy storage devices, slurry for energy storage device electrodes, energy storage device electrodes, and energy storage devices

[0001] The present invention relates to a resin composition for energy storage devices, a slurry for electrodes of energy storage devices, electrodes for energy storage devices, and energy storage devices.

[0002] In recent years, there has been a growing demand for energy storage devices with high voltage and high energy density to power electronic devices. Lithium-ion batteries and lithium-ion capacitors are among the promising energy storage devices.

[0003] Electrodes used in energy storage devices are manufactured by applying and drying a resin composition for energy storage devices (slurry for energy storage device electrodes) containing an active material and a polymer that functions as a binder onto the surface of a current collector. The properties required of the polymer used as a binder include, for example, (i) the bonding strength between the active materials, (ii) the adhesion strength of the active material to the current collector, (iii) abrasion resistance in the process of winding the electrodes, and (iv) powder shedding resistance, which prevents fine powder of the active material from falling off the applied and dried composition coating (hereinafter also referred to as the "active material layer") even after cutting. The polymer used as a binder exhibits good adhesion of the active material layer to the current collector, and by reducing the internal resistance of the battery caused by the polymer, good charge and discharge characteristics can be given to the energy storage device.

[0004] Furthermore, empirically, it has become clear that the performance of (i) the bonding strength between active materials, (ii) the adhesion strength of the active material to the current collector, and (iv) the resistance to powder shedding are roughly proportional. Therefore, in this specification, these may be collectively referred to as "adhesion."

[0005] Recently, research has been conducted on using active materials with high reactivity to water in order to fabricate electrochemical devices with excellent capacity and charge-discharge cycle characteristics. Furthermore, when manufacturing slurries for energy storage device electrodes, which include active materials and binders, the use of water-based binders is being considered with the aim of reducing costs, safety, and environmental impact.

[0006] Against this backdrop, resin compositions containing various binder materials have been proposed (see, for example, Patent Documents 1 to 3).

[0007] However, no resin composition for energy storage devices has yet been developed that can form an active material layer with improved water solubility of the polymer and improved adhesion to the current collector. There has been a strong demand for the development of such a resin composition for energy storage devices.

[0008] Japanese Patent Publication No. 2023-49607, International Publication No. 2020 / 095466, Japanese Patent Publication No. 2019-194944

[0009] In view of the above problems, the present invention aims to provide a resin composition for energy storage devices that can form an active material layer with improved water solubility of the polymer and improved adhesion to a current collector, a slurry for energy storage device electrodes using the resin composition for energy storage devices, an energy storage device electrode using the slurry for the energy storage device electrodes, and an energy storage device using the energy storage device electrode.

[0010] The present inventors conducted diligent studies to solve the above problems and have found that by including (i) a polymer (A) containing 1 to 90% by mass of structural units (a1) derived from a predetermined unsaturated carboxylic acid, 1 to 90% by mass of structural units (a2) derived from an unsaturated carboxylic acid ester having a number average molecular weight of less than 1300, and 1 to 30% by mass of structural units (a3) ​​derived from an unsaturated carboxylic acid ester having a number average molecular weight of 1300 to 36000, and (ii) a liquid medium (B), it is possible to form an active material layer in which the water solubility of polymer (A) is improved and the adhesion to the current collector is improved, thus completing the present invention. Furthermore, the mechanism of action of the present invention is presumed to be that the polymer (A) contains 1 to 30% by mass of structural units derived from unsaturated carboxylic acid esters with a number average molecular weight of 1,300 to 36,000, and that these structural units interact with the active material, thereby improving the adhesion of the active material layer to the current collector, and thus protecting against electrode corrosion even if hydroxide ions are generated. In other words, the present invention is as follows: [1] A resin composition for energy storage devices comprising a polymer and a liquid medium, wherein the polymer contains 1 to 90% by mass of structural units derived from an unsaturated carboxylic acid, 1 to 90% by mass of structural units derived from an unsaturated carboxylic acid ester having a number average molecular weight of less than 1,300, and 1 to 30% by mass of structural units derived from an unsaturated carboxylic acid ester having a number average molecular weight of 1,300 to 36,000. [2] The resin composition for energy storage devices according to [1], wherein the unsaturated carboxylic acid ester having a number average molecular weight of 1300 to 36000 is a monofunctional monomer having one (meth)acryloyloxy group in one molecule. [3] The resin composition for energy storage devices according to [2], wherein the number of urethane bonds in one molecule of the monofunctional monomer is one or more. [4] The resin composition for energy storage devices according to [2] or [3], wherein the monofunctional monomer contains a curable component obtained by urethane reaction between a polyoxyalkylene monool represented by the following formula (1a) and a compound represented by the following formula (1b). (In equation (1a), R １２ R is an alkylene group having 2 to 4 carbon atoms. １３R is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms, and b is an integer from 20 to 600. In formula (1b), R １１ (where a is a hydrogen atom or a methyl group, and a is an integer from 1 to 4.) [5] A resin composition for energy storage devices according to any one of [1] to [4] above, wherein the total amount of structural units derived from the unsaturated carboxylic acid and structural units derived from the unsaturated carboxylic acid ester having a number average molecular weight of less than 1300 is 50% by mass or more in 100% by mass of the total amount of structural units of the polymer. [6] A resin composition for energy storage devices according to any one of [1] to [5] above, wherein the solubility of the polymer in water at 25°C and 1 atm is 1 g or more per 100 g of water. [7] A resin composition for energy storage devices according to any one of [1] to [6] above, wherein the liquid medium is water. [8] A slurry for an electrode of an energy storage device containing the resin composition for an energy storage device according to any one of [1] to [7] above and an active material. [9] The slurry for an electrode of an energy storage device according to [8], wherein the active material contains at least one selected from the group consisting of olivine-type lithium-containing phosphate compounds, lithium cobaltate, lithium nickelate, lithium manganate, and ternary nickel-cobalt-manganate lithium.

[10] The slurry for an electrode of an energy storage device according to [8], wherein the active material contains a silicon compound, and the silicon compound is a compound having lithium and oxygen.

[11] An electrode of an energy storage device comprising a current collector and an active material layer formed by coating and drying the slurry for an electrode of an energy storage device according to any one of [8] to

[10] on the surface of the current collector.

[12] An energy storage device comprising the electrode of an energy storage device according to

[11] .

[0011] The present invention provides a resin composition for energy storage devices capable of forming an active material layer with improved water solubility of the polymer and improved adhesion to a current collector, a slurry for energy storage device electrodes using the resin composition, an energy storage device electrode using the slurry, and an energy storage device using the electrode.

[0012] Next, embodiments of the present invention will be described. The following embodiments are illustrative for explaining the present invention and are not intended to limit the present invention to these embodiments only. The present invention can be implemented in various forms without departing from its spirit.

[0013] The definitions and meanings of terms and notations used in this specification are given below. The content percentage (mass%) of each structural unit constituting polymer (A), when the total amount of structural units contained in polymer (A) is taken as 100% by mass, is calculated in the examples of this specification using the mixing ratio. If the mixing ratio is unknown, the resin composition, etc., is subjected to NMR analysis. １ H-NMR spectrum and / or １３It can be calculated from the integral ratio of the C-NMR spectrum. "(meth)acryloyloxy group" is a general term for acryloyloxy groups and methacryloyloxy groups. "(meth)acrylate" is a general term for acrylates and methacrylates. Similarly, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid. "Number of functional groups" means the number of (meth)acryloyloxy groups in one molecule unless otherwise specified. "Average number of functional groups" means the average number of (meth)acryloyloxy groups in one molecule, per formula weight obtained based on the chemical formula or with the number-average molecular weight (Mn) as one unit, unless otherwise specified. "Curing component" means a compound having a (meth)acryloyloxy group. In the reaction between an isocyanate group-containing compound and a hydroxyl group-containing compound, the "index" is the value obtained by dividing the number of moles of isocyanate groups in the isocyanate group-containing compound by the number of moles of hydroxyl groups in the hydroxyl group-containing compound and multiplying the result by 100. The hydroxyl value of hydroxyl-containing compounds is obtained by measurement in accordance with JIS K1557 (2007 edition). The molecular weight converted to hydroxyl value is calculated by applying the hydroxyl value to the formula "56100 / (hydroxyl value) × (number of active hydrogen atoms of the initiator)". The number average molecular weight (Mn) is the polystyrene-converted molecular weight obtained by measurement using gel permeation chromatography (GPC) with a calibration curve created using standard polystyrene samples with known molecular weights. If a peak of unreacted low molecular weight components (monomers, etc.) appears during GPC measurement, this peak is excluded when determining the number average molecular weight (Mn). "pH" is the value measured in accordance with JIS Z8802:2011 at 25°C using a pH meter with a glass electrode calibrated with neutral phosphate standard solution and borate standard solution as pH standard solutions. There are no particular restrictions on the pH meter used; for example, the "HM-7J" manufactured by Toa DKK Corporation and the "D-51" manufactured by Horiba, Ltd. are examples. "Solid content" refers to the components excluding the solvent. "Liquid medium" refers to a medium with a viscosity of 1000 mPa·s or less at 25°C. "Average number of hydroxyl groups" can be calculated from the measured values ​​of the hydroxyl value and Mn of each polymer using the formula: hydroxyl value × Mn / 56100.

[0014] [Resin Composition for Energy Storage Device] The resin composition for an energy storage device of the present invention (hereinafter sometimes simply referred to as "resin composition") contains a polymer (A) and a liquid medium (B), and may further contain other additives as required. Hereinafter, each component contained in the resin composition for an energy storage device of the present invention will be described in detail.

[0015] <Polymer (A)> The polymer (A) in the resin composition for an energy storage device of the present invention contains 1 to 90% by mass of a structural unit (a1) derived from an unsaturated carboxylic acid, 1 to 90% by mass of a structural unit (a2) derived from an unsaturated carboxylic acid ester having a number average molecular weight (Mn) of less than 1300, and 1 to 30% by mass of a structural unit (a3) derived from an unsaturated carboxylic acid ester having a number average molecular weight (Mn) of 1300 to 36000. In addition to the structural units (a1) to (a3), the polymer (A) may contain a structural unit derived from another monomer copolymerizable therewith.

[0016] The polymer (A) in the resin composition for an energy storage device of the present invention may be in the form of a latex dispersed in the liquid medium (B) or may be in a state dissolved in the liquid medium (B), but it is preferably in a state dissolved in the liquid medium (B). When the polymer (A) is in a state dissolved in the liquid medium (B), the stability of the slurry for an energy storage device electrode (hereinafter also simply referred to as "slurry") prepared by mixing with the active material is good, and the coating property of the slurry on the current collector is good, which is preferable.

[0017] <<Structural units constituting polymer (A)>> (Structural unit (a1) derived from unsaturated carboxylic acid)When the total of the structural units contained in polymer (A) is 100% by mass, the content ratio of the structural unit (a1) derived from unsaturated carboxylic acid is not particularly limited as long as it is 1 to 90% by mass, but is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, and particularly preferably 1 to 6% by mass. When polymer (A) contains the structural unit (a1) within the above range, the dispersibility of the active material becomes good, and it becomes possible to produce a uniform active material layer. As a result, the structural defects of the electrode plate disappear, and good charge-discharge characteristics are exhibited. Further, when polymer (A) contains the structural unit (a1) within the above range, when an active material containing a silicon material is used, the bonding strength between the active materials can be increased, so that an active material layer excellent in flexibility and adhesion to the current collector can be obtained. [[ID=!]]

[0018] The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid; dicarboxylic acids (including anhydrides); and the like. These may be used alone or in combination of two or more. As the unsaturated carboxylic acid, acrylic acid is preferred.

[0019] (Structural unit (a2) derived from unsaturated carboxylic acid ester having a number average molecular weight (Mn) of less than 1300) When the total of the structural units contained in polymer (A) is 100% by mass, the content ratio of the structural unit (a2) derived from unsaturated carboxylic acid ester having a number average molecular weight (Mn) of less than 1300 is not particularly limited as long as it is 1 to 90% by mass, but is preferably 60 to 89% by mass, more preferably 70 to 88% by mass, and particularly preferably 75 to 87% by mass. When polymer (A) contains the structural unit (a2) within the above range, the dispersibility of the active material becomes good, and it becomes possible to produce a uniform active material layer. As a result, the structural defects of the electrode plate disappear, and good charge-discharge characteristics are exhibited.

[0020] There are no particular restrictions on unsaturated carboxylic acid esters having a number average molecular weight (Mn) of less than 1300. Examples include hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate, and other (meth)acrylate esters having hydroxyl groups; and (meth)acrylate esters without hydroxyl groups such as butyl acrylate. These may be used individually or in combination of two or more. Among these, (meth)acrylate esters having hydroxyl groups are preferred, and 2-hydroxyethyl (meth)acrylate is more preferred.

[0021] When the total amount of structural units contained in polymer (A) is taken as 100% by mass, the total amount of structural units (a1) derived from unsaturated carboxylic acid and structural units (a2) derived from unsaturated carboxylic acid esters with a number average molecular weight of less than 1300 is not particularly limited, but is preferably 50% by mass or more, more preferably 52% by mass or more, and particularly preferably 55% by mass or more. When the total amount of structural units (a1) and structural units (a2) is within the above range, the dispersibility of the active material is improved, the flexibility of the active material layer and the adhesion of the active material layer to the current collector are improved, resulting in good repeated charge-discharge characteristics and charge-discharge durability characteristics.

[0022] (Structural units (a3) ​​derived from unsaturated carboxylic acid esters with a number-average molecular weight (Mn) of 1300 to 36000) The content of structural units (a3) ​​derived from unsaturated carboxylic acid esters with a number-average molecular weight (Mn) of 1300 to 36000, when the total amount of structural units contained in polymer (A) is 100% by mass, is not particularly limited as long as it is between 1 and 30% by mass, but is preferably 2 to 28% by mass, more preferably 3 to 26% by mass, and particularly preferably 4 to 24% by mass. By polymer (A) containing structural units (a3) ​​within the above range, the flexibility of the active material layer can be improved, the hysteresis loss of the active material layer can be reduced to improve shrinkage reproducibility, and the glass transition temperature of the resin composition can be prevented from rising.

[0023] As long as the unsaturated carboxylic acid ester has a number-average molecular weight (Mn) of 1300 to 36000, there are no particular restrictions, and suitable examples include monofunctional monomers, which will be described later. These may be used individually or in combination of two or more.

[0024] The number-average molecular weight (Mn) of the unsaturated carboxylic acid ester is not particularly limited as long as it is between 1,300 and 36,000, but from the viewpoint of imparting flexibility to the active material layer and water solubility, it is preferably between 1,800 and 32,000, more preferably between 2,300 and 28,000, even more preferably between 2,800 and 24,000, and particularly preferably between 3,000 and 24,000.

[0025] ((Monofunctional Monomers)) Monofunctional monomers have one (meth)acryloyloxy group in one molecule, and preferably further have a polyoxyalkylene chain and a urethane bond derived from an isocyanate group-containing compound. When the resin composition for energy storage devices of the present invention is UV curable, the (meth)acryloyloxy group in the monofunctional monomer is preferably an acryloyloxy group.

[0026] Monofunctional monomers suppress shrinkage during curing, easily reduce the elastic modulus after curing, and easily suppress the occurrence of whitening when repeatedly bent. In addition, because they have one (meth)acryloyloxy group, they have better stability after curing and suppress the occurrence of bleed-out.

[0027] The monofunctional monomer preferably has a polyoxyalkylene chain. Examples of polyoxyalkylene chains include polymerization chains having ethylene oxide units, polymerization chains having propylene oxide units, polymerization chains having ethylene oxide units and propylene oxide units, polymerization chains having butylene oxide units, polymerization chains having tetramethylene oxide units, polymerization chains having propylene oxide units and butylene oxide units, polymerization chains consisting of ethylene oxide units, polymerization chains consisting of propylene oxide units, polymerization chains consisting of butylene oxide units, polymerization chains consisting of tetramethylene oxide units, polymerization chains consisting of ethylene oxide units and propylene oxide units, and polymerization chains consisting of propylene oxide units. Polymerization chains having propylene oxide units, polymerization chains having ethylene oxide units and propylene oxide units, and polymerization chains consisting of propylene oxide units are preferred, and polymerization chains consisting of propylene oxide units are particularly preferred. When the monofunctional monomer has a polyoxyalkylene chain, it is preferable that there are 20 to 600 alkylene oxide units in one molecule, and more preferably 50 to 500 units.

[0028] The number of urethane bonds in one molecule of monofunctional monomer is preferably one or two, more preferably one, as this suppresses shrinkage during curing and makes it easier to reduce the elastic modulus after curing. There are no particular restrictions on the concentration (proportion) of urethane bonds in one molecule of monofunctional monomer, but from the viewpoint of obtaining better tackiness, it is preferably 0.35 to 1.9% by mass, more preferably 0.4 to 1.3% by mass, and particularly preferably 0.5 to 1.2% by mass. The concentration of urethane bonds can be calculated by assuming that the total amount of isocyanate groups in the isocyanate group-containing compound used in the production of the monofunctional monomer forms urethane bonds, using the following formula: (Number of moles of isocyanate groups in the isocyanate group-containing compound × Molecular weight of urethane bonds (59) / Mass of monofunctional monomer) × 100 (%)

[0029] The number-average molecular weight (Mn) of the monofunctional monomer is not particularly limited as long as it is between 1,300 and 36,000, but is preferably between 1,800 and 32,000, more preferably between 2,300 and 28,000, even more preferably between 2,800 and 24,000, and particularly preferably between 3,000 and 24,000. When the number-average molecular weight (Mn) of the monofunctional monomer is within the above range, it is easier to adjust the viscosity of the resin composition. Also, when the number-average molecular weight (Mn) of the monofunctional monomer is above the lower limit, the curing shrinkage rate of the resin composition tends to be low. When the resin composition contains two or more monofunctional monomers, it is preferable that the number-average molecular weight (Mn) of each monofunctional monomer is within the above range.

[0030] In the manufacturing process of monofunctional monomers, by-products containing polyoxyalkylene chains other than monofunctional monomers may be produced. Examples of by-products containing polyoxyalkylene chains include compounds having two (meth)acryloyloxy groups, compounds without (meth)acryloyloxy groups, and compounds without urethane bonds. There are no particular restrictions on the content of monofunctional monomers in the product, but from the viewpoint of fully exhibiting the function of monofunctional monomers, it is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and particularly preferably 90 to 100% by mass. When the product contains monofunctional monomers in the above content, the function of the monofunctional monomers is fully exhibited, and therefore the product can be considered a monofunctional monomer.

[0031] If the above product can be considered as a monofunctional monomer, the average number of functional groups obtained from the number-average molecular weight (Mn) and the number of functional groups of the product can be considered as the average number of functional groups of the monofunctional monomer. In this case, there are no particular restrictions on the average number of functional groups in the product, but it is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. Products with an average number of functional groups within the above range tend to fully exhibit the functions of the monofunctional monomer. The above average number of functional groups can be adjusted to this range by adjusting the amount of impurities contained in the raw materials for the production of the monofunctional monomer or by adjusting the index described later. Furthermore, in this specification, the average number of functional groups can be calculated using the average number of functional groups of the raw materials described later and the index.

[0032] Specific examples of monofunctional monomers include the reaction products (1), (2), and (3) shown below. These may be used individually or in combination of two or more. In particular, it is preferable that the resin composition contains one or more monofunctional monomers selected from the group consisting of reaction product (1) and reaction product (2). Among the monofunctional monomers, reaction product (1) is more preferable because it has a lower by-product content compared to other reaction products, and yields a resin composition with excellent flexibility and curing shrinkage rate.

[0033] There are no particular restrictions on the total content of reaction product (1) and reaction product (2) relative to the monofunctional monomer, but it is preferably 50% by mass or more, more preferably 80% by mass or more, and particularly preferably 100% by mass. When the total content of reaction product (1) and reaction product (2) is above the lower limit of the above range, a resin composition with excellent flexibility and curing shrinkage rate can be obtained. When the monofunctional monomer contains reaction product (1) and reaction product (2), the mass ratio of these (reaction product (1):reaction product (2)) is preferably 1:0.001 to 1:1.

[0034] Reaction product (1): Equimolar reaction product of polyoxyalkylene monool and a compound having an isocyanate group and a (meth)acryloyloxy group. Reaction product (2): Equimolar reaction product of polyoxyalkylene monool, diisocyanate, and a compound having a group that reacts with an isocyanate group and a (meth)acryloyloxy group. Reaction product (3): Equimolar reaction product of polyoxyalkylene polyol and a compound having an isocyanate group and a (meth)acryloyloxy group.

[0035] As the starting materials for reaction products (1) and (3), compounds having an isocyanate group and a (meth)acryloyloxy group, (meth)acrylates having one isocyanate group are preferred, and isocyanate alkyl (meth)acrylates are more preferred.

[0036] Examples of diisocyanates used as raw materials for reaction product (2) include non-yellowing modified aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and various modified forms of these diisocyanates (modified forms having two isocyanate groups). These may be used individually or in combination of two or more. Among these, aliphatic diisocyanates and alicyclic diisocyanates are preferred because they have excellent light resistance, weather resistance, and heat resistance, and can maintain transparency.

[0037] There are no particular restrictions on the non-yellowing aromatic diisocyanates, and examples include xylylene diisocyanate and tetramethylxylylene diisocyanate. These may be used individually or in combination of two or more. There are no particular restrictions on the aliphatic diisocyanates, and examples include 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate. These may be used individually or in combination of two or more. There are no particular restrictions on the alicyclic diisocyanates, and examples include isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate. These may be used individually or in combination of two or more. There are no particular restrictions on the compound having a group that reacts with the isocyanate group, which is the raw material for reaction product (2), and a (meth)acryloyloxy group, but (meth)acrylates having one hydroxyl group are preferred, hydroxyalkyl (meth)acrylates and hydroxycycloalkyl (meth)acrylates are more preferred, and hydroxyalkyl (meth)acrylates with 8 or fewer carbon atoms in the hydroxyalkyl group are particularly preferred.

[0038] There are no particular restrictions on the average number of hydroxyl groups per molecule of the polyoxyalkylene monool, which is the raw material for reaction products (1) and (2), but it is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and most preferably 0.9 to 1.1. There are no particular restrictions on the hydroxyl value of the polyoxyalkylene monool, but in order to obtain a monofunctional monomer with a urethane bond concentration in a predetermined range, it is preferably 1.6 to 18.1 mg KOH / g, more preferably 2.8 to 14 mg KOH / g, and most preferably 3.1 to 11.2 mg KOH / g.

[0039] Polyoxyalkylene monools are compounds obtained by ring-opening addition polymerization of an alkylene oxide to an initiator having an active hydrogen-containing group and having one or more active hydrogen atoms. They have initiator residues, a polyoxyalkylene chain, and hydroxyl groups corresponding to the number of active hydrogen atoms in the initiator.

[0040] There are no particular restrictions on the alkylene oxide; for example, alkylene oxides having 2 to 4 carbon atoms, such as propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide, are preferred. These may be used individually or in combination of two or more.

[0041] There are no particular restrictions on the active hydrogen-containing group of the initiator, and examples include hydroxyl groups, carboxyl groups, and amino groups having one hydrogen atom bonded to a nitrogen atom. These may be used individually or in combination of two or more. Among these, hydroxyl groups and carboxyl groups are preferred, and alcoholic hydroxyl groups are more preferred.

[0042] Examples of initiators with one active hydrogen include monohydric alcohols, monohydric phenols, monohydric carboxylic acids, and amine compounds having one hydrogen atom bonded to a nitrogen atom. These may be used individually or in combination of two or more. Among these, monohydric aliphatic alcohols and monohydric aliphatic carboxylic acids are preferred. There are no particular restrictions on the number of carbon atoms in monohydric aliphatic alcohols, but they are preferably 1 to 20, more preferably 1 to 14, and most preferably 2 to 8. There are no particular restrictions on the number of carbon atoms in monohydric carboxylic acids, but including the carbon atoms of the carboxyl group, they are preferably 2 to 20, more preferably 2 to 14, and most preferably 2 to 8. In addition, a polyoxyalkylene monool with a lower molecular weight than the target polyoxyalkylene monool may be used as an initiator.

[0043] The oxyalkylene groups in the polyoxyalkylene monool are preferably composed solely of oxypropylene groups or a combination of oxypropylene groups and other oxyalkylene groups. Among the oxyalkylene groups other than oxypropylene groups, oxyethylene groups are preferred. There are no particular restrictions on the ratio of oxypropylene groups to the total oxyalkylene groups in the polyoxyalkylene monool, but it is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and particularly preferably 80 to 100% by mass. If the initiator is a polyoxyalkylene monool with a lower molecular weight than the target polyoxyalkylene monool, the oxyalkylene groups in the initiator are considered to be the oxyalkylene groups in the obtained polyoxyalkylene monool.

[0044] Low hydroxyl value polyoxyalkylene monools can be produced by ring-opening addition polymerization of an alkylene oxide (preferably propylene oxide) having 3 or more carbon atoms as an initiator in the presence of a complex metal cyanide catalyst. Low hydroxyl value polyoxyalkylene monools having an oxyethylene group can also be produced by ring-opening addition polymerization of an alkylene oxide having 3 or more carbon atoms as an initiator using a high hydroxyl value (preferably 50 mg KOH / g or more) polyoxyalkylene monool having an oxyethylene group as an initiator in the presence of a complex metal cyanide catalyst. High hydroxyl value polyoxyalkylene monools can also be produced using an alkaline catalyst such as KOH.

[0045] In the production of polyoxyalkylene monools, the initiator and alkylene oxide introduced into the reaction system are usually those with low moisture content, obtained by removing water through methods such as degassing under reduced pressure. There are no particular restrictions on the moisture content of the initiator in the production of polyoxyalkylene monools, but the lower the better, preferably 500 ppm by mass or less, more preferably 400 ppm by mass or less, and particularly preferably 300 ppm by mass or less. When the moisture content is within the above range, the amount of polyoxyalkylenediol produced from water is suppressed, so the amount of by-products resulting from the polyoxyalkylenediol is ultimately suppressed, and it is easy to adjust the upper limit of the average number of hydroxyl groups in the resulting polyoxyalkylene monool to 1.2 or less. Furthermore, there are no particular restrictions on the moisture content of the polyoxyalkylene monools used as raw materials for reaction products (1) and (2), but the lower the better, preferably 300 ppm by mass or less, more preferably 250 ppm by mass or less, and particularly preferably 50 to 200 ppm by mass relative to the polyoxyalkylene monool. When the moisture content is within the above range, the formation of by-products, which are reaction products of moisture and isocyanate group-containing compounds, is reduced, improving the stability of reaction products (1) and (2). Furthermore, it is easier to suppress changes in the appearance of the curable composition containing reaction products (1) and (2) over time, and the elastic modulus of the cured product tends to be good.

[0046] Polyoxyalkylene diol is preferred as the polyoxyalkylene polyol used as the raw material for reaction product (3). There are no particular restrictions on the average number of hydroxyl groups in one molecule of the polyoxyalkylene polyol, but it is preferably 1.6 to 2.1, more preferably 1.7 to 2.0, and most preferably 1.8 to 1.96. In other words, polyoxyalkylene diol is preferred as the polyoxyalkylene polyol used as the raw material for reaction product (3). There are no particular restrictions on the content of oxypropylene groups relative to the total oxyalkylene groups in the polyoxyalkylene polyol, but it is preferably 80 to 100% by mass. There are no particular restrictions on the hydroxyl value of the polyoxyalkylene polyol, but from the viewpoint of obtaining a monofunctional monomer with a urethane bond concentration in a predetermined range, it is preferably 1.6 to 19 mg KOH / g, more preferably 2.2 to 16 mg KOH / g, and most preferably 2.8 to 14 mg KOH / g.

[0047] -Reaction Product (1)- Reaction product (1) is an equimolar reaction product of a polyoxyalkylene monool and a compound having an isocyanate group and a (meth)acryloyloxy group. There are no particular restrictions on the compound having an isocyanate group and a (meth)acryloyloxy group, but for example, isocyanate alkyl (meth)acrylates are preferred.

[0048] Since polyoxyalkylene monool and isocyanate alkyl (meth)acrylate each have one group capable of urethane formation in one molecule, it is easy to control the number of urethane bonds in one molecule of reaction product (1). A small number of urethane bonds in one molecule of reaction product (1) tends to result in low viscosity. Therefore, it is preferable that the monofunctional monomer in the resin composition contains reaction product (1) because it is easy to obtain a cured product with low viscosity and excellent flexibility. Furthermore, since both polyoxyalkylene monool and isocyanate alkyl (meth)acrylate are compounds that have one reactive group, they are less likely to produce by-products, and it is easy to obtain a highly pure reaction product (1) by removing unreacted material. If unreacted material remains, it is preferable from the viewpoint of the stability of the reaction product that the unreacted material is polyoxyalkylene monool. In order to obtain a reaction product with little unreacted material, it is preferable to react the two at an index of 90 to 100, and more preferably at an index of 100. There are no particular restrictions on the average number of functional groups of the reaction product (1), but it is preferably 0.9 to 1.1. A resin composition containing the reaction product (1) within the above range tends to reduce shrinkage during curing and tends to reduce the elastic modulus after curing.

[0049] -Reaction Product (2)- Reaction product (2) is an equimolar reaction product of a polyoxyalkylene monool, a diisocyanate, and a compound having a group that reacts with the isocyanate group and a (meth)acryloyloxy group. There are no particular restrictions on the diisocyanate, and suitable examples include aliphatic diisocyanates and alicyclic diisocyanates. There are no particular restrictions on the compound having a group that reacts with the isocyanate group and a (meth)acryloyloxy group, and suitable examples include hydroxyalkyl (meth)acrylates with hydroxyalkyl groups having 8 or fewer carbon atoms. Examples of reaction products (2) include (a) a reaction product obtained by reacting a polyoxyalkylene monool with diisocyanate at an index of 200, and then reacting the resulting reaction product (a reaction product having an isocyanate group) with hydroxyalkyl (meth)acrylate at an index of 100, and (b) a reaction product obtained by simultaneously reacting a polyoxyalkylene monool with an equimolar amount of hydroxyalkyl (meth)acrylate relative to the polyoxyalkylene monool and an amount of diisocyanate at an index of 100 relative to the sum of the polyoxyalkylene monool and the hydroxyalkyl (meth)acrylate. Among these, reaction product (a) is preferred because it produces fewer by-products. When producing reaction product (a), the amount of hydroxyalkyl (meth)acrylate used may be in excess, and the excess hydroxyalkyl (meth)acrylate can be included in the resin composition together with reaction product (a) as part of other photosensitive monomers described later. There are no particular restrictions on the average number of functional groups of the reaction product (2), but it is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and most preferably 0.9 to 1.1. A resin composition containing the reaction product (2) within the above range tends to reduce shrinkage during curing and tends to reduce the elastic modulus after curing.

[0050] -Reaction Product (3)- Reaction product (3) is an equimolar reaction product of a polyoxyalkylene polyol and a compound having an isocyanate group and a (meth)acryloyloxy group. There are no particular restrictions on the polyoxyalkylene polyol, for example, polyoxyalkylenediol is preferred. There are no particular restrictions on the compound having an isocyanate group and a (meth)acryloyloxy group, for example, isocyanate alkyl (meth)acrylate is preferred. Note that reaction product (3) is a reaction product having a hydroxyl group, and the number of hydroxyl groups is not limited to one. Therefore, as long as the compound having an isocyanate group and a (meth)acryloyloxy group is a compound having one isocyanate group and is an equimolar reaction product, the starting material polyoxyalkylene polyol may be a compound having two or more hydroxyl groups. There are no particular restrictions on the average number of functional groups of the reaction product (3), but it is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and most preferably 0.9 to 1.1. Reaction product (3) within the above range tends to reduce shrinkage during curing and tends to reduce the elastic modulus after curing.

[0051] Monofunctional monomers contribute to reducing shrinkage during curing and lowering the elastic modulus of the cured product. Furthermore, because they have a (meth)acryloyloxy group as a curable functional group, they exhibit excellent stability in the cured product and are less prone to bleed-out.

[0052] A specific example of a monofunctional monomer is the monomer (IB-1).

[0053] -Monomer (IB-1)- Monomer (IB-1) contains a curable component represented by the following formula (1) which has one curable functional group. The curable component represented by the following formula (1) is obtained by urethane reaction between a polyoxyalkylene monool (1a) represented by the following formula (1a) and a compound (1b) represented by the following formula (1b).

[0054]

[0055] In equations (1) and (1b), R １１is a hydrogen atom or a methyl group, preferably a hydrogen atom. In formulas (1) and (1a), R １２ is an alkylene group having 2 to 4 carbon atoms, and a plurality of R present in one molecule １２ may be the same as or different from each other. When two or more types of R １２ are present in one molecule, the chain of -OR １２ - may be a block or random. R １２ is preferably an ethylene group or a propylene group. In formulas (1) and (1a), R １３ is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms. The carboxylic acid residue is a monovalent group obtained by removing one hydrogen atom from a monocarboxylic acid having 1 to 20 carbon atoms including the carbon atom in the carboxy group (-COOH). As R １３ , in terms of ease of reaction, it is preferably an alkyl group, more preferably an alkyl group having 2 to 8 carbon atoms. In formulas (1) and (1b), a is an integer of 1 to 4, preferably an integer of 1 to 2. In formulas (1) and (1a), b is an integer of 20 to 600, preferably an integer of 35 to 500, more preferably an integer of 65 to 250.

[0056] In the production of the curable component represented by formula (1), the polyoxyalkylene monool (1a) represented by formula (1a) is produced as follows. The polyoxyalkylene monool (1a) represented by formula (1a) may be used in the form of a composition containing a diol as a by-product in addition to the polyoxyalkylene monool (1a). The resulting curable component is used as monomer (IB-1).

[0057] The polyoxyalkylene monool (1a) represented by formula (1a) and the compound (1b) represented by formula (1b) each have one group capable of undergoing a urethanization reaction in one molecule. Therefore, the urethane bond in one molecule of monomer (IB-1) is easily controlled to an average of one. When the number of urethane bonds in one molecule of monomer (IB-1) is small, the viscosity tends to be low. Therefore, by containing monomer (IB-1), the resin composition has a low viscosity and it is easy to obtain a cured product having excellent flexibility.

[0058] The hydroxyl value of the polyoxyalkylene monool (1a) represented by formula (1a) is not particularly limited, but is preferably 1.6 to 56.1 mg KOH / g, more preferably 2.8 to 14.0 mg KOH / g, and particularly preferably 3.5 to 12.5 mg KOH / g. The molecular weight calculated from the hydroxyl value of the polyoxyalkylene monool (1a) represented by formula (1a) is not particularly limited, but is preferably 1000 to 35000, more preferably 4000 to 20000, and particularly preferably 4500 to 16000.

[0059] The polyoxyalkylene monool (1a) component, which includes the polyoxyalkylene monool (1a) represented by formula (1a), can be obtained, for example, by ring-opening addition polymerization of an alkylene oxide with an initiator such as a monohydric alcohol or a carboxylic acid. There are no particular restrictions on the catalyst used for ring-opening addition polymerization, and examples include alkali metal compound catalysts, complex metal cyanide catalysts (hereinafter also referred to as DMC catalysts), phosphazene compound catalysts, and boron-based cation catalysts which are Lewis acids. These may be used individually or in combination of two or more. Among these, DMC catalysts are preferred because they can reduce the inclusion of low molecular weight bifunctional polyols, i.e., diols, which are by-products of ring-opening addition polymerization using water as an initiator, and because they facilitate the production of high molecular weight monools. The molecular weight of polyoxyalkylene monool (1a) produced using a DMC catalyst, calculated from its hydroxyl value, is not particularly limited, but is preferably 1,000 to 35,000, more preferably 4,000 to 20,000, and most preferably 4,500 to 16,000.

[0060] The molecular weight of the by-product low molecular weight diol is twice that of polyoxyalkylene monool (1a). It is preferable to produce a polyoxyalkylene monool (1a) component containing polyoxyalkylene monool (1a) represented by formula (1a) in such a way that the amount of the low molecular weight diol is reduced. When a polyoxyalkylene monool (1a) component produced using a DMC catalyst is used, a total of 0.01 to 100 ppm by mass of Zn and Co is present in the resin composition as residue.

[0061] The polyoxyalkylene monool (1a) component obtained in this manner may contain a diol produced as a by-product during manufacturing, in addition to the polyoxyalkylene monool (1a) represented by formula (1a). The amount of the diol is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 18% by mass or less, relative to the total amount of the produced polyoxyalkylene monool (1a) component. In the production of the polyoxyalkylene monool (1a) represented by formula (1a), the amount of diol produced as a by-product can be kept within the above range by reducing the amount of water in the reaction system.

[0062] In the production of the polyoxyalkylene monool represented by formula (1a), there are no particular restrictions on the total amount of water in the reaction system, but it is preferably 250 ppm by mass or less, more preferably 225 ppm by mass or less, and particularly preferably 200 ppm by mass or less. When the amount of water in the reaction system is within this range, the formation of a water-initiated diol, which is a by-product of the polyoxyalkylene monool represented by formula (1a), is suppressed. In the production of monomer (IB-1), using a polyoxyalkylene monool (1a) component with a suppressed diol content makes it easier to suppress the amount of bifunctional photosensitive monomer derived from the diol, and monomer (IB-1) containing a predetermined amount of the curable component shown in formula (1) can be easily obtained.

[0063] To keep the moisture content in the reaction system within the above range, the moisture may be removed under reduced pressure after the initiator is supplied to the reaction vessel. Alternatively, the moisture content in the reaction system can be adjusted by keeping the moisture content of the added alkylene oxide to 200 ppm by mass or less. Therefore, the moisture content of the added alkylene oxide is preferably 200 ppm by mass or less, and more preferably 150 ppm by mass or less. When the ring-opening addition polymerization catalyst is an alkali metal compound catalyst, it is usually used as an aqueous solution containing the catalyst with a solid content of 85% to 95% by mass, and the moisture content in the reaction system tends to be high, so the moisture is removed under reduced pressure after the hydroxyl groups of the initiator are alcoholized. DMC catalysts are preferred because they have a low moisture content.

[0064] The ratio of polyoxyalkylene monool (1a) represented by formula (1a) to the diol in the polyoxyalkylene monool (1a) component can be determined by GPC measurement of the manufactured polyoxyalkylene monool (1a) component. The average number of hydroxyl groups of polyoxyalkylene monool (1a) represented by formula (1a) can be determined by GPC measurement of the manufactured monool (1a) component.

[0065] When reacting the polyoxyalkylene monool (1a) represented by formula (1a) with the compound (1b) represented by formula (1b) using the polyoxyalkylene monool (1a) component, there are no particular restrictions on the mixing ratio of the compound represented by formula (1b) to the polyoxyalkylene monool (1a) component, but the index (NCO / OH ratio) is preferably 80 to 100, more preferably 90 to 100, and most preferably 100. By setting the index within the above range, the number of curable functional groups per molecule of monomer (IB-1) can be brought closer to one on average.

[0066] In particular, R present in one molecule of the curable component shown in formula (1) １２ It is preferable that monomer (IB-1-PO) contains monomer (1-PO) having a propylene group content of 50 to 100% by mass relative to the total amount, in monomer (IB). In monomer (1-PO), the R １２ The proportion of propylene groups to the total amount is not particularly limited, but is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and most preferably 100% by mass. １２ Of these, the alkylene group other than the propylene group is preferably an ethylene group.

[0067] Furthermore, when using monomer (IB-1-PO), there are no particular restrictions on the content of monomer (IB-1-PO) relative to monomer (IB), but it is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and particularly preferably 80 to 100% by mass. When the content of monomer (IB-1-PO) is above the lower limit of the above range, a cured product with low viscosity and excellent flexibility can be obtained.

[0068] There are no particular restrictions on the total amount of structural units (a1), structural units (a2), and structural units (a3) ​​when the total amount of structural units contained in polymer (A) is taken as 100% by mass, but it is preferably 80% by mass or more, more preferably 85% by mass or more, and particularly preferably 90% by mass or more. When the total amount of structural units (a1), structural units (a2), and structural units (a3) ​​is within the above range, an active material layer with excellent flexibility and adhesion to the current collector can be obtained.

[0069] (Other structural units) Polymer (A) may or may not contain structural units derived from other monomers copolymerizable with structural units (a1) to (a3), in addition to the structural units (a1) to (a3). There are no particular restrictions on structural units derived from other monomers copolymerizable with structural units (a1) to (a3), and examples include structural unit (a4) derived from an aromatic vinyl compound (hereinafter also simply referred to as "structural unit (a4)"), structural unit (a5) derived from (meth)acrylamide (hereinafter also simply referred to as "structural unit (a5)"), structural unit derived from an α,β-unsaturated nitrile compound, structural unit derived from a compound having a sulfonic acid group, structural unit derived from a cationic monomer, etc.

[0070] ((Structural units (a4) derived from aromatic vinyl compounds)) There are no particular restrictions on the content of structural units (a4) derived from aromatic vinyl compounds when the total amount of structural units contained in polymer (A) is taken as 100% by mass, but it is preferably 0.1 to 30% by mass, more preferably 0.2 to 27% by mass, and particularly preferably 0.5 to 25% by mass. When polymer (A) contains structural units (a4) within the above range, it exhibits good binding strength to the active material, and in some cases an energy storage device electrode with excellent flexibility of the active material layer and excellent adhesion of the active material layer to the current collector can be obtained.

[0071] There are no particular restrictions on the aromatic vinyl compound, and examples include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and divinylbenzene. These may be used individually or in combination of two or more.

[0072] (((Meth)acrylamide-derived structural unit (a5))) There are no particular restrictions on the content of structural unit (a5) when the total amount of structural units contained in polymer (A) is 100% by mass, but it is preferably 0 to 10% by mass, more preferably 1 to 8% by mass, and particularly preferably 2 to 5% by mass. When polymer (A) contains structural unit (a5) in the above range, the dispersibility of active material and filler in the slurry may be improved. Also, when polymer (A) contains structural unit (a5) in the above range, the flexibility of the resulting active material layer becomes appropriate, and the adhesion of the active material layer to the current collector may be improved. Furthermore, when polymer (A) contains structural unit (a5) in the above range, the bonding strength between active materials containing carbon materials such as graphite or silicon materials can be increased, so an active material layer with better flexibility and adhesion to the current collector may be obtained.

[0073] There are no particular restrictions on the (meth)acrylamide, and examples include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide, maleic acid amide, acrylamide tert-butylsulfonic acid, etc. These may be used individually or in combination of two or more.

[0074] ((Structural units derived from α,β-unsaturated nitrile compounds)) When the total amount of structural units derived from α,β-unsaturated nitrile compounds contained in polymer (A) is taken as 100% by mass, there are no particular restrictions on the content ratio of structural units derived from α,β-unsaturated nitrile compounds, but it is preferably 0 to 60% by mass, more preferably 0.5 to 55% by mass, and particularly preferably 1 to 50% by mass. By polymer (A) containing structural units derived from α,β-unsaturated nitrile compounds within the above range, it is possible to reduce the dissolution of polymer (A) into the electrolyte, and in some cases, it is possible to suppress the decrease in the adhesion of the active material layer to the current collector by the electrolyte. Furthermore, by polymer (A) containing structural units derived from α,β-unsaturated nitrile compounds within the above range, it is possible to suppress the increase in internal resistance due to the polymer components dissolved in the energy storage device becoming electrical resistance components.

[0075] There are no particular restrictions on the α,β-unsaturated nitrile compound, and examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and vinylidene cyanide. These may be used individually or in combination of two or more. Among these, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred.

[0076] ((Structural units derived from compounds having sulfonic acid groups)) When the total amount of structural units contained in polymer (A) is taken as 100% by mass, the content of structural units derived from compounds having sulfonic acid groups is preferably 0 to 10% by mass, more preferably 0.5 to 8% by mass, and particularly preferably 1 to 5% by mass. By polymer (A) containing structural units derived from compounds having sulfonic acid groups within the above range, the dispersibility of the active material is improved, and a uniform active material layer can be produced, thus eliminating structural defects in the electrode plate and potentially exhibiting good charge-discharge characteristics.

[0077] There are no particular limitations on the compounds having a sulfonic acid group, and examples include vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-alyloxy-2-hydroxypropanesulfonic acid, and alkali salts of these compounds. These may be used individually or in combination of two or more.

[0078] ((Structural units derived from cationic monomers)) There are no particular restrictions on the cationic monomers, and examples include secondary amines (salts), tertiary amines (salts), quaternary ammonium salts, etc. These may be used individually or in combination of two or more. There are no particular limitations on specific examples of cationic monomers, such as 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate methyl chloride quaternary salt, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl (meth)acrylate, 2-(0-[1'-methylpropyleneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methacloylcholinchloride, tris(2-) isocyanurate Examples include acryloyloxyethyl ester, 2-vinylpyridine, quinaldine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazole dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichlormid, N-allylbenzylamine, N-allylaniline, 2,4-diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, and trans-N-(6,6-dimethyl-2-heptene-4-inyl)-N-methyl-1-naphthylmethylamine hydrochloride. These may be used individually or in combination of two or more.

[0079] <<Physical Properties of Polymer (A)>> (Solubility in Water (Water-Soluble)) Polymer (A) is preferably a water-soluble polymer. In this invention, "water-soluble polymer" refers to a polymer whose solubility in water at 25°C and 1 atm is 1 g or more per 100 g of water. When Polymer (A) is a water-soluble polymer, the surface of the active material is more easily coated by Polymer (A), so the shedding of the active material due to expansion and contraction during charging and discharging can be effectively suppressed, and an energy storage device exhibiting good charge-discharge durability characteristics can be easily obtained. Furthermore, when Polymer (A) is a water-soluble polymer, the stability of the slurry is good, and the applicability of the slurry to the current collector is also good, which is preferable.

[0080] (Swelling Rate) When polymer (A) is immersed in a solvent consisting of ethylene carbonate / ethyl methyl carbonate in a volume fraction of 1:1 at 70°C for 24 hours, the swelling rate is not particularly limited, but is preferably 100 to 150% by mass, more preferably 105 to 145% by mass, and most preferably 110 to 140% by mass. When the swelling rate of polymer (A) is within the above range, polymer (A) can swell appropriately in relation to the electrolyte, and as a result, solvated lithium ions can easily reach the active material, reducing the internal resistance of the electrode and achieving better repeated charge-discharge characteristics. Furthermore, when the swelling rate of polymer (A) is within the above range, polymer (A) does not undergo a large volume change, resulting in excellent adhesion of the active material layer to the current collector. The swelling rate of polymer (A) can be measured by the method described later.

[0081] (Measurement of Swelling Rate) A film is prepared by drying polymer (A) in a constant temperature bath at 85°C for 24 hours. 1 g of this film is immersed in 20 mL of a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mass ratio 1 / 1, hereafter referred to as "EC / EMC") and shaken at 70°C for 24 hours. Next, the insoluble matter is separated by filtration through a 300-mesh wire mesh, and the weight of the remaining material (Y (g)) obtained by evaporating and removing the dissolved EC / EMC is measured. Furthermore, the EC / EMC adhering to the surface of the insoluble matter (film) separated by the above filtration is absorbed and removed by paper, and the weight of the insoluble matter (film) (Z (g)) is measured. The swelling rate of polymer (A) is calculated using the following formula: Swelling rate (mass%) = (Z / (1 - Y)) × 100

[0082] (Viscosity) The viscosity of an aqueous solution of polymer (A) with a solid content of 5% by mass, measured using a B-type viscometer at a temperature of 25°C and pH 8, is preferably 500 to 150,000 mPa·s / 30 rpm, more preferably 1,000 to 150,000 mPa·s / 30 rpm, and particularly preferably 2,000 to 150,000 mPa·s / 30 rpm. When the viscosity of the aqueous solution of polymer (A) is within the above range, the dispersibility of the active material is good, making it easy to produce a homogeneous active material layer, and as a result, electrodes without structural defects can be obtained, exhibiting good charge-discharge characteristics, which is preferable. The viscosity can be measured in accordance with JIS Z8803:2011. As a B-type viscometer, for example, "RB-80L" or "TVB-10" manufactured by Toki Sangyo Co., Ltd. can be used.

[0083] <<Method for producing polymer (A)>> There are no particular restrictions on the method for producing polymer (A), and examples include emulsion polymerization carried out in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. There are no particular restrictions on the emulsifier (surfactant), chain transfer agent, and polymerization initiator, and examples include compounds described in Japanese Patent Publication No. 5999399, etc.

[0084] The emulsion polymerization method for synthesizing polymer (A) may be carried out as a single-step polymerization or as a multi-step polymerization of two or more steps.

[0085] When polymer (A) is synthesized by one-step polymerization, the above monomer mixture can be subjected to emulsion polymerization in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc., preferably at 40 to 80°C for 4 to 36 hours.

[0086] When polymer (A) is synthesized by two-step polymerization, it is preferable to set the polymerization steps as follows.

[0087] There are no particular restrictions on the proportion of monomers used in the first stage polymerization, but it is preferably 20 to 100% by mass, more preferably 25 to 100% by mass, relative to the total mass of monomers (the sum of the mass of monomers used in the first stage polymerization and the mass of monomers used in the second stage polymerization). By performing the first stage polymerization with such a proportion of monomers, it is possible to obtain polymer (A) particles that have excellent dispersion stability and are less prone to agglomeration, and it is also possible to suppress the increase in viscosity of the resin composition over time.

[0088] The types and proportions of monomers used in the second polymerization step may be the same as, or different from, the types and proportions of monomers used in the first polymerization step.

[0089] The polymerization conditions at each stage are preferably as follows in order to improve the dispersibility of the resulting polymer (A): • First stage polymerization: preferably a temperature of 40 to 80°C; preferably a polymerization time of 2 to 36 hours; preferably a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more. • Second stage polymerization: preferably a temperature of 40 to 80°C; preferably a polymerization time of 2 to 18 hours.

[0090] By setting the total solids content concentration in emulsion polymerization to preferably 50% by mass or less, more preferably 48% by mass or less, and particularly preferably 45% by mass or less, the polymerization reaction can proceed while the resulting polymer (A) has good dispersion stability.

[0091] Whether polymer (A) is synthesized as a single-step polymerization or a two-step polymerization method, the pH can be adjusted to 7.0 to 8.5, preferably 7.2 to 8.5, and more preferably 7.5 to 8.4, by adding a neutralizing agent to the polymerization mixture after emulsion polymerization is complete. Setting the pH within this range ensures good stability of polymer (A). Furthermore, by concentrating the polymerization mixture after the neutralization treatment, the solid content concentration can be increased while maintaining the good stability of polymer (A). There are no particular restrictions on the neutralizing agent; examples include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; and the like.

[0092] <<Content ratio of polymer (A)>> There are no particular restrictions on the content ratio of polymer (A) in the resin composition for energy storage devices of the present invention, but it is preferably 10 to 100% by mass, more preferably 20 to 100% by mass, and particularly preferably 25 to 100% by mass, of 100% by mass of the polymer component. Here, the polymer component includes polymer (A), polymers other than polymer (A) described later, thickeners, etc. If it is above the lower limit of the above range, the flexibility of the active material layer and the adhesion of the active material layer to the current collector are excellent.

[0093] There are no particular restrictions on the content of polymer (A) in the resin composition for energy storage devices of the present invention, but it is preferably 1 to 50% by mass, more preferably 2 to 30% by mass, and particularly preferably 5 to 20% by mass, of 100% by mass of the resin composition. If it is above the lower limit of the above range, the flexibility of the active material layer and the adhesion of the active material layer to the current collector are excellent, and if it is below the upper limit of the above range, the water solubility tends to be good.

[0094] <Liquid Medium (B)> There are no particular restrictions on the liquid medium (B), but preferably it is an aqueous medium containing water, and more preferably it is water. The aqueous medium may contain a non-aqueous medium other than water. There are no particular restrictions on the non-aqueous medium, and examples include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc. These may be used individually or in combination of two or more. By using an aqueous medium as the liquid medium (B) in the resin composition for energy storage devices of the present invention, the degree of adverse effects on the environment is reduced and the safety for handling workers is also increased.

[0095] There are no particular restrictions on the proportion of the non-aqueous medium contained in the aqueous medium, but it is preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably substantially absent, based on 100% by mass of the aqueous medium. Here, "substantially absent" means that the non-aqueous medium is not intentionally added as the liquid medium (B), and it may contain the non-aqueous medium that is inevitably mixed in when preparing the resin composition for the energy storage device of the present invention.

[0096] <<Content ratio of liquid medium (B)>> There are no particular restrictions on the content ratio of liquid medium (B) in the resin composition for energy storage devices of the present invention, but it is preferably 50 to 99% by mass, more preferably 70 to 98% by mass, and particularly preferably 80 to 95% by mass, of 100% by mass of the resin composition.

[0097] <Other Additives> The resin composition for energy storage devices of the present invention may contain additives other than those described above, as needed. Such additives are not particularly limited and include, for example, polymers other than polymer (A), preservatives, thickeners, etc.

[0098] <<Polymers other than polymer (A)>> There are no particular restrictions on polymers other than polymer (A), and examples include acrylic polymers containing unsaturated carboxylic acid esters or their derivatives as structural units, fluorine polymers such as PVDF (polyvinylidene fluoride), and styrene-butadiene polymers (hereinafter also referred to as "SBR"). These may be used individually or in combination of two or more. By including polymers other than polymer (A), it may be possible to form an active material layer with improved flexibility and adhesion to the current collector.

[0099] <<Preservatives>> There are no particular restrictions on specific examples of preservatives, but examples include compounds described in Japanese Patent Publication No. 5477610, etc. By including a preservative, it may be possible to suppress the growth of bacteria, mold, etc. and the generation of foreign matter when the resin composition is stored.

[0100] <<Thickening Agent>> By including a thickening agent, it may be possible to further improve the applicability of the slurry and the charge / discharge characteristics of the resulting energy storage device.

[0101] There are no particular limitations on specific examples of thickeners, but examples include cellulose compounds such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose; poly(meth)acrylic acid; ammonium salts of cellulose compounds, alkali metal salts of cellulose compounds, ammonium salts of poly(meth)acrylic acid, and alkali metal salts of poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; and saponified copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid with vinyl esters; and other water-soluble polymers. These may be used individually or in combination of two or more. Among these, alkali metal salts of carboxymethylcellulose and alkali metal salts of poly(meth)acrylic acid are preferred.

[0102] There are no particular restrictions on commercially available thickeners, but examples include alkali metal salts of carboxymethylcellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0103] When the resin composition for energy storage devices of the present invention contains a thickening agent, there are no particular restrictions on the percentage of the thickening agent, but it is preferably 5% by mass or less, and more preferably 0.1 to 4% by mass, based on 100% by mass of the total solid content of the resin composition.

[0104] <<Content Ratio of Other Additives>> There are no particular restrictions on the content ratio of other additives in the resin composition for energy storage devices of the present invention, but it is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, and particularly preferably 0 to 5% by mass, of 100% by mass of the resin composition. If it is below the upper limit of the above range, the effects of each additive can be easily exerted while suppressing a decrease in the flexibility of the active material layer and the adhesion of the active material layer to the current collector.

[0105] <pH of the resin composition> There are no particular restrictions on the pH of the resin composition, but it is preferably 7.0 to 8.5, more preferably 7.2 to 8.5, and most preferably 7.5 to 8.4. If the pH is within the above range, it is possible to suppress the occurrence of problems such as insufficient leveling and liquid dripping, and it becomes easy to manufacture energy storage device electrodes that achieve both good electrical characteristics and good adhesion of the active material layer to the current collector.

[0106] [Slurry for Energy Storage Device Electrodes] The slurry for energy storage device electrodes of the present invention contains the above-described resin composition and an active material, and optionally contains other components. The above-described resin composition is used as a material for producing an energy storage device electrode (active material layer) with improved adhesion of the active material layer to the current collector (bonding strength between active materials, adhesion strength of the active material to the current collector, and resistance to powder shedding). The slurry for energy storage device electrodes will be described in detail below.

[0107] <Resin Composition> The resin composition is as described above, so no further explanation will be given.

[0108] <Active Material> The active material used in the slurry for the electrodes of the energy storage device of the present invention is not particularly limited, and includes, for example, oxides containing lithium atoms, carbon materials, silicon materials, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacene, A Ｘ B Ｙ O Ｚ Examples include composite metal oxides and other metal oxides represented as (wherein A is an alkali metal or transition metal, B is at least one selected from cobalt, nickel, aluminum, tin, and manganese, O represents an oxygen atom, and X, Y, and Z are numbers in the range of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively). These may be used individually or in combination of two or more. The active material preferably contains at least one selected from the group consisting of olivine-type lithium-containing phosphate compounds, lithium cobaltate, lithium nickelate, lithium manganeseate, and ternary nickel-cobalt-manganate lithium. There are no particular limitations on specific examples of the active material, and examples include compounds described in Japanese Patent Publication No. 5999399.

[0109] <<Oxides containing lithium atoms>> Examples of oxides containing lithium atoms include one or more selected from lithium atom-containing oxides (olivine-type lithium-containing phosphate compounds) that are represented by the following general formula (10) and have an olivine-type crystal structure.

[0110] Li １－ｘ M ｘ (AO ４ )・・・・・(10) (In general formula (10), M is an ion of at least one metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, and Sn, A is at least one selected from the group consisting of Si, S, P, and V, and x is a number that satisfies the relationship 0 < x < 1.) The value of x in the above general formula (10) is selected according to the valencies of M and A, such that the overall valency of the above general formula (10) becomes 0.

[0111] There are no particular restrictions on the olivine-type lithium-containing phosphate compound; for example, LiFePO ４ LiCoPO ４ LiMnPO ４ Li ０．９０ Ti ０．０５ Nb ０．０５ Fe ０．３０ Co ０．３０ Mn ０．３０ PO ４ These are some examples. These may be used individually or in combination of two or more. Among these, LiFePO is chosen because the raw material iron compound is readily available and inexpensive. ４ Lithium iron phosphate is preferred.

[0112] There are no particular restrictions on the average particle size of the olivine-type lithium-containing phosphate compound, but it is preferably 1 to 30 μm, more preferably 1 to 25 μm, and most preferably 1 to 20 μm.

[0113] <<Carbon Materials>> There are no particular restrictions on carbon materials, and examples include amorphous carbon, graphite, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, etc.

[0114] <<Silicon Materials>> There are no particular restrictions on silicon materials; for example, elemental silicon; silicon oxides; silicon alloys; SiC, SiO ｘ C ｙ (0<x≦3, 0<y≦5), Si ３ N ４ Si ２ N ２ O, SiO ｘExamples include Si oxide composites expressed as (0 < x ≤ 2) (for example, materials described in Japanese Patent Publication No. 2004-185810 and Japanese Patent Publication No. 2005-259697); silicon materials described in Japanese Patent Publication No. 2004-185810; silicon compounds containing lithium and oxygen described in Japanese Patent Publication No. 2017-097952; etc. These may be used individually or in combination of two or more. Among these, silicon compounds containing lithium and oxygen are preferred. By pre-containing lithium and oxygen in the silicon compound, a portion of the silicon material reacts with lithium during charging to form SiO ２ The generation of irreversible components such as can be suppressed, and the charge-discharge characteristics can be improved. The silicon material may be single crystal, polycrystalline, or amorphous. There are no particular restrictions on the silicon oxide; for example, a material with the compositional formula SiO ｘ Suitable silicon oxides are those represented by (0 < x < 2, preferably 0.1 ≤ x ≤ 1). There are no particular restrictions on the silicon alloy, but suitable examples include alloys of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron, and molybdenum. These transition metal silicon alloys are preferred because they have high electronic conductivity and high strength. Furthermore, the inclusion of these transition metals in the active material is preferable because it oxidizes the transition metals present on the surface of the active material to form oxides with hydroxyl groups on the surface, resulting in better bonding strength with the binder. More preferably, silicon-nickel alloys or silicon-titanium alloys are used as the silicon alloy, and even more preferably, silicon-titanium alloys are used. There are no particular restrictions on the silicon content in the silicon alloy, but it is preferably 10 mol% or more, more preferably 20 to 70 mol%, relative to the total amount of metal elements in the alloy.

[0115] There are no particular limitations on the silicon compound containing lithium and oxygen, for example, silicon oxide (SiO ｘ (0.5 ≤ x ≤ 1.6) and crystalline Li ２ SiO ３Examples include silicon compounds containing silicon compound particles (hereinafter also referred to as "lithium-silicon compound particles") containing SiO. ２ Among lithium silicates with altered properties, Li is stable in water. ２ SiO ３ Because of the large amount of these particles present, stability to the aqueous slurry used during electrode fabrication is improved, and the cycle characteristics of the energy storage device are also improved, which is desirable. There are no particular restrictions on the median diameter of the lithium-silicon compound particles, but it is preferably 1.0 μm or more and 15 μm or less. If the median diameter is 1.0 μm or more, the charge-discharge characteristics are improved due to the increase in surface area per unit mass, while if the median diameter is 15 μm or less, the particles become less likely to break, making it less likely for new surfaces to appear.

[0116] <<Composite Metal Oxides>> There are no particular restrictions on specific examples of composite metal oxides, but examples include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and ternary nickel-cobalt-manganese oxide lithium.

[0117] The slurry for energy storage device electrodes of the present invention can be used when manufacturing either the positive or negative electrode of an energy storage device, but it is preferable to use it for both the positive and negative electrodes.

[0118] When preparing cathode slurries, using a liquid medium primarily composed of water presented a challenge: poor charge-discharge characteristics. This is thought to be partly due to the high reactivity of cathode active materials with water, and the resulting hydroxide ions that corrode the cathode surface.

[0119] However, even when a liquid medium mainly composed of water is used as the liquid medium for the positive electrode slurry of the present invention, the electrodes of the energy storage device prepared using the slurry of the present invention exhibit good charge and discharge characteristics without the problems described above occurring. This is because polymer (A) contains 1 to 30% by mass of structural units (a3) ​​derived from unsaturated carboxylic acid esters with a number average molecular weight of 1,300 to 36,000. These structural units (a3) ​​(especially polyoxyalkylene chains) interact with the electrode and active material, thus protecting against electrode corrosion even if hydroxide ions are generated.

[0120] On the other hand, when manufacturing a negative electrode, it is preferable to use a silicon material among the active materials exemplified above. Since silicon materials have a larger lithium absorption capacity per unit weight compared to other active materials, including a silicon material as the negative electrode active material can increase the energy storage capacity of the energy storage device, and as a result, the output and energy density of the energy storage device can be increased.

[0121] However, when silicon materials are used as the negative electrode active material, there is a problem in that the adhesion of the active material layer to the current collector is easily impaired when a liquid medium mainly composed of water is used. One of the reasons for this is thought to be that silicon materials readily react with water to generate hydroxide ions, and these hydroxide ions decompose the polymer components.

[0122] Furthermore, the decomposition of the polymer components reduces the stress on the polymer coating the active material, making it unable to follow the expansion and contraction of the active material. As a result, electrode expansion increases, and the silicon material (negative electrode active material) becomes isolated, leading to a deterioration in the charge and discharge characteristics of the energy storage device.

[0123] Energy storage device electrodes fabricated using the slurry for energy storage device electrodes according to this embodiment can exhibit good adhesion of the active material layer to the current collector without the problems described above occurring, even when silicon materials are used. This is because the polymer (A) contains 1 to 30% by mass of structural units (a3) ​​derived from unsaturated carboxylic acid esters with a number average molecular weight of 1,300 to 36,000. These structural units (a3) ​​(especially polyoxyalkylene chains) interact with the electrode and the active material, thus protecting against electrode corrosion even if hydroxide ions are generated.

[0124] There are no particular restrictions on the content of silicon material in 100% by mass of the active material, but it is preferably 1% by mass or more, more preferably 1 to 50% by mass, even more preferably 5 to 45% by mass, and particularly preferably 10 to 40% by mass. When the content of silicon material in 100% by mass of the active material is within the above range, an energy storage device can be obtained that has an excellent balance between improved output and energy density of the energy storage device and charge / discharge durability characteristics.

[0125] There are no particular restrictions on the shape of the active material, but particulate matter is preferred. There are no particular restrictions on the average particle diameter of the active material, but it is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm. Here, the average particle diameter of the active material refers to the volume-average particle diameter calculated from the particle size distribution measured using a particle size distribution analyzer that uses laser diffraction as its measurement principle. There are no particular restrictions on such a laser diffraction particle size distribution analyzer, and examples include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by HORIBA, Ltd.).

[0126] There are no particular restrictions on the ratio of active material used, but it is preferable to use polymer (A) in a ratio of 0.5 to 8 parts by mass per 100 parts by mass of active material, more preferably 1 to 7 parts by mass per 100 parts by mass of active material, and particularly preferably 2 to 6 parts by mass per 100 parts by mass of active material. By using such ratios, it is possible to manufacture electrodes that have superior adhesion of the active material layer to the current collector, low electrode resistance, and superior charge-discharge characteristics.

[0127] <Other Ingredients> There are no particular restrictions on other ingredients, and examples include polymers other than polymer (A), thickeners, liquid media, conductivity imparters, pH adjusters, corrosion inhibitors, cellulose fibers, etc. "Polymers other than polymer (A)" and "thickeners" can be appropriately selected from the compounds exemplified in the "<Other Additives>" section above and used for the same purpose and in the same proportions.

[0128] <<Liquid Medium>> In addition to the liquid medium brought in from the resin composition, a liquid medium may be further added to the slurry for the energy storage device electrode of the present invention. The added liquid medium may be the same type as the liquid medium (B) contained in the resin composition, or it may be different, but it is preferable to select and use from the liquid media exemplified in the section "<Liquid Medium (B)>".

[0129] There are no particular restrictions on the content ratio of the liquid medium (including the portion introduced from the resin composition) in the slurry for the electrodes of the energy storage device of the present invention, but it is preferable that the solid content concentration in the slurry (meaning the ratio of the total mass of components other than the liquid medium in the slurry to the total mass of the slurry; the same applies hereinafter) be 30 to 70% by mass, and more preferably that the solid content concentration in the slurry be 40 to 60% by mass.

[0130] <<Conductivity-Imparting Agent>> The slurry for the electrode of the energy storage device of the present invention may further contain a conductivity-imparting agent for the purpose of imparting conductivity and buffering the volume change of the active material due to the movement of lithium ions.

[0131] There are no particular limitations on specific examples of conductivity imparters, and examples include activated carbon, acetylene black, Ketjen black, furnace black, graphite, carbon fiber, fullerene, carbon nanotubes, and other carbon materials. These may be used individually or in combination of two or more. Among these, acetylene black and carbon nanotubes are preferred. There are no particular limitations on the content ratio of the conductivity imparter, but it is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass per 100 parts by mass of active material.

[0132] <<pH Adjusting Agent>> Depending on the type of active material, a pH adjusting agent may be further added to the slurry for the electrodes of the energy storage device of the present invention for the purpose of suppressing corrosion of the current collector. There are no particular restrictions on the pH adjusting agent, and examples include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. These may be used individually or in combination of two or more. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred. Alternatively, one can be selected and used from the "neutralizing agents" described in the "<<Method for Producing Polymer (A)>>" section above.

[0133] <<Corrosion Inhibitor>> Depending on the type of active material, a corrosion inhibitor may be further added to the slurry for the electrodes of the energy storage device of the present invention for the purpose of suppressing corrosion of the current collector. There are no particular restrictions on the corrosion inhibitor, and examples include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, potassium molybdate, etc. These may be used individually or in combination of two or more. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0134] <<Cellulose Fiber>> Cellulose fibers may be further added to the slurry for the electrodes of the energy storage device of the present invention. Adding cellulose fibers may improve the adhesion strength of the active material to the current collector. It is thought that the fibrous cellulose fibers can prevent the detachment of the active material and improve the adhesion strength of the active material to the current collector by binding adjacent active materials together through linear adhesion or linear contact.

[0135] The average fiber length of the cellulose fiber can be selected from a wide range of 0.1 to 1000 μm, and there are no particular restrictions, but it is preferably 1 to 750 μm, more preferably 1.3 to 500 μm, even more preferably 1.4 to 250 μm, and particularly preferably 1.8 to 25 μm. If the average fiber length is within the above range, the surface smoothness (coating film uniformity) will be good, and the adhesion strength of the active material to the current collector may be improved.

[0136] The fiber length of the cellulose fiber may or may not be uniform. The coefficient of variation of the fiber length of the cellulose fiber ([standard deviation of fiber length / average fiber length] × 100) is not particularly limited, but is preferably 0.1 to 100, more preferably 0.5 to 50, and most preferably 1 to 30. The maximum fiber length of the cellulose fiber is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, even more preferably 100 μm or less, and most preferably 50 μm or less.

[0137] There are no particular restrictions on the average fiber length of the cellulose fibers, but from the viewpoint of surface smoothness (coating uniformity) and the adhesion strength of the active material to the current collector, it is preferably 0.01 to 5 times, more preferably 0.02 to 3 times, and particularly preferably 0.03 to 2 times, the average thickness of the active material layer.

[0138] There are no particular restrictions on the average fiber diameter of the cellulose fiber, but it is preferably 1 nm to 10 μm, more preferably 5 nm to 2.5 μm, even more preferably 20 nm to 700 nm, and particularly preferably 30 nm to 200 nm. When the average fiber diameter of the cellulose fiber is within the above range, the occupied volume of the fiber does not become too large, and it may be possible to increase the packing density of the active material. For this reason, it is preferable that the cellulose fiber is a cellulose nanofiber with an average fiber diameter of nanometer size (for example, a cellulose nanofiber with an average fiber diameter of 10 to 500 nm, preferably about 25 to 250 nm).

[0139] The fiber diameter of the cellulose fiber may or may not be uniform. There are no particular restrictions on the coefficient of variation of the fiber diameter of the cellulose fiber ([standard deviation of fiber diameter / average fiber diameter] × 100), but it is preferably 1 to 80, more preferably 5 to 60, and most preferably 10 to 50. There are no particular restrictions on the maximum fiber diameter of the cellulose fiber, but it is preferably 30 μm or less, more preferably 5 μm or less, and most preferably 1 μm or less.

[0140] There are no particular restrictions on the ratio of the average fiber length to the average fiber diameter (aspect ratio) of the cellulose fiber, but it is preferably 10 to 5000, more preferably 20 to 3000, and most preferably 50 to 2000. When the aspect ratio of the cellulose fiber is within the above range, the adhesion strength of the active material to the current collector is good, and the surface smoothness (coating uniformity) of the electrode may be good without weakening the breaking strength of the fiber.

[0141] In the present invention, the average fiber length, the standard deviation of the fiber length distribution, the maximum fiber length, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter may be values ​​calculated from fibers (n=20 or so) measured based on electron microscope images.

[0142] There are no particular restrictions on the material of the cellulose fiber, but polysaccharides having a β-1,4-glucan structure are preferred. There are no particular restrictions on the cellulose fiber itself, but examples include cellulose fibers derived from higher plants (e.g., wood fibers (wood pulp from conifers, hardwoods, etc.), bamboo fibers, sugarcane fibers, seed hair fibers (e.g., cotton linters, bombax cotton, kapok, etc.), gin bark fibers (e.g., hemp, paper mulberry, mitsumata, etc.), leaf fibers (e.g., Manila hemp, New Zealand hemp, etc.), and other natural cellulose fibers (pulp fibers), cellulose fibers derived from animals (e.g., sea squirt cellulose), cellulose fibers derived from bacteria (e.g., cellulose contained in nata de coco), and chemically synthesized cellulose fibers (e.g., rayon, cellulose esters (cellulose acetate, etc.), cellulose ethers (e.g., cellulose derivatives such as hydroxyethylcellulose (HEC), hydroxyalkylcellulose such as hydroxypropylcellulose, methylcellulose, ethylcellulose, etc.)). These may be used individually or in combination of two or more.

[0143] Among these, cellulose fibers derived from pulp, such as wood fibers (wood pulp from coniferous trees, hardwoods, etc.) and seed hair fibers (cotton linters, etc.), are preferred because they make it easier to prepare nanofibers with an appropriate aspect ratio.

[0144] There are no particular limitations on the method for producing cellulose fibers, and depending on the desired fiber length and fiber diameter, conventional methods, such as those described in Japanese Patent Publication No. 60-19921, Japanese Unexamined Patent Publication No. 2011-26760, Japanese Unexamined Patent Publication No. 2012-25833, Japanese Unexamined Patent Publication No. 2012-36517, Japanese Unexamined Patent Publication No. 2012-36518, Japanese Unexamined Patent Publication No. 2014-181421, etc., may be used.

[0145] There are no particular restrictions on the proportion of other components, but preferably it is 20 parts by mass or less, more preferably 1 to 15 parts by mass, and most preferably 2 to 10 parts by mass per 100 parts by mass of active material. Within this range, it is easier to improve the adhesion strength of the active material to the current collector.

[0146] <Method for preparing slurry for energy storage device electrodes> The slurry for energy storage device electrodes of the present invention may be manufactured by any method, as long as it contains the resin composition and active material described above. From the viewpoint of producing a slurry with better dispersibility and stability more efficiently and inexpensively, it is preferable to manufacture it by adding the active material and optional additives used as needed to the resin composition and mixing them. Specific manufacturing methods include, for example, the method described in Japanese Patent Publication No. 6544150.

[0147] [Energy Storage Device Electrode] The energy storage device electrode of the present invention comprises a current collector and an active material layer formed by applying and drying the above-mentioned slurry for energy storage device electrodes on the surface of the current collector. The energy storage device electrode can be manufactured by applying the above-mentioned slurry for energy storage device electrodes to the surface of a current collector such as metal foil to form a coating film, and then drying the coating film to form an active material layer. In the energy storage device electrode manufactured in this way, an active material layer containing the above-mentioned polymer (A), active material, and optionally added components is bonded to the surface of the current collector, thereby suppressing the occurrence of corrosion on the electrode surface, providing excellent adhesion of the active material layer to the current collector, and improving the charge / discharge durability characteristics of the energy storage device.

[0148] As long as the current collector is made of a conductive material, there are no particular restrictions. When the energy storage device electrode is used in a lithium-ion secondary battery, examples of current collectors include those made of metal such as iron, copper, aluminum, nickel, and stainless steel. These may be used individually or in combination of two or more types. Among these, aluminum and copper current collectors are preferred.

[0149] There are no particular restrictions on the current collector used when the electrodes of an energy storage device are used in a lithium-ion secondary battery. Examples include current collectors made of perforated metal, expanded metal, wire mesh, foamed metal, mesh metal fiber sintered body, metal-plated resin plate, etc. These may be used individually or in combination of two or more types.

[0150] There are no particular restrictions on the shape and thickness of the current collector, but a sheet-like shape with a thickness of about 1 μm to 0.5 mm is preferred. There are no particular restrictions on the application method for coating the surface of the current collector with the slurry for the energy storage device electrodes, and examples include the doctor blade method, dip method, reverse roll method, direct roll method, gravure method, extrusion method, immersion method, brush application method, etc. These may be used individually or in combination of two or more methods.

[0151] There are no particular restrictions on the amount of slurry applied to the electrodes of the energy storage device, but it is preferable to apply an amount such that the thickness of the positive electrode active material layer formed after removing the liquid medium (a concept encompassing water and any non-aqueous medium) is 5 μm to 5 mm, and it is more preferable to apply an amount such that the thickness of the positive electrode active material layer formed after removing the liquid medium is 10 μm to 2 mm.

[0152] By having the thickness of the active material layer within the aforementioned range, the electrolyte can be efficiently impregnated into the active material layer. As a result, the exchange of metal ions between the active material and the electrolyte in the active material layer during charging and discharging is facilitated, which further reduces the internal resistance of the electrode.

[0153] Furthermore, because the thickness of the active material layer is within the aforementioned range, even when the electrode is processed by folding or winding, the adhesion of the active material layer to the current collector is good, and the active material layer is less likely to peel off from the current collector. In other words, it is preferable because it is easier to obtain an energy storage device electrode with a highly flexible active material layer.

[0154] There are no particular limitations on the drying method for a coating film formed by applying a slurry for energy storage device electrodes (method for removing water and any optionally used non-aqueous media), and examples include drying with hot air, hot air, or low-humidity air; vacuum drying; and drying by irradiation with (far) infrared rays, electron beams, etc. These methods may be used individually or in combination of two or more.

[0155] There are no particular restrictions on the drying rate when drying a coating film formed by applying a slurry for energy storage device electrodes. For example, it can be set appropriately so that the liquid medium can be removed as quickly as possible, under conditions where stress concentration does not cause cracks in the active material layer or the active material layer peels off from the current collector.

[0156] After the coating film formed by applying the slurry for energy storage device electrodes dries, it is preferable to increase the density of the active material layer by pressing the energy storage device electrodes, and to adjust the density and porosity in the active material layer to the ranges shown below.

[0157] There are no particular restrictions on the density of the active material layer after pressing at the negative electrode, but it is preferably 1.1 to 4.1 g / cm³. ３ More preferably 1.2 to 3.5 g / cm³ ３ More preferably 1.3 to 2.5 g / cm³ ３ Particularly preferably 1.4 to 2.0 g / cm³ ３ The density of the active material layer after pressing at the positive electrode is not particularly limited, but is preferably 2.5 to 3.5 g / cm³. ３ More preferably 2.6 to 3.4 g / cm³ ３ More preferably 2.7 to 3.3 g / cm³ ３ Particularly preferably 2.8 to 3.2 g / cm³ ３Therefore, by setting the density of the active material layer within the aforementioned range, it is possible to obtain an energy storage device electrode that exhibits good bonding between the current collector and the active material layer, excellent powder shedding properties, and superior electrical characteristics.

[0158] There are no particular restrictions on the porosity of the active material layer after pressing, but it is preferably 10 to 50%, more preferably 15 to 45%, and most preferably 20 to 40%. By setting the porosity of the active material layer within the above range, it is possible to obtain an energy storage device electrode that has good bonding between the current collector and the active material layer, excellent powder shedding properties, and excellent electrical characteristics.

[0159] Furthermore, by setting the porosity of the active material layer within the aforementioned range, the electrolyte can be sufficiently permeated into the active material layer, and sufficient contact can be made between the surface of the active material and the electrolyte. As a result, the transfer of lithium ions between the active material and the electrolyte becomes easier, and good charge-discharge characteristics can be achieved.

[0160] There are no particular restrictions on the pressing method used to press the electrodes of the energy storage device; for example, die pressing and roll pressing are used. There are no particular restrictions on the pressing conditions used to press the electrodes of the energy storage device; they can be set appropriately depending on the type of pressing equipment used, the desired values ​​of the porosity and density of the active material layer, etc. The pressing conditions can be easily set by a person skilled in the art through a few preliminary experiments.

[0161] When using the roll press method, the pressing conditions can be as follows, for example: • Linear pressure of the roll press machine: 0.1 to 10 (t / cm), preferably 0.5 to 5 (t / cm). • Roll temperature: 20 to 100°C. • Feed speed of the energy storage device electrode (roll rotation speed): 0.5 to 50 m / min, preferably 1 to 30 m / min.

[0162] [Energy Storage Device] The energy storage device of the present invention comprises the above-described energy storage device electrodes, further contains an electrolyte, and can be manufactured by conventional methods using components such as separators. There are no particular limitations on the method of manufacturing the energy storage device, and examples include stacking a negative electrode and a positive electrode via a separator, winding or folding them according to the battery shape and storing them in a battery container, and then injecting the electrolyte into the battery container and sealing it. There are no particular limitations on the shape of the battery, and examples include coin-type, cylindrical, prismatic, laminate-type, etc.

[0163] The electrolyte may be in liquid or gel form, and depending on the type of active material, one can be selected from known electrolytes used in energy storage devices that effectively exhibit battery function. The electrolyte may also be a solution obtained by dissolving the electrolyte in a suitable solvent. There are no particular restrictions on such electrolytes and solvents; for example, compounds described in Japanese Patent Publication No. 5999399 can be cited.

[0164] The above-described energy storage device is applicable to lithium-ion secondary batteries, electric double-layer capacitors, and lithium-ion capacitors, preferably lithium-ion secondary batteries, that require discharge at high current density. In the energy storage device electrodes and energy storage device, components other than the resin composition can be those of known lithium-ion secondary batteries, electric double-layer capacitors, and lithium-ion capacitors.

[0165] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the invention. In the examples, "parts" and "%" are by mass unless otherwise specified. In this specification, the polymer (A) produced in Example 1 will be referred to as "polymer (A-1)", and similarly, the polymers (A) produced in Examples 2 to 18 will be referred to as "polymers (A-2) to (A-18)", etc. Examples 2 to 4, 6 to 11, and 15 to 18 are examples, and Examples 1, 5, and 12 to 14 are comparative examples.

[0166] <Number-average molecular weight (Mn)> The number-average molecular weight (Mn) of each sample is the polystyrene-equivalent molecular weight obtained by measuring it by gel permeation chromatography (GPC) under the following conditions, using a calibration curve prepared using standard polystyrene samples with known molecular weights. <<GPC Measurement Conditions>> Instrument used: HLC-8320GPC (Tosoh Corporation) Column used: G7000HXL + GMHXL + GMHXL (Tosoh Corporation) Column size: 7.8 mmφ × 30 cm each, total 90 cm Column temperature: 40°C Flow rate: 0.8 mL / min Injection volume: 100 μL Eluent: Tetrahydrofuran Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0167] (Manufacturing Example 1) <Manufacturing and property evaluation of polymer (A)> <<Manufacturing of polymer (A)>> In a 7-liter separable flask, 900 parts by mass of water, 0.5 parts by mass of dodecylbenzenesulfonic acid as an emulsifier (surfactant), 5 parts by mass of acrylic acid (AA), 5 parts by mass of butyl acrylate (BA), and 85 parts by mass of 2-hydroxyethyl acrylate (HEA) were added. Then, 2 parts by mass of styrene (ST) and 3 parts by mass of acrylamide (AAM) were added, and the mixture was stirred thoroughly to prepare a monomer emulsion containing the above monomer mixture. The heating of the inside of the separable flask was started, and when the internal temperature reached 60°C, 0.5 parts by mass of ammonium persulfate was added as a polymerization initiator. When the internal temperature of the separable flask reached 70°C, the addition of the monomer emulsion prepared above was started, and the monomer emulsion was slowly added over 3 hours while maintaining the internal temperature of the separable flask at 70°C. Subsequently, the temperature inside the separable flask was raised to 85°C, and this temperature was maintained for 3 hours to carry out the polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then a 10% by mass sodium hydroxide aqueous solution was added to adjust the pH to 8.0, thereby obtaining a polymer aqueous solution containing 10% by mass of polymer (A-1).

[0168] <<Evaluation of the physical properties of polymer (A)>> (Evaluation of water solubility) The aqueous solution of polymer (A-1) obtained above was diluted with water so that the concentration of polymer (A-1) was 1% by mass. The transparency of the 1% by mass aqueous solution of polymer (A-1) obtained in this way was visually confirmed at 1 atmosphere and 25°C. The results are shown in Table 1. If the diluted solution was transparent, it was judged to be "water soluble" and labeled "A", if it was semi-transparent, it was judged to be "semi-water soluble" and labeled "B", and if the diluted solution was cloudy white, it was judged to be "water insoluble" and labeled "C".

[0169] (Production Examples 2-18) Polymers (A-2) to (A-18) were obtained in the same manner as in the "Production of Polymer (A)" section above, except that the types and amounts of monomers were as shown in Table 1 below, and the water solubility evaluation described above was carried out. The abbreviations for each component in Table 1 represent the following compounds or trade names. <Unsaturated Carboxylic Acids> ・AA: Acrylic Acid <Unsaturated Carboxylic Acid Esters with a Number Average Molecular Weight of Less Than 1300> ・HEA: 2-Hydroxyethyl Acrylate ・BA: Butyl Acrylate <Unsaturated Carboxylic Acid Esters with a Number Average Molecular Weight of 1300 to 36000> ・Unsaturated Carboxylic Acid Ester a3-1: Produced in Production Example 2-1 below ・Unsaturated Carboxylic Acid Ester a3-2: Produced in Production Example 2-2 below ・Unsaturated Carboxylic Acid Ester a3-3: Produced in Production Example 2-3 below <Aromatic Vinyl Compounds> ・ST: Styrene <Acrylamide> ・AAM: Acrylamide

[0170] <Production Example 1-1: Production of Monool (1)> In a pressure reactor equipped with a stirrer and a nitrogen inlet tube, 0.2 g of a zinc hexacyanocobaltate-tert-butyl alcohol complex, a complex metal cyanide catalyst, and 30 g of n-butanol, an initiator, were charged. Under a nitrogen atmosphere at 130°C, 1310 g of propylene oxide was added at a constant rate over 7 hours. After confirming that the decrease in the internal pressure of the pressure reactor had stopped, 1340 g of the product was withdrawn. The main component of the product, excluding by-products and metals derived from the catalyst, was polyoxypropylene monool (monool (1)) with a hydroxyl value of 17.0 mg KOH / g (molecular weight based on hydroxyl value: 3300) and an average number of hydroxyl groups of 1.0.

[0171] <Production Example 2-1: Production of Unsaturated Carboxylic Acid Ester a3-1> In a reaction vessel equipped with a stirrer and a nitrogen inlet tube, 928.1 g of monool (1) obtained in Production Example 1-1 and 26.8 g of 2-acryloyloxyethyl isocyanate (Kalenz AOI, Showa Denko Co., Ltd. product name) were charged and reacted at 70°C for 3 hours in the presence of 0.0955 g of dioctyl tin distearate (DOTDS) to obtain unsaturated carboxylic acid ester a3-1. The number average molecular weight (Mn) of the obtained unsaturated carboxylic acid ester a3-1 was 3500. The content of 2-acryloyloxyethyl isocyanate relative to monool (1) was 100 in index (NCO / OH ratio).

[0172] <Production Example 2-2: Production of Unsaturated Carboxylic Acid Ester a3-2> Monool (2) was produced by appropriately changing the amount of propylene oxide added in Production Example 1-1, and unsaturated carboxylic acid ester a3-2 was obtained in the same manner as in Production Example 2-1. The number-average molecular weight (Mn) of the obtained unsaturated carboxylic acid ester a3-2 was 13,000. The content of 2-acryloyloxyethyl isocyanate relative to monool (2) was 100 in index (NCO / OH ratio).

[0173] <Production Example 2-3: Production of Unsaturated Carboxylic Acid Ester a3-3> Monool (3) was produced by appropriately changing the amount of propylene oxide added in Production Example 1-1, and unsaturated carboxylic acid ester a3-3 was obtained in the same manner as in Production Example 2-1. The number-average molecular weight (Mn) of the obtained unsaturated carboxylic acid ester a3-3 was 20,000. The content of 2-acryloyloxyethyl isocyanate relative to monool (3) was 100 in index (NCO / OH ratio).

[0174] <Production Example 2-4: Production of Unsaturated Carboxylic Acid Ester a3-4> Monool (4) was produced by appropriately changing the amount of propylene oxide added in Production Example 1-1, and unsaturated carboxylic acid ester a3-4 was obtained in the same manner as in Production Example 2-1. The number-average molecular weight (Mn) of the obtained unsaturated carboxylic acid ester a3-4 was 10,000. The content of 2-acryloyloxyethyl isocyanate relative to monool (4) was 100 in index (NCO / OH ratio).

[0175] <Production Example 2-5: Production of Unsaturated Carboxylic Acid Ester a3-5> Monool (5) was produced by appropriately changing the amount of propylene oxide added in Production Example 1-1, and unsaturated carboxylic acid ester a3-5 was obtained in the same manner as in Production Example 2-1. The number-average molecular weight (Mn) of the obtained unsaturated carboxylic acid ester a3-5 was 16,000. The content of 2-acryloyloxyethyl isocyanate relative to monool (5) was 100 in index (NCO / OH ratio).

[0176]

[0177] <Preparation of Resin Composition> (Example 1) 100 parts by mass of polymer (A-1) was mixed with 900 parts by mass of water as a liquid medium to prepare a resin composition as a 10% by mass aqueous solution of polymer (A-1).

[0178] <Fabrication and Evaluation of Cathodes for Energy Storage Devices> <<Preparation of Slurry for Cathodes of Energy Storage Devices>> In a twin-screw planetary mixer (Primix Corporation, product name "TK Hibiscus Mix 2P-03"), 4 parts by mass of the resin composition (10% by mass aqueous solution of polymer (A-1)), 100 parts by mass of NMC622 (composite metal oxide: ternary nickel cobalt manganese lithium: product name "ME-8A", manufactured by Beijing Dangsheng Co., Ltd.) as a cathode active material, 5 parts by mass of acetylene black and 20 parts by mass of water were added and stirred at 60 rpm for 1 hour. Note that NMC622 is an example of a cathode active material.

[0179] The mixture was then stirred for another hour to obtain a paste. Water was added to the paste to adjust the solid content to 70% by mass, and then the mixture was stirred and degassed using a stirring and degassing machine (manufactured by Thinky Co., Ltd., product name "Awatori Rentaro") at 200 rpm for 2 minutes, then at 1800 rpm for 5 minutes, and finally under vacuum (approximately 5.0 x 10⁻⁶). ３ A slurry for the positive electrode of an energy storage device was prepared by stirring and mixing at 1800 rpm for 1.5 minutes in Pa.

[0180] <<Fabrication of positive electrode for energy storage device>> The slurry for the positive electrode of the energy storage device obtained above was uniformly applied to the surface of a current collector made of 20 μm thick aluminum foil using the doctor blade method so that the film thickness after drying would be 100 μm, and dried at 120°C for 20 minutes. After that, the density of the formed film (positive electrode active material layer) was 3.0 g / cm³. ３ A positive electrode for an energy storage device was obtained by press processing using a roll press machine to achieve the desired result.

[0181] <<Evaluation of Adhesion Strength of Active Material Layer to Current Collector>> On the surface of the positive electrode for the energy storage device obtained above, 10 cuts were made vertically and horizontally at 2 mm intervals using a knife to create a grid pattern, with the cuts reaching the current collector from the active material layer, and the active material layer was divided into small pieces. An 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Sellotape (registered trademark)", specified in JIS Z1522:2009) was applied to the surface of the cut active material layer and immediately peeled off, and the degree of detachment of the small pieces of active material layer was evaluated by visual inspection. The evaluation criteria are as follows. The evaluation results are shown in Table 2 below. (Evaluation Criteria) ・5 points: 0 pieces of active material detached. ・4 points: 1 to 5 pieces of active material detached. ・3 points: 6 to 20 pieces of active material detached. ・2 points: 21 to 40 pieces of active material detached. - 1 point: More than 41 active material particles have been lost.

[0182] <Fabrication and Evaluation of Negative Electrodes for Energy Storage Devices> <<Preparation of Slurry for Negative Electrodes of Energy Storage Devices>> In a twin-screw planetary mixer (manufactured by Primix Corporation, product name "TK Hibiscus Mix 2P-03"), 4 parts by mass of the resin composition (10% by mass aqueous solution of polymer (A-1)), 100 parts by mass of a mixed negative electrode active material prepared by the method described in Japanese Patent Application Publication No. 2017-097952, which is a mixture of a lithium and oxygen-containing silicon compound and a carbon-based active material in a mass ratio of 1:9 (here, as the carbon-based active material, a mixture of natural graphite and artificial graphite in a mass ratio of 5:5 was used), 5 parts by mass of acetylene black, and 68 parts by mass of water were added and stirred at 60 rpm for 1 hour.

[0183] Subsequently, the mixture was stirred for another hour to obtain a paste. After adding water to the obtained paste to adjust the solid content to 50%, the slurry for the negative electrode of the energy storage device was prepared by stirring and mixing using a stirring and defoaming machine (manufactured by Thinky Co., Ltd., product name "Awatori Rentaro") at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then at 1800 rpm for 1.5 minutes under vacuum (approximately 5.0 × 10³ Pa).

[0184] <<Fabrication of Negative Electrode for Energy Storage Device>> The slurry for the negative electrode of the energy storage device obtained above was uniformly applied to the surface of a current collector made of copper foil with a thickness of 20 μm using the doctor blade method so that the film thickness after drying would be 80 μm, and then dried at 120°C for 20 minutes. After that, the density of the formed film (negative electrode active material layer) was 1.9 g / cm³. ３ A negative electrode for an energy storage device was obtained by press processing using a roll press machine to achieve the desired result.

[0185] <<Assembly of Lithium-ion Battery Cells>> In a glove box where Ar replacement was performed to ensure a dew point of -80°C or lower, the negative electrode for the energy storage device manufactured above was punched out into a circular shape with a diameter of 15.95 mm and placed on a two-electrode coin cell (manufactured by Hosen Co., Ltd., product name "HS Flat Cell").

[0186] Next, a separator made of a porous polypropylene membrane punched out in a 24 mm diameter circle (manufactured by Cellguard Co., Ltd., product name "Cellguard #2400") was placed on top, and then 500 μL of electrolyte was injected to prevent air from entering. Then, the positive electrode for the energy storage device manufactured above, which had been punched out and molded in a 16.16 mm diameter circle, was placed on top of the separator, and the outer body of the two-electrode coin cell was sealed by closing it with screws, thereby assembling a lithium-ion battery cell (an example of an energy storage device). The electrolyte used here was an ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio) solvent with LiPF ６ This is a solution obtained by dissolving [the substance] at a concentration of 1 mole / L.

[0187] <<Evaluation of Cycle Endurance of Lithium-ion Batteries>> The lithium-ion batteries manufactured as described above were charged at a constant current (1.0C) in a constant temperature bath maintained at 25°C. Charging was continued at a constant voltage (4.2V) when the voltage reached 4.2V, and the charge was completed (cutoff) when the current reached 0.01C. Discharging was then started at a constant current (1.0C), and the discharge was completed (cutoff) when the voltage reached 3.0V, and the discharge capacity for the first cycle was calculated. This charge-discharge cycle was repeated 100 times. The capacity retention rate was calculated using the following formula and evaluated according to the following criteria. The evaluation results are shown in Table 2 below. Capacity Retention Rate (%) = (Discharge Capacity at 100 Cycles) / (Discharge Capacity at 1 Cycle) (Evaluation Criteria) ・5 points: Capacity retention rate of 95% or more. ・4 points: Capacity retention rate of 90% or more but less than 95%. ・3 points: Capacity retention rate of 85% or more but less than 90%. - 2 points: Volume retention rate is 80% or more but less than 85%. - 1 point: Volume retention rate is 75% or more but less than 80%. - 0 points: Volume retention rate is less than 75%.

[0188] (Examples 2-18) In the "Production of Resin Compositions" section above, slurry for positive and negative electrodes of energy storage devices, positive and negative electrodes for energy storage devices, and lithium-ion batteries were prepared in the same manner as in Example 1, except that the type and amount of polymer were as shown in Table 2 below. For Examples 12-14, evaluation was not performed because the polymer was water-insoluble.

[0189]

[0190] As is clear from Tables 1 and 2, the resin compositions for positive electrodes of energy storage devices prepared using the resin compositions according to the present invention shown in Examples 2-4, 6-11, and 15-18 show improved water solubility of the polymer and improved adhesion to the current collector compared to Examples 1, 5, and 12-14. This allows for the formation of an active material layer, resulting in a resin composition for energy storage devices, a slurry for electrodes of energy storage devices using the resin composition, an electrode for energy storage devices using the slurry, and an energy storage device using the electrode.

[0191] The present invention provides for industrial applicability as a resin composition for energy storage devices capable of forming an active material layer with improved water solubility of the polymer and improved adhesion to a current collector, a slurry for energy storage device electrodes using the resin composition, an energy storage device electrode using the slurry, and an energy storage device using the electrode.

Claims

1. A resin composition for energy storage devices, comprising a polymer and a liquid medium, wherein the polymer contains 1 to 90% by mass of structural units derived from an unsaturated carboxylic acid, 1 to 90% by mass of structural units derived from an unsaturated carboxylic acid ester having a number average molecular weight of less than 1300, and 1 to 30% by mass of structural units derived from an unsaturated carboxylic acid ester having a number average molecular weight of 1300 to 36000.

2. The resin composition for energy storage devices according to claim 1, wherein the unsaturated carboxylic acid ester having a number average molecular weight of 1,300 to 36,000 is a monofunctional monomer having one (meth)acryloyloxy group in one molecule.

3. The resin composition for energy storage devices according to claim 2, wherein the number of urethane bonds in one molecule of the monofunctional monomer is one or more.

4. The resin composition for energy storage devices according to claim 2, wherein the monofunctional monomer contains a curable component obtained by urethane reaction between a polyoxyalkylene monool represented by the following formula (1a) and a compound represented by the following formula (1b). (In equation (1a), R １２ R is an alkylene group having 2 to 4 carbon atoms. １３ R is an alkyl group having 1 to 20 carbon atoms or a carboxylic acid residue having 1 to 20 carbon atoms, and b is an integer from 20 to 600. In formula (1b), R １１ (where a is a hydrogen atom or a methyl group, and a is an integer from 1 to 4.) 5. The resin composition for energy storage devices according to claim 1, wherein the total amount of structural units derived from the unsaturated carboxylic acid and structural units derived from the unsaturated carboxylic acid ester having a number average molecular weight of less than 1300 is 50% by mass or more of the total amount of structural units of the polymer.

6. The resin composition for energy storage devices according to claim 1, wherein the polymer has a solubility in water at 25°C and 1 atm of 1 g or more per 100 g of water.

7. The resin composition for energy storage devices according to claim 1, wherein the liquid medium is water.

8. A slurry for an electrode of an energy storage device, comprising the resin composition for an energy storage device according to any one of claims 1 to 7, and an active material.

9. The slurry for an energy storage device electrode according to claim 8, wherein the active material contains at least one selected from the group consisting of olivine-type lithium-containing phosphate compounds, lithium cobaltate, lithium nickelate, lithium manganate, and ternary nickel-cobalt-manganate lithium.

10. The slurry for an electrode of an energy storage device according to claim 8, wherein the active material contains a silicon compound, and the silicon compound is a compound having lithium and oxygen.

11. An energy storage device electrode comprising a current collector and an active material layer formed by applying and drying the slurry for energy storage device electrodes described in claim 8 to the surface of the current collector.

12. An energy storage device comprising the energy storage device electrodes described in claim 11.

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