Composition for energy storage device, slurry for energy storage device electrode, energy storage device electrode, and energy storage device

Abstract

To provide a composition for a power storage device, which suppresses occurrence of electrode corrosion and decomposition of polymer components by preventing temporal pH increase in slurry for a power storage device electrode, and can improve adhesion and charge / discharge endurance characteristics of a power storage device electrode.SOLUTION: A composition for a power storage device according to the present invention contains a polymer (A) and a liquid medium (B). When the total of repeating units that are included in the polymer (A) is 100 mass%, the polymer (A) contains 5-90 mass% of repeating units (a1) derived from an unsaturated carboxylic acid, 5-90 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester with a hydroxyl group, and 1-50 mass% of repeating units (a3) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester with a hydroxyl group). At least a part of a hydroxyl group contained in the unsaturated carboxylic acid ester with a hydroxyl group is protected with a protecting group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a composition for a power storage device, a slurry for a power storage device electrode, a power storage device electrode, and a power storage device.

Background Art

[0002] In recent years, as a power source for driving electronic devices, a power storage device having a high voltage and a high energy density has been demanded. As such a power storage device, a lithium ion battery, a lithium ion capacitor, etc. are expected.

[0003] An electrode used in such a power storage device is manufactured by applying and drying a composition (slurry for a power storage device electrode) containing an active material and a polymer functioning as a binder on the surface of a current collector. Characteristics required for the polymer used as the binder include the binding ability between active materials, the adhesion ability between the active material and the current collector, the abrasion resistance in the process of winding the electrode, and the resistance to powder dropping such that fine powder of the active material does not fall off from the coated and dried composition coating film (hereinafter, also referred to as "active material layer") even by subsequent cutting. By such a binder material exhibiting good adhesion and reducing the internal resistance of the battery caused by the binder material, good charge and discharge characteristics can be imparted to the power storage device.

[0004] It has been empirically clarified that the binding ability between the above-mentioned active materials, the adhesion ability between the active material and the current collector, and the resistance to powder dropping are almost in a proportional relationship in terms of performance. Therefore, in this specification, these may be collectively referred to as "adhesion" using the term hereinafter.

[0005] Recently, in order to produce an electrochemical device excellent in capacity and charge-discharge cycle characteristics, the use of an active material having high reactivity with water has been studied. And when manufacturing a slurry for a power storage device electrode containing an active material and a binder, the use of an aqueous binder has been studied for the purpose of cost reduction, safety improvement, and environmental load reduction.

[0006] Under such circumstances, various binder materials have been proposed to solve the problems of slurries for electrodes of energy storage devices (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, when using slurries for electrodes of energy storage devices containing the binder materials disclosed in Patent Documents 1 and 2 above, there were several problems. For example, water in the slurry reacts with the active material to generate hydroxide ions (OH - ), and points such as the electrode being corroded by these hydroxide ions and the polymer component being decomposed can be cited. In addition, the energy storage device electrodes manufactured using such slurries for electrodes of energy storage devices were not sufficient in terms of characteristics such as adhesion and charge-discharge durability characteristics, and further improvement was required.

[0009] Some aspects of the present invention prevent the pH of the slurry for the power storage device electrode from rising over time, thereby suppressing the occurrence of corrosion of the electrode or the decomposition of the polymer component, and improving the adhesion and charge / discharge durability characteristics of the power storage device electrode. Also, some aspects of the present invention prevent the pH change over time, thereby suppressing the occurrence of corrosion of the electrode or the decomposition of the polymer component, and improving the adhesion and charge / discharge durability characteristics of the slurry for the power storage device electrode. Further, some aspects of the present invention provide a power storage device electrode in which corrosion is suppressed and the adhesion and charge / discharge durability characteristics can be improved. Furthermore, some aspects of the present invention provide a power storage device having excellent charge / discharge durability characteristics.

Means for Solving the Problems

[0010] The present invention has been made to solve at least a part of the above-described problems and can be realized as any of the following aspects.

[0011] One aspect of the composition for a power storage device according to the present invention is containing a polymer (A) and a liquid medium (B), when the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) is 5 to 90% by mass of repeating units (a1) derived from an unsaturated carboxylic acid, 5 to 90% by mass of repeating units (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group, 1 to 50% by mass of repeating units (a3) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group), and containing at least a part of the hydroxyl groups contained in the unsaturated carboxylic acid ester having a hydroxyl group is protected by a protecting group.

[0012] In one aspect of the composition for a power storage device, The total amount of the repeating unit (a1) and the repeating unit (a2) may be 50% by mass or more.

[0013] In any aspect of the composition for a power storage device, The protecting group may be deprotected by the action of a base.

[0014] In any aspect of the composition for a power storage device, The protecting group may be an acyl group.

[0015] In any aspect of the composition for a power storage device, The polymer (A) may further contain 0.1 to 30% by mass of a repeating unit (a4) derived from an aromatic vinyl compound.

[0016] In any aspect of the composition for a power storage device, The solubility of the polymer (A) in water at 25°C and 1 atm may be 1 g or more per 100 g of water.

[0017] In any aspect of the composition for a power storage device, When the polymer (A) is immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under the conditions of 70°C for 24 hours, the swelling ratio may be 100% by mass or more and 150% by mass or less.

[0018] In any aspect of the composition for a power storage device, The viscosity of a 5% by mass aqueous solution of the polymer (A) at 25°C and pH 8 may be 500 to 150,000 mPa·s / 30 rpm.

[0019] In any aspect of the composition for a power storage device, The liquid medium (B) may be water.

[0020] One aspect of the slurry for a power storage device electrode according to the present invention is It contains a composition for a power storage device according to any of the above aspects and an active material.

[0021] In one aspect of the slurry for a power storage device electrode, it may further contain at least one polymer selected from the group consisting of styrene-butadiene polymers, acrylic polymers, and fluoropolymers.

[0022] In any aspect of the slurry for a power storage device electrode, as the active material, it may contain at least one selected from the group consisting of olivine-type lithium-containing phosphate compounds, lithium cobaltate, lithium nickelate, lithium manganate, and lithium nickel cobalt manganate.

[0023] In any aspect of the slurry for a power storage device electrode, as the active material, it may contain a lithium compound and a silicon compound containing oxygen.

[0024] One aspect of the power storage device electrode according to the present invention is composed of a current collector and an active material layer formed by applying and drying the slurry for a power storage device electrode according to any of the above aspects on the surface of the current collector.

[0025] One aspect of the power storage device according to the present invention is equipped with the power storage device electrode according to the above aspect.

Advantages of the Invention

[0026] According to the composition for a power storage device of the present invention, by preventing the pH increase of the slurry for a power storage device electrode over time, the occurrence of electrode corrosion or the decomposition of the polymer component is suppressed, and a power storage device electrode excellent in adhesion and charge-discharge durability characteristics can be manufactured.

Embodiments for Carrying Out the Invention

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, but also includes various modifications implemented within the scope without changing the gist of the present invention.

[0028] In this specification, “(meth)acrylic acid~” is a concept encompassing both “acrylic acid~” and “methacrylic acid~”. Also, “~(meth)acrylate” is a concept encompassing both “~acrylate” and “~methacrylate”.

[0029] 1. Composition for a power storage device The composition for a power storage device according to an embodiment of the present invention contains a polymer (A) and a liquid medium (B). When the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 5 to 90% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid, 5 to 90% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group, and 1 to 50% by mass of a repeating unit (a3) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having the hydroxyl group). At least a part of the hydroxyl groups contained in the unsaturated carboxylic acid ester having the hydroxyl group is protected by a protecting group. Hereinafter, each component contained in the composition for a power storage device according to this embodiment will be described in detail.

[0030] 1.1. Polymer (A) The composition for an electric storage device according to this embodiment contains a polymer (A). When the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 5 to 90% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid (hereinafter also simply referred to as "repeating unit (a1)"), 5 to 90% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group (hereinafter also simply referred to as "repeating unit (a2)"), and 1 to 50% by mass of a repeating unit (a3) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group) (hereinafter also simply referred to as "repeating unit (a3)"). Further, in addition to the repeating units (a1) to (a3), the polymer (A) may contain a repeating unit derived from another monomer copolymerizable therewith.

[0031] The polymer (A) contained in the composition for an electric storage device according to this embodiment may be in the form of a latex dispersed in a 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 electric storage device electrode (hereinafter also simply referred to as "slurry") prepared by mixing with the active material is good, and the coatability of the slurry on the current collector is good, which is preferable.

[0032] Hereinafter, the repeating units constituting the polymer (A), the physical properties of the polymer (A), and the production method will be described in this order.

[0033] 1.1.1. Repeating units constituting the polymer (A) 1.1.1.1. Repeating unit (a1) derived from an unsaturated carboxylic acid The polymer (A) contains a repeating unit (a1) derived from an unsaturated carboxylic acid. The content ratio of the repeating unit (a1) derived from an unsaturated carboxylic acid is 5 to 90% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a1) is preferably 7% by mass, more preferably 10% by mass. The upper limit of the content ratio of the repeating unit (a1) is preferably 89% by mass, more preferably 88% by mass. By the polymer (A) containing the repeating 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. Furthermore, when an active material containing a silicon material is used, the binding ability between the active materials can be enhanced, so that an active material layer excellent in flexibility and adhesion to the current collector can be obtained.

[0034] The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these can be used. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

[0035] 1.1.1.2. Repeating unit (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group The polymer (A) contains a repeating unit (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group. The content ratio of the repeating unit (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group is 5 to 90% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a2) is preferably is 7% by mass, more preferably 10% by mass. The upper limit of the content ratio of the repeating unit (a2) is preferably 89% by mass, more preferably 88% by mass. By containing the repeating unit (a2) in the above range in the polymer (A), the dispersibility of the active material becomes good, and it becomes possible to produce a uniform active material layer. As a result, structural defects of the electrode plate disappear, and good charge and discharge characteristics are exhibited.

[0036] Among the unsaturated carboxylic acid esters having a hydroxyl group, (meth)acrylic acid esters having a hydroxyl group can be preferably used. Specific examples of the (meth)acrylic acid ester having a hydroxyl group include, for example, 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, etc. One or more selected from these can be used. Among these, it is preferably one or more selected from 2-hydroxyethyl (meth)acrylate, glycerin mono(meth)acrylate and glycerin di(meth)acrylate, and particularly preferably 2-hydroxyethyl (meth)acrylate.

[0037] At least a part of the hydroxyl group of the repeating unit (a2) is protected by a protecting group. When a liquid medium mainly composed of water is used to prepare the slurry, water reacts with the active material to generate hydroxide ions, and the pH shifts to the basic side, resulting in problems such as corrosion of the electrode and inhibition of the function of the polymer component. The composition for an electricity storage device according to the present embodiment contains a polymer (A) having a repeating unit (a2), and the protecting group in the repeating unit (a2) captures hydroxide ions which are bases and is deprotected, whereby the hydroxide ions in the system are consumed and an increase in the pH of the slurry over time can be prevented. Thereby, the occurrence of electrode corrosion and the deterioration of the function of the polymer component can be effectively suppressed.

[0038] The protecting group is not particularly limited as long as it can be used as a protecting group for a hydroxyl group, but it is preferably one that is hydrolyzed and deprotected by the action of a base. Examples of such protecting groups include trihydrocarbylsilyl groups such as trimethylsilyl group and tert-butyldimethylsilyl group; and acyl groups such as acetyl group, benzoyl group, and pival group. Among these, an acyl group is preferable in order to facilitate the introduction into the repeating unit (a2).

[0039] Examples of the acyl group include aliphatic acyl groups and aromatic acyl groups. The aliphatic acyl group may be linear or branched, and a linear one is preferable in order to improve both solubility in organic solvents and water solubility. Also, the aliphatic acyl group may be saturated or unsaturated, and a saturated one is preferable in order to improve oxidation resistance. The number of carbon atoms of the aliphatic acyl group is preferably 2 to 20, more preferably 2 to 15, and even more preferably 2 to 10 in order to improve both solubility in organic solvents and water solubility. The aliphatic hydrocarbon group in the aliphatic acyl group may have heteroatoms such as oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, and silicon. Specific examples of the aliphatic acyl group include acyl groups derived from fatty acids such as acetic acid, propionic acid, and pivalic acid. Also, the aromatic acyl group is not particularly limited as long as it is an acyl group derived from an aromatic carboxylic acid. The number of carbon atoms of the aromatic acyl group is preferably 6 to 20, more preferably 6 to 15, and even more preferably 6 to 10 in order to improve both solubility in organic solvents and water solubility. The aromatic hydrocarbon group in the aromatic acyl group may have heteroatoms such as oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, and silicon. Specific examples of the aromatic acyl group include acyl groups derived from aromatic carboxylic acids such as benzoic acid, 4-methoxybenzoic acid, naphthalene-1-carboxylic acid, and naphthalene-2-carboxylic acid.

[0040] These protecting groups may be used alone or in any combination of two or more.

[0041] The substitution ratio of the hydroxyl group in the repeating unit (a2) by a protecting group (hereinafter also referred to as "substitution ratio of the hydroxyl group") is preferably 30 mol% or more, more preferably 45 mol% or more, and particularly preferably 65 mol% or more in order to suppress the increase in the slurry pH. And in order to simplify the synthesis, it is preferably 99 mol% or less, more preferably 98 mol% or less, and particularly preferably 97 mol% or less. The substitution ratio of the hydroxyl group can be calculated using the solid content concentration, gas chromatography or 1 1H-NMR, and specifically can be calculated by the method described in the examples. By setting the substitution ratio of the hydroxyl group within the above range, the increase in pH of the slurry over time can be prevented, and as a result, the occurrence of electrode corrosion and the deterioration of the function of the polymer component can be effectively suppressed.

[0042] As a method for substituting the hydroxyl group in the repeating unit (a2) with a protecting group, a method of reacting the repeating unit (a2) with a compound for introducing the protecting group can be mentioned. Examples of the compound for introducing an acyl group include, for example, R 1 -(C=O)-X (where R 1 represents a linear or branched alkyl group or alkenyl group, or an aryl group, and X represents a halogen atom) or a compound represented by R 1 -(C=O)-O-(C=O)-R 1 (where R 1 is the same as above, and a plurality of R 1 may be the same or different).

[0043] The timing of substituting the hydroxyl group in the repeating unit (a2) with a protecting group may be simultaneous with the production of the polymer (A) or after the production of the polymer (A). Examples of being simultaneous with the production of the polymer (A) include, in the method for producing the polymer (A) described later, a method of reacting a compound for introducing the protecting group together with a monomer mixture, a suitable emulsifier, a chain transfer agent, and a polymerization initiator; a method of reacting a compound for introducing the protecting group after the completion of emulsion polymerization and before adding a neutralizing agent; and a method of reacting a compound for introducing the protecting group after adding a neutralizing agent. When reacting a compound for introducing a protecting group after the completion of emulsion polymerization, an organic solvent in which the compound for introducing the protecting group dissolves may be present. Examples of such organic solvents include aliphatic hydrocarbon solvents such as pentane, hexane, and octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; halogen solvents such as dichloromethane and 1,2-dichloroethane; amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide; ether solvents such as tetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, diglyme, and triglyme; ketone solvents such as acetone, dibutyl ketone, and methyl isobutyl ketone; nitrile solvents such as acetonitrile, propanenitrile, and benzonitrile, etc. However, there is no particular limitation as long as it is a solvent in which the compound for introducing the protecting group dissolves. These organic solvents may be used alone or as a mixture of two or more.

[0044] On the other hand, examples of the timing of substituting the hydroxyl group in the repeating unit (a2) with a protecting group after the production of the polymer (A) include a method of dissolving the polymer obtained by concentrating the polymerization mixture in a suitable organic solvent and reacting a compound for introducing the protecting group. Such an organic solvent can be selected from among organic solvents in which the compound for introducing the protecting group dissolves. However, since the polymer (A) dissolves and the reaction efficiency can be improved, tetrahydrofuran, acetone, and acetonitrile are preferred.

[0045] At this time, if necessary, nitrogen-containing compounds having no N-H bond such as tertiary amines, amidine compounds, diazabicyclo[2,2,2]octane, pyridine, 4-dimethylaminopyridine; metal hydroxides such as sodium hydroxide and potassium hydroxide may be added.

[0046] In addition, the polymer (A) can also be obtained by polymerizing an unsaturated carboxylic acid ester in which at least a part of the hydroxyl group is protected by a protecting group (hereinafter also referred to as "protecting group and hydroxyl group-containing unsaturated carboxylic acid ester").

[0047] Examples of the protecting group and hydroxyl group-containing unsaturated carboxylic acid ester include compounds in which at least a part of the hydroxyl group of the unsaturated carboxylic acid ester containing a hydroxyl group described in the repeating unit (a2) is protected by the above-mentioned protecting group.

[0048] When the total of the repeating units contained in the polymer (A) is 100% by mass, the total amount of the repeating unit (a1) and the repeating unit (a2) 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 the repeating unit (a1) and the repeating unit (a2) is within the above range, the dispersibility of the active material becomes good, and the flexibility and adhesiveness are improved, so that good charge-discharge cycle characteristics and charge-discharge durability characteristics are exhibited.

[0049] 1.1.1.3. Repeating unit (a3) derived from unsaturated carboxylic acid ester The polymer (A) contains a repeating unit (a3) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having the hydroxyl group). The content ratio of the repeating unit (a3) is 1 to 50% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a3) is preferably 2% by mass, more preferably 3% by mass. The upper limit of the content ratio of the repeating unit (a3) is preferably 49% by mass, particularly preferably 48% by mass. When the polymer (A) contains the repeating unit (a3) within the above range, the polymer (A) can exist in an aqueous solution state, so that the coating property on the active material is enhanced, a uniform active material layer can be formed, and the structural defects of the electrode plate are reduced. Further, since the polymer (A) has high electrolyte affinity, it is possible to suppress an increase in the internal resistance due to becoming an electric resistance component even when the active material is coated.

[0050] Among unsaturated carboxylic acid esters, (meth)acrylic acid esters can be preferably used. Examples of the (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, etc. One or more selected from these can be used. Among these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate and ethylene glycol di(meth)acrylate are preferable, and methyl (meth)acrylate is particularly preferable.

[0051] 1.1.1.4. Other repeating units In addition to the repeating units (a1) to (a3), the polymer (A) may contain repeating units derived from other monomers copolymerizable therewith. Examples of such repeating units include repeating units (a4) derived from aromatic vinyl compounds (hereinafter also simply referred to as "repeating units (a4)"), repeating units (a5) derived from (meth)acrylamide (hereinafter also simply referred to as "repeating units (a5)"), repeating units (a6) derived from α,β-unsaturated nitrile compounds (hereinafter also simply referred to as "repeating units (a6)"), repeating units (a7) derived from compounds having a sulfonic acid group (hereinafter also simply referred to as )"repeating units (a7)"), repeating units derived from cationic monomers, and the like.

[0052] <Repeating unit (a4) derived from an aromatic vinyl compound> Polymer (A) may contain a repeating unit (a4) derived from an aromatic vinyl compound. When the total of the repeating units contained in polymer (A) is 100% by mass, the content ratio of the repeating unit (a4) is preferably 0.1 to 30% by mass. The lower limit of the content ratio of the repeating unit (a4) is more preferably 0.2% by mass, and particularly preferably 0.5% by mass. The upper limit of the content ratio of the repeating unit (a4) is more preferably 27% by mass, and particularly preferably 25% by mass. When polymer (A) contains the repeating unit (a4) within the above range, it may exhibit good adhesion to active materials and the like, and a power storage device electrode excellent in flexibility and adhesion may be obtained.

[0053] The aromatic vinyl compound is not particularly limited, and examples thereof include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used.

[0054] <Repeating unit (a5) derived from (meth)acrylamide> The polymer (A) may contain a repeating unit (a5) derived from (meth)acrylamide. The content ratio of the repeating unit (a5) is preferably 0 to 10% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a5) is more preferably 1% by mass, and particularly preferably 2% by mass. The upper limit of the content ratio of the repeating unit (a5) is more preferably 8% by mass, and particularly preferably 5% by mass. When the polymer (A) contains the repeating unit (a5) within the above range, the dispersibility of the active material and the filler in the slurry may be improved. In addition, the flexibility of the obtained active material layer may be appropriate, and the adhesion between the current collector and the active material layer may be improved. Furthermore, since the binding ability between the active materials containing a carbon material such as graphite or a silicon material can be enhanced, an active material layer having better flexibility and adhesion to the current collector may be obtained.

[0055] (Meth)acrylamide is not particularly limited, and examples thereof 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 amide, acrylamide tert-butylsulfonic acid, etc. One or more selected from these can be used.

[0056] <Repeating unit (a6) derived from an α,β-unsaturated nitrile compound> The polymer (A) may contain a repeating unit (a6) derived from an α,β-unsaturated nitrile compound. The content ratio of the repeating unit (a6) is preferably 0 to 60% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a6) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a6) is more preferably 55% by mass, and particularly preferably 50% by mass. When the polymer (A) contains the repeating unit (a6) within the above range, it becomes possible to reduce the dissolution of the polymer (A) in the electrolyte solution, and it may be possible to suppress a decrease in adhesion due to the electrolyte solution. Further, it may be possible to suppress an increase in internal resistance due to the dissolved polymer component becoming an electric resistance component in the power storage device.

[0057] The α,β-unsaturated nitrile compound is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, etc., and one or more selected from these can be used. Among these, one or more selected from the group consisting of acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is particularly preferable.

[0058] <Repeating unit (a7) derived from a compound having a sulfonic acid group> The polymer (A) may contain a repeating unit (a7) derived from a compound having a sulfonic acid group. The content ratio of the repeating unit (a7) is preferably 0 to 10% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a7) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a7) is more preferably 8% by mass, and particularly preferably 5% by mass. When the polymer (A) contains the repeating unit (a7) within the above range, the dispersibility of the active material becomes good, and it becomes possible to produce a uniform active material layer. Therefore, there may be no structural defects in the electrode plate, and good charge and discharge characteristics may be exhibited.

[0059] The compounds having a sulfonic acid group are not particularly limited, and examples thereof include compounds such as vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali salts thereof. One or more selected from these can be used.

[0060] <Repeating unit derived from a cationic monomer> The polymer (A) may contain repeating units derived from a cationic monomer. The cationic monomer is not particularly limited, but is preferably at least one monomer selected from the group consisting of secondary amine (salt), tertiary amine (salt), and quaternary ammonium salt. Specific examples of these cationic monomers are not particularly limited, but include 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'-methylpropylideneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methacryloylcholine chloride, tris(2-acryloyloxyethyl) isocyanurate, 2-vinylpyridine, quinacridine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazoles dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichloramide, N-allylbenzylamine, N-allylaniline, 2,4-diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-hepten-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, and the like. One or more selected from these can be used.

[0061] 1.1.2. Physical properties of the polymer (A) 1.1.2.1. Solubility in water The polymer (A) is preferably a water-soluble polymer. The "water-soluble polymer" in the present invention means that the solubility in water at 25°C and 1 atm is 1 g or more per 100 g of water. It refers to a polymer. When the polymer (A) is a water-soluble polymer, the surface of the active material is easily coated with the polymer (A) which is excellent in flexibility and adhesion. Therefore, it is possible to effectively suppress the peeling due to the expansion and contraction of the active material during charge and discharge, and it is easy to obtain a power storage device showing good charge and discharge durability characteristics. In addition, it is preferable because the stability of the slurry becomes good and the coatability of the slurry on the current collector also becomes good.

[0062] 1.1.2.2. Swelling ratio When the polymer (A) is immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under the conditions of 70 ° C for 24 hours, the swelling ratio is preferably 100% by mass or more and 150% by mass or less. The lower limit of the swelling ratio is more preferably 105% by mass, and particularly preferably 110% by mass. The upper limit of the swelling ratio is more preferably 145% by mass, and particularly preferably 140% by mass. When the swelling ratio is within the above range, the polymer (A) can swell moderately with respect to the electrolytic solution. As a result, the solvated lithium ions can easily reach the active material, reduce the internal resistance of the electrode, and realize better repeated charge and discharge characteristics. In addition, if the swelling ratio is within the above range, no large volume change occurs, so the adhesion is also excellent. The swelling ratio of the polymer (A) can be measured by the method described in the examples below.

[0063] 1.1.2.3. Viscosity Regarding the aqueous solution of the polymer (A) with a solid content concentration of 5% and a pH of 8, when the viscosity at a temperature of 25 ° C is measured using a B-type viscometer, it 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 the polymer (A) is within the above range, the dispersibility of the active material becomes good, and it is easy to produce a homogeneous active material layer. As a result, an electrode or the like without structural defects is obtained, which is preferable because it shows good charge and discharge characteristics. This viscosity measurement can be carried out in accordance with JIS Z8803. As the B-type viscometer, for example, "RB-80L", "TVB-10" manufactured by Toki Sangyo Co., Ltd. can be used.

[0064] 1.1.3. Method for Producing Polymer (A) The method for producing the polymer (A) is not particularly limited. For example, it can be carried out by an emulsion polymerization method in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. As the emulsifier (surfactant), chain transfer agent, and polymerization initiator, the compounds described in Japanese Patent No. 5999399 etc. can be used.

[0065] The emulsion polymerization method for synthesizing the polymer (A) may be carried out by single-stage polymerization or multi-stage polymerization of two or more stages.

[0066] When the synthesis of the polymer (A) is carried out by single-stage 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, preferably for 4 to 36 hours.

[0067] When the synthesis of the polymer (A) is carried out by two-stage polymerization, the polymerization in each stage is preferably set as follows.

[0068] The usage ratio of the monomer used in the first-stage polymerization is preferably in the range of 20 to 100% by mass, more preferably in the range of 25 to 100% by mass, based on the total mass of the monomers (the sum of the mass of the monomer used in the first-stage polymerization and the mass of the monomer used in the second-stage polymerization). By carrying out the first-stage polymerization with such a usage ratio of the monomer, it is possible to obtain particles of the polymer (A) having excellent dispersion stability and being less likely to form aggregates, and it is also preferable that the temporal viscosity increase of the composition for the power storage device is suppressed. It is also preferable that the temporal viscosity increase is suppressed.

[0069] The type and usage ratio of the monomer used in the second-stage polymerization may be the same as or different from the type and usage ratio of the monomer used in the first-stage polymerization.

[0070] In order to improve the dispersibility of the resulting polymer (A), the polymerization conditions in each stage are preferably as follows. ·First-stage polymerization; preferably at a temperature of 40 to 80 °C; preferably with a polymerization time of 2 to 36 hours; preferably with a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more. ·Second-stage polymerization; preferably at a temperature of 40 to 80 °C; preferably with a polymerization time of 2 to 18 hours.

[0071] By setting the total solid concentration in emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed with good dispersion stability of the resulting polymer (A). This total solid concentration is preferably 48% by mass or less, more preferably 45% by mass or less.

[0072] Whether the synthesis of polymer (A) is carried out by one-stage polymerization or by a two-stage polymerization method, after the emulsion polymerization is completed, a neutralizing agent is added to the polymerization mixture to adjust the pH to 7.0 to 8.5, preferably 7.2 to 8.5, more preferably 7.5 to 8.4. The neutralizing agent used here is not particularly limited, and examples include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia, etc. By setting the pH within the above range, the stability of polymer (A) becomes good. After the neutralization treatment, the polymerization mixture is concentrated to increase the solid concentration while maintaining good stability of polymer (A).

[0073] The timing of substituting the hydroxyl group of the repeating unit (a2) with a protecting group when synthesizing polymer (A) may be simultaneous with the emulsion polymerization or after the emulsion polymerization is completed. However, since the operation is easy, it is preferably after the emulsion polymerization is completed. When provided after the emulsion polymerization is completed, it may be at any stage before or after adding the neutralizing agent, and a liquid medium in which the compound for introducing the protecting group dissolves may be appropriately added. The liquid medium is not particularly limited as long as it can dissolve the compound for introducing the protecting group, but is preferably a non-aqueous medium. Adding the liquid medium may improve the introduction ratio of the compound for introducing the protecting group.

[0074] 1.1.4. Content ratio of polymer (A) In the composition for a power storage device according to this embodiment, the content ratio of polymer (A) is preferably 10 to 100% by mass, more preferably 20 to 95% by mass, and particularly preferably 25 to 90% by mass in 100% by mass of the polymer components. Here, the polymer components include polymer (A), polymers other than polymer (A) described later, thickeners, and the like.

[0075] 1.2. Liquid medium (B) The composition for a power storage device according to this embodiment contains a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium can contain a non-aqueous medium other than water. Examples of this non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc., and one or more selected from these can be used. By using an aqueous medium as the liquid medium (B) in the composition for a power storage device according to this embodiment, the degree of adverse impact on the environment is reduced, and the safety for handling workers is also increased.

[0076] The content ratio of the non-aqueous medium contained in the aqueous medium is preferably 1 0% by mass or less, more preferably 5% by mass or less, and particularly preferably substantially not contained in 100% by mass of the aqueous medium. Here, "substantially not contained" means to the extent that a non-aqueous medium is not intentionally added as the liquid medium (B), and it may include non-aqueous media that are unavoidably mixed in when preparing the composition for a power storage device.

[0077] 1.3. Other additives The composition for a power storage device according to this embodiment can contain additives other than the above-described components as needed. Examples of such additives include polymers other than polymer (A), preservatives, thickeners, and the like.

[0078] 1.3.1. Polymers other than polymer (A) The composition for an electric storage device according to this embodiment may contain a polymer other than polymer (A). Such polymers are not particularly limited, and examples thereof include acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as constituent units, fluorine-based polymers such as PVDF (polyvinylidene fluoride), and styrene-butadiene polymers (hereinafter also referred to as "SBR"). These polymers may be used alone or in combination of two or more. By containing these polymers, flexibility and adhesion may be further improved in some cases.

[0079] 1.3.2. Preservative The composition for an electric storage device according to this embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, mold, etc. and the generation of foreign substances when the composition for an electric storage device is stored. Specific examples of the preservative include the compounds described in Japanese Patent No. 5477610 and the like.

[0080] 1.3.3. Thickener The composition for an electric storage device according to this embodiment may contain a thickener. By containing a thickener, the coating property of the slurry and the charge / discharge characteristics of the obtained electric storage device may be further improved in some cases.

[0081] Specific examples of the thickener include, for example, cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the cellulose compounds or the poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer; and water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid and vinyl esters. Among these, alkali metal salts of carboxymethyl cellulose, alkali metal salts of poly(meth)acrylic acid, etc. are preferable.

[0082] Examples of commercially available products of these thickeners include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0083] When the composition for a power storage device according to this embodiment contains a thickener, the content ratio of the thickener is preferably 5% by mass or less, more preferably 0.1 to 4% by mass, based on 100% by mass of the total solid content of the composition for a power storage device.

[0084] 1.4. pH of the Composition for a Power Storage Device The pH of the composition for a power storage device according to this embodiment is preferably 7.0 to 8.5, more preferably 7.2 to 8.5, and particularly preferably 7.5 to 8.4. If the pH is within the above range, problems such as insufficient leveling property and liquid dripping can be suppressed, and it becomes easy to manufacture a power storage device electrode that achieves both good electrical characteristics and adhesion.

[0085] As used herein, "pH" refers to a physical property measured as follows. At 25°C, it is the value measured in accordance with JIS Z8802:2011 using a pH meter calibrated with neutral phosphate standard solution and borate standard solution as pH standard solutions and a glass electrode. Examples of such pH meters include "HM-7J" manufactured by Toa DKK Corporation and "D-51" manufactured by Horiba, Ltd.

[0086] It should be noted that although it is not denied that the pH of the composition for a power storage device is affected by the monomer composition constituting the polymer (A), it is added that it is not determined only by the monomer composition. That is, it is generally known that even with the same monomer composition, the pH of the composition for a power storage device changes depending on polymerization conditions and the like, and the examples in the present specification only show one example of this.

[0087] ​For example, even with the same monomer composition, when all of the unsaturated carboxylic acid is initially charged into the polymerization reaction solution and then other monomers are sequentially added, and when monomers other than the unsaturated carboxylic acid are charged into the polymerization reaction solution and the unsaturated carboxylic acid is finally added, the amount of carboxy groups derived from the unsaturated carboxylic acid exposed on the surface of the resulting polymer is different. Thus, even by simply changing the order of adding the monomers in the polymerization method, the pH of the composition for the power storage device is considered to be significantly different.

[0088] 2. Slurry for the power storage device electrode The slurry for the power storage device electrode according to one embodiment of the present invention contains the above-described composition for the power storage device and an active material. The above-described composition for the power storage device is used as a material for producing a power storage device electrode (active material layer) with improved binding ability between active materials, adhesion ability between the active material and the current collector, and powder falling resistance. Hereinafter, the slurry for the power storage device electrode will be described in detail.

[0089] 2.1. Composition for the power storage device The composition for the power storage device has been described above, so the description will be omitted.

[0090] The content ratio of the polymer component in the slurry for the power storage device electrode according to the present embodiment is preferably 1 to 8 parts by mass, more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 6 parts by mass with respect to 100 parts by mass of the active material. When the content ratio of the polymer component is within the above range, the dispersibility of the active material in the slurry is good, and the coatability of the slurry is excellent. Here, the polymer component includes polymer (A), polymers other than polymer (A), a thickener, and the like.

[0091] 2.2. Active material Examples of the active material used in the slurry for the power storage device electrode according to the present embodiment include 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(However, A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively). Examples include complex metal oxides represented by the formula, and other metal oxides. Specific examples thereof include the compounds described in Japanese Patent No. 5999399 and the like.

[0092] Examples of the oxide containing a lithium atom include at least one selected from lithium atom-containing oxides (olivine-type lithium-containing phosphates) represented by the following general formula (1) and having an olivine-type crystal structure. and the like.

[0093] Li 1-x M x (AO4) ·····(1) (In formula (1), 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 satisfying the relationship 0 < x < 1.) Note that the value of x in the general formula (1) is selected so that the valence of the entire general formula (1) becomes 0 in accordance with the valences of M and A.

[0094] Examples of the olivine-type lithium-containing phosphate compound include LiFePO4, LiCoPO4, LiMnPO4, Li 0.90 Ti 0.05 Nb 0.05 Fe 0.30 Co 0.30 Mn 0.30 PO4 and the like. Among these, LiFePO4 (lithium iron phosphate) is particularly preferred because the iron compound used as a raw material is easily available and inexpensive.

[0095] The average particle size of the olivine-type lithium-containing phosphate compound is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.

[0096] Examples of the carbon material include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and the like.

[0097] Examples of the silicon material include elemental silicon, silicon oxide, silicon alloy, etc. In addition, for example, SiC, SiO x C y (0 < x ≤ 3, 0 < y ≤ 5), Si3N4, Si2N2O, SiO x (0 < x ≤ 2) silicon oxide composites (such as the materials described in JP-A-2004-185810 and JP-A-2005-259697), and the silicon materials described in JP-A-2004-185810 can be used. Also, the lithium compound and the silicon compound containing oxygen described in JP-A-2017-097952 can be used. Examples of the silicon oxide include the composition formula SiO xSilicon oxides represented by (0 < x < 2, preferably 0.1 ≦ x ≦ 1) are preferred. As the silicon alloy, an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron, and molybdenum is preferred. These transition metal silicon alloys are preferably used because they have high electronic conductivity and high strength. Further, when the active material contains these transition metals, the transition metals present on the surface of the active material are oxidized to form oxides having hydroxyl groups on the surface, which is also preferred in that the binding force with the binder becomes better. As the silicon alloy, it is more preferable to use a silicon-nickel alloy or a silicon-titanium alloy, and it is particularly preferable to use a silicon-titanium alloy. The content ratio of silicon in the silicon alloy is preferably 10 mol% or more with respect to all of the metal elements in the alloy, and more preferably 20 to 70 mol%. Note that the silicon material may be any of single crystal, polycrystal, and amorphous.

[0098] Examples of the silicon compound containing the lithium compound and oxygen include silicon compounds (SiO x : 0.5 ≦ x ≦ 1.6) and silicon compound particles containing crystalline Li2SiO3 (hereinafter also referred to as "lithium-silicon compound particles"). Among the lithium silicates obtained by changing SiO2, the lithium-silicon compound particles contain a large amount of Li2SiO3 that is stable to water, so the stability with respect to the aqueous slurry used during electrode fabrication is improved, and the cycle characteristics of the power storage device are also improved, which is preferable. The median diameter of the lithium-silicon compound particles 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 electrical characteristics become good. On the other hand, by setting the median diameter to 15 μm or less, the particles are less likely to crack, so it is difficult for new surfaces to appear.

[0099] Further, in the active material layer, conductive polymers such as polyacene; A X B Y O Z(However, A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively). Composite metal oxides represented by the above formula, or other metal oxides, etc. may be included. Examples of the composite metal oxides include lithium cobaltate, lithium nickelate, lithium manganate, ternary lithium nickel cobalt manganate, etc.)

[0100] The slurry for a power storage device electrode according to this embodiment can be used when manufacturing either the positive electrode or the negative electrode of the power storage device, but it is preferably used for both the positive electrode and the negative electrode.)

[0101] When a liquid medium mainly composed of water is used to prepare the slurry for the positive electrode, there is a problem of poor charge-discharge characteristics. It is known that the positive electrode active material has high reactivity with water, and it is considered that one of the factors is that the hydroxide ions generated by the reaction between the positive electrode active material and water corrode the surface of the positive electrode.)

[0102] However, the power storage device electrode manufactured using the slurry for a power storage device electrode according to this embodiment can exhibit good charge-discharge characteristics without the occurrence of the above problems even when a liquid medium mainly composed of water is used as the liquid medium of the slurry for the positive electrode. The reason for this is considered to be that the protecting group of the polymer (A) reacts with the hydroxide ions generated by the reaction between the positive electrode active material and water and is deprotected, so that the hydroxide ions in the system are consumed and the corrosion of the positive electrode surface can be suppressed.)

[0103] On the other hand, when manufacturing a negative electrode, it is preferable to use a silicon material among the above-exemplified active materials. Since the silicon material has a larger lithium storage amount per unit weight compared to other active materials, by containing a silicon material as the negative electrode active material, the storage capacity of the power storage device can be increased, and as a result, the output and energy density of the power storage device can be increased.

[0104] Moreover, among silicon materials, a silicon compound containing a lithium compound and oxygen is more preferable. The silicon material may react with lithium during charging to generate SiO2, which becomes an irreversible component. Therefore, by previously containing a lithium compound and oxygen in the silicon compound, the generation of the irreversible component can be suppressed, and the charge-discharge characteristics can be improved.

[0105] However, when using a silicon compound containing a lithium compound and oxygen as the negative electrode active material, there is a problem that the adhesion is likely to be impaired when using a liquid medium mainly composed of water. The silicon compound containing a lithium compound and oxygen easily reacts with water to generate hydroxide ions, and it is considered that this hydroxide ion decomposes the polymer component, which is one of the factors.

[0106] In addition, when the polymer component is decomposed, the stress of the polymer component covering the active material decreases, and it becomes impossible to follow the expansion and contraction of the active material. As a result, there is a problem that the electrode expansion becomes large, and the isolation of the silicon compound (negative electrode active material) containing a lithium compound and oxygen causes deterioration of the charge-discharge characteristics of the power storage device.

[0107] The power storage device electrode produced using the slurry for the power storage device electrode according to this embodiment can exhibit good adhesion without causing the above-described problems even when a silicon compound containing a lithium compound and oxygen is used. The reason for this is thought to be that the hydroxide ions generated by the reaction between the negative electrode active material and water react with the protecting groups of the polymer (A) and are deprotected, thus consuming the hydroxide ions in the system and suppressing the decomposition of the polymer component.

[0108] The content ratio of the silicon material in 100% by mass of the active material is preferably 1% by mass or more, more preferably 1 to 50% by mass, still more preferably 5 to 45% by mass, and particularly preferably 10 to 40% by mass. When the content ratio of the silicon material in 100% by mass of the active material is within the above range, a power storage device excellent in the balance between the output and energy density improvement of the power storage device and the charge-discharge durability characteristics can be obtained.

[0109] The shape of the active material is preferably particulate. The average particle diameter of the active material is preferably 0.1 to 100 μm, 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 measuring device based on the laser diffraction method as the measurement principle. Examples of such a laser diffraction type particle size distribution measuring device include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by Horiba, Ltd.).

[0110] The usage ratio of the active material is preferably such that the content ratio of the polymer (A) with respect to 100 parts by mass of the active material is 0.5 to 8 parts by mass, more preferably such that it is 1 to 7 parts by mass, and particularly preferably such that it is 2 to 6 parts by mass. By setting the usage ratio in this way, an electrode with excellent adhesion, small electrode resistance, and excellent charge-discharge characteristics can be manufactured.

[0111] 2.3. Other Components In the slurry for the electrode of the energy storage device according to this embodiment, other components may be added as necessary in addition to the components described above. Examples of such components include polymers other than polymer (A), thickeners, liquid media, conductivity-imparting agents, pH adjusters, corrosion inhibitors, cellulose fibers, and the like. As the polymer other than polymer (A) and the thickener, they can be appropriately selected from the compounds exemplified in the section of "1.3. Other Additives" and used at the same purpose and content ratio.

[0112] <Liquid Medium> In the slurry for the electrode of the energy storage device according to this embodiment, in addition to the carry-over from the composition for the energy storage device, a liquid medium may be further added. The added liquid medium may be of the same type or different from the liquid medium (B) contained in the composition for the energy storage device, but it is preferably selected from the liquid media exemplified in the section of "1.2. Liquid Medium (B)" and used.

[0113] The content ratio of the liquid medium (including the carry-over from the composition for the energy storage device) in the slurry for the electrode of the energy storage device according to this embodiment is preferably such that the solid content concentration in the slurry (which refers to the ratio of the total mass of the components other than the liquid medium in the slurry to the total mass of the slurry. The same applies hereinafter) is 30 to 70% by mass, and more preferably 40 to 60% by mass.

[0114] <Conductivity-Imparting Agent> In the slurry for the electrode of the energy storage device according to this embodiment, for the purpose of imparting conductivity and buffering the volume change of the active material due to the ingress and egress of lithium ions, a conductivity-imparting agent may be further added.

[0115] Specific examples of the conductivity-imparting agent include carbons such as activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotube. Among these, acetylene black or carbon nanotube can be preferably used. The content ratio of the conductivity-imparting agent 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 with respect to 100 parts by mass of the active material.

[0116] <pH adjuster / corrosion inhibitor> For the slurry for the power storage device electrode according to the present embodiment, a pH adjuster or a corrosion inhibitor or both may be further added for the purpose of suppressing the corrosion of the current collector according to the type of the active material.

[0117] Examples of the pH adjuster 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. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferable. Also, it can be selected and used from among the neutralizing agents described in the method for producing the polymer (A).

[0118] Examples of the corrosion inhibitor 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. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferable.

[0119] <Cellulose fiber> Cellulose fibers may be further added to the slurry for the electrode of the energy storage device according to this embodiment. By adding cellulose fibers, the adhesion of the active material to the current collector may be improved. It is considered that the fibrous cellulose fibers can prevent the active material from falling off and improve the adhesion to the current collector by fiber-bonding adjacent active materials by wire adhesion or wire contact.

[0120] The average fiber length of the cellulose fibers can be selected from a wide range of 0.1 to 1000 μm. For example, it is preferably 1 to 750 μm, more preferably 1.3 to 500 μm, still 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) is good, and the adhesion of the active material to the current collector may be improved.

[0121] The fiber length of the cellulose fibers may be uniform, and the coefficient of variation of the fiber length ([standard deviation of fiber length / average fiber length] × 100) is, for example, preferably 0.1 to 100, more preferably 0.5 to 50, and particularly preferably 1 to 30. The maximum fiber length of the cellulose fibers is, for example, preferably 500 μm or less, more preferably 300 μm or less, still more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0122] When the average fiber length of the cellulose fibers is 5 times or less the average thickness of the active material layer, it is advantageous because the surface smoothness (coating film uniformity) and the adhesion of the active material to the current collector are further improved. That is, the average fiber length of the cellulose fibers 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.

[0123] The average fiber diameter of the cellulose fiber is preferably from 1 nm to 10 μm, more preferably from 5 nm to 2.5 μm, still more preferably from 20 nm to 700 nm, and particularly preferably from 30 nm to 200 nm. When the average fiber diameter 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. Therefore, the cellulose fiber is preferably a cellulose nanofiber having a nanometer-sized average fiber diameter (for example, a cellulose nanofiber having an average fiber diameter of 10 nm to 500 nm, preferably about 25 nm to 250 nm).

[0124] The fiber diameter of the cellulose fiber is also uniform, and the coefficient of variation of the fiber diameter ([standard deviation of fiber diameter / average fiber diameter] × 100) is preferably from 1 to 80, more preferably from 5 to 60, and particularly preferably from 10 to 50. The maximum fiber diameter of the cellulose fiber is preferably 30 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less.

[0125] The ratio (aspect ratio) of the average fiber length to the average fiber diameter of the cellulose fiber is, for example, preferably from 10 to 5000, more preferably from 20 to 3000, and particularly preferably from 50 to 2000. When the aspect ratio is within the above range, the adhesion of the active material to the current collector becomes good, and the surface smoothness (coating film uniformity) of the electrode may become good without weakening the breaking strength of the fiber.

[0126] 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 = about 20) measured based on electron micrographs.

[0127] The material of the cellulose fiber only needs to be formed of a polysaccharide having a β-1,4-glucan structure. Examples of the cellulose fiber include cellulose fibers derived from higher plants (e.g., wood fibers (such as wood pulp from coniferous trees, broad-leaved trees, etc.), bamboo fibers, sugarcane fibers, seed hair fibers (e.g., cotton linter, bombax cotton, kapok, etc.), bast fibers (e.g., hemp, mulberry, kozo, etc.), leaf fibers (e.g., manila hemp, New Zealand hemp, etc.), etc., such as natural cellulose fibers (pulp fibers)), cellulose fibers derived from animals (e.g., ascidian cellulose, etc.), cellulose fibers derived from bacteria (e.g., cellulose contained in nata de coco, etc.), and chemically synthesized cellulose fibers (e.g., rayon, cellulose esters (such as cellulose acetate, etc.), cellulose ethers (e.g., hydroxyalkyl celluloses such as hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, etc., alkyl celluloses such as methyl cellulose, ethyl cellulose, etc., such as cellulose derivatives, etc.)). These cellulose fibers may be used alone or in combination of two or more.

[0128] Among these cellulose fibers, cellulose fibers derived from pulp, such as cellulose fibers derived from higher plants (e.g., wood fibers (such as wood pulp from coniferous trees, broad-leaved trees, etc.) and seed hair fibers (such as cotton linter pulp, etc.)), are preferred because it is easy to prepare nanofibers having an appropriate aspect ratio.

[0129] The method for producing the cellulose fiber is not particularly limited, and a conventional method can be used according to the target fiber length and fiber diameter, for example, the methods described in Japanese Patent Publication No. 60-19921, Japanese Patent Application Laid-Open No. 2011-26760, Japanese Patent Application Laid-Open No. 2012-25833, Japanese Patent Application Laid-Open No. 2012-36517, Japanese Patent Application Laid-Open No. 2012-36518, Japanese Patent Application Laid-Open No. 2014-181421, etc. may be used.

[0130] 2.4. Method for Preparing a Slurry for an Electrode of an Electric Energy Storage Device The slurry for a power storage device electrode according to this embodiment may be produced by any method as long as it contains the above-described composition for a power storage device and the active material. From the viewpoint of producing a slurry having better dispersibility and stability more efficiently and inexpensively, it is preferable to add the active material and optional components used as necessary to the composition for a power storage device and mix them. Specific production methods include, for example, the methods described in Japanese Patent No. 6544150 and the like.

[0131] 3. Power Storage Device Electrode A power storage device electrode according to an embodiment of the present invention includes a current collector and an active material layer formed by applying and drying the above-described slurry for a power storage device electrode on the surface of the current collector. Such a power storage device electrode can be produced by applying the above-described slurry for a power storage device electrode on the surface of a current collector such as a metal foil to form a coating film, and then drying the coating film to form an active material layer. The power storage device electrode produced in this way has an active material layer containing the above-described polymer (A), active material, and optional components added as necessary bound to the surface of the current collector. Therefore, the occurrence of corrosion on the electrode surface is suppressed, the adhesion is excellent, and the charge-discharge durability characteristics of the power storage device can be improved.

[0132] The current collector is not particularly limited as long as it is made of a conductive material. However, when the power storage device electrode is used in a lithium-ion secondary battery, for example, a current collector made of a metal such as iron, copper, aluminum, nickel, stainless steel, etc. can be used. In particular, an aluminum or copper current collector is preferable.

[0133] When the power storage device electrode is used in a nickel-metal hydride secondary battery, for example, a current collector made of punched metal, expanded metal, wire mesh, foamed metal, sintered body of reticulated metal fibers, metal-plated resin plate, etc. can be used.

[0134] The shape and thickness of the current collector are not particularly limited. For example, a sheet-shaped current collector with a thickness of about 0.001 to 0.5 mm is preferred. When applying the slurry for the electrode of the power storage device to the surface of the current collector, the application method is not particularly limited. As the application method, for example, the doctor blade method, dip method, reverse roll method, direct roll method, gravure method, extrusion method, dipping method, brush coating method, etc. can be appropriately used.

[0135] The coating amount of the slurry for the electrode of the power storage device is not particularly limited. A coating amount that results in a thickness of the positive electrode active material layer of 0.005 to 5 mm after applying the slurry for the electrode of the power storage device and removing the liquid medium (a concept that includes both water and optionally used non-aqueous media) is preferred, and a coating amount that results in a thickness of 0.01 to 2 mm is more preferred.

[0136] When the thickness of the active material layer is within the above range, the electrolyte can be efficiently infiltrated into the active material layer. As a result, the transfer of metal ions accompanying the charge and discharge between the active material and the electrolyte in the active material layer can be easily performed, so that the internal resistance of the electrode can be further reduced.

[0137] In addition, when the thickness of the active material layer is within the above range, even when the electrode is processed by folding, winding, etc., the adhesion between the active material layer and the current collector is good, and the active material layer is difficult to peel off from the current collector. That is, it is also preferable in that a power storage device electrode rich in flexibility can be easily obtained.

[0138] The drying method (the method for removing water and optionally used non-aqueous media) of the coating film formed by applying the slurry for the electrode of the power storage device is not particularly limited. For example, drying by warm air, hot air, low humidity air; vacuum drying; drying by irradiation with (far) infrared rays, electron beams, etc. can be used. For example, drying by warm air, hot air, low humidity air; vacuum drying; drying by irradiation with (far) infrared rays, electron beams, etc. can be used.

[0139] When drying the coating film formed by applying the slurry for the electrode of the power storage device, the drying rate can be appropriately set so that the liquid medium can be removed as quickly as possible under the conditions that, for example, cracks do not occur in the active material layer due to stress concentration and the active material layer does not peel off from the current collector.

[0140] After drying the coating film formed by applying the slurry for the electrode of the power storage device, it is preferable to increase the density of the active material layer by pressing the electrode of the power storage device and adjust the density and the porosity in the active material layer to the ranges shown below.

[0141] The density of the active material layer after pressing is preferably 1.1 to 2.1 g / cm 3 for the negative electrode, more preferably 1.2 to 2.0 g / cm 3 even more preferably 1.3 to 1.8 g / cm 3 even more preferably 1.4 to 1.7 g / cm 3 and particularly preferably 1.4 to 1.7 g / cm. For the positive electrode, it is preferably 2.5 to 3.5 g / cm 3 more preferably 2.6 to 3.4 g / cm 3 even more preferably 2.7 to 3.3 g / cm 3 even more preferably 2.8 to 3.2 g / cm 3 and particularly preferably 2.8 to 3.2 g / cm. If the density of the active material layer is within the above range, a power storage device electrode with good adhesion between the current collector and the active material layer, excellent powder falling property, and excellent electrical characteristics can be obtained.

[0142] The porosity of the active material layer after pressing is preferably 10 to 50%, more preferably 15 to 45%, and particularly preferably 20 to 40%. If the porosity of the active material layer is within the above range, a power storage device electrode with good adhesion between the current collector and the active material layer, excellent powder falling property, and excellent electrical characteristics can be obtained.

[0143] Moreover, if the porosity of the active material layer is within the above range, the electrolyte can be sufficiently impregnated into the active material layer, and the active material surface and the electrolyte can be sufficiently in contact with each other. As a result, the transfer of lithium ions between the active material and the electrolyte becomes easy, and good charge and discharge characteristics can be exhibited.

[0144] Examples of the pressing method include methods such as die pressing and roll pressing. The pressing conditions can be appropriately set according to 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 small number of preliminary experiments by those skilled in the art.

[0145] When using the roll pressing method, the pressing conditions can be, for example, as follows. · Linear pressure of the roll press: 0.1 to 10 (t / cm), preferably 0.5 to 5 (t / cm). · Roll temperature: 20 to 100 °C. · Feed rate of the energy storage device electrode (rotation speed of the roll): 0.5 to 50 m / min, preferably 1 to 30 m / min.

[0146] 4. Energy storage device The energy storage device according to an embodiment of the present invention includes the above-described energy storage device electrode, further contains an electrolyte, and can be manufactured according to a conventional method using components such as a separator. Specific manufacturing methods include, for example, a method of stacking a negative electrode and a positive electrode via a separator, winding, folding, etc. according to the battery shape, storing them in a battery container, injecting an electrolyte into the battery container, and sealing it. The shape of the battery can be an appropriate shape such as a coin type, a cylindrical type, a rectangular type, a laminate type, etc.

[0147] The electrolyte may be in a liquid state or a gel state, and may be selected from known electrolytes used in energy storage devices according to the type of active material so as to effectively exhibit the function as a battery. The electrolyte can be a solution in which an electrolyte is dissolved in a suitable solvent. Examples of such electrolytes and solvents include compounds described in, for example, Japanese Patent No. 5999399.

[0148] The above-described power storage device is applicable to a lithium-ion secondary battery, an electric double layer capacitor, a lithium-ion capacitor, etc. that require discharge at a high current density. Among these, a lithium-ion secondary battery is particularly preferable. In the power storage device electrode and the power storage device according to the present embodiment, members other than the composition for the power storage device can be members known for use in a lithium-ion secondary battery, an electric double layer capacitor, or a lithium-ion capacitor.

[0149] 5. Examples Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified. In this specification, the polymer (A) produced in Example 1 is referred to as "polymer (A-1)", and similarly, the polymer (A) produced in Example 2 is referred to as "polymer (A-2)", etc.

[0150] 5.1. Example 1 5.1.1. Production and Physical Property Evaluation of Polymer (A) 5.1.1.1. Production of Polymer (A) Into a separable flask with a capacity of 7 liters, 900 parts by mass of water, 0.5 part by mass of dodecylbenzenesulfonic acid, 30 parts by mass of acrylic acid, 1 part by mass of 2-ethylhexyl acrylate (2EHA), 20 parts by mass of 2-hydroxyethyl methacrylate (HEMA), and 40 parts by mass of 2-hydroxyethyl acrylate (HEA) were added. Then, 8 parts by mass of styrene and 1 part by mass of divinylbenzene were added, and the mixture was stirred well to prepare a monomer emulsion containing the mixture of the above monomers. The temperature rise inside the separable flask was started. When the internal temperature reached 60°C, 0.5 parts by mass of ammonium persulfate was added as a polymerization initiator. Then, 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. Thereafter, the internal temperature of the separable flask was raised to 85°C, and this temperature was maintained for 3 hours to conduct a polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then a 10 wt% aqueous sodium hydroxide solution was added to adjust the pH to 8.0, thereby obtaining an aqueous polymer solution containing 10% by mass of the polymer. Next, the acylating agent shown in Table 1 was charged and reacted at 80°C for 4 hours to obtain an aqueous polymer solution containing a polymer (A-1) in which a part of the hydroxyl groups of the polymer was substituted with acyl groups.

[0151] 5.1.1.2. Physical Property Evaluation of Polymer (A) For the polymer (A-1) obtained above, evaluations of pH, viscosity, swelling ratio, and water solubility were conducted. In the evaluations of pH, viscosity, and water solubility, an aqueous solution of the polymer (A-1) was used as the measurement sample. The results are shown in Table 1.

[0152] <Measurement of pH> For the aqueous solution of the polymer (A-1) obtained above, the pH at 25°C was measured using a pH meter (manufactured by Horiba, Ltd.).

[0153] <Measurement of Viscosity> For the aqueous solution of the polymer (A-1) obtained above, water was added so that the concentration of the polymer (A-1) became 5 mass %. For the aqueous solution of the polymer (A-1) thus obtained, the viscosity at 25°C was measured using a B-type viscometer.

[0154] <Measurement of Swelling Ratio> The polymer (A-1) obtained above was dried in a constant temperature bath at 85 °C for 24 hours to prepare a film. 1 g of this film was immersed in 20 mL of a mixed solution composed of propylene carbonate (PC) and diethyl carbonate (DEC) (PC / DEC = 1 / 1 (volume ratio), hereinafter this mixed solution is referred to as "PC / DEC"), and shaken at 70 °C for 24 hours. Next, it was filtered through a 300-mesh wire mesh to separate the insoluble matter, and then the weight (Y (g)) of the residue obtained by evaporating and removing PC / DEC of the dissolved matter was measured. Also, after removing the PC / DEC adhering to the surface of the insoluble matter (film) separated by the above filtration by absorbing it with paper, the weight (Z (g)) of the insoluble matter (film) was measured. The swelling ratio of the polymer (A-1) was determined by the following formula. Swelling ratio (mass %) = (Z / (1 - Y)) × 100

[0155] <Evaluation of water solubility> The aqueous solution of the polymer (A-1) obtained above was diluted by adding water so that the concentration of the polymer (A-1) became 1 mass %. The transparency of the thus-obtained composition for a power storage device at 1 atm and 25 °C was visually confirmed. The results are shown in Table 1. When the dilution was transparent or translucent, it was judged as "water-soluble" and denoted as "A", and when the dilution was cloudy, it was judged as "water-insoluble" and denoted as "B".

[0156] <Substitution rate of hydroxyl group> The acyl group substitution rate of the hydroxyl group possessed by the polymer (A-1) was calculated as shown in formula (ii) using formula (i).

Number

[0157] 5.1.2. Preparation and Physical Property Evaluation of Slurry for Positive Electrode of Energy Storage Device 5.1.2.1. Preparation of Slurry for Positive Electrode of Energy Storage Device Into a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK High Bis Mix 2P - 03"), 4 mass parts of the polymer (A - 1) (in terms of solid content value, added as a 10 mass% aqueous solution of the polymer (A - 1) obtained above), 100 mass parts of NMC622 (trade name "ME - 8A", manufactured by Beijing Easpring Material Technology Co., Ltd.) as the positive electrode active material, 5 mass parts of acetylene black, and 20 mass parts of water were charged, and stirring was carried out at 60 rpm for 1 hour. Note that the NMC622 is an example of the positive electrode active material.

[0158] Thereafter, stirring was continued for another 1 hour to obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 70%, using a stirring and defoaming machine (manufactured by Shinchi Co., Ltd., trade name "Awa Tori Rentaro"), stirring was carried out at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under vacuum (about 5.0×10 3 Pa) to prepare a slurry for the positive electrode of the energy storage device.

[0159] 5.1.2.2. pH Evaluation of Slurry for Positive Electrode of Energy Storage Device The slurry for the positive electrode of the energy storage device obtained above was left standing at 25°C for 4 days. When the pH at 25°C at 1 day and 4 days later was measured with a pH meter (manufactured by Horiba, Ltd.), they were 8.6 and 9.2 respectively. The evaluation results are shown in Table 1 below.

[0160] 5.1.3. Fabrication and Evaluation of Positive Electrode for Energy Storage Device 5.1.3.1. Fabrication of the Positive Electrode for the Energy Storage Device On the surface of the current collector made of an aluminum foil with a thickness of 20 μm, the slurry for the positive electrode of the energy storage device obtained above was uniformly applied by the doctor blade method so that the film thickness after drying would be 100 μm, and then dried at 120 °C for 20 minutes. Then, in order for the density of the formed film (positive electrode active material layer) to be 3.0 g / cm 3 , a positive electrode for the energy storage device was obtained by pressing using a roll press machine.

[0161] 5.1.3.2. Evaluation of Adhesion Strength On the surface of the positive electrode for the energy storage device obtained above, using a knife, ten cuts were made vertically and horizontally at 2 mm intervals reaching from the active material layer to the depth of the current collector to create a grid of cuts. An adhesive tape with a width of 18 mm (manufactured by Nichiban Co., Ltd., trade name "Cellotape" (registered trademark), specified in JIS Z1522) was attached to these cuts and immediately peeled off, and the degree of active material dropout was visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below. (Evaluation Criteria) · 5 points: The number of dropouts of the active material layer is 0. · 4 points: The number of dropouts of the active material layer is 1 - 5. · 3 points: The number of dropouts of the active material layer is 6 - 20. · 2 points: The number of dropouts of the active material layer is 21 - 40. · 1 point: The number of dropouts of the active material layer is 41 or more.

[0162] 5.1.4. Fabrication and Evaluation of the Energy Storage Device 5.1.4.1. Preparation of the Slurry for the Negative Electrode of the Energy Storage Device Into a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK High Visc Mix 2P - 03"), 1 part by mass (in terms of solid content) of a thickener (trade name "CMC2200", manufactured by Daicel Corporation), 100 parts by mass (in terms of solid content) of graphite as the negative electrode active material, and 68 parts by mass of water were charged, and stirring was carried out at 60 rpm for 1 hour.

[0163] Next, SBR (trade name "TRD105A", manufactured by JSR Corporation) was added in an amount corresponding to 2 parts by mass (in terms of solid content), and the mixture was further stirred for 1 hour to obtain a paste. Water was added to the obtained paste, and after adjusting the solid content to 50%, using a stirring and defoaming machine (manufactured by Shinki Corporation, trade name "Awa Toriren Tarou"), it was stirred and mixed at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under vacuum to prepare a slurry for the negative electrode of the power storage device.

[0164] 5.1.4.2. Fabrication of the Negative Electrode for the Power Storage Device On the surface of a current collector made of a copper foil with a thickness of 20 μm, the slurry for the negative electrode of the power storage device obtained above was uniformly applied by the doctor blade method so that the film thickness after drying would be 80 μm. Then, it was dried at 120°C for 20 minutes. After that, the formed film (negative electrode active material layer) was pressed using a roll press machine so that the density would be 1.9 g / cm 3 to obtain a negative electrode for the power storage device.

[0165] 5.1.4.3. Assembly of the Lithium-Ion Battery Cell In a glove box purged with Ar so that the dew point would be -80°C or lower, a negative electrode for the power storage device manufactured above, which was punched and formed into a circle with a diameter of 15.95 mm, was placed on a two-pole coin cell (manufactured by Hokuen Co., Ltd., trade name "HS Flat Cell").

[0166] Next, a separator made of a porous polypropylene film punched into a circle with a diameter of 24 mm (manufactured by Celgard LLC, trade name "Celgard #2400") was placed. Further, after injecting 500 μL of the electrolyte so that air would not enter, a positive electrode for the power storage device manufactured above, which was punched and formed into a circle with a diameter of 16.16 mm, was placed on top of the separator and then covered with the outer body of the two-pole coin cell and sealed with a screw to assemble a lithium-ion battery cell (an example of a power storage device). The electrolyte used here is a solution in which LiPF6 is dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0167] 5.1.4.4. Evaluation of Cycle Characteristics of Lithium-Ion Batteries For the lithium-ion battery manufactured above, in a thermostatic bath adjusted to 25°C, charging was started at a constant current (1.0C). When the voltage reached 4.2V, charging was continued at a constant voltage (4.2V). The time when the current value reached 0.01C was defined as the completion of charging (cut-off). Thereafter, discharging was started at a constant current (1.0C), and the time when the voltage reached 3.0V was defined as the completion of discharging (cut-off), and the discharge capacity of the first cycle was calculated. In this way, 100 charge-discharge cycles were repeated. The capacity retention rate was calculated by the following formula and evaluated according to the following criteria. The evaluation results are shown in Table 1 below. Capacity Retention Rate (%) = (Discharge Capacity of the 100th Cycle) / (Discharge Capacity of the First Cycle) (Evaluation Criteria) · 5 points: The capacity retention rate is 95% or more. · 4 points: The capacity retention rate is 90% or more and less than 95%. · 3 points: The capacity retention rate is 85% or more and less than 90%. · 2 points: The capacity retention rate is 80% or more and less than 85%. · 1 point: The capacity retention rate is 75% or more and less than 80%. · 0 point: The capacity retention rate is less than 75%.

[0168] 5.2. Examples 2 to 13, Comparative Examples 1 to 8 In the section of "5.1.1.1. Production of Polymer (A)" above, except that the types and amounts of the monomer and the acylating agent were the same as those described in Table 1 or Table 2 below, an aqueous polymer solution having a pH of 8.0 and containing 10% by mass of the polymer was obtained in the same manner. Except for using the aqueous polymer solution thus obtained, a slurry for a positive electrode of an electric storage device, a positive and negative electrode for an electric storage device, and a lithium-ion battery were produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1.

[0169] 5.3. Example 14 In the same manner as in Example 2, an aqueous polymer solution having a pH of 8.0 and containing 10% by mass of polymer (A-2) was obtained. Next, 1 part by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation) (in terms of solid content, added as an aqueous solution with a concentration of 2% by mass), and 3 parts by mass of polymer (A-2) (in terms of solid content, added as an aqueous polymer solution having a pH of 8.0 and containing 10% by mass of polymer (A-2) obtained above) were used. Except for these changes, a slurry for a positive electrode of an electric storage device was prepared in the same manner as in Example 1.

[0170] Except for using the slurry for a positive electrode of an electric storage device prepared above, positive and negative electrodes for an electric storage device and a lithium-ion battery were produced in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

[0171] 5.4. Examples 15 to 27 Except for changing the composition of the slurry for a positive electrode of an electric storage device as shown in Table 3 below, slurries for a positive electrode of an electric storage device were prepared in the same manner as in Example 14, positive and negative electrodes for an electric storage device and a lithium-ion battery were produced, and evaluated in the same manner as in Example 14.

[0172] 5.5. Example 28 5.5.1. Preparation and Physical Property Evaluation of Slurry for Negative Electrode of Electric Storage Device In the same manner as in Example 1, an aqueous polymer solution having a pH of 8.0 and containing 10% by mass of polymer (A-1) was obtained. Next, into a twin-screw planetary mixer (manufactured by Primix Corporation, trade name "TK High Vis Mix 2P-03"), 4 parts by mass of polymer (A-1) (in terms of solid content, added as an aqueous polymer solution having a pH of 8.0 and containing 10% by mass of polymer (A-1) obtained above), a mixed negative electrode active material in which a silicon compound containing a lithium compound and oxygen prepared by the method described in JP-A-2017-097952 and a carbon-based active material were mixed at a mass ratio of 1:9 (here, as the carbon-based active material, a mixture of natural graphite and artificial graphite coated with a pitch layer at a mass ratio of 5:5 was used), 100 parts by mass, 5 parts by mass of acetylene black, and 68 parts by mass of water were charged, and stirred at 60 rpm for 1 hour.

[0173] Thereafter, it was further stirred for 1 hour to obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 50%, using a stirring and defoaming machine (manufactured by Shinchi Co., Ltd., trade name "Awatori Rentaro"), it was stirred and mixed at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under vacuum (about 5.0×10 3 Pa), thereby preparing a slurry for a negative electrode of an electric storage device.

[0174] 5.5.2. Evaluation of pH of Slurry for Negative Electrode of Electric Storage Device The slurry for a negative electrode of an electric storage device obtained above was left standing at 25°C for 1 day. When the pH at 25°C at the time after 1 day was measured with a pH meter (manufactured by Horiba, Ltd.), it was 10.2. The evaluation results are shown in Table 4 below.

[0175] 5.5.3. Fabrication and Evaluation of Negative Electrode for Electric Storage Device 5.5.3.1. Fabrication of Negative Electrode for Electric Storage Device On the surface of a current collector made of a copper foil with a thickness of 20 μm, the slurry for a negative electrode of an electric storage device obtained above was uniformly applied by the doctor blade method so that the film thickness after drying would be 80 μm, and it was dried at 120°C for 20 minutes. Thereafter, by pressing using a roll press machine so that the density of the formed film (negative electrode active material layer) would be 1.9 g / cm 3 a negative electrode for an electric storage device was obtained.

[0176] 5.5.3.2. Evaluation of Adhesion Strength Evaluation was carried out in the same manner as the method described in "5.1.3.2. Evaluation of Adhesion Strength" except that the negative electrode for an electric storage device obtained above was used.

[0177] 5.5.4. Fabrication and Evaluation of Electric Storage Device A slurry for a positive electrode of an electric storage device was prepared in the same manner as in Example 1, and a positive electrode for an electric storage device was fabricated. A lithium-ion battery was fabricated in the same manner as in Example 1 except that the positive electrode for an electric storage device thus obtained and the negative electrode for an electric storage device obtained above were used, and evaluation was carried out in the same manner as in Example 1.

[0178] 5.6. Examples 29 to 40, Comparative Examples 9 to 16 The slurries for the negative electrodes of the power storage devices were each prepared in the same manner as in Example 28, except that the type of polymer added to the slurries for the negative electrodes of the power storage devices was changed as shown in Table 4 or Table 5 below. The positive and negative electrodes for the power storage devices and the lithium ion batteries were each fabricated, and evaluated in the same manner as in Example 28.

[0179] 5.7. Example 41 An aqueous polymer solution having a pH of 8.0 and containing 10% by mass of polymer (A-4) was obtained in the same manner as in Example 4. Next, 1 part by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation) (converted to solid content value, added as an aqueous solution having a concentration of 2% by mass) and 3 parts by mass of polymer (A-4) (converted to solid content value, added as an aqueous polymer solution having a pH of 8.0 and containing 10% by mass of polymer (A-4) obtained above) were used. The slurry for the negative electrode of the power storage device was prepared in the same manner as in Example 28, except for the above changes.

[0180] The positive and negative electrodes for the power storage device and the lithium ion battery were each fabricated in the same manner as in Example 28, except that the slurry for the negative electrode of the power storage device prepared above was used, and evaluated in the same manner as in Example 28.

[0181] 5.8. Examples 42 to 54 The slurries for the negative electrodes of the power storage devices were each prepared in the same manner as in Example 41, except that the composition of the slurries for the negative electrodes of the power storage devices was changed as shown in Table 6 below. The positive and negative electrodes for the power storage devices and the lithium ion batteries were each fabricated, and evaluated in the same manner as in Example 41.

[0182] 5.9. Evaluation Results Table 1 to Table 6 below show the polymer compositions used in Examples 1 to 54 and Comparative Examples 1 to 16, and the evaluation results for each. The numerical values representing the polymer compositions shown in Table 1 to Table 2 represent mass%, and the numerical values representing the compositions shown in Table 3 and Table 6 represent parts by mass.

[0183]

Table 1

[0184]

Table 2

[0185]

Table 3

[0186]

Table 4

[0187]

Table 5

[0188]

Table 6

[0189] In addition, the abbreviations of each component in the above Tables 1 to 6 represent the following compounds or trade names, respectively. <Unsaturated carboxylic acid> ·TA: Itaconic acid ·AA: Acrylic acid ·MAA: Methacrylic acid <Unsaturated carboxylic acid ester having a hydroxyl group> ·HEMA: 2-Hydroxyethyl methacrylate ·HEA: 2-Hydroxyethyl acrylate ·GLM: Glycerin monomethacrylate <Unsaturated carboxylic acid ester> ·MMA: Methyl methacrylate ·CHMA: Cyclohexyl methacrylate ·2EHA: 2-Ethylhexyl acrylate ·BA: Butyl acrylate ·EA: Ethyl acrylate ·AMA: Allyl acrylate <Aromatic vinyl compound> ·ST: Styrene ·DVB: Divinylbenzene <(Meth)acrylamide> ·AAM: Acrylamide ·MAM: Methacrylamide <α,β-unsaturated nitrile compound> ·AN: Acrylonitrile <Compound having a sulfonic acid group> ·NASS: Sodium styrenesulfonate <Acylating agent> ·A: Acetic anhydride ·B: Benzoyl chloride ·P: Pivaloyl chloride <Thickening agent> ·CMC: Trade name "CMC2200", manufactured by Daicel Corporation ·Alginic acid: Trade name "Sodium alginate 80 - 120", manufactured by Fujifilm Wako Pure Chemical Corporation <Binder> ·SBR: Trade name "TRD105A", manufactured by JSR Corporation ·AE: An acrylic binder manufactured by the following procedure was used. ·FAE: Trade name "TRD202A", manufactured by JSR Corporation

[0190] (Synthesis of acrylic binder (AE)) 150 parts by mass of water and 0.2 part by mass of sodium dodecylbenzenesulfonate were charged into a separable flask with a volume of 7 liters, and the inside of the separable flask was sufficiently purged with nitrogen. On the other hand, in another container, 60 parts by mass of water, 0.8 part by mass of an ether sulfate type emulsifier (trade name "Adeka Resope SR1025", manufactured by ADEKA Corporation) as an emulsifier, 1 part by mass of cyclohexyl methacrylate, 3 parts by mass of acrylonitrile, 58 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of n-butyl acrylate, 5 parts by mass of n-butyl methacrylate, 5 parts by mass of ethyl acrylate, 2 parts by mass of allyl methacrylate as monomers, 2 parts by mass of acrylamide, 10 parts by mass of styrene, 1 part by mass of sodium styrene sulfonate, and 3 parts by mass of acrylic acid were added and stirred well to prepare a monomer emulsion containing the mixture of the above monomers. The temperature rise inside the separable flask was started. When the internal temperature reached 60°C, 0.5 part by mass of ammonium persulfate was added as a polymerization initiator. Then, 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. Thereafter, the internal temperature of the separable flask was raised to 85°C and this temperature was maintained for 3 hours to carry out a polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then ammonia water was added to adjust the pH to 8.0, thereby obtaining an aqueous dispersion containing 30% by mass of particles composed of an acrylic polymer (AE).

[0191] As is clear from Table 1 to Table 2 above, the slurry for a positive electrode of an electricity storage device prepared using the composition for an electricity storage device according to the present invention shown in Examples 1 to 13 can preferably bind active materials to each other as compared with the cases of Comparative Examples 1 to 8, and a positive electrode for an electricity storage device having good charge-discharge durability characteristics was obtained. In the polymer (A) contained in the composition for an electricity storage device of Examples 1 to 13 shown in Table 1 above, a part of the hydroxyl groups in the repeating unit is protected by a protecting group. It is presumed that the protecting group was deprotected by the hydroxide ions generated by the contact between the liquid medium (B) and the active material, and the hydroxide ions in the system could be consumed, so that the corrosion of the electrode surface could be suppressed. As a result, it is presumed that the resistance could be lowered and good charge-discharge durability characteristics were exhibited.

[0192] Also, as is clear from the results in Table 3 above, in the slurry for a positive electrode of an electricity storage device prepared using the composition for an electricity storage device according to the present invention shown in Examples 14 to 27, the active materials can be more preferably bound to each other by using the polymer (A) in combination with a thickener than by using the polymer (A) alone, and moreover, it was found that the adhesion between the active material layer and the current collector can be maintained more favorably.

[0193] Furthermore, as is clear from the results in Table 4 to Table 5 above, according to the slurry for a negative electrode of a power storage device prepared using the composition for a power storage device according to the present invention shown in Examples 28 to 40, it was found that good results were shown even when a negative electrode active material was used. The polymer (A) contained in the composition for a power storage device of Examples 28 to 40 shown in Table 4 to Table 5 above has a part of the hydroxyl groups in the repeating unit protected by a protecting group. The protecting group is deprotected by hydroxide ions generated by the contact of the liquid medium (B) and the active material, and can consume the hydroxide ions in the system, suppressing the hydrolysis of CMC and alginic acid used as the polymer or the thickener, and also enabling good dispersion of the active material and the filler. Therefore, it is considered that excellent adhesion strength was shown. Furthermore, since the coating property of the polymer (A) to the active material could be maintained high, it is presumed that electrode expansion was suppressed and as a result, good charge-discharge durability characteristics were shown.

[0194] As is clear from the results in Table 6 above, the slurry for a negative electrode of a power storage device prepared using the composition for a power storage device according to the present invention shown in Examples 41 to 54 can bind the active materials to each other more preferably by using it in combination with a thickener rather than using the polymer (A) alone, and moreover, it was found that the adhesion between the active material layer and the current collector can be maintained in a better state.

[0195] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations having the same functions, methods, and results, or configurations having the same purposes and effects). The present invention also includes configurations in which non-essential parts of the configurations described in the above embodiments are replaced with other configurations. Furthermore, the present invention also includes configurations that exhibit the same operational effects as the configurations described in the above embodiments or configurations that can achieve the same purposes. Furthermore, the present invention also includes configurations in which known technologies are added to the configurations described in the above embodiments.

Claims

1. A composition for a power storage device, comprising a polymer (A) and a liquid medium (B), wherein when the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 5 to 90% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid, 5 to 90% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester having a hydroxyl group, 1 to 50% by mass of a repeating unit (a3) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group), and at least a part of the hydroxyl groups contained in the unsaturated carboxylic acid ester having a hydroxyl group is protected by a protecting group.

2. The composition for a power storage device according to claim 1, wherein the total amount of the repeating unit (a1) and the repeating unit (a2) is 50% by mass or more.

3. The composition for a power storage device according to claim 1 or claim 2, wherein the protecting group is deprotected by the action of a base.

4. The composition for a power storage device according to any one of claims 1 to 3, wherein the protecting group is an acyl group.

5. The composition for a power storage device according to any one of claims 1 to 4, wherein the polymer (A) further contains 0.1 to 30% by mass of a repeating unit (a4) derived from an aromatic vinyl compound.

6. The composition for a power storage device according to any one of claims 1 to 5, wherein the solubility of the polymer (A) in water at 25°C and 1 atm is 1 g or more per 100 g of water.

7. The composition for a power storage device according to any one of claims 1 to 6, wherein the swelling ratio when the polymer (A) is immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 at 70°C for 24 hours is 100% by mass or more and 150% by mass or less.

8. The composition for a power storage device according to any one of claims 1 to 7, wherein the viscosity of a 5% by mass aqueous solution of the polymer (A) at 25°C and pH 8 is 500 to 150,000 mPa·s / 30 rpm.

9. The composition for a power storage device according to any one of claims 1 to 8, wherein the liquid medium (B) is water.

10. A slurry for a power storage device electrode, comprising the composition for a power storage device according to any one of claims 1 to 9 and an active material.

11. The slurry for a power storage device electrode according to claim 10, further containing at least one polymer selected from the group consisting of styrene-butadiene polymers, acrylic polymers, and fluorine polymers.

12. The slurry for a power storage device electrode according to claim 10 or claim 11, containing at least one selected from the group consisting of olivine-type lithium-containing phosphate compounds, lithium cobaltate, lithium nickelate, lithium manganate, and lithium nickel cobalt manganate as the active material.

13. The slurry for a power storage device electrode according to claim 10 or claim 11, containing a lithium compound and a silicon compound having oxygen as the active material.

14. A power storage device electrode comprising a current collector and an active material layer formed by applying and drying the slurry for a power storage device electrode according to any one of claims 10 to 13 on the surface of the current collector.

15. A power storage device comprising the power storage device electrode according to claim 14.

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