Binder for electrodes, electrode, and energy storage device

Abstract

To provide a binder which is soluble in a solvent and exhibits high adhesiveness to an active material and to an electrode, specifically a binder suitable for an inorganic solid electrolyte battery.SOLUTION: Through repeated research to achieve the above problem, it was discovered that the problem can be solved by an acrylic binder containing an acrylic copolymer having structural units derived from (meth)acrylic acid esters and structural units derived from unsaturated monomers having a halogen group or a carboxy group.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an electrode binder used in secondary batteries such as lithium ion secondary batteries and nickel hydrogen secondary batteries, and electricity storage devices such as electrochemical capacitors, particularly inorganic solid electrolyte batteries using an inorganic solid electrolyte, an electrode containing the electrode binder, and an inorganic solid electrolyte battery equipped with the electrode. [Background technology]

[0002] Electricity storage devices such as lithium-ion secondary batteries and electrochemical capacitors are used in electronic devices such as mobile phones and laptops. Recently, due to growing awareness of environmental protection and the establishment of related laws, their application as in-vehicle use in electric vehicles and hybrid electric vehicles, and as storage batteries for home power storage has been progressing.

[0003] At the same time as these applications progress, there is a demand for higher performance in electricity storage devices, and improvements are being made to components such as electrodes. Electrodes used in such electricity storage devices are usually obtained by coating an electrode material consisting of an active material, a conductive additive, a binder, and a solvent on a current collector and drying it.

[0004] In recent years, therefore, attempts have been made to improve the binders used in electrodes. It has been proposed that improving the binders will improve the adhesion between active materials, between the active materials and conductive assistants, and between the active materials and current collectors, thereby improving electrical properties (e.g., cycle properties, output properties at low temperatures, and low resistance).

[0005] The binder is required to have excellent binding properties when used in an electrode and to impart excellent electrical properties to an electricity storage device, and new binders have been proposed. However, in recent years, there has been a demand for binders with particularly excellent binding properties, and further investigation is required.

[0006] Also, an acrylic polymer has been disclosed as a binder composition for an all-solid-state secondary battery capable of forming a solid electrolyte-containing layer capable of imparting excellent high-temperature cycle characteristics to the all-solid-state secondary battery (see Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2020 / 066952 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a binder that is soluble in a solvent and has high adhesion to an active material and an electrode, and is particularly useful for inorganic solid electrolyte batteries. [Means for solving the problem]

[0009] Means for Solving the Problems The present inventors have conducted extensive research to achieve the above object, and as a result have found that the above object can be achieved by using an acrylic binder containing an acrylic copolymer having a structural unit derived from a (meth)acrylic acid ester and a structural unit derived from an unsaturated monomer having a halogen group or a carboxy group, thereby completing the present invention.

[0010] That is, the present invention relates to the following. Item 1: An acrylic binder containing an acrylic copolymer having a structural unit derived from a (meth)acrylic acid ester and a structural unit derived from an unsaturated monomer having a halogen group or a carboxy group. Item 2. The acrylic binder according to item 1, which is for an inorganic solid electrolyte battery. Item 3. The acrylic binder according to item 1, which is an acrylic copolymer having 50 to 99.9% by mass of structural units derived from a (meth)acrylic acid ester and 0.1 to 10% by mass of structural units derived from an unsaturated monomer having a halogen group or a carboxy group. Item 4. A slurry for an electrode comprising the acrylic binder according to any one of items 1 to 3. Item 5. An electrode comprising the acrylic binder according to any one of items 1 to 3. Item 6. An electricity storage device comprising the electrode according to item 5. Effect of the Invention

[0011] The binder of the present invention is a binder that has solubility in a solvent and high adhesion to an active material and an electrode. An electricity storage device using the binder of the present invention is useful for use in an in-vehicle application such as an electric vehicle or a hybrid electric vehicle, or in an electricity storage device such as a storage battery for home power storage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In this specification, the term "electric storage device" includes secondary batteries (lithium ion secondary batteries, nickel-hydrogen secondary batteries, etc.) and electrochemical capacitors. In addition, in this specification, "(meth)acrylate" means "acrylate or methacrylate", and the same applies to similar expressions.

[0013] In this specification, a numerical value connected with "~" means a numerical range including the numerical values ​​before and after "~" as the lower limit and upper limit. When multiple lower limit values ​​and multiple upper limit values ​​are listed separately, any lower limit value and upper limit value can be selected and connected with "~".

[0014] <1. Acrylic binder> The present invention is an acrylic binder containing an acrylic copolymer having a structural unit derived from a (meth)acrylic acid ester and a structural unit derived from an unsaturated monomer having a halogen group or a carboxy group.

[0015] Examples of the structural unit derived from the (meth)acrylic acid ester include a structural unit derived from an alkyl (meth)acrylic acid ester and a structural unit derived from an alkoxyalkyl (meth)acrylic acid ester. Among these, a structural unit derived from an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms and a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group with 2 to 8 carbon atoms are preferred, a structural unit derived from an alkyl acrylate having an alkyl group with 2 to 6 carbon atoms and / or a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group with 2 to 6 carbon atoms are more preferred, a structural unit derived from an alkyl acrylate having an alkyl group with 2 to 4 carbon atoms and / or a structural unit derived from an alkoxyalkyl acrylate having an alkoxyalkyl group with 2 to 4 carbon atoms are even more preferred, and a structural unit derived from an alkyl acrylate having an alkyl group with 2 to 4 carbon atoms is particularly preferred. The structural unit derived from the (meth)acrylic acid ester may be a single structural unit derived from one or more (meth)acrylic acid esters.

[0016] Specific examples of (meth)acrylic acid alkyl esters include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, ethyl (meth)acrylate and n-butyl (meth)acrylate are preferred. Specific examples of the (meth)acrylic acid alkoxyalkyl ester include (meth)acrylic acid esters such as methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-methoxypropyl (meth)acrylate, 2-ethoxypropyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, 2-methoxyethyl (meth)acrylate is preferred.

[0017] The content of the structural units derived from (meth)acrylic acid ester in the acrylic copolymer is preferably 50% by mass or more, more preferably 60% by mass or more, and may be 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on all the structural units in the acrylic copolymer. The upper limit is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99% by mass or less.

[0018] The proportion of (meth)acrylic acid alkyl ester in the structural units derived from (meth)acrylic acid ester is preferably 80 mass % or more, more preferably 90 mass % or more, and may be 95 mass % or more.

[0019] The acrylic copolymer has a constitutional unit derived from an unsaturated monomer having a halogen group (e.g., a chlorine group, etc.) or a constitutional unit derived from an unsaturated monomer having a carboxy group. These may be used alone or in combination of two or more. Among these, the constitutional unit derived from an unsaturated monomer having a halogen group is most preferred.

[0020] Examples of unsaturated monomers having a halogen group include vinyl monochloroacetate and allyl chloroacetate. These may be used alone or in combination of two or more. Among these, vinyl monochloroacetate is preferred.

[0021] Examples of the unsaturated monomer having a carboxyl group include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, 2-pentenoic acid, and cinnamic acid, unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid, carboxylic anhydrides such as maleic anhydride and citraconic anhydride, butenedioic acid mono-chain alkyl esters such as monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, mono-2-ethylhexyl maleate, and mono-n-butyl maleate, butenedioic acid mono-cyclic alkyl esters such as monocyclopentyl fumarate, monocyclohexyl fumarate, monocyclopentyl maleate, and monocyclohexyl maleate, and itaconic acid monoesters such as monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate, etc. These may be used alone or in combination of two or more. Among these, unsaturated dicarboxylic acid monoesters such as monoethyl fumarate, monopropyl fumarate, monobutyl fumarate, monoethyl itaconate, monopropyl itaconate, and monobutyl itaconate are preferred.

[0022] The content of structural units derived from unsaturated monomers having a halogen group or a carboxy group in the acrylic copolymer is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and particularly preferably 0.5 mass% or more, and is preferably 10 mass% or less, more preferably 5 mass% or less, and particularly preferably 2.5 mass% or less, based on all structural units of the acrylic copolymer.

[0023] In the acrylic copolymer, the total content of the structural units derived from the (meth)acrylic acid ester and the structural units derived from the unsaturated monomer having a halogen group or a carboxy group is preferably 55 mass% or more, more preferably 65 mass% or more, even more preferably 75 mass% or more, even more preferably 85 mass% or more, particularly preferably 95 mass% or more, and may be 100 mass%.

[0024] The acrylic copolymer may contain a structural unit derived from a copolymerizable antioxidant, and the copolymerizable antioxidant means an antioxidant to which a substituent having a structure with an external double bond and / or a structure with an internal double bond is bonded. The structural unit derived from the copolymerizable antioxidant may be used alone or in combination of two or more kinds.

[0025] Examples of the constituent units derived from copolymerizable antioxidants include constituent units derived from copolymerizable amine-based antioxidants such as N-(4-anilinophenyl)methacrylamide, N-(4-anilinophenyl)acrylamide, N-(4-anilinophenyl)maleimide, N-(4-p-toluidinylphenyl)maleimide, N-(4-anilino-1-naphthyl)maleimide, 4-hydroxyphenylmaleimide, and 3-hydroxyphenylmaleimide; and constituent units derived from copolymerizable phenol-based antioxidants such as 2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl acrylate, 1'-hydroxy[2,2'-ethylidenebis[4,6-bis(1,1-dimethylpropyl)benzene]]-1-yl acrylate, hydroxycinnamic acid, ferulic acid, and allyl cresol. In the present invention, the constituent unit derived from a copolymerizable antioxidant is preferably a constituent unit derived from a copolymerizable amine-based antioxidant or a constituent unit derived from a copolymerizable phenol-based antioxidant, and more preferably a constituent unit derived from a copolymerizable amine-based antioxidant.

[0026] In the acrylic copolymer, the content of the constituent units derived from the copolymerizable antiaging agent is preferably 0% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.075% by mass or more, and particularly preferably 0.1% by mass or more, as the lower limit, based on all the constituent units of the acrylic copolymer, and is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, as the upper limit.

[0027] In the acrylic copolymer, the total content of the structural units derived from a (meth)acrylic acid ester, the structural units derived from an unsaturated monomer having a halogen group or a carboxy group, and the structural units derived from a copolymerizable antiaging agent is preferably 55 mass% or more, more preferably 65 mass% or more, even more preferably 75 mass% or more, still more preferably 85 mass% or more, particularly preferably 95 mass% or more, and may be 100 mass% based on all the structural units of the acrylic copolymer.

[0028] The acrylic copolymer may contain, as a constituent unit of the acrylic copolymer, a copolymerizable monomer other than the above-mentioned monomers, so long as it does not deviate from the spirit of the present invention, and examples of the other monomers include ethylenically unsaturated nitrile monomers, (meth)acrylamide monomers, aromatic vinyl monomers, conjugated diene monomers, non-conjugated diene monomers, other olefin monomers, etc. These may be used alone or in combination of two or more.

[0029] Examples of ethylenically unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, vinylidene cyanide, etc. These may be used alone or in combination of two or more.

[0030] Examples of (meth)acrylamide monomers include acrylamide, methacrylamide, diacetone acrylamide, diacetone methacrylamide, N-butoxymethyl acrylamide, N-butoxymethyl methacrylamide, N-butoxyethyl acrylamide, N-butoxyethyl methacrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-propoxymethyl acrylamide, N-propoxymethyl methacrylamide, N-methyl acrylamide, N-methyl methacrylamide, N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N-methylolacrylamide, N-methylolacrylamide, ethacrylamide, crotonamide, cinnamic acid amide, maleindiamide, itacondiamide, methylmaleamide, methyl itaconamide, maleimide, itaconimide, etc. These may be used alone or in combination of two or more.

[0031] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, α-fluorostyrene, p-trifluoromethylstyrene, p-methoxystyrene, p-aminostyrene, p-dimethylaminostyrene, p-acetoxystyrene, styrenesulfonic acid or a salt thereof, α-vinylnaphthalene, 1-vinylnaphthalene-4-sulfonic acid or a salt thereof, 2-vinylfluorene, 2-vinylpyridine, 4-vinylpyridine, divinylbenzene, diisopropenylbenzene, vinylbenzyl chloride, etc. These may be used alone or in combination of two or more.

[0032] Examples of conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,2-dichloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-neopentyl-1,3-butadiene, 2-bromo-1,3-butadiene, 2-cyano-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, chloroprene, piperylene, etc. These may be used alone or in combination of two or more.

[0033] Examples of non-conjugated diene monomers include 1,4-pentadiene, 1,4-hexadiene, ethylidenenorbornene, norbornadiene, dicyclopentadiene, etc. These may be used alone or in combination of two or more.

[0034] Other olefin monomers include, for example, esters such as dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, dicyclopentadienyl ethyl acrylate, dicyclopentadienyl ethyl methacrylate, ethylene, propylene, vinyl chloride, vinylidene chloride, 1,2-dichloroethylene, vinyl acetate, vinyl fluoride, vinylidene fluoride, 1,2-difluoroethylene, vinyl bromide, vinylidene bromide, 1,2-dibromoethylene, ethyl vinyl ether, butyl vinyl ether, etc. These may be used alone or in combination of two or more.

[0035] In the acrylic copolymer, the content of the structural units can be determined by the nuclear magnetic resonance spectrum of the obtained polymer.

[0036] The weight average molecular weight of the acrylic copolymer is preferably 100,000 or more, more preferably 300,000 or more, and more preferably 500,000 or more, and although there is no particular upper limit, it is preferably 3 million or less, and may be 2 million or less. The weight average molecular weight is calculated by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent in terms of standard polystyrene.

[0037] The viscosity range of the acrylic copolymer is determined by the Mooney viscosity (ML 1+4 ) is preferably 10 to 100, more preferably 15 to 90, and even more preferably 20 to 80.

[0038] As the form of the polymerization reaction, any of emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization can be used. From the viewpoint of ease of control of the polymerization reaction, however, it is preferable to use emulsion polymerization under normal pressure, which is generally used as a conventional method for producing acrylic polymers.

[0039] In the case of emulsion polymerization, a conventional method may be used, and the polymerization initiator, emulsifier, chain transfer agent, polymerization terminator and the like may be any of the conventionally known agents that are generally used.

[0040] The emulsifier used in the present invention is not particularly limited, and nonionic emulsifiers and anionic emulsifiers generally used in emulsion polymerization methods can be used. Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. Examples of anionic emulsifiers include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyalkylene alkyl ether phosphates or their salts, fatty acid salts, and the like, and these may be used alone or in combination. Representative examples of anionic emulsifiers include sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and triethanolamine dodecyl sulfate.

[0041] The amount of the emulsifier used in the present invention may be an amount generally used in emulsion polymerization. Specifically, it is in the range of 0.01 to 10 parts by mass, preferably 0.03 to 7 parts by mass, and more preferably 0.05 to 5 parts by mass, relative to 100 parts by mass of the monomer constituting the acrylic copolymer. When a reactive surfactant is used as a monomer component, the addition of an emulsifier is not necessarily required.

[0042] The polymerization initiator used in the present invention is not particularly limited, and polymerization initiators generally used in emulsion polymerization methods can be used. Specific examples thereof include inorganic polymerization initiators such as persulfates, such as potassium persulfate, sodium persulfate, and ammonium persulfate, 2,2-di(4,4-di(t-butylperoxy)cyclohexyl)propane, 1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, 4,4-di(t-butylperoxy)n-butyl valerate, 2,2-di(t-butylperoxy)butane, t-butyl hydroperoxide, and cumene hydroperoxide. Side, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, disuccinic acid peroxide peroxydicarbonate, dibenzoyl peroxide, di(3-methylbenzoyl) peroxide, benzoyl(3-methylbenzoyl) peroxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, cumyl peroxyneodecanate, 1,1,3,3-tetramethylbutyl peroxyneodecanate Canate, t-hexylperoxyneodecanate, t-butylperoxyneodecanate, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, t-hexylperoxy-2-ethylhexanate, t-butylperoxy-2-ethylhexanate, t-butylperoxylaurate, t-butylperoxy-3,5,Polymerization initiators of organic peroxides such as 5-trimethylhexanate, t-hexylperoxyisopropyl monocarbonate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, t-hexylperoxybenzoate, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, hydroperoxides, azobisisobutyronitrile, 4-4'-azobis(4- Examples of the azo initiator include 2-2'-azobis[2-(2-imidazolin-2-yl)propane, 2-2'-azobis(propane-2-carboxamidine), 2-2'-azobis[N-(2-carboxyethyl)-2-methylpropanamide, 2-2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}, 2-2'-azobis(1-imino-1-pyrrolidino-2-methylpropane) and 2-2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propanamide}. These polymerization initiators can be used alone or in combination of two or more.

[0043] The amount of the polymerization initiator used in the present invention may be an amount generally used in emulsion polymerization, specifically, in the range of 0.01 to 5 parts by mass per 100 parts by mass of the monomer constituting the acrylic copolymer.

[0044] In addition, the organic peroxide and inorganic peroxide as the polymerization initiator can be used as a redox polymerization initiator by combining with a reducing agent. The reducing agent to be used in combination is not particularly limited, but includes compounds containing metal ions in a reduced state such as ferrous sulfate and cuprous naphthenate, methane compounds such as sodium formaldehyde sulfoxylate and sodium methanesulfonate, amine compounds such as dimethylaniline, ascorbic acid and its salts, and inorganic salts having reducing properties such as alkali metal salts of sulfurous acid and thiosulfuric acid. These reducing agents can be used alone or in combination of two or more. The amount of the reducing agent used is preferably 0.0003 to 10.0 parts by mass relative to 100 parts by mass of the monomer constituting the acrylic copolymer.

[0045] Chain transfer agents can be used as necessary. Specific examples of chain transfer agents include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan, xanthogen compounds such as 2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, dimethyl xanthogen disulfide, and diisopropyl xanthogen disulfide, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide. Thiuram compounds, phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, etc., may be used alone or in combination. The amount of these chain transfer agents is not particularly limited, but is usually used in an amount of 0 to 5 parts by mass relative to 100 parts by mass of the monomers constituting the acrylic copolymer, and may be used in an amount of 0 to 3 parts by mass.

[0046] Examples of the polymerization terminator include hydroxylamine, hydroxylamine sulfate, diethylhydroxyamine, hydroxylamine sulfonic acid and its alkali metal salt, sodium dimethyldithiocarbamate, and quinone compounds such as hydroquinone. These may be used alone or in combination of two or more. The amount of the polymerization terminator used is not particularly limited, but is usually 0 to 2 parts by mass relative to 100 parts by mass of the monomer constituting the acrylic copolymer.

[0047] Furthermore, the pH of the polymer obtained by the above method can be adjusted by using a base as a pH adjuster as necessary. Specific examples of the base include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium hydrogen carbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. The pH range is pH 1 to 11, preferably pH 1.5 to 10.5, and more preferably pH 2 to 10.

[0048] In addition, polymerization secondary materials such as particle size regulators, chelating agents, and oxygen scavengers can be used as necessary.

[0049] The emulsion polymerization may be any of batch, semi-batch, and continuous. The polymerization time and temperature are not particularly limited. They can be appropriately selected depending on the type of polymerization initiator used, but generally, the polymerization temperature is 10°C to 100°C, and the polymerization time is 0.5 hours to 100 hours.

[0050] The method for recovering the polymer obtained by the above method is not particularly limited, and a commonly used method can be adopted. One example of the method is to continuously or batchwise supply the polymerization liquid obtained by emulsion polymerization or the like to an aqueous solution containing a coagulant, and this operation produces water-containing crumbs. In this case, the temperature of the aqueous solution containing the coagulant is affected by the coagulation conditions such as the type and amount of monomer used, and the shear force due to stirring, and therefore cannot be uniformly specified, but is generally 50°C to 100°C, and preferably 60°C to 100°C.

[0051] Furthermore, an antioxidant can be added during the coagulation process. Specific examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, phosphanol-based antioxidants, and hindered amine-based antioxidants. These can be used alone or in combination of two or more.

[0052] Furthermore, the pH of the hydrous crumb obtained by the above method can be adjusted by using a base as a pH adjuster as necessary. Specific examples of the base include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium hydrogen carbonate, ammonia, inorganic ammonium compounds, and organic amine compounds. The pH range is pH 1 to 11, preferably pH 2 to 10, and more preferably pH 4 to 8.

[0053] The hydrous crumb obtained by the above method is preferably washed with water to remove the coagulant. If washing with water is not performed at all or is insufficient, there is a risk that ion residues derived from the coagulant will precipitate.

[0054] The acrylic copolymer can be obtained by removing water from the water-containing crumbs after washing and drying them. The drying method is not particularly limited, but is generally performed using a flash dryer or a fluidized bed dryer. In addition, a dehydration step using a centrifuge or the like may be performed before the drying step.

[0055] <2. Slurry for electrodes> The electrode slurry of the present invention contains the binder of the present invention described in the above section "1. Acrylic Binder" together with a solvent. The solvent can be water or an organic solvent. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as diethyl ether, dioxane, and tetrahydrofuran, amide polar organic solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone (NMP), and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene.

[0056] The content of the binder in the electrode slurry of the present invention is not particularly limited, but the binder is preferably contained so that the binder concentration is 0.2 to 30 mass%, more preferably 0.5 to 20 mass%, and particularly preferably 0.5 to 10 mass%.

[0057] The pH of the electrode slurry of the present invention can be adjusted by using a base as a pH adjuster as necessary. Specific examples of the base include alkali metal (Li, Na, K, Rb, Cs) hydroxides, ammonia, inorganic ammonium compounds, organic amine compounds, etc. The pH range is pH 2 to 11, preferably pH 3 to 10, and more preferably pH 4 to 9.

[0058] The electrode slurry of the present invention may contain an inorganic solid electrolyte, and is preferably a sulfide-based inorganic solid electrolyte.

[0059] The sulfide solid electrolyte is not particularly limited, as long as it contains sulfur, has the ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation. For example, a lithium ion conductive solid electrolyte having a composition represented by the following formula can be used. Li a M b P c S d A e In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge. Among them, B, Sn, Si, Al, and Ge are preferable, and Sn, Al, and Ge are more preferable. A represents I, Br, Cl, and F, and I and Br are preferable, and I is particularly preferable. a to e represent the composition ratio of each element, and a:b:c:d:e satisfies 1-12:0-1:1:2-12:0-5. a is more preferably 1-9, and more preferably 1.5-4. b is more preferably 0-0.5. d is more preferably 3-7, and more preferably 3.25-4.5. e is more preferably 0-3, and more preferably 0-2.

[0060] In the formula, the composition ratios of Li, M, P, S and A may be such that b and e are 0, b=0, e=0 and the ratio of a, c and d (a:c:d) is a:c:d=1-9:1:3-7, or b=0, e=0 and a:c:d=1.5-4:1:3.25-4.5.

[0061] The sulfide solid electrolyte may have a crystalline sulfide solid electrolyte, and the crystal structure of the crystalline sulfide solid electrolyte may be an argyrodite crystal structure. An example of the argyrodite crystal structure is Li 7 P.S. 6 The crystal structure is Li 7 -xPS 6 -xHax (Ha is Cl or Br, x is preferably 0.2 to 1.8). 7 P.S. 6 In this case, a part of P may be replaced by Si.

[0062] A specific example of a sulfide-based solid electrolyte is Li 2 S / SiS 2 , Li 2 S-SiS 2 / P 2 S 5 , Li 2 S / P 2 S 5 , Li 2 S / GeS 2 , Li 2 S / GeS 2 / Ga 2 S 3 , Li 2 S / B 2 S 3 , Li 2 S / Ga 2 S 3 , Li 2 S / Al 2 S 3 , Li 2 S / GeS 2 / P 2 S 5 , Li 2 S / Al 2 S 3 / P 2 S 5 , Li 2 S / P 2 S 3 , Li 2 S / P 2 S 3 / P 2 S 5 , Li 2 S / SiS 2 / Li 4 SiO 4 , Li 2 S / SiS 2 / Li 3 PO 4 , LiX / Li 2 S / P 2 S 5 , LiX / Li 2 S / SiS 2 , LiX / Li 2 S / B 2 S 3 (X is a halogen atom (Br, Cl or I)) and the like can be mentioned as examples.

[0063] When the sulfide solid electrolyte is in the form of particles, the particle size is, for example, 0.01 to 100 μm, and preferably 0.1 to 20 μm.

[0064] The content of the inorganic solid electrolyte in the slurry is not particularly limited, but the concentration of the inorganic solid electrolyte is preferably 3 to 30 mass %, more preferably 4 to 25 mass %, and particularly preferably 5 to 20 mass %.

[0065] In the case where an inorganic solid electrolyte is contained, the acrylic copolymer is contained in an amount of preferably 3 to 50 parts by mass, more preferably 5 to 40 parts by mass, and particularly preferably 10 to 30 parts by mass, per 100 parts by mass of the inorganic solid electrolyte.

[0066] The electrode slurry of the present invention may contain an active material. The positive electrode slurry contains a positive electrode active material, and the negative electrode slurry contains a negative electrode active material.

[0067] The positive electrode active material is LiMO 2 , LiM 2 O 4 , Li 2 MO 3 , LiMEO 4 The lithium metal-containing composite oxide powder has any one of the following compositions. In the formula, M is mainly composed of a transition metal and contains at least one of Co, Mn, Ni, Cr, Fe, and Ti. M is composed of a transition metal, but may contain Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. in addition to the transition metal. E contains at least one of P and Si. The particle size of the positive electrode active material is preferably 50 μm or less, and more preferably 20 μm or less. These active materials have an electromotive force of 3 V (vs. Li / Li+) or more.

[0068] Specific examples of the positive electrode active material include lithium cobalt oxide, lithium nickel oxide, nickel / cobalt / lithium manganese oxide (ternary system), spinel-type lithium manganese oxide, and lithium iron phosphate.

[0069] The negative electrode active material is a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (intercalation compound) capable of absorbing and releasing alkali metal ions such as lithium ions, or a metal such as lithium, an aluminum-based compound, a tin-based compound, a silicon-based compound, or a titanium-based compound capable of absorbing and releasing alkali metal ions such as lithium ions. In the case of a powder, the particle size is preferably 10 nm or more and 100 μm or less, more preferably 20 nm or more and 20 μm or less. A mixed active material of a metal and a carbon material may also be used.

[0070] Examples of carbon materials include graphite, low-crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen black, acetylene black, channel black, lamp black, oil furnace black, thermal black, etc.), fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, phenol resin fired body, polyacrylonitrile-based carbon fiber, etc., and graphite is preferred.

[0071] Examples of silicon-based compounds include Si element, alloys with Si, oxides containing Si, carbides containing Si, etc., such as Si, SiB 4 、SiB 6 、Mg 2 Si、Ni 2 Si、TiSi 2 、MoSi 2 、CoSi 2 、NiSi 2 、CaSi 2 、CrSi 2 、Cu 5 Si、FeSi 2 、MnSi 2 、NbSi 2 、TaSi 2 、VSi 2 、WSi 2 、ZnSi 2 、SiC、Si 3 N 4 、Si 2 N 2 O、SiO x (0 < x ≤ 2), SnSiO x 、LiSiO can be exemplified, and SiO x (0 < x ≤ 2) is preferred, and it is silicon monoxide (SiO), etc.

[0072] When a carbon material and a silicon-based compound are used in combination in the active material, it is preferably contained as follows. The content of the carbon material relative to the total amount of active material (100 mass%) is preferably at least 20 mass%, more preferably at least 40 mass%, particularly preferably at least 60 mass%, and may be at least 70 mass%, and is preferably at most 99 mass%, more preferably at most 98 mass%, and particularly preferably at most 96 mass%. The content of the silicon-based compound relative to the total amount of the active material (100% by mass) is preferably at least 1% by mass, more preferably at least 2% by mass, and particularly preferably at least 4% by mass, and is preferably at most 80% by mass, more preferably at most 60% by mass, and particularly preferably at most 40% by mass, and may be at most 30% by mass.

[0073] The content of the active material in the slurry is not particularly limited, but it is preferable that the active material be contained so that the concentration is 5 to 70 mass%, more preferably 10 to 60 mass%, and particularly preferably 15 to 50 mass%.

[0074] When an active material is contained, the acrylic copolymer is preferably contained in an amount of 2 to 20 parts by mass, more preferably 3 to 15 parts by mass, and particularly preferably 5 to 10 parts by mass, per 100 parts by mass of the active material.

[0075] When a conductive assistant is used in the slurry, a known conductive assistant can be used, and examples thereof include conductive carbon black such as graphite, furnace black, acetylene black, and ketjen black, carbon fibers such as carbon nanotubes, and metal powder. One or more of these conductive assistants may be used. When a conductive assistant is used, the content of the conductive assistant is not particularly limited, but the upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less, relative to 100 parts by mass of the total amount of the active material. The lower limit of the content of the conductive assistant is usually 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.5 parts by mass or more, and 2 parts by mass or more.

[0076] When a thickener is used in the slurry, examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose and their salts (alkali metal salts such as sodium salts, ammonium salts), polyvinyl alcohol, polyacrylates, polyethylene oxide, etc. These thickeners may be used alone or in combination. These thickeners are preferably added in an amount of 5 parts by mass or less, more preferably 3 parts by mass or less, for example 0.01 to 2 parts by mass, based on 100 parts by mass of the active material. In addition, when the viscosity of the coating liquid is low, a thickener can be used in combination.

[0077] The method for preparing the electrode slurry is not particularly limited, and the binder of the present invention, the inorganic solid electrolyte, the positive electrode active material or the negative electrode active material, the conductive assistant, the solvent, etc. may be dispersed using a normal stirrer, disperser, kneader, planetary ball mill, homogenizer, etc. In order to increase the efficiency of dispersion, the materials may be heated within a range that does not affect them.

[0078] <3. Electrode> The electrode of the present invention comprises an electrode material layer on a current collector.

[0079] For the electrodes of the present invention, known current collectors can be used. Specifically, metals such as aluminum, nickel, stainless steel, gold, platinum, and titanium are used for the positive electrode. Metals such as copper, nickel, stainless steel, gold, platinum, titanium, and aluminum are used for the negative electrode.

[0080] The method for producing the electrodes is not particularly limited, and a general method can be used. The electrode slurry described in the section "2. Electrode Slurry" is uniformly applied to an appropriate thickness on the surface of a current collector (metal electrode substrate) by a doctor blade method, applicator method, silk screen method, or the like to form an electrode material layer.

[0081] For example, in the doctor blade method, the electrode slurry is applied to a metal electrode substrate, and then uniformized to an appropriate thickness using a blade with a specified slit width. After the active material is applied to the electrode, the electrode is dried, for example, with hot air at 100°C or in a vacuum at 80°C to remove excess organic solvent and water. The dried electrode is press molded using a press device to produce an electrode material. After pressing, the electrode may be heat-treated again to remove the solvent, emulsifier, etc.

[0082] <4. Energy storage devices> The electricity storage device of the present invention is characterized by comprising the positive electrode, negative electrode, and electrolyte described in the above section "3. Electrode". That is, the electrode used in the electricity storage device of the present invention contains the electrode binder of the present invention. Details of the electrode of the present invention are as described above. Note that, for the electricity storage device of the present invention, it is sufficient that at least one of the positive electrode and the negative electrode uses an electrode material containing the electrode binder of the present invention, and for the electrode not using the electrode material containing the electrode binder of the present invention, a known electrode can be used, but it is preferable that the electricity storage device uses at least a negative electrode containing the electrode binder of the present invention.

[0083] The electrolyte is not particularly limited, and examples thereof include polymer electrolytes and inorganic solid electrolytes, and is preferably a sulfide-based inorganic solid electrolyte. The sulfide-based solid electrolyte may be the sulfide-based solid electrolyte described in the section "2. Slurry for electrodes."

[0084] The method of manufacturing the electricity storage device is not particularly limited, and the device is composed of a positive electrode, a negative electrode, and an electrolyte, and is manufactured by a known method. For example, in the case of a laminated lithium ion battery, a laminated body composed of a positive electrode, an electrolyte, and a negative electrode is manufactured, and after connecting leads to the positive and negative electrodes, the battery is vacuum sealed using a laminated packaging material or the like. The shape of the battery is not limited, and examples include a laminated type, a coin type, a cylindrical type, and the like, and may be a structure in which two or more batteries are stacked. EXAMPLES

[0085] Specific embodiments for carrying out the present invention will be described below with reference to examples. However, the present invention is not limited to the following examples as long as it does not deviate from the gist of the present invention. The various physical properties were evaluated according to the following methods.

[0086] <Mooney viscosity (ML1+4, 100℃)> The Mooney viscosity (ML1+4) of the acrylic copolymer was measured at a measurement temperature of 100° C. using a Mooney Viscometer AM-3 manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with the Mooney viscosity test of the uncrosslinked rubber physical testing method of JIS K6300.

[0087] <Molecular weight measurement> The weight average molecular weight (Mw) of the acrylic rubber was measured by gel permeation chromatography (GPC). Specifically, the measurement was performed using a column consisting of two TSKgel SuperHM-H columns (Tosoh, column size 6.0 mm x 15 cm) connected in series to a liquid chromatograph (Waters, instrument name). Tetrahydrofuran was used as the eluent, and the column temperature was set to 50°C. The weight average molecular weight (Mw) was measured as a polystyrene equivalent value.

[0088] <Solubility in solvents, stability in solvent solutions> 5% by mass of the acrylic copolymer was charged into methyl isobutyl ketone and diisobutyl ketone, respectively, and dissolved on a mix rotor at room temperature (23° C.), and the state of dissolution was visually observed. Solubility was visually observed one day after the start of dissolution, and dissolution stability was visually observed three days after leaving the material to stand after dissolution. Solvent solubility was judged as ◯ if it dissolved well, and × if it did not dissolve. Solvent dissolution stability was judged as ◯ if there was no aggregation or precipitation, and × if there was aggregation or precipitation.

[0089] [Preparation of samples for measuring 180 degree peel strength] A test piece was prepared by cutting the negative electrode to a length of 60 mm and a length of 10 mm. A 200 mm piece of cellophane tape (Nichiban Co., Ltd.) was cut to one end of the test piece, and the cut edge was used to pinch the end by about 10 mm. For the remaining part, a handle of about 90 mm was attached by bonding the cellophane tape together.

[0090] [180 degree peel test] The negative electrode mixture layer side was fixed to a SUS plate using double-sided tape (Nistack 02, Nichiban Co., Ltd.), and a 180-degree peel test was performed by pulling the handle to peel off the copper foil using a universal testing machine (E0-L Toyo Seiki Seisakusho Co., Ltd.) (travel distance 100 mm, 50 mm / min). The peel strength was calculated by averaging the section excluding the measurement value from immediately after the start of the measurement to about 10 mm, and was calculated as the average value of three trials. In the 180-degree peel test, peeling occurs at the weakest bond between the active material bonds and between the active material and the copper current collector foil, and this is a method to measure the peel strength of the weakest bond. Peeling that occurs between active materials is called cohesive failure, and peeling that occurs between the active material and the copper current collector foil is called interfacial peeling.

[0091] [SAICAS (Surface And Interfacial Cutting Analysis System) method] The peel strength evaluation of the negative electrode in this test was performed using a SAICAS test device (EN-W type manufactured by Daipla Wintes Co., Ltd.). Cutting was performed for 2 minutes using a diamond cutting blade (cutting edge 1 mm, rake angle 20°, clearance angle 10°) in constant speed mode (horizontal speed 10 μm / sec, vertical speed 1 μm / sec, cutting limit 25 μm). After reaching a depth of 25 μm, the peel strength was calculated from the average value of the part where the waveform of the horizontal force was stable. With the cutting depth of the SAICAS method in this case, the cutting blade cuts the inside of the negative electrode mixture layer, so the peel strength between active materials is evaluated.

[0092] [ 31 [Confirmation test of sulfide solid electrolyte stability by PNMR] The sulfide stability of the copolymer was evaluated in the following experiment. The copolymer was dissolved in ultra-dehydrated grade butyl butyrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to a concentration of 5% by weight under conditions of a dew point of -60°C or less. Next, a sulfide solid electrolyte (LPSC1 manufactured by NEI Corporation) and the butyl butyrate solution of the copolymer prepared above were mixed in an Ar atmosphere to a weight ratio of copolymer / sulfide solid electrolyte = 20 / 80, and the butyl butyrate was removed at 80°C under vacuum. The copolymer / sulfide solid electrolyte mixture thus prepared was 31 Measurements were performed using P NMR under the following conditions: Observation frequency: 202.46 MHz, Observation width: 121.951 kHz, Probe: 4.0 mm, Rotation speed: 10 kHz, Measurement temperature: Room temperature, Pulse width: 3.0 μs (90° pulse), Repetition waiting time: 2000 s, Number of integrations: 16, Standard substance: Ammonium dihydrogen phosphate (1 ppm). When measured under these conditions, P, a decomposition product of the sulfide solid electrolyte, was found at 86-90 ppm. 2 S 7 -4 If a peak was observed, it was determined that the sulfide solid electrolyte was not stable, and if not, it was determined that the sulfide solid electrolyte was stable.

[0093] [Production Example 1] (Production of Acrylic Copolymer A) In a polymerization reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube and a pressure reducing device, 200 parts by mass of water, 1.7 parts by mass of polyoxyalkylene alkyl ether phosphate ester, 67.8 parts by mass of ethyl acrylate as a monomer, 30.0 parts by mass of n-butyl acrylate and 2.2 parts by mass of vinyl monochloroacetate were charged, and oxygen was sufficiently removed by repeatedly degassing under reduced pressure and replacing with nitrogen, and then 0.1 parts by mass of sodium ascorbate and 0.1 parts by mass of potassium persulfate were added to start an emulsion polymerization reaction under normal pressure and normal temperature, and the reaction was continued until the polymerization conversion rate reached 95%, and 0.0075 parts by mass of hydroquinone was added to terminate the polymerization. The obtained emulsion polymerization liquid was coagulated with a 7% by mass aqueous solution of sodium sulfate, washed with water and dried to obtain an acrylic copolymer A. The obtained acrylic copolymer A had a Mooney viscosity of 37 and a weight average molecular weight of 1.1 million. The results are shown in Table 1.

[0094] [Production Example 2] (Production of Acrylic Copolymer B) The same procedure as in Production Example 1 was carried out, except that the monomers constituting the acrylic copolymer and their amounts were changed to 49.3 parts by mass of ethyl acrylate, 49.3 parts by mass of n-butyl acrylate, and 1.4 parts by mass of monoethyl fumarate from Production Example 1. The same procedure as in Production Example 1 was carried out, except that the coagulation conditions were changed to 1% by mass of magnesium sulfate from Production Example 1. The Mooney viscosity of the obtained acrylic copolymer B was 37, and the weight average molecular weight was 1.27 million. The results are shown in Table 1.

[0095] [Production Example 3] (Production of Acrylic Copolymer C) The same procedure as in Production Example 1 was carried out, except that the monomers constituting the acrylic copolymer and their amounts were changed to 53.0 parts by mass of ethyl acrylate, 23.0 parts by mass of n-butyl acrylate, 23.0 parts by mass of 2-methoxymethyl acrylate, and 1.0 part by mass of allyl glycidyl ether. The same procedure as in Production Example 1 was carried out, except that the coagulation conditions were changed to 1% by mass of magnesium sulfate from Production Example 1. The Mooney viscosity of the obtained acrylic copolymer C was 34, and the weight average molecular weight was 830,000. The results are shown in Table 1.

[0096] [Table 1]

[0097] <Solvent solubility> The solvent solubility of the obtained acrylic copolymer is shown in Table 2. As Comparative Example 1, the solvent solubility of PVdF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene), manufactured by Sigma-Aldrich) is shown in Table 2. Acrylic copolymers A, B, and C were well soluble in both methyl isobutyl ketone and diisobutyl ketone, and after standing, there was no tendency for aggregation or precipitation, and the dissolution state was stable. PVdF-HFP was not soluble in either methyl isobutyl ketone or diisobutyl ketone. Since PVdF-HFP was not soluble in the solvent, the solvent dissolution stability was not evaluated.

[0098] [Table 2]

[0099] <Sulfide solid electrolyte stability> The results of the sulfide solid electrolyte stability of the obtained acrylic copolymers are shown in Table 3. The sulfide solid electrolyte was shown to be stable for the acrylic copolymers A, B, and C. [Table 3]

[0100] [Example 1] Preparation of negative electrode using copolymer A To the diisobutyl ketone solution (solid content 5% by mass) of copolymer A obtained in Production Example 1, silicon active material (Silgrain e-Si409 manufactured by Elkem) was added as a negative electrode active material so that the weight ratio of silicon powder / copolymer A was 95 / 5, and the mixture was thoroughly mixed using a planetary stirrer (Thinki Awatori Rentaro manufactured by Shinki) to obtain a negative electrode slurry. The obtained negative electrode slurry was applied to a copper current collector having a thickness of 10 μm using a Baker-type applicator with a gap of 80 μm. The electrode was left at room temperature in a draft chamber until it was apparently dry, and then dried in an oven at 80 ° C. for 20 minutes or more to prepare a negative electrode with a silicon powder / copolymer A layer thickness of 60 μm. The obtained negative electrode was evaluated by the above-mentioned 180-degree peel test and SAICAS method. The results are shown in Table 4.

[0101] [Example 2] Preparation of negative electrode using copolymer B A negative electrode was prepared in the same manner as in Example 1, except that a diisobutyl ketone solution (solid content: 5% by mass) of the copolymer B obtained in Production Example 2 was used. The obtained negative electrode was evaluated by the 180-degree peel test and SAICAS method described above. The results are shown in Table 4.

[0102] [Comparative Example 1] Preparation of negative electrode using copolymer C A negative electrode was prepared in the same manner as in Example 1, except that a diisobutyl ketone solution (solid content: 5% by mass) of the copolymer C obtained in Production Example 3 was used. The obtained negative electrode was evaluated by the 180-degree peel test and SAICAS method described above. The results are shown in Table 4.

[0103] [Comparative Example 2] Preparation of negative electrode using PVdF-HFP Silicon active material (Elkem's Silgrain e-Si409) was added as the negative electrode active material to an N-methyl-2-pyrrolidone (NMP) solution (solid content 5% by mass) of PVdF-HFP (Sigma-Aldrich, product number: 427187) so that the weight ratio of silicon powder / copolymer PVdF-HFP was 95 / 5, and the mixture was thoroughly mixed using a rotating and revolving mixer (Thinki Awatori Rentaro) to obtain a negative electrode slurry. The obtained negative electrode slurry was applied to a copper current collector with a thickness of 10 μm using a Baker-type applicator with a gap of 80 μm. The electrode was left on a hot plate at 80 degrees in a draft chamber until it was apparently dry, and then dried in an oven at 80 ° C for more than 20 minutes to prepare a negative electrode with a silicon powder / PVdF-HFP layer thickness of 50 μm. The reason why NMP was used to prepare the PVdF-HFP solution is that PVdF-HFP is insoluble in solvents other than NMP. The obtained negative electrode was evaluated by the above-mentioned 180-degree peel test and SAICAS method. The results are shown in Table 4.

[0104] [Table 4]

[0105] In both the 180-degree peel test and the SAICAS method, the peel strength of Examples 1 and 2 was greater than that of the comparative examples, and the peel mode observed in the 180-degree peel test was cohesive failure. This indicates that the copolymers A and B bonded sufficiently strongly between the silicon active materials, and between the silicon active materials and the copper current collector foil, respectively, and that the bonding strength between the silicon active materials was relatively weak, resulting in cohesive failure. In contrast, in Comparative Example 1, the peel strength in the 180-degree peel test was significantly small, and the peel mode was also interfacial peeling. This indicates that copolymer C was not able to bond between the silicon active material and the copper foil current collector. The peel strength by the SAICAS method was also small compared to the examples, so the adhesion between the silicon active materials was also weak. In Comparative Example 2, the peel strength in the 180-degree peel test was reasonably large, but the peel mode was a mixture of interfacial peeling and cohesive failure. Since the peel strength of the part where interfacial peeling occurred was detected as small, it is considered that the distribution of the polymer was non-uniform and uneven. This is considered to be due to poor compatibility in the negative electrode compared to the copolymers of the examples. Therefore, copolymers A and B, which have excellent compatibility with silicon active materials and excellent binding properties between silicon active materials and between silicon active materials and copper current collector foils, are useful as binders for high-capacity secondary batteries in which silicon active materials are used. [Industrial Applicability]

[0106] The binder has solubility in a solvent and high adhesion to an active material and an electrode. The binder of the present invention is useful for use in an electricity storage device such as an in-vehicle device for electric vehicles and hybrid electric vehicles, or an electricity storage device such as a storage battery for home power storage.

Claims

1. An acrylic binder containing an acrylic copolymer having a structural unit derived from a (meth)acrylic acid ester and a structural unit derived from an unsaturated monomer having a halogen group or a carboxy group.

2. 2. The acrylic binder according to claim 1, which is for an inorganic solid electrolyte battery.

3. The acrylic binder according to claim 1, which is an acrylic copolymer having 50 to 99.9 mass% of structural units derived from a (meth)acrylic acid ester and 0.1 to 10 mass% of structural units derived from an unsaturated monomer having a halogen group or a carboxy group.

4. A slurry for electrodes comprising the acrylic binder according to any one of claims 1 to 3.

5. An electrode comprising the acrylic binder according to any one of claims 1 to 3.

6. An electricity storage device comprising the electrode according to claim 5 .

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