Binder composition for power storage devices, slurry for power storage device electrodes, power storage device electrode, and power storage device

Abstract

The present invention provides a binder composition for power storage devices, the binder composition enabling the production of a power storage device electrode that has an excellent surface state, adhesion, and ion conductivity, and the binder composition being capable of improving the cycle life characteristics of the power storage device.　A binder composition for power storage devices according to the present invention contains a polymer (A), a nonionic surfactant (B), and a liquid medium (C). When the total of the repeating units contained in the polymer (A) is taken as 100% by mass, the polymer (A) contains 1-50% by mass of a repeating unit (a1) that is derived from an α,β-unsaturated nitrile compound and 40-80% by mass of a repeating unit (a2) that is derived from an unsaturated carboxylic acid ester. The content ratio of the nonionic surfactant (B) is 0.1-10 parts by mass relative to 100 parts by mass of the polymer (A), and the liquid medium (C) is composed of at least one substance that is selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

Description

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

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

[0002] In recent years, there has been a demand for high-voltage, high-energy-density power storage devices as power sources for electronic devices. Lithium-ion batteries and lithium-ion capacitors are expected to be such power storage devices.

[0003] Electrodes used in such energy storage devices are produced by applying a composition (slurry for energy storage device electrodes) containing an active material and a polymer that functions as a binder to the surface of a current collector and drying the composition. The polymer used as a binder is required to have the ability to bind active materials together and to adhere to the current collector. Other properties required include resistance to powder shedding, which prevents fine powder of the active material from falling off when the applied and dried composition coating (hereinafter also referred to as the "active material layer") is cut. Such binder materials exhibit good adhesion, reducing the internal resistance of the battery due to the binder material, thereby imparting good charge / discharge characteristics to the energy storage device.

[0004] It has been empirically demonstrated that the bonding ability between the active materials, the adhesion ability between the active material and the current collector, and the resistance to powder shedding are almost proportional to each other in performance. Therefore, in this specification, these are sometimes collectively referred to as "adhesion."

[0005] Recently, the use of positive electrode active materials with high water reactivity has been investigated to fabricate electrochemical devices with excellent capacity and charge / discharge cycle characteristics. Polyvinylidene fluoride (PVdF) is the most widely used binder for organic solvent-based energy storage device electrodes. While PVdF has good binding properties and oxidation resistance, it contains fluorine atoms, which places a heavy burden on the environment. Furthermore, the instability of raw material supply is becoming apparent (see, for example, Patent Document 1).

[0006] Under these circumstances, various binder materials have been proposed to solve the various problems associated with positive electrode slurries (see, for example, Patent Documents 1 and 2).

[0007] JP 10-298386 A JP 2019-194944 A

[0008] However, in the method using a conventionally used positive electrode slurry containing PVdF or sulfonated PVdF disclosed in Patent Document 1, it is known that crosslinks are formed due to dehydrofluorination (HF), especially under basic conditions. If such crosslinks are formed in the positive electrode slurry, adhesion may be impaired. Furthermore, when a conventionally used positive electrode slurry is applied, craters may occur on the surface of the coating due to bubble breakage caused by the influence of emulsifiers, etc., remaining in the slurry. Such surface defects must be prevented because they lead to a decrease in product yield.

[0009] Some aspects of the present invention provide a binder composition for an electricity storage device that can produce an electricity storage device electrode that is excellent in surface condition, adhesion, and ion conductivity, and that can improve the cycle life characteristics of the electricity storage device.

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

[0011] One aspect of the binder composition for an electrical storage device according to the present invention comprises a polymer (A), a nonionic surfactant (B), and a liquid medium (C), wherein, when the total amount of repeating units contained in the polymer (A) is taken as 100 mass%, the polymer (A) comprises 1 to 50 mass% of repeating units (a1) derived from an α,β-unsaturated nitrile compound and 40 to 80 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester, the content of the nonionic surfactant (B) is 0.1 to 10 parts by mass per 100 parts by mass of the polymer (A), and the liquid medium (C) is at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

[0012] In one embodiment of the binder composition for an electricity storage device, the polymer (A) may be polymer particles, and the number average particle diameter of the polymer particles may be 50 nm or more and 1,000 nm or less.

[0013] In any of the above-described binder compositions for a storage battery device, the polymer (A) may further contain 0.1 to 10 mass % of a repeating unit (a3) ​​derived from an unsaturated carboxylic acid.

[0014] In any of the above-described binder compositions for a storage battery device, the polymer (A) may further contain 0.1 to 10 mass % of a repeating unit (a6) derived from (meth)acrylamide.

[0015] In any of the above-described embodiments of the binder composition for a storage battery device, the polymer (A) may further contain 0.1 to 10 mass % of a repeating unit (a7) derived from a compound having a sulfonic acid group.

[0016] One aspect of the slurry for an electrode of an electricity storage device according to the present invention contains the binder composition for an electricity storage device according to any one of the above aspects and an active material.

[0017] In one embodiment of the slurry for an electricity storage device electrode, the slurry may further contain a thickener.

[0018] In any of the embodiments of the slurry for an electrode of an electricity storage device, the active material may be a positive electrode active material.

[0019] In any embodiment of the slurry for an electrode of a power storage device, the positive electrode active material may contain at least one selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, and an olivine-type lithium-containing phosphate compound.

[0020] One aspect of the electricity storage device electrode according to the present invention includes a current collector and an active material layer formed by applying the electricity storage device electrode slurry according to any one of the above aspects to the surface of the current collector and drying the applied slurry.

[0021] An aspect of the electricity storage device according to the present invention includes the electricity storage device electrode of the above aspect.

[0022] The binder composition for an electricity storage device according to the present invention makes it possible to prepare an electricity storage device electrode having excellent surface condition, adhesion, and ionic conductivity, and thus improve the cycle life characteristics of the electricity storage device.

[0023] Preferred embodiments of the present invention will be described in detail below. It should be understood that the present invention is not limited to the embodiments described below, but also includes various modifications that are implemented within the scope of the present invention.

[0024] In this specification, "(meth)acrylic acid..." refers to "acrylic acid..." or "methacrylic acid...", "(meth)acrylate..." refers to "acrylate..." or "methacrylate...", and "(meth)acrylamide" refers to "acrylamide" or "methacrylamide".

[0025] In this specification, a numerical range described as "X to Y" is interpreted as including the numerical value X as the lower limit and the numerical value Y as the upper limit.

[0026] 1. Binder Composition for Electrical Storage Devices A binder composition for electrical storage devices according to one embodiment of the present invention contains a polymer (A), a nonionic surfactant (B), and a liquid medium (C). The polymer (A) contains 1 to 50 mass% of repeating units (a1) derived from an α,β-unsaturated nitrile compound and 40 to 80 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester, where the total amount of repeating units contained in the polymer (A) is 100 mass%. The content of the nonionic surfactant (B) is 0.1 to 10 mass parts per 100 mass parts of the polymer (A). The liquid medium (C) is at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides. The components contained in the binder composition for electrical storage devices according to this embodiment are described in detail below.

[0027] 1.1. Polymer (A) The binder composition for an electricity storage device according to this embodiment contains a polymer (A). The polymer (A) is preferably dispersed in particulate form in a liquid medium (C) described below. When the polymer (A) is dispersed in particulate form in the liquid medium (C), the stability of the composition (hereinafter also referred to as "slurry") prepared by mixing the polymer (A) with the active material is improved, and the applicability of the slurry to the current collector is also improved, which is preferable. Furthermore, the presence of a particulate binder makes the active material more slippery during pressing, facilitating densification. Furthermore, excessive coating of the conductive additive can be suppressed, allowing for the formation of good conductive paths.

[0028] The repeating units constituting the polymer (A), the physical properties of the polymer (A), and the production method thereof will be described below in this order.

[0029] 1.1.1. Repeating units constituting polymer (A) When the total repeating units contained in polymer (A) is taken as 100% by mass, polymer (A) contains 1 to 50% by mass of repeating units (a1) (hereinafter also referred to as "repeating units (a1)") derived from an α,β-unsaturated nitrile compound and 40 to 80% by mass of repeating units (a2) (hereinafter also referred to as "repeating units (a2)") derived from an unsaturated carboxylic acid ester. In addition to repeating units (a1) and repeating units (a2), polymer (A) may also contain repeating units derived from other monomers copolymerizable with these repeating units.

[0030] 1.1.1.1. Repeating Unit (a1) Derived from an α,β-Unsaturated Nitrile Compound The content of the repeating unit (a1) derived from an α,β-unsaturated nitrile compound is 1 to 50% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The content of the repeating unit (a1) is preferably 2% by mass or more, and more preferably 3% by mass or more. The content of the repeating unit (a1) is preferably 48% by mass or less, and more preferably 45% by mass or less. The content of the repeating unit (a1) is preferably 2 to 48% by mass, and more preferably 3 to 45% by mass. By containing the repeating unit (a1) within the above range in the polymer (A), the affinity between the polymer (A) and the liquid medium (C) is improved, and the polymer (A) is more likely to maintain its particle shape. Furthermore, the affinity between the polymer (A) and the electrolyte is improved, and an increase in internal resistance due to the polymer (A) becoming an electrical resistance component in the electricity storage device can be suppressed.

[0031] 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 preferred, and acrylonitrile is particularly preferred.

[0032] 1.1.1.2. Repeating Unit (a2) Derived from Unsaturated Carboxylic Acid Ester The content of the repeating unit (a2) derived from an unsaturated carboxylic acid ester is 40 to 80% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The content of the repeating unit (a2) is preferably 43% by mass or more, and more preferably 45% by mass or more. The content of the repeating unit (a2) is preferably 75% by mass or less, and more preferably 70% by mass or less. The content of the repeating unit (a2) is preferably 43 to 75% by mass, and more preferably 45 to 70% by mass. When the polymer (A) contains the repeating unit (a2) within the above range, the affinity between the polymer (A) and the electrolyte solution is improved, and an increase in internal resistance due to the polymer (A) becoming an electrical resistance component in the electricity storage device can be suppressed.

[0033] Among unsaturated carboxylic acid esters, (meth)acrylic acid esters can be preferably used. Specific examples of (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, tri(meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, methyl ... Examples of suitable acrylates include trimethylolpropane acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, 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, and glycerin di(meth)acrylate. One or more selected from these may 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, ethylene glycol di(meth)acrylate, and 2-hydroxyethyl (meth)acrylate are preferred, with methyl (meth)acrylate being particularly preferred.

[0034] 1.1.1.3. Other Repeating Units In addition to the repeating units (a1) and (a2), the polymer (A) may contain repeating units derived from other monomers copolymerizable therewith. Examples of such repeating units include a repeating unit (a3) ​​derived from an unsaturated carboxylic acid (hereinafter also referred to as "repeating unit (a3)"), a repeating unit (a4) derived from an aromatic vinyl compound (hereinafter also referred to as "repeating unit (a4)"), a repeating unit (a5) derived from a conjugated diene compound (hereinafter also referred to as "repeating unit (a5)"), a repeating unit (a6) derived from (meth)acrylamide (hereinafter also referred to as "repeating unit (a6)"), a repeating unit (a7) derived from a compound having a sulfonic acid group (hereinafter also referred to as "repeating unit (a7)"), and a repeating unit derived from a cationic monomer.

[0035] <Repeating Unit (a3) ​​Derived from Unsaturated Carboxylic Acid> The polymer (A) may contain a repeating unit (a3) ​​derived from an unsaturated carboxylic acid. The content of the repeating unit (a3) ​​derived from an unsaturated carboxylic acid is preferably 0.1 to 10% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The content of the repeating unit (a3) ​​is more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. The content of the repeating unit (a3) ​​is more preferably 9% by mass or less, and particularly preferably 8% by mass or less. The content of the repeating unit (a3) ​​is preferably 0.5 to 9% by mass, and more preferably 1 to 8% by mass. By containing the repeating unit (a3) ​​in the polymer (A) within the above range, the adhesion between the current collector and the active material layer can be improved, and the adhesion strength of the electrode may be improved.

[0036] The unsaturated carboxylic acid is not particularly limited, but includes monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc., and one or more selected from these can be used. Among these, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

[0037] <Repeating Unit (a4) Derived from an Aromatic Vinyl Compound> The content of the repeating unit (a4) derived from an aromatic vinyl compound is preferably 1 to 50% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The content of the repeating unit (a4) is more preferably 3% by mass or more, and particularly preferably 5% by mass or more. The content of the repeating unit (a4) is more preferably 47% by mass or less, and particularly preferably 45% by mass or less. The content of the repeating unit (a4) is preferably 3 to 47% by mass, and more preferably 5 to 45% by mass. By including the repeating unit (a4) in the polymer (A) within the above range, fusion between the polymers (A) dispersed in the active material layer is suppressed, resulting in good slurry properties and improved coatability. Furthermore, the permeability of the electrolyte can be improved, which may result in good repeated charge / discharge characteristics.

[0038] The aromatic vinyl compound is not particularly limited, but examples thereof include styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used. Among these, styrene is particularly preferred.

[0039] <Repeating Unit (a5) Derived from a Conjugated Diene Compound> The content of the repeating unit (a5) derived from a conjugated diene compound is preferably 0 to 5% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The content of the repeating unit (a5) is more preferably 0.5% by mass or more, particularly preferably 1% by mass or more. The content of the repeating unit (a5) is more preferably 4% by mass or less, particularly preferably 3% by mass or less. The content of the repeating unit (a5) is preferably 0.5 to 4% by mass, and more preferably 1 to 3% by mass. By containing the repeating unit (a5) within the above range in the polymer (A), the dispersibility of the active material and filler is improved, making it possible to prepare a homogeneous active material layer and protective film, thereby eliminating structural defects in the electrode plate and potentially exhibiting good repeated charge-discharge characteristics. In addition, the polymer (A) coating the surface of the active material can be imparted with elasticity, and the elasticity of the polymer (A) can improve adhesion, potentially resulting in good charge-discharge durability.

[0040] The conjugated diene compound is not particularly limited, but examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and 1,3-heptadiene, and one or more selected from these can be used. Among these, 1,3-butadiene is particularly preferred.

[0041] <Repeating Unit (a6) Derived from (Meth)acrylamide> The polymer (A) may contain a repeating unit (a6) derived from (meth)acrylamide. The content of the repeating unit (a6) derived from (meth)acrylamide is preferably 0.1 to 10% by mass, relative to the total amount of repeating units contained in the polymer (A) taken as 100% by mass. The content of the repeating unit (a6) is more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. The content of the repeating unit (a6) is more preferably 9% by mass or less, and particularly preferably 8% by mass or less. The content of the repeating unit (a6) is preferably 0.5 to 9% by mass, and more preferably 1 to 8% by mass. By containing the repeating unit (a6) in the polymer (A) within the above range, the dispersibility of the active material and filler in the slurry may be improved. Furthermore, the flexibility of the resulting active material layer may be appropriate, which may improve the adhesion between the current collector and the active material layer.

[0042] The (meth)acrylamide is not particularly limited, but 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-methylol acrylamide, N-methylolmethacrylamide, diacetone acrylamide, and maleic acid amide, and one or more selected from these can be used. Of these, acrylamide and methacrylamide are particularly preferred.

[0043] <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 of the repeating unit (a7) derived from a compound having a sulfonic acid group is preferably 0.1 to 10% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The content of the repeating unit (a7) is more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. The content of the repeating unit (a7) is more preferably 9% by mass or less, and particularly preferably 8% by mass or less. The content of the repeating unit (a7) is preferably 0.5 to 9% by mass, and more preferably 1 to 8% by mass. When the polymer (A) contains the repeating unit (a7) within the above ranges, the dispersibility of the active material and filler is improved, and a homogeneous active material layer or protective film may be obtained. Furthermore, the improved adhesion between the current collector and the active material layer may eliminate structural defects in the electrode plate, resulting in good charge-discharge characteristics.

[0044] The compound having a sulfonic acid group is not particularly limited, but examples thereof include compounds such as vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, acrylamido tert-butylsulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid, as well as alkali salts thereof, and one or more selected from these can be used. Of these, styrene sulfonic acid is particularly preferred.

[0045] <Repeating Units Derived from Cationic Monomers> 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 amines (salts), tertiary amines (salts), and quaternary ammonium salts. Specific examples of the cationic monomer 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, methcroylcholine chloride, tris(2-acryloyloxyethyl) isocyanurate, and 2-vinylpiperidinyl. Examples of the surfactant include lysine, quinaldine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazole dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichlormid, N-allylbenzylamine, N-allylaniline, 2,4-diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-hepten-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, and the like. One or more surfactants selected from these may be used.

[0046] 1.1.2. Physical Properties of Polymer (A) <Number Average Particle Diameter> When the polymer (A) is in the form of particles, the number average particle diameter of the particles is preferably 50 nm or more and 1,000 nm or less, more preferably 70 nm or more and 950 nm or less, and particularly preferably 90 nm or more and 900 nm or less. When the number average particle diameter of the polymer (A) particles is within the above range, the polymer (A) particles are easily adsorbed to the surface of the active material, and therefore, the polymer (A) particles can move in conjunction with the movement of the active material. As a result, migration can be suppressed, which may reduce deterioration of electrical properties.

[0047] The number average particle size of the particles of polymer (A) is the average value of particle sizes measured with a concentrated particle size analyzer using dynamic light scattering (DLS). Examples of concentrated particle size analyzers include "FPA-1000" manufactured by Otsuka Electronics Co., Ltd.

[0048] 1.1.3. Method for Producing Polymer (A) <Polymerization Step> The method for producing the polymer (A) can be an emulsion polymerization method carried out in the presence of the nonionic surfactant (B), other emulsifiers, chain transfer agents, polymerization initiators, etc.

[0049] As the nonionic surfactant (B), one or more compounds selected from the compounds described in "1.2. Nonionic surfactant (B)" below can be used.

[0050] Other emulsifiers include fluorine-based surfactants such as sulfate salts of higher alcohols, alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkyldiphenyletherdisulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, naphthalenesulfonic acid-formalin condensates, perfluorobutylsulfonates, perfluoroalkyl group-containing phosphate esters, perfluoroalkyl group-containing carboxylates, and perfluoroalkylethylene oxide adducts, and one or more selected from these may be used.

[0051] Specific examples of the chain transfer agent and polymerization initiator include compounds described in Japanese Patent No. 5,999,399.

[0052] The emulsion polymerization method for synthesizing the polymer (A) may be carried out in a single-stage polymerization or in a multi-stage polymerization of two or more stages.

[0053] When the synthesis of the polymer (A) is carried out by single-stage polymerization, the monomer mixture can be subjected to emulsion polymerization in the presence of the nonionic surfactant (B), other emulsifiers, chain transfer agents, polymerization initiators, etc., preferably at a temperature of 0 to 80°C for a polymerization time of preferably 4 to 36 hours.

[0054] When the synthesis of the polymer (A) is carried out by two-stage polymerization, it is preferable to set the polymerization in each stage as follows.

[0055] The proportion of the monomer used in the first-stage polymerization is preferably in the range of 20 to 99 mass %, more preferably in the range of 25 to 99 mass %, based on the total mass of the monomers (the sum of the mass of the monomers used in the first-stage polymerization and the mass of the monomers used in the second-stage polymerization). By carrying out the first-stage polymerization at such a proportion of the monomers, it is possible to obtain particles of polymer (A) that are excellent in dispersion stability and are less likely to form aggregates, and it is also preferable because an increase in viscosity over time of the binder composition for an electrical storage device after coagulation is suppressed.

[0056] The types and proportions of monomers used in the second-stage polymerization may be the same as or different from the types and proportions of monomers used in the first-stage polymerization.

[0057] From the viewpoint of the dispersibility of the particles of the resulting polymer (A), the polymerization conditions for each stage are preferably as follows: First-stage polymerization: A temperature of preferably 0 to 80°C, a polymerization time of preferably 2 to 36 hours, and a polymerization conversion rate of preferably 50% by mass or more, more preferably 60% by mass or more. Second-stage polymerization: A temperature of preferably 0 to 80°C, a polymerization time of preferably 2 to 18 hours.

[0058] When the synthesis of the polymer (A) is carried out by three-stage polymerization, it is preferable to set the polymerization in each stage as follows.

[0059] The proportion of the monomer used in the first-stage polymerization is preferably in the range of 20 to 90 mass %, more preferably in the range of 25 to 80 mass %, based on the total mass of the monomers (the sum of the mass of the monomers used in the first-stage polymerization, the mass of the monomers used in the second-stage polymerization, and the mass of the monomers used in the third-stage polymerization). By carrying out the first-stage polymerization at such a proportion of the monomers, it is possible to obtain particles of polymer (A) that are excellent in dispersion stability and are less likely to form aggregates, and it is also preferable because an increase in viscosity over time of the binder composition for an electrical storage device after coagulation is suppressed.

[0060] The types and proportions of monomers used in the second-stage polymerization may be the same as or different from the types and proportions of monomers used in the first-stage polymerization.

[0061] The types and proportions of monomers used in the third-stage polymerization may be the same as or different from the types and proportions of monomers used in the first-stage polymerization and the types and proportions of monomers used in the second-stage polymerization.

[0062] From the viewpoint of the dispersibility of the particles of the obtained polymer (A), the polymerization conditions for each stage are preferably as follows: First-stage polymerization: A temperature of preferably 0 to 80°C, a polymerization time of preferably 2 to 36 hours, and a polymerization conversion of preferably 50% by mass or more, more preferably 60% by mass or more. Second-stage polymerization: A temperature of preferably 0 to 80°C, and a polymerization time of preferably 2 to 18 hours. Third-stage polymerization: A temperature of preferably 0 to 80°C, and a polymerization time of preferably 2 to 9 hours.

[0063] By controlling the total solids concentration in the emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed in a state in which the dispersion stability of the resulting polymer (A) particles is good. This total solids concentration is preferably 45% by mass or less, and more preferably 40% by mass or less.

[0064] Whether the synthesis of polymer (A) is carried out by single-stage polymerization or multi-stage polymerization, it is preferable to neutralize the polymerization mixture after the completion of emulsion polymerization by adding a neutralizing agent. The neutralizing agent used here is not particularly limited, but examples thereof include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; etc.

[0065] The binder composition for an electrical storage device according to this embodiment can be obtained, for example, by substituting a latex aqueous dispersion produced in an aqueous dispersion medium for the dispersion medium, and dispersing the resulting mixture in a liquid medium (C), which is an organic dispersion medium. This method requires the removal of water. When the boiling point of the liquid medium (C) is higher than that of water, the liquid medium (C) can be added to the resulting aqueous latex dispersion, and the water can be removed by evaporation using an evaporator or the like. When the liquid medium (C) is azeotropic with water, the liquid medium (C) can be added to the resulting aqueous latex dispersion, and the azeotropic mixture with water can be removed using an evaporator or the like to reduce the amount of water to a certain extent. After this, a water-absorbing agent such as a molecular sieve or a reverse osmosis membrane can be used to remove the water.

[0066] Other methods for producing the binder composition for a storage battery device according to this embodiment include a method in which the polymer (A) produced in an aqueous dispersion medium is first coagulated and dried, then pulverized, and dispersed in a liquid medium (C), or a method in which the coagulated and dried polymer (A) is mixed with a liquid medium (C) and pulverized. Dispersion can be carried out using a conventional disperser such as a ball mill or a sand mill; an ultrasonic disperser; a homogenizer, or the like. Furthermore, when the polymer (A) is produced in a liquid medium (C) to obtain a block of the polymer (A), a particle dispersion of the polymer (A) dispersed in the liquid medium (C) can also be obtained by pulverizing the block using a disperser such as a ball mill or a sand mill.

[0067] 1.2. Nonionic Surfactant (B) The binder composition for a storage battery device according to this embodiment contains a nonionic surfactant (B). The content of the nonionic surfactant (B) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 9 parts by mass, and particularly preferably 1 to 8 parts by mass, per 100 parts by mass of the polymer (A). It has been found that by including the nonionic surfactant (B) within the above range, the polymer (A) is more likely to maintain its particle shape in the liquid medium (C). Because the nonionic surfactant (B) has a high affinity for both the polymer (A) and the liquid medium (C), the nonionic surfactant (B) adsorbed to the particle interface of the polymer (A) possesses mobility in the liquid medium (C), and its steric hindrance is thought to enable the polymer (A) to maintain its particle shape without agglomerating. By allowing the polymer (A) to maintain its particle shape, excessive coating on the positive electrode active material and conductive additive is suppressed, resulting in the formation of a good conductive path. Furthermore, flexibility and adhesiveness derived from the particles can be imparted.

[0068] As described above, nonionic surfactant (B) and other emulsifiers are used during polymerization of the polymer (A). However, the amount of residual emulsifier varies depending on the conditions of subsequent coagulation and washing processes. Therefore, it is common for residual emulsifiers to be improperly controlled. It has been discovered that the binder composition for an electrical storage device according to this embodiment exhibits good battery characteristics by properly controlling the content of the nonionic surfactant (B) during the manufacturing process. That is, when the content of the nonionic surfactant (B) is equal to or less than the upper limit, the formation of craters on the surface of the slurry coating due to bubble breakage caused by the emulsifier can be effectively suppressed. Furthermore, when the content of the nonionic surfactant (B) is equal to or greater than the lower limit, the polymer (A) can maintain its particle shape in the liquid medium (C), forming a good conductive path in the electrode layer and suppressing an increase in internal resistance, thereby exhibiting good repeated charge / discharge characteristics. In particular, if the electronic conductive path in the electrode layer cannot be maintained, lithium ion conductivity decreases and resistance increases, so it is important to suppress the obstruction of the conductive path due to fusion between polymer (A) particles.

[0069] Examples of the nonionic surfactant (B) include ether-type nonionic surfactants, ester-type nonionic surfactants, and ester-ether-type nonionic surfactants.

[0070] Examples of ether-type nonionic surfactants include polyoxyalkylene glycols (e.g., polyoxyethylene polyoxypropylene glycol), and types in which an oxyalkylene group (e.g., ethylene oxide) is added to a hydrocarbon group having a hydroxyl group (e.g., polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers; polyoxyethylene phenyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene styrenated phenyl ethers, etc.). Examples of hydrocarbon groups having a hydroxyl group include alcohol compounds and phenol compounds. Examples of alcohol compounds include linear alkyl alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, heneicosanol, docosanol, tricosanol, tetracosanol, pentacosanol, hexacosanol, heptacosanol, octacosanol, nonacosanol, and triacontanol; and linear alkyl alcohols such as isopropanol, isobutanol, isohexanol, 2-ethylhexanol, isononanol, isodecanol, isotridecanol, isotetradecanol, and isotridecanoic acid. Examples of the alcohol include branched alkyl alcohols such as acontanol, isohexadecanol, isoheptadecanol, isooctadecanol, isononadecanol, isoeicosanol, isoheneicosanol, isodocosanol, isotricosanol, isotetracosanol, isopentacosanol, isohexacosanol, isoheptacosanol, isooctacosanol, isononacosanol, and isopentadecanol; linear alkenyl alcohols such as tetradecenol, hexadecenol, heptadecenol, octadecenol, and nonadecenol; branched alkenyl alcohols such as isohexadecenol and isooctadecenol; cyclic alkyl alcohols such as cyclopentanol and cyclohexanol, and aromatic alcohols such as benzyl alcohol.Examples of phenol compounds include phenol, alkylphenols, monostyrenated phenol, distyrenated phenol, tristyrenated phenol, etc. Among these, chain higher alcohols having 10 to 20 carbon atoms are desirable, and the number of carbon atoms of the higher alcohol may be 11 to 17, or 11 to 15 (or even 12 to 13).

[0071] Examples of ester-type nonionic surfactants include those having an ester bond between a polyhydric alcohol and a higher fatty acid. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol, 2,3-dimethyl-2,3-butanediol, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol, trimethylolpropane, sorbitan, pentaerythritol, sorbitol, glycerin, and sucrose. Examples of higher fatty acids include linear alkyl carboxylic acids such as octylic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid (lauric acid), tridecanoic acid, tetradecanoic acid (myristic acid), pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid (stearic acid), nonadecanoic acid, eicosanoic acid, heneicosanoic acid, and docosanoic acid; branched alkyl carboxylic acids such as 2-ethylhexanoic acid, isododecanoic acid, isotridecanoic acid, isotetradecanoic acid, isohexadecanoic acid, and isooctadecanoic acid; and linear alkenyl carboxylic acids such as octadecenoic acid, octadecadienoic acid, octadecatrienoic acid, and oleic acid. Among these, oleic acid, stearic acid, lauric acid, and myristic acid are preferred. Examples of ester-type nonionic surfactants include polyglycerin fatty acid esters, polysorbitan fatty acid esters, and sucrose fatty acid esters.

[0072] Examples of ester-ether type nonionic surfactants include those having both an ester bond and an ether bond in the molecule (e.g., fatty acid methyl ester ethoxylates), as well as those in which ethylene oxide is added to an ester of a fatty acid with a polyhydric alcohol such as glycerin or sorbitol, fatty acid polyethylene glycol, and fatty acid polyoxyethylene sorbitan.

[0073] Among these, ether-type nonionic surfactants are preferred, polyoxyalkylene alkyl ethers and polyoxyalkylene phenyl ethers are more preferred, and polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers and polyoxyethylene distyrenated phenyl ethers are particularly preferred.

[0074] 1.3. Liquid Medium (C) The binder composition for an electricity storage device according to this embodiment contains a liquid medium (C). The liquid medium (C) is not particularly limited, but may be an aliphatic hydrocarbon such as hexane, heptane, octane, decane, or dodecane; an alicyclic hydrocarbon such as cyclohexane, cycloheptane, cyclooctane, or cyclodecane; an aromatic hydrocarbon such as toluene, xylene, mesitylene, naphthalene, or tetralin; a ketone such as methylhexyl ketone or dipropyl ketone; an ester such as butyl acetate, butyl butyrate, or methyl butanoate; an ether such as dibutyl ether, tetrahydrofuran, or anisole; a β-lactam, a γ-lactam, a σ-lactam, an N-methyl lactam, or a methyl lactam. Examples of the liquid medium (C) that can be used include lactams such as 2-pyrrolidone and 2-pyrrolidone; glycol ethers such as (mono-, di-, tri-, or poly)ethylene glycol monomethyl ether, (mono-, di-, tri-, or poly)ethylene glycol dimethyl ether, and ethylene glycol phenyl ether; lactones such as α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone; and amides such as N-methylacetamide, dimethylacetamide, N-methylformamide, and dimethylformamide. These liquid media (C) can be used either individually or in combination of two or more.

[0075] The liquid medium (C) may contain water as long as it contains an organic solvent as the main solvent. The phrase "containing an organic solvent as the main solvent" means that the organic solvent accounts for more than 50% by mass when the total mass of the liquid medium (C) is 100% by mass.

[0076] 1.4 Other Additives The binder composition for an electricity storage device according to this embodiment may contain additives other than the components described above, as necessary. Examples of such additives include polymers other than the polymer (A) and preservatives.

[0077] <Polymers Other than Polymer (A)> The binder composition for an electrical storage device according to this embodiment may contain a polymer other than the polymer (A). Examples of such polymers include, but are not limited to, acrylic polymers containing an unsaturated carboxylic acid ester or a derivative thereof as a structural unit that is soluble in the liquid medium (C), styrene-butadiene polymers containing a conjugated diene as a structural unit, acrylonitrile-butadiene copolymers, and fluoropolymers such as PVDF (polyvinylidene fluoride). These polymers may be used alone or in combination of two or more. The inclusion of these polymers may result in good slurry properties, further improving the flexibility and adhesion of the electrode.

[0078] <Preservative> The binder composition for a storage battery device according to this embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, mold, and the like, and the generation of foreign matter, when the binder composition for a storage battery device is stored. Specific examples of preservatives include the compounds described in Japanese Patent No. 5,477,610, etc.

[0079] 2. Slurry for Electricity Storage Devices A slurry for an electricity storage device according to one embodiment of the present invention contains the above-described binder composition for an electricity storage device. The above-described binder composition for an electricity storage device can be used as a material for producing a protective film for suppressing short circuits caused by dendrites that occur during charging and discharging, or as a material for producing an electricity storage device electrode (active material layer) that has improved bonding ability between active materials, improved adhesion ability between the active material and the current collector, and improved resistance to powder shedding. Hereinafter, the slurry for an electricity storage device for producing a protective film (hereinafter also referred to as "slurry for protective film") and the slurry for an electricity storage device for producing an active material layer of an electricity storage device electrode (hereinafter also referred to as "slurry for electricity storage device electrode") will be described separately.

[0080] 2.1. Slurry for Protective Film The term "slurry for protective film" refers to a dispersion liquid used to form a protective film on the surface of an electrode or a separator, or both, by applying the slurry to the surface of an electrode or a separator, or both, and then drying the dispersion liquid. The slurry for protective film according to this embodiment may consist solely of the binder composition for an electrical storage device described above, or may further contain an inorganic filler. Examples of inorganic fillers include the inorganic fillers described in JP 2020-184461 A.

[0081] 2.2. Slurry for Electricity Storage Device Electrode The term "slurry for electricity storage device electrode" refers to a dispersion liquid used for forming an active material layer on the surface of a current collector by applying the dispersion liquid to the surface of the current collector and then drying the same. The slurry for electricity storage device electrode according to this embodiment contains the above-described binder composition for electricity storage devices and an active material.

[0082] Hereinafter, the components contained in the slurry for an electrical storage device electrode according to this embodiment will be described.

[0083] 2.2.1 Polymer (A) The composition, physical properties, production method, etc. of the polymer (A) are as described above, and therefore further explanation is omitted.

[0084] The content of the polymer component in the slurry for an electrical storage device electrode according to this 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, per 100 parts by mass of the active material. When the content of the polymer component is within this range, the dispersibility of the active material in the slurry is good, and the coating properties of the slurry are also excellent. Here, the polymer component includes polymer (A) and polymers other than polymer (A) that are added as needed.

[0085] Active materials used in the slurry for an electrode of an electric storage device according to this embodiment include a positive electrode active material and a negative electrode active material. Specific examples of these include carbon materials, silicon materials, oxides containing lithium atoms, sulfur compounds, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacenes, A Ｘ B Ｙ O Ｚ (wherein A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, and manganese, O is an oxygen atom, and X, Y, and Z are numbers within the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.50, respectively), as well as other metal oxides. Examples of the composite metal oxide include lithium cobalt oxide, lithium nickel oxide, lithium manganate, and ternary nickel cobalt manganate.

[0086] The slurry for an electrode of an electricity storage device according to this embodiment can be used when producing either a positive electrode or a negative electrode, but is particularly preferably used for a positive electrode.

[0087] The positive electrode active material preferably contains at least one selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganate, ternary lithium nickel cobalt manganate, and olivine-type lithium-containing phosphate compounds, more preferably contains at least one selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganate, and ternary lithium nickel cobalt manganate, and particularly preferably contains ternary lithium nickel cobalt manganate.

[0088] An electricity storage device electrode produced using the electricity storage device electrode slurry according to this embodiment can exhibit good electrical properties even when such a positive electrode active material is used, which is thought to be because the polymer (A) can firmly bind the positive electrode active material and can maintain the strongly bound state of the positive electrode active material even during charge and discharge.

[0089] The average particle size of the positive electrode active material is preferably in the range of 0.5 to 30 μm, more preferably in the range of 0.5 to 25 μm, and particularly preferably in the range of 0.5 to 20 μm.

[0090] On the other hand, when preparing a negative electrode, among the active materials exemplified above, those containing a silicon material and / or a carbon material are preferred, and a mixture of a silicon material and a carbon material is more preferred. Silicon materials have a larger lithium absorption capacity per unit weight than other active materials, so the storage capacity of the resulting energy storage device can be increased, and as a result, the output and energy density of the energy storage device can be increased. On the other hand, carbon materials have a smaller volume change during charging and discharging than silicon materials, so by using a mixture of a silicon material and a carbon material as the negative electrode active material, the effect of the volume change of the silicon material can be mitigated, and the adhesion between the active material layer and the current collector can be further improved.

[0091] 2.2.3. Other Components In addition to the components described above, the slurry for an electricity storage device electrode according to this embodiment may contain, as necessary, components such as a polymer other than the polymer (A), a liquid medium, a conductive additive, a corrosion inhibitor, and cellulose fiber. The polymer other than the polymer (A) may be appropriately selected from the compounds exemplified in the above section "1.4. Other Additives" and used for the same purpose.

[0092] <Liquid medium> A liquid medium may be further added to the slurry for an electrical storage device electrode according to this embodiment in addition to the liquid medium carried over from the binder composition for an electrical storage device. The liquid medium to be added may be the same as or different from the liquid medium (C) contained in the binder composition for an electrical storage device, but is preferably selected from the liquid media exemplified in the above section "1.3. Liquid medium (C)".

[0093] The content of the liquid medium (including the portion carried over from the binder composition for a storage battery device) in the slurry for an electrode of a storage battery device according to this embodiment is preferably such that the solids concentration in the slurry (meaning the proportion 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 90 mass%, and more preferably 40 to 80 mass%.

[0094] <Conductive Aid> A conductive aid may be further added to the slurry for an electricity storage device electrode according to this embodiment for the purposes of imparting conductivity and buffering the volume change of the active material due to the inflow and outflow of lithium ions.

[0095] Specific examples of the conductive additive include activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, fullerene, carbon nanotubes, and other carbons. Among these, acetylene black, ketjen black, and carbon nanotubes are preferably used. The content of the conductive additive is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass, per 100 parts by mass of the active material.

[0096] <Corrosion Inhibitor> A corrosion inhibitor may be further added to the slurry for an electricity storage device electrode according to this embodiment, depending on the type of active material, for the purpose of suppressing corrosion of the current collector.

[0097] 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, and potassium molybdate. Of these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0098] <Cellulose Fiber> Cellulose fiber may be further added to the slurry for an electricity storage device electrode according to this embodiment. Known cellulose fibers can be used. Adding cellulose fiber may improve the adhesion of the active material to the current collector. It is believed that the fibrous cellulose fiber bonds adjacent active materials together in a fibrous state through linear adhesion or linear contact, thereby preventing the active material from falling off and improving the adhesion to the current collector.

[0099] 2.2.4. Method for Preparing Slurry for Electricity Storage Device Electrode The slurry for an electricity storage device electrode according to this embodiment may be produced by any method as long as it contains the above-described binder composition for an electricity storage device and active material. From the viewpoint of producing a slurry with better dispersibility and stability more efficiently and inexpensively, it is preferable to produce the slurry by adding the active material and optional additive components used as needed to the binder composition for an electricity storage device and mixing them. Specific production methods include, for example, the method described in Japanese Patent No. 5,999,399.

[0100] 3. Electricity Storage Device Electrode An electricity storage device electrode according to one embodiment of the present invention comprises a current collector and an active material layer formed by applying and drying the above-described electricity storage device electrode slurry to the surface of the current collector. Such an electricity storage device electrode can be produced by applying the above-described electricity storage device electrode slurry to 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 electricity storage device electrode produced in this manner has an active material layer containing the above-described polymer (A), an active material, and optional components added as needed, bound to the surface of the current collector, and therefore has excellent adhesion. In addition, expansion of the electrode due to repeated charge and discharge is suppressed, resulting in excellent charge and discharge durability.

[0101] The current collector is not particularly limited as long as it is made of a conductive material, and examples thereof include the current collectors described in Japanese Patent No. 5,999,399 and the like.

[0102] 4. Energy Storage Device An energy storage device according to one embodiment of the present invention includes the above-described energy storage device electrodes, further contains an electrolyte solution, and can be manufactured by a conventional method using components such as a separator. Specific manufacturing methods include, for example, stacking a negative electrode and a positive electrode with a separator interposed therebetween, and then wrapping or folding the stack according to the battery shape to house the stack in a battery container, and then injecting an electrolyte solution into the battery container and sealing it. The battery can have any suitable shape, such as a coin shape, a cylindrical shape, a rectangular shape, or a laminate shape.

[0103] The electrolyte may be liquid or gel, and may be selected from known electrolytes used in electricity storage devices to effectively exhibit the functions of a battery depending on the type of active material. The electrolyte may be a solution in which an electrolyte is dissolved in a suitable solvent. Examples of such electrolytes and solvents include those described in Japanese Patent No. 5,999,399.

[0104] The above-described electricity storage device can be applied to lithium ion secondary batteries, electric double layer capacitors, lithium ion capacitors, and the like that require discharge at a high current density. Among these, lithium ion secondary batteries are particularly preferred. In the electricity storage device electrode and electricity storage device according to this embodiment, components other than the binder composition for electricity storage devices can be known components for lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors.

[0105] 5. Examples The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the examples and comparative examples are by mass unless otherwise specified.

[0106] 5.1. Examples 1 to 12 and Comparative Examples 1 to 6 5.1.1. Preparation of Binder Composition for Electrical Storage Device Example 1 A polymer (A1) dispersion was obtained by single-stage polymerization as shown below. A reactor was charged with 300 parts by weight of water, a monomer mixture consisting of 1 part by weight of acrylonitrile, 5 parts by weight of methyl methacrylate, 5 parts by weight of butyl acrylate, 58 parts by weight of 2-ethylhexyl acrylate, 2 parts by weight of allyl methacrylate, 25 parts by weight of styrene, 1 part by weight of acrylic acid, 1 part by weight of methacrylic acid, 1 part by weight of acrylamide, and 1 part by weight of sodium styrenesulfonate, 0.01 parts by weight of tert-dodecyl mercaptan as a chain transfer agent, 0.2 parts by weight of sodium dodecylbenzenesulfonate and 4 parts by weight of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade name "Emulgen 147") as emulsifiers, and 0.6 parts by weight of potassium persulfate as a polymerization initiator, and the mixture was polymerized with stirring at 70°C for 10 hours to obtain a latex of polymer (A1). The conversion of the polymer at this time was 98%.

[0107] Next, 80 parts by mass of the obtained latex (20 parts by mass of solids) and 230 parts by mass of N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") were added to a recovery flask, and a dehydration process was carried out at 85°C for 6 hours under reduced pressure in an evaporator. Since only water is removed in this dehydration process, polyoxyethylene lauryl ether remains in the binder composition for an electricity storage device. In this way, the dispersion medium was replaced from water to NMP, thereby obtaining the binder composition for an electricity storage device of Example 1. The solids concentration of the obtained binder composition for an electricity storage device was 8% by mass.

[0108] Examples 2 to 12 and Comparative Examples 1 to 6 In Examples 2 to 12 and Comparative Examples 1 to 6, each polymer was synthesized by single-stage polymerization in the same manner as in Example 1, except that the types and amounts of monomers were as shown in Tables 1 and 2 below, respectively, and each binder composition for an electricity storage device was obtained in the same manner as in Example 1.

[0109] 5.1.2. Evaluation of Physical Properties of Binder Compositions for Electrical Storage Devices <Method for Measuring Polymerization Conversion Rate> The polymerization conversion rate in the synthesis of each of the above polymers was measured as follows. After polymerization for a predetermined time, the reaction solution was extracted and placed in a pre-weighed aluminum dish (X (g)), and the weight of the reaction solution (Y (g)) was measured. This was dried at 155°C for 15 minutes using a hot air dryer. The aluminum dish was removed and allowed to cool, and then its weight (Z (g)) was measured. The polymerization conversion rate (%) was calculated from the weights X, Y, and Z measured in this way using the following formula (1): Polymerization conversion rate (%) = ((Z-X) / Y) x 100 (1)

[0110] <Measurement of Number Average Particle Diameter> The binder composition for a storage battery device obtained above was diluted with NMP to a solids concentration of 0.1 wt %, and used as a measurement sample. The obtained measurement sample was measured using dynamic light scattering (DLS) under the following conditions to determine the number average particle diameter of each polymer. Temperature: 25°C NMP refractive index: 1.47

[0111] 5.1.3. Preparation of Lithium-Ion Secondary Battery Positive Electrode Slurry

[0049] 1 part by mass (solids equivalent, added as an 8% NMP solution) of PVdF (Arkema, product name "HSV900"), 2 parts by mass (solids equivalent, added as the binder composition for an electrical storage device obtained above) of polymer (A), 100 parts by mass of NMC811 (Beijing Dangsheng Co., Ltd., product name "ME-83SC") as a positive electrode active material, 6 parts by mass of acetylene black, and 1.8 parts by mass of NMP were added to a biaxial planetary mixer (Primix Corporation, product name "TK Hibismix 2P-03"), adjusted to a solids concentration of approximately 75% and stirred at 60 rpm for 1 hour. NMC811 is an abbreviation for ternary nickel-cobalt-manganese lithium oxide (Ni:Mn:Co=8:1:1).

[0112] Thereafter, NMP was added to the obtained paste to adjust the solid content concentration to 68%, and then the mixture was deaerated using a stirring deaerator (manufactured by Thinky Corporation, product name "Awatori Rentaro") at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then further deaerated under vacuum (approximately 5.0 × 10 ３ The mixture was stirred and mixed at 1800 rpm for 1.5 minutes at 1000 kPa (2000 kPa) to prepare a slurry for a lithium ion secondary battery positive electrode.

[0113] 5.1.4. Preparation of a Lithium-ion Secondary Battery Positive Electrode and Evaluation of Its Physical Properties <Preparation of a Lithium-ion Secondary Battery Positive Electrode> The slurry for a lithium-ion secondary battery positive electrode obtained above was uniformly applied to the surface of a 20 μm-thick current collector made of aluminum foil by a doctor blade method so that the film thickness after drying would be 100 μm, and the slurry was dried at 120° C. for 20 minutes. Thereafter, the density of the formed film (positive electrode active material layer) was 3.0 g / cm ３ The resultant was pressed using a roll press machine so as to obtain a positive electrode for a lithium ion secondary battery.

[0114] <Evaluation of Electrode Condition> The lithium-ion secondary battery positive electrode obtained above was cut into a 10 cm x 10 cm piece, and the number of broken bubble marks on the surface was visually counted. The evaluation criteria were as follows. The evaluation results are shown in Tables 1 and 2 below. Those with no visible damage to the active material layer had reduced coating defects due to residual emulsifier, indicating good cycle characteristics. (Evaluation Criteria) 5 points: If there were no broken bubble marks, there were no coating defects due to residual emulsifier, and the result was good. 4 points: If there were 1 to 5 broken bubble marks, there were almost no coating defects due to residual emulsifier, and the result was good. 3 points: If there were 6 to 10 broken bubble marks, there were few coating defects due to residual emulsifier, and the result was good. 2 points: If there were 11 to 15 broken bubble marks, there were some coating defects due to residual emulsifier, and the result was difficult to use. 1 point: If the number of broken particle traces is 16 or more, there are many coating defects due to residual emulsifier, and the coating cannot be used.

[0115] <Evaluation of Adhesion Strength> A knife was used to make 10 incisions in each direction, 2 mm apart, on the surface of the lithium-ion secondary battery positive electrode obtained above, from the active material layer to the current collector, creating a grid pattern. An 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Cellotape" (registered trademark), as defined in JIS Z1522:2009) was attached to the incisions and immediately peeled off, and the degree of active material loss was evaluated by visual inspection. The evaluation criteria were as follows. The evaluation results are shown in Tables 1 and 2 below. (Evaluation Criteria) 5 points: 0 active material layers lost. 4 points: 1 to 5 active material layers lost. 3 points: 6 to 20 active material layers lost. 2 points: 21 to 40 active material layers lost. 1 point: 41 or more active material layers lost.

[0116] 5.1.5. Fabrication of Lithium-ion Secondary Battery and Evaluation of Physical Properties <Preparation of Slurry for Lithium-ion Secondary Battery Negative Electrode> 1 part by mass (solid content equivalent) of a thickener (trade name "CMC2200", manufactured by Daicel Corporation), 100 parts by mass (solid content equivalent) of graphite as the negative electrode active material, and 68 parts by mass of water were added to a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK Hivismix 2P-03"), and the mixture was stirred at 60 rpm for 1 hour.

[0117] Next, SBR (trade name "TRD105A", manufactured by ENEOS Materials Corporation) was added in an amount equivalent to 2 parts by mass (converted to solid content), and the mixture was further stirred for 1 hour to obtain a paste. Water was added to the obtained paste to adjust the solid content to 50%, and then the mixture was stirred and mixed using a stirring defoamer (manufactured by Thinky Corporation, trade name "Awatori Rentaro") at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under vacuum to prepare a slurry for a lithium-ion secondary battery negative electrode.

[0118] <Preparation of negative electrode for lithium ion secondary battery> The slurry for the negative electrode for lithium ion secondary battery prepared above was uniformly applied to the surface of a current collector made of copper foil with a thickness of 20 μm by a doctor blade method so that the film thickness after drying would be 120 μm, and the coating was dried at 120° C. for 20 minutes. After that, the density of the formed film (negative electrode active material layer) was 1.9 g / cm ３ The negative electrode for a lithium ion secondary battery was obtained by pressing the negative electrode using a roll press machine so that the negative electrode became as follows:

[0119] <Assembly of Lithium-Ion Secondary Battery> In a glove box purged with Ar to maintain a dew point of −80° C. or lower, the lithium-ion secondary battery negative electrode prepared above was punched into a circle with a diameter of 16.16 mm and placed on a two-electrode coin cell (manufactured by Hosen Co., Ltd., product name "HS Flat Cell"). Next, a separator made of a polypropylene porous film punched into a circle with a diameter of 24 mm (manufactured by Celgard Co., Ltd., product name "Celgard #2400") was placed on top of the lithium-ion secondary battery negative electrode. Furthermore, 500 μL of electrolyte was poured into the cell to prevent air from entering, and then the lithium-ion secondary battery positive electrode prepared above was punched into a circle with a diameter of 15.95 mm and placed on top of the separator. The exterior body of the two-electrode coin cell was screwed shut to seal the cell, thereby assembling a lithium-ion secondary battery. The electrolyte used here was a solution of ethylene carbonate / ethyl methyl carbonate (mass ratio: 1 / 1) in a solvent containing LiPF ６ It is a solution in which the above is dissolved at a concentration of 1 mol / L.

[0120] <Evaluation of Resistance Increase Rate> The lithium ion secondary battery prepared above was charged at a constant current (1.0 C) in a thermostatic chamber controlled at 25°C. When the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). The charge completion (cutoff) was determined when the current reached 0.01 C. Discharge was then initiated at a constant current (0.05 C). The discharge completion (cutoff) was determined when the voltage reached 2.5 V, and the discharge capacity at the 0th cycle was calculated. Furthermore, charging was initiated at a constant current (1.0 C). When the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). The charge completion (cutoff) was determined when the current reached 0.01 C. Discharge was then initiated at a constant current (1.0 C). The discharge completion (cutoff) was determined when the voltage reached 2.5 V, and the discharge capacity at the 1st cycle was calculated. Charge and discharge were repeated 100 times in this manner. After repeating charge and discharge 100 times, charge and discharge were performed in the same manner as in the 0th cycle, and the discharge capacity in the 101st cycle was evaluated. The resistance increase rate was calculated using the following formula (2) and evaluated according to the following criteria. The results are shown in Tables 1 and 2 below. Resistance increase rate (%) = (discharge capacity at 101st cycle - discharge capacity at 100th cycle) / (discharge capacity at 0th cycle - discharge capacity at 1st cycle) x 100 (2) (Evaluation criteria) - 5 points: Resistance increase rate is 100% or more and less than 110%. - 4 points: Resistance increase rate is 110% or more and less than 120%. - 3 points: Resistance increase rate is 120% or more and less than 130%. - 2 points: Resistance increase rate is 130% or more and less than 140%. - 1 point: Resistance increase rate is 140% or more and less than 150%. - 0 point: Resistance increase rate is 150% or more.

[0121] <Evaluation of Cycle Characteristics> The lithium-ion secondary battery fabricated above was charged at a constant current (1.0 C) in a thermostatic chamber maintained at 25°C. When the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). Charging was completed (cutoff) when the current reached 0.01 C. Discharge was then initiated at a constant current (1.0 C). Discharge was completed (cutoff) when the voltage reached 2.5 V, and the discharge capacity at the first cycle was calculated. This cycle was repeated 100 times. The capacity retention was calculated using the following formula (3) and evaluated according to the following criteria. The results are shown in Tables 1 and 2 below. Capacity Retention (%) = (Discharge Capacity at 100th Cycle) / (Discharge Capacity at First Cycle) (3) (Evaluation Criteria) 5 points: Capacity retention of 95% or more. 4 points: Capacity retention of 90% or more but less than 95%. 3 points: Capacity retention of 85% or more but less than 90%.・2 points: Capacity retention rate is 80% or more but less than 85%. ・1 point: Capacity retention rate is 75% or more but less than 80%. ・0 point: Capacity retention rate is less than 75%.

[0122] 5.2. Examples 13 to 19, Comparative Example 7 In Example 13, 80 parts by mass (solid content 20 parts by mass) of the latex of polymer (A3) synthesized in Example 3 and 230 parts by mass of γ-butyrolactone were added to a recovery flask, and a dehydration step was carried out at 85°C for 6 hours under reduced pressure in an evaporator. In this way, a binder composition for an electricity storage device was obtained in the same manner as in Example 3, except that the dispersion medium was replaced from water to γ-butyrolactone, and evaluations were performed in the same manner as in Example 3. The solid content concentration of the obtained binder composition for an electricity storage device was 8% by mass.

[0123] In Examples 14 to 19, binder compositions for electricity storage devices were obtained in the same manner as in Example 3, except that the dispersion medium was replaced from water to a liquid medium (C) shown in Table 3 below, and evaluations were performed in the same manner as in Example 3. In Comparative Example 7, a binder composition for electricity storage devices was obtained in the same manner as in Example 3, except that the latex of polymer (A3) synthesized in Example 3 was diluted with water to a solids concentration of 8 mass %.

[0124] 5.3. Examples 20 to 25 Binder compositions for electricity storage devices were obtained in the same manner as in Example 3, except that the contents of PVdF and polymer (A3) contained in the slurry for the positive electrode of a lithium ion secondary battery were set to the amounts shown in Table 4 below, and the same evaluations as in Example 3 were performed.

[0125] 5.4 Example 26 A binder composition for an electricity storage device was obtained in the same manner as in Example 3, except that an acrylic polymer soluble in NMP was used instead of PVdF, and the same evaluations were carried out as in Example 3. A synthesis example of the acrylic polymer used in Example 26 is shown below.

[0126] <Synthesis of Acrylic Polymer> An acrylic polymer dispersion was obtained by single-stage polymerization as shown below. A reactor was charged with 500 parts by mass of water, a monomer mixture consisting of 64 parts by mass of 2-ethylhexyl acrylate, 1 part by mass of styrene, 5 parts by mass of acrylic acid, and 30 parts by mass of acrylonitrile, 0.5 parts by mass of tert-dodecyl mercaptan as a chain transfer agent, 1 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, and 0.3 parts by mass of potassium persulfate as a polymerization initiator, and the mixture was polymerized at a polymerization temperature of 75°C for 8 hours to obtain an acrylic polymer dispersion. The conversion rate of the polymer at this time was 99%.

[0127] Next, 1 part by mass of 2,6-di-tert-butyl-p-cresol was added as an antioxidant, and the acrylic polymer dispersion was added dropwise to 3,000 parts by mass of a 0.5% aqueous calcium chloride solution. The resulting aggregates were washed with water, and a portion of the resulting aggregates was dried at 80°C, and the amount of emulsifier contained in the aggregates was analyzed. Thereafter, the same procedure was repeated, and when no decrease in the amount of emulsifier remaining in the aggregates was observed, all of the remaining aggregates were dried at 80°C and completely recovered.

[0128] The acrylic polymer obtained above was added to NMP and stirred overnight to prepare an acrylic polymer solution in which the acrylic polymer was dissolved in NMP. The content of the acrylic polymer was adjusted to 8% by mass when the total amount of the acrylic polymer solution was taken as 100% by mass.

[0129] 5.5. Evaluation Results Tables 1 and 2 below show the polymer compositions, property measurement results, and evaluation results used in Examples 1 to 12 and Comparative Examples 1 to 6. Table 3 below shows the lithium ion secondary battery positive electrode slurry compositions used in Examples 13 to 19 and Comparative Example 7, and the evaluation results. Table 4 below shows the lithium ion secondary battery positive electrode slurry compositions used in Examples 20 to 25, and the evaluation results. Table 5 below shows the lithium ion secondary battery positive electrode slurry composition used in Example 26, and the evaluation results. Note that the numerical values ​​representing the compositions shown in Tables 1 to 5 below represent parts by mass.

[0130]

[0131]

[0132]

[0133]

[0134]

[0135] The polymer numbers synthesized in each example are listed in the lines below the example numbers and comparative example numbers in Tables 1 and 2. The monomers, emulsifiers, and polymers in Tables 1 to 5 represent the following compounds, respectively. <Monomers> (α,β-unsaturated nitrile compounds) AN: Acrylonitrile MAN: Methacrylonitrile (unsaturated carboxylic acid ester) MMA: Methyl methacrylate BA: Butyl acrylate 2EHA: 2-ethylhexyl acrylate CHMA: Cyclohexyl methacrylate AMA: Allyl methacrylate TENPA: Trimethylolpropane triacrylate EDMA: Ethylene glycol dimethacrylate HEMA: Hydroxyethyl methacrylate HEA: Hydroxyethyl acrylate (unsaturated carboxylic acid) TA: Itaconic acid AA: Acrylic acid MAA: Methacrylic acid (aromatic vinyl compound) ST: Styrene DVB: Divinylbenzene (conjugated diene compound) BD: 1,3-butadiene ((meth)acrylamide) AAM: Acrylamide MAM: Methacrylamide (Compounds having a sulfonic acid group) NaSS: Sodium styrene sulfonate <Emulsifiers> (Sulfonic acid emulsifiers) Sodium alkyl diphenyl ether sulfonate: Trade name "Pelex SS-L", manufactured by Kao Corporation Sodium dodecylbenzenesulfonate: Trade name "Neopelex G-65", manufactured by Kao Corporation (Carboxylic acid emulsifiers) Semi-hardened beef tallow fatty acid soda soap: Trade name "NS Soap", manufactured by Kao Corporation Potassium rosinate: Trade name "Diplodin A-100", manufactured by Toho Chemical Industry Co., Ltd. (Nonionic surfactants) Polyoxyethylene lauryl ether: Trade name "Emulgen 147", manufactured by Kao Corporation Polyoxyethylene alkyl ether: Trade name "Emulgen 1108", manufactured by Kao Corporation Polyoxyalkylene alkyl ether: Trade name "Emulgen LS-110", manufactured by Kao Corporation Polyoxyethylene distyrenated phenyl ether: Trade name "Emulgen A-90", manufactured by Kao Corporation <Polymer> PVdF: Trade name "HSV900", manufactured by Arkema, polyvinylidene fluoride

[0136] In Examples 1 to 26, a slurry for a lithium-ion secondary battery positive electrode containing the binder composition for an electrical storage device of the present invention and an active material was used. As a result, the active material layer formed using this slurry had a good surface condition, and during peel strength measurement, the active material layer itself did not become brittle, causing the active material to fall off or cracks, and it was confirmed that the binder had sufficient binding strength. It was also confirmed that the resulting lithium-ion secondary battery had a low rate of resistance increase and improved cycle characteristics. It is believed that the inclusion of an appropriate amount of nonionic surfactant (B) in the slurry for a lithium-ion secondary battery positive electrode allows the polymer (A) to maintain its particle shape in the liquid medium (C), forming a good conductive path within the formed active material layer, thereby reducing the rate of resistance increase and improving cycle characteristics. Therefore, it was found that the use of the binder composition for an electrical storage device of the present invention made it possible to prepare a lithium-ion secondary battery positive electrode with excellent surface condition, adhesion, and ionic conductivity, and also improved the cycle characteristics of the lithium-ion secondary battery.

[0137] In Examples 13 to 19 and Comparative Example 7, slurries for lithium ion secondary battery positive electrodes containing a liquid medium other than NMP were used. As a result, it was found that when a slurry for lithium ion secondary battery positive electrodes containing a predetermined organic solvent was used, a lithium ion secondary battery positive electrode excellent in surface condition, adhesion, and ionic conductivity could be produced, and the cycle characteristics of the lithium ion secondary battery could be improved. On the other hand, when a slurry for lithium ion secondary battery positive electrodes containing water was used, good results were not obtained.

[0138] In Examples 20 to 25, slurries for lithium ion secondary battery positive electrodes in which the content ratio of PVdF and / or polymer (A3) was appropriately changed were used. As a result, it was found that in all Examples, positive electrodes for lithium ion secondary batteries excellent in surface condition, adhesion, and ionic conductivity could be produced, and the cycle characteristics of the lithium ion secondary batteries could be improved.

[0139] In Example 26, a slurry for a lithium ion secondary battery positive electrode using an acrylic polymer soluble in NMP was used instead of PVdF. Even in this case, it was found that a lithium ion secondary battery positive electrode excellent in surface condition, adhesion, and ionic conductivity could be produced, and the cycle characteristics of the lithium ion secondary battery could be improved.

[0140] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially identical to the configurations described in the embodiments (for example, configurations with the same function, method, and result, or configurations with the same purpose and effect). 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 achieve the same effects or purposes as the configurations described in the above embodiments. Furthermore, the present invention also includes configurations in which publicly known technology is added to the configurations described in the above embodiments.

Claims

1. A binder composition for an electrical storage device comprising a polymer (A), a nonionic surfactant (B), and a liquid medium (C), wherein, when the total amount of repeating units contained in the polymer (A) is taken as 100 mass%, the polymer (A) contains 1 to 50 mass% of repeating units (a1) derived from an α,β-unsaturated nitrile compound and 40 to 80 mass% of repeating units (a2) derived from an unsaturated carboxylate ester, the content of the nonionic surfactant (B) is 0.1 to 10 parts by mass per 100 parts by mass of the polymer (A), and the liquid medium (C) is at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

2. The binder composition for a storage battery device according to claim 1, wherein the polymer (A) is in the form of polymer particles, and the number average particle size of the polymer particles is 50 nm or more and 1,000 nm or less.

3. The binder composition for a storage battery device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 mass % of a repeating unit (a3) ​​derived from an unsaturated carboxylic acid.

4. The binder composition for a storage battery device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 mass % of a repeating unit (a6) derived from (meth)acrylamide.

5. The binder composition for a storage battery device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 mass % of a repeating unit (a7) derived from a compound having a sulfonic acid group.

6. A slurry for an electrode of a storage battery device, comprising the binder composition for a storage battery device according to claim 1 or 2 and an active material.

7. The slurry for an electric storage device electrode according to claim 6, further comprising a thickener.

8. The slurry for an electrode of a storage battery device according to claim 6, wherein the active material is a positive electrode active material.

9. A slurry for an electrode of a power storage device according to claim 8, wherein the positive electrode active material contains at least one selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, and an olivine type lithium-containing phosphate compound.

10. An electricity storage device electrode comprising: a current collector; and an active material layer formed by applying the slurry for an electricity storage device electrode according to claim 6 onto the surface of the current collector and drying the slurry.

11. An electricity storage device comprising the electricity storage device electrode according to claim 10.

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