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

Abstract

Provided is a binder composition for a power storage device, which is capable of producing a power storage device electrode having excellent surface state, adhesion, and ion conductivity, and which is capable of improving the cycle life characteristics of a power storage device. This binder composition for an electricity storage device contains a polymer (A), a nonionic surfactant (B), and a liquid medium (C), and the polymer (A) contains an alpha, beta-unsaturated compound derived from an alpha, beta-unsaturated compound when the total of repeating units contained in the polymer (A) is taken as 100 mass%. The polymer (A) contains 1-50 mass% of a repeating unit (a1) derived from a [beta]-unsaturated nitrile compound and 40-80 mass% of a repeating unit (a2) derived from an unsaturated carboxylic acid ester, and the content ratio of the nonionic surfactant (B) is 0.1-10 parts by mass per 100 parts by mass of the polymer (A). The liquid medium (C) is at least one substance selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

Description

Technical Field

[0001] This invention relates to adhesive compositions for energy storage devices, slurries for electrodes of energy storage devices, electrodes for energy storage devices, and energy storage devices. Background Technology

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

[0003] The electrodes used in such energy storage devices are manufactured by coating a composition (energy storage device electrode slurry) containing active materials and a polymer acting as a binder onto the surface of the current collector and then drying it. Among the required characteristics of the polymer used as the binder are the ability of the active materials to bond with each other and the ability of the active materials to adhere tightly to the current collector. Additionally, examples include resistance to powdering, where microparticles of the active material do not detach from the active material layer when the coated and dried composition film (hereinafter also referred to as the "active material layer") is cut. By ensuring that such a binder material exhibits good adhesion, the internal resistance of the battery caused by the binder material is reduced, thereby imparting good charge and discharge characteristics to the energy storage device.

[0004] It should be noted that, empirically, it is known that the binding ability of the aforementioned active materials to each other, the adhesion between the active materials and the current collector, and the resistance to powder shedding are generally proportional to the quality of performance. Therefore, in this specification, the term "adhesion" is sometimes used to describe these generalizations.

[0005] In recent years, in order to fabricate electrochemical devices with excellent capacity and charge-discharge cycle characteristics, the use of positive electrode active materials with high reactivity with water has been studied. Moreover, polyvinylidene fluoride (PVdF) is the most widely used adhesive for electrodes of energy storage devices as an organic solvent. Although PVdF has good adhesion and oxidation resistance, it has a high environmental impact due to the presence of fluorine atoms, and the instability of raw material supply is becoming increasingly prominent (see, for example, Patent Document 1).

[0006] Against this backdrop, various adhesive materials have been proposed to solve various problems of positive electrode slurry (see, for example, Patent Documents 1-2).

[0007] Patent Document 1: Japanese Patent Application Publication No. 10-298386

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-194944 Summary of the Invention

[0009] However, in methods using cathode slurries containing conventionally used PVdF or sulfonated PVdF disclosed in Patent Document 1, it is known that crosslinks accompanied by defluorinated acid (HF) can form, particularly under alkaline conditions. If such crosslinks form in the cathode slurry, adhesion can sometimes be impaired. Furthermore, if conventionally used cathode slurries are applied, pits caused by bubble breakage can sometimes form on the surface of the coating due to the influence of residual emulsifiers in the slurry. Such surface defects lead to a decrease in product yield and therefore need to be prevented.

[0010] Several aspects of the present invention provide adhesive compositions for energy storage devices that can produce electrodes with excellent surface condition, adhesion and ion conductivity, and can improve the cycle life characteristics of energy storage devices.

[0011] This invention was made to solve at least a part of the above-mentioned problems and can be implemented in any of the following ways.

[0012] One embodiment of the adhesive composition for storage devices of the present invention comprises a polymer (A), a nonionic surfactant (B), and a liquid medium (C). When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains 1 to 50% by mass of repeating units (a1) from α,β-unsaturated nitrile compounds and 40 to 80% by mass of repeating units (a2) from unsaturated carboxylic acid esters. The proportion of the nonionic surfactant (B) is 0.1 to 10 parts by mass relative to 100 parts by mass of the polymer (A). The liquid medium (C) is selected from at least one of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

[0013] In one embodiment of the above-mentioned adhesive composition for storage devices, the polymer (A) is polymer particles, and the number-average particle size of the polymer particles can be 50 nm to 1000 nm.

[0014] In any of the above-mentioned adhesive compositions for storage devices, the polymer (A) further contains 0.1 to 10 by mass of repeating units (a3) ​​from unsaturated carboxylic acids.

[0015] In any of the above-mentioned adhesive compositions for energy storage devices,

[0016] The polymer (A) may further contain 0.1 to 10 by mass of repeating unit (a6) from (meth)acrylamide.

[0017] In any of the above-described adhesive compositions for storage devices, the polymer (A) may further contain 0.1 to 10 by mass of repeating units (a7) from compounds having sulfonic acid groups.

[0018] One embodiment of the slurry for the electrode of the energy storage device of the present invention comprises an adhesive composition for energy storage devices according to any of the above embodiments, and an active substance.

[0019] In one embodiment of the slurry for electrodes of the aforementioned energy storage devices, a thickener may be further included.

[0020] In any of the above-mentioned electrode slurries for energy storage devices, the active material can be a positive electrode active material.

[0021] In any of the above-mentioned electrode slurries for energy storage devices, the positive electrode active material may contain at least one selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, and olivine-type lithium phosphate compounds.

[0022] One embodiment of the energy storage device electrode of the present invention includes a current collector and an active material layer formed by coating the surface of the current collector with a slurry for energy storage device electrodes of any of the above embodiments and drying it.

[0023] One embodiment of the energy storage device of the present invention includes the energy storage device electrodes of the above embodiment.

[0024] The adhesive composition for energy storage devices according to the present invention can produce energy storage device electrodes with excellent surface condition, adhesion and ion conductivity, and can improve the cycle life characteristics of energy storage devices. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail. It should be noted that the present invention is not limited to the embodiments described below, but should be understood to include various modifications implemented without altering the spirit of the invention.

[0026] In this specification, “(meth)acrylic acid ~” means “acrylic acid ~” or “methacrylic acid ~”, “~(meth)acrylate” means “~acrylate” or “~methacrylate”, and “(meth)acrylamide” means “acrylamide” or “methacrylamide”.

[0027] In this specification, the numerical range recorded as “X~Y” is interpreted as including the value X as the lower limit and the value Y as the upper limit.

[0028] 1. Adhesive composition for energy storage devices

[0029] An adhesive composition for a storage device according to one embodiment of the present invention comprises a polymer (A), a nonionic surfactant (B), and a liquid medium (C). When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains 1 to 50% by mass of repeating units (a1) from α,β-unsaturated nitrile compounds and 40 to 80% by mass of repeating units (a2) from unsaturated carboxylic acid esters. Furthermore, the proportion of the nonionic surfactant (B) is 0.1 to 10 parts by mass relative to 100 parts by mass of the polymer (A). Furthermore, the liquid medium (C) is selected from at least one of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides. Hereinafter, the components contained in the adhesive composition for a storage device according to this embodiment will be described in detail.

[0030] 1.1. Polymer (A)

[0031] The adhesive composition for energy storage devices according to this embodiment contains a polymer (A). The polymer (A) is preferably dispersed in particulate form in the liquid medium (C) described later. When the polymer (A) is dispersed in particulate form in the liquid medium (C), the composition prepared by mixing it with the active material (hereinafter also referred to as "slurry") exhibits good stability, and the slurry has good coatability to the current collector, which is therefore preferred. Furthermore, due to the presence of particulate adhesive, the active material is easily slidable during pressing, facilitating high-density application. Moreover, over-coating of the conductive additive can be suppressed, enabling the formation of good conductive pathways.

[0032] The repeating units constituting polymer (A), the physical properties of polymer (A), and the manufacturing method will be described in turn.

[0033] 1.1.1. Repeating units constituting polymer (A)

[0034] When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains 1 to 50% by mass of repeating units (a1) (hereinafter also referred to as "repeating units (a1)") from α,β-unsaturated nitrile compounds, and 40 to 80% by mass of repeating units (a2) (hereinafter also referred to as "repeating units (a2)") from unsaturated carboxylic acid esters. In addition, the polymer (A) may contain repeating units from other monomers that can be copolymerized with them, besides repeating units (a1) and repeating units (a2).

[0035] 1.1.1.1. Repeating unit (a1) from α,β-unsaturated nitrile compounds

[0036] When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a1) from α,β-unsaturated nitrile compounds is 1 to 50% by mass. The proportion of repeating units (a1) is preferably 2% by mass or more, more preferably 3% by mass or more. The proportion of repeating units (a1) is preferably 48% by mass or less, more preferably 45% by mass or less. The proportion of repeating units (a1) is preferably 2 to 48% by mass, more preferably 3 to 45% by mass. By containing repeating units (a1) within the above range, polymer (A) exhibits good affinity with the liquid medium (C), and polymer (A) easily maintains its particle shape. Furthermore, polymer (A) exhibits good affinity with the electrolyte, which can suppress the increase in internal resistance caused by polymer (A) becoming a resistive component in the energy storage device.

[0037] As an α,β-unsaturated nitrile compound, there is no particular limitation, and examples 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 acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred.

[0038] 1.1.1.2. Repeating units from unsaturated carboxylic acid esters (a2)

[0039] When the total number of repeating units in polymer (A) is set to 100% by mass, the content of repeating units (a2) derived from unsaturated carboxylic acid esters is 40-80% by mass. The content of repeating units (a2) is preferably 43% by mass or more, more preferably 45% by mass or more. The content of repeating units (a2) is preferably 75% by mass or less, more preferably 70% by mass or less. The content of repeating units (a2) is preferably 43-75% by mass, more preferably 45-70% by mass. By containing repeating units (a2) within the above range, polymer (A) exhibits good affinity with the electrolyte, thus suppressing the increase in internal resistance caused by polymer (A) becoming a resistive component in the energy storage device.

[0040] Among unsaturated carboxylic acid esters, (meth)acrylates are preferred. Specific examples of (meth)acrylates include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, nonyl methacrylate, decyl methacrylate, di(meth)acrylate, and di(meth)acrylate. Propylene glycol acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl methacrylate, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 5-hydroxypentyl methacrylate, 6-hydroxyhexyl methacrylate, glyceryl mono(meth)acrylate, and glyceryl di(meth)acrylate, etc., may be used, and one or more selected from these may be used. Among these, one or more selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, ethylene glycol di(meth)acrylate, and 2-hydroxyethyl methacrylate are preferred, and methyl methacrylate is particularly preferred.

[0041] 1.1.1.3. Other repeating units

[0042] In addition to repeating units (a1) and (a2), polymer (A) may also contain repeating units from other monomers that can copolymerize with it. Examples of such repeating units include repeating units (a3) ​​from unsaturated carboxylic acids (hereinafter also referred to as "repeating unit (a3)"), repeating units (a4) from aromatic vinyl compounds (hereinafter also referred to as "repeating unit (a4)"), repeating units (a5) from conjugated diene compounds (hereinafter also referred to as "repeating unit (a5)"), repeating units (a6) from (meth)acrylamide (hereinafter also referred to as "repeating unit (a6)"), repeating units (a7) from compounds having sulfonic acid groups (hereinafter also referred to as "repeating unit (a7)"), and repeating units from cationic monomers.

[0043] <Repeating unit (a3) ​​from unsaturated carboxylic acids>

[0044] Polymer (A) may contain repeating units (a3) ​​derived from unsaturated carboxylic acids. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a3) ​​derived from unsaturated carboxylic acids is preferably 0.1% to 10% by mass. The proportion of repeating units (a3) ​​is more preferably 0.5% by mass or more, particularly preferably 1% by mass or more. The proportion of repeating units (a3) ​​is more preferably 9% by mass or less, particularly preferably 8% by mass or less. The proportion of repeating units (a3) ​​is preferably 0.5% to 9% by mass, more preferably 1% to 8% by mass. By containing repeating units (a3) ​​within the above range, polymer (A) can improve the adhesion between the current collector and the active material layer, and the adhesion strength of the electrode may sometimes be increased.

[0045] The unsaturated carboxylic acid is not particularly limited, and examples include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. One or more of these can be used. Among these, one or more of acrylic acid, methacrylic acid, and itaconic acid are preferred.

[0046] <Repeating unit (a4) from aromatic vinyl compounds>

[0047] When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a4) from aromatic vinyl compounds is preferably 1 to 50% by mass. The proportion of repeating units (a4) is more preferably 3% by mass or more, particularly preferably 5% by mass or more. The proportion of repeating units (a4) is more preferably 47% by mass or less, particularly preferably 45% by mass or less. The proportion of repeating units (a4) is preferably 3 to 47% by mass, more preferably 5 to 45% by mass. By containing repeating units (a4) within the above range, polymer (A) can suppress the fusion of polymers (A) dispersed in the active material layer, exhibiting good slurry properties and improved coatability. Furthermore, since it can improve the permeability of the electrolyte, it sometimes exhibits good repeated charge-discharge characteristics.

[0048] As an aromatic vinyl compound, there are no particular limitations, and examples include styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, divinylbenzene, etc., and one or more of these can be used. Among these, styrene is particularly preferred.

[0049] <Repeating unit (a5) from conjugated diene compounds>

[0050] When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a5) from the conjugated diene compound is preferably 0 to 5% by mass. The proportion of repeating units (a5) is more preferably 0.5% by mass or more, particularly preferably 1% by mass or more. The proportion of repeating units (a5) is more preferably 4% by mass or less, particularly preferably 3% by mass or less. The proportion of repeating units (a5) is preferably 0.5 to 4% by mass, more preferably 1 to 3% by mass. By containing repeating units (a5) within the above range, polymer (A) exhibits good dispersion of active materials and fillers, enabling the formation of a homogeneous active material layer and protective film. Therefore, structural defects in the electrode plate disappear, sometimes exhibiting good repeated charge-discharge characteristics. Furthermore, the polymer (A) coated with active materials can be given stretchability, and the stretching of polymer (A) improves adhesion, thus sometimes exhibiting good charge-discharge durability characteristics.

[0051] The conjugated diene compound is not particularly limited, and examples 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, etc., and one or more selected from these can be used. Among these, 1,3-butadiene is particularly preferred.

[0052] <Repeating unit (a6) from (meth)acrylamide>

[0053] Polymer (A) may further contain repeating units (a6) from (meth)acrylamide. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a6) from (meth)acrylamide is preferably 0.1% to 10% by mass. The proportion of repeating units (a6) is more preferably 0.5% by mass or more, particularly preferably 1% by mass or more. The proportion of repeating units (a6) is more preferably 9% by mass or less, particularly preferably 8% by mass or less. The proportion of repeating units (a6) is preferably 0.5% to 9% by mass, more preferably 1% to 8% by mass. By containing repeating units (a6) within the above range, the dispersibility of the active material and filler in the slurry in polymer (A) sometimes becomes better. Furthermore, the softness of the resulting active material layer becomes moderate, and sometimes the adhesion between the current collector and the active material layer is improved.

[0054] The (meth)acrylamide is not particularly limited, and examples include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, diacetone acrylamide, maleic acid amide, etc., and one or more selected from these can be used. Among these, acrylamide and methacrylamide are particularly preferred.

[0055] <Repeating unit (a7) from compounds containing sulfonic acid groups>

[0056] Polymer (A) may contain repeating units (a7) from compounds having sulfonic acid groups. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a7) from compounds having sulfonic acid groups is preferably 0.1% to 10% by mass. The proportion of repeating units (a7) is more preferably 0.5% by mass or more, particularly preferably 1% by mass or more. The proportion of repeating units (a7) is more preferably 9% by mass or less, particularly preferably 8% by mass or less. The proportion of repeating units (a7) is preferably 0.5% to 9% by mass, more preferably 1% to 8% by mass. By containing repeating units (a7) within the above range, polymer (A) exhibits good dispersion of active materials and fillers, and sometimes a homogeneous active material layer and protective film can be obtained. Furthermore, due to the good adhesion between the current collector and the active material layer, structural defects in the electrode plate disappear, and sometimes good charge-discharge characteristics are exhibited.

[0057] The compounds having a sulfonic acid group are not particularly limited, and examples include vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, ethyl sulfonate (meth)acrylate, propyl sulfonate (meth)acrylate, butyl sulfonate (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide tert-butyl sulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and their base salts, etc., and one or more selected from these can be used. Among these, styrene sulfonic acid is particularly preferred.

[0058] <Repeating units from cationic monomers>

[0059] Polymer (A) may contain repeating units derived from cationic monomers. The cationic monomer is not particularly limited, but is preferably selected from at least one monomer chosen from secondary amines (salts), tertiary amines (salts), and quaternary ammonium salts. Specific examples of cationic monomers include 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate methyl 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-(O-[1'-methylpropyleneamino]carboxylamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methacryloyloxyethyltrimethylammonium chloride, and tri(2-propenyl)isocyanurate. Acyloxyethyl ester, 2-vinylpyridine, quinalidine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazyl-2-indazole dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazolium, diallylamine, diallylamine hydrochloride, triallylamine, diallyl dimethylammonium chloride, dichloropropyleneamine, 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-heptene-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, etc., may be selected from one or more of these.

[0060] 1.1.2. Physical properties of polymer (A)

[0061] <Number-average particle size>

[0062] When polymer (A) is in the form of particles, the number average particle size is preferably 50 nm to 1000 nm, more preferably 70 nm to 950 nm, and particularly preferably 90 nm to 900 nm. If the number average particle size of polymer (A) is within the above range, the particles of polymer (A) are easily adsorbed onto the surface of the active material, and therefore, as the active material moves, the particles of polymer (A) can also move. As a result, migration can be suppressed, and thus, in some cases, the degradation of electrical properties can be reduced.

[0063] It should be noted that the number-average particle size of polymer (A) is the average particle size measured using a dense particle size analyzer with dynamic light scattering (DLS). Examples of dense particle size analyzers include the "FPA-1000" manufactured by Otsuka Electronics Co., Ltd.

[0064] 1.1.3. Method for manufacturing polymer (A)

[0065] <Polymerization Process>

[0066] Regarding the manufacturing method of polymer (A), emulsion polymerization can be carried out in the presence of nonionic surfactant (B), other emulsifiers, chain transfer agents, polymerization initiators, etc.

[0067] As a nonionic surfactant (B), one or more compounds selected from those described in “1.2. Nonionic Surfactants (B)” below may be used.

[0068] Other emulsifiers include sulfated salts of higher alcohols, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabirates, naphthalene sulfonic acid-formaldehyde condensates, perfluorobutyl sulfonates, perfluoroalkyl-containing phosphates, perfluoroalkyl-containing carboxylates, perfluoroalkyl ethylene oxide adducts, and other fluorinated surfactants, and one or more of these can be used.

[0069] As specific examples of chain transfer agents and polymerization initiators, compounds described in Japanese Patent No. 5999399 and the like can be used.

[0070] Emulsion polymerization for synthesizing polymer (A) can be carried out through single-stage polymerization or through multi-stage polymerization of two or more stages.

[0071] In the case of synthesizing polymer (A) by a single-stage polymerization, the monomer mixture can be subjected to emulsion polymerization in the presence of a nonionic surfactant (B), other emulsifiers, chain transfer agents, polymerization initiators, etc., at a temperature preferably 0 to 80°C and a polymerization time preferably 4 to 36 hours.

[0072] When polymer (A) is synthesized by two-stage polymerization, the polymerization of each stage is preferably set as follows.

[0073] The proportion of monomers used in the first stage polymerization relative to the total mass of monomers (the sum of the mass of monomers used in the first stage polymerization and the mass of monomers used in the second stage polymerization) is preferably in the range of 20 to 99% by mass, and more preferably in the range of 25 to 99% by mass. By carrying out the first stage polymerization with such a proportion of monomers, it is possible to obtain polymer (A) particles with excellent dispersion stability and low tendency to form aggregates, and it is also possible to suppress the increase in viscosity over time of the adhesive composition for energy storage devices after solidification, which is therefore preferred.

[0074] The types and proportions of monomers used in the second stage of polymerization can be the same as or different from those used in the first stage of polymerization.

[0075] From the viewpoint of the dispersion of the particles of the obtained polymer (A), the polymerization conditions for each stage are preferred as follows.

[0076] • First stage polymerization: preferably a temperature of 0 to 80°C, preferably a polymerization time of 2 to 36 hours, preferably a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more.

[0077] • Second stage polymerization: preferably at a temperature of 0 to 80°C, preferably for a polymerization time of 2 to 18 hours.

[0078] When polymer (A) is synthesized by three-stage polymerization, the polymerization of each stage is preferably set as follows.

[0079] The proportion of monomers used in the first stage polymerization relative to the total mass of monomers (the sum of the mass of monomers used in the first stage polymerization, the mass of monomers used in the second stage polymerization, and the mass of monomers used in the third stage polymerization) is preferably in the range of 20 to 90% by mass, and more preferably in the range of 25 to 80% by mass. By carrying out the first stage polymerization with such a proportion of monomers, it is possible to obtain polymer (A) particles with excellent dispersion stability and that are not prone to agglomeration, and it is also possible to suppress the increase in viscosity over time of the adhesive composition for energy storage devices after solidification, which is therefore preferred.

[0080] The types and proportions of monomers used in the second stage of polymerization can be the same as or different from those used in the first stage of polymerization.

[0081] The types and proportions of monomers used in the third stage of polymerization can be the same as or different from those used in the first stage of polymerization and the second stage of polymerization.

[0082] From the viewpoint of the dispersion of the particles of the obtained polymer (A), the polymerization conditions for each stage are preferred as follows.

[0083] • First stage polymerization: preferably a temperature of 0 to 80°C, preferably a polymerization time of 2 to 36 hours, preferably a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more.

[0084] • Second stage polymerization: preferably at a temperature of 0 to 80°C, preferably for a polymerization time of 2 to 18 hours.

[0085] • Third stage polymerization: preferably at a temperature of 0 to 80°C, preferably for a polymerization time of 2 to 9 hours.

[0086] By keeping the total solids concentration in the emulsion polymerization at 50% by mass or less, the polymerization reaction can be carried out with good dispersion stability of the resulting polymer (A) particles. This total solids concentration is preferably 45% by mass or less, and more preferably 40% by mass or less.

[0087] Whether the synthesis of polymer (A) is carried out through single-stage polymerization or multi-stage polymerization, it is preferable to add a neutralizing agent to the polymerization mixture after the emulsion polymerization is completed for neutralization. There are no particular limitations on the neutralizing agent used herein; examples include metal hydroxides such as sodium hydroxide and potassium hydroxide, and ammonia.

[0088] The adhesive composition for energy storage devices according to this embodiment can be obtained, for example, by displacing the dispersion medium of an aqueous latex dispersion prepared in an aqueous dispersion medium and dispersing it in a liquid medium (C) that serves as an organic dispersion medium. In this method, water needs to be removed. If the boiling point of the liquid medium (C) is higher than that of water, the water can be removed simply by adding the liquid medium (C) to the obtained aqueous latex dispersion and evaporating it using an evaporator or similar device. If the liquid medium (C) azeotropically reacts with water, the water can be removed by adding the liquid medium (C) to the obtained aqueous latex dispersion, azeotropically reacting it with water, reducing the water volume to a certain extent using an evaporator or similar device, and then removing the water using a water-absorbing agent such as a molecular sieve or a reverse osmosis membrane.

[0089] Other methods for manufacturing the adhesive composition for energy storage devices according to this embodiment include: temporarily solidifying and drying a polymer (A) manufactured in an aqueous dispersion medium, then pulverizing it to disperse it in a liquid medium (C); or mixing the solidified and dried polymer (A) with the liquid medium (C) and pulverizing it. Dispersion can be performed using conventional dispersers such as ball mills and sand mills; ultrasonic dispersers; homogenizers, etc. Furthermore, when a block polymer (A) is obtained by manufacturing the polymer (A) in the liquid medium (C), a particle dispersion of the polymer (A) dispersed in the liquid medium (C) can also be obtained by pulverizing it using a disperser such as a ball mill or sand mill.

[0090] 1.2. Nonionic surfactants (B)

[0091] The adhesive composition for energy storage devices according to this embodiment contains a nonionic surfactant (B). The proportion of nonionic surfactant (B) relative to 100 parts by mass of polymer (A) 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. It has been found that by containing nonionic surfactant (B) within the above range, polymer (A) readily maintains its particle shape in the liquid medium (C). Since nonionic surfactant (B) has high affinity for both polymer (A) and liquid medium (C), it is believed that the nonionic surfactant (B) adsorbed at the particle interface of polymer (A) is mobile in the liquid medium (C), and due to its steric hindrance, it can maintain its particle shape without causing polymer (A) to aggregate. Because polymer (A) can maintain its particle shape, over-coating of the positive electrode active material and conductive additives can be suppressed, forming a good conductive pathway. Furthermore, it can impart softness and adhesion to the particles.

[0092] As described above, a nonionic surfactant (B) and other emulsifiers are used when polymerizing polymer (A), but the amount of residual emulsifier varies depending on the conditions of subsequent coagulation and cleaning processes. Therefore, residual emulsifiers are usually not properly managed. It has been found that the adhesive composition for energy storage devices of this embodiment exhibits good battery characteristics by properly managing the content ratio of nonionic surfactant (B) during the manufacturing process. That is, if the content ratio of nonionic surfactant (B) is below the above-mentioned upper limit, the formation of pits on the surface of the slurry coating caused by the defoaming of emulsifiers can be effectively suppressed. In addition, if the content ratio of nonionic surfactant (B) is above the above-mentioned lower limit, polymer (A) can maintain its particle shape in the liquid medium (C), forming a good conductive path in the electrode layer and suppressing the increase of internal resistance, thus exhibiting good charge-discharge characteristics. In particular, if the electrode layer cannot maintain the electronic conductive path, the lithium-ion conductivity decreases and the resistance increases, so it is important to suppress the obstruction of the conductive path caused by the fusion of polymer (A) particles.

[0093] Examples of nonionic surfactants (B) include ether-type nonionic surfactants, ester-type nonionic surfactants, and ester-ether type nonionic surfactants.

[0094] Examples of ether-type nonionic surfactants include polyoxyethylene glycols (e.g., polyoxyethylene polyoxypropylene glycol) and those that undergo addition oxidation of an alkenyl group (e.g., ethylene oxide) to a hydrocarbon group containing a hydroxyl group (e.g., polyoxyethylene alkyl ethers and other polyoxyalkylene alkyl ethers; polyoxyethylene phenyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene styrene phenyl ethers and other polyoxyalkylene phenyl ethers). Examples of hydrocarbon groups containing hydroxyl groups include alcohols and phenols. Examples of alcohol compounds include methanol, ethanol, propanol, butanol, pentanol, hexanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosaneol, dodecanol, docosaneol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, triadecanol, and other straight-chain alkyl alcohols; isopropanol, isobutanol, isohexanol, 2-ethylhexanol, isononanol, isodecanol, isotriadecanol, and isodecanecanol. Branched alkyl alcohols such as tetraalkylol, isotriacontanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, isohexadecanol, and isohexadecanol; straight-chain alkenyl alcohols such as tetradecenol, hexadecenol, heptadecenol, octadecenol, and nonadecenol; branched alkenyl alcohols such as isohexadecanol and isohexadecanol; cyclic alkyl alcohols such as cyclopentanol and cyclohexanol; and aromatic alcohols such as benzyl alcohol. Examples of phenolic compounds include phenol, alkylphenols, monostyrene-modified phenol, stilbene-modified phenol, and tristyrene-modified phenol. Among these, chain-like higher alcohols with 10 to 20 carbon atoms are preferred, although the number of carbon atoms in higher alcohols can be 11 to 17, or 11 to 15 (and further, 12 to 13).

[0095] Examples of ester-type nonionic surfactants include those with ester bonds between polyols and higher fatty acids. Examples of polyols 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, sorbitol, pentaerythritol, sorbitol, glycerol, and sucrose. Examples of higher fatty acids include straight-chain alkyl carboxylic acids such as octanoic 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, dodecanoic acid, and docosanoic acid; branched-chain alkyl carboxylic acids such as 2-ethylhexanoic acid, isododecanoic acid, isotriadecanoic acid, isotetradecanoic acid, isohexadecanoic acid, and isooctadecanoic acid; and straight-chain alkenyl carboxylic acids such as octadecenoic acid, octadecadienoic acid, octadectrienoic acid, and oleic acid. Among these, oleic acid, stearic acid, lauric acid, and myristic acid are preferred. Examples of ester-type nonionic surfactants include polyglycerol fatty acid esters, polysorbate fatty acid esters, and sucrose fatty acid esters.

[0096] Examples of ester-ether type nonionic surfactants include those with both ester and ether bonds in their molecules (e.g., fatty acid methyl ester ethoxylates). Examples of ester-ether type nonionic surfactants include those formed by the addition of ethylene oxide to esters of fatty acids such as glycerol and sorbitol, fatty acid polyethylene glycol, and fatty acid polyoxyethylene sorbitan esters.

[0097] Among these, ether-type nonionic surfactants are preferred, polyoxyethylene alkyl ethers and polyoxyethylene phenyl ethers are more preferred, and polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene styrene phenyl ethers are particularly preferred.

[0098] 1.3. Liquid medium (C)

[0099] The adhesive composition for energy storage devices according to this embodiment contains a liquid medium (C). The liquid medium (C) is not particularly limited and can include aliphatic hydrocarbons such as hexane, heptane, octane, decane, and dodecane; alicyclic hydrocarbons such as cyclohexane, cycloheptane, cyclooctane, and cyclodecane; aromatic hydrocarbons such as toluene, xylene, mesitylene, naphthalene, and tetrahydronaphthalene; ketones such as methyl hexyl ketone and dipropyl ketone; esters such as butyl acetate, butyl butyrate, and methyl butyrate; ethers such as dibutyl ether, tetrahydrofuran, and anisole; and β-lactams and γ-lactams. Amines, σ-lactams, N-methyl-2-pyrrolidone, 2-pyrrolidone, and other lactams; glycol ethers such as (mono, di, tri, or poly)ethylene glycol monomethyl ether, (mono, di, tri, or poly)ethylene glycol dimethyl ether, ethylene glycol phenyl ether, etc.; lactones such as α-acetyllactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, etc.; amides such as N-methylacetamide, dimethylacetamide, N-methylformamide, dimethylformamide, etc. These liquid media (C) can be used alone or in combination of two or more.

[0100] It should be noted that liquid medium (C) may contain water as long as the main solvent is an organic solvent. "Main solvent is an organic solvent" means that when the total mass of liquid medium (C) is set as 100% by mass, the organic solvent accounts for more than 50% by mass.

[0101] 1.4. Other additives

[0102] The adhesive composition for energy storage devices according to this embodiment may contain additives other than those described above, as needed. Examples of such additives include polymers other than polymer (A) and preservatives.

[0103] <Polymers other than polymer (A)>

[0104] The adhesive composition for energy storage devices according to this embodiment may also contain polymers other than polymer (A). Such polymers are not particularly limited, and examples include acrylic polymers comprising unsaturated carboxylic acid esters or their derivatives soluble in a liquid medium (C), styrene-butadiene polymers comprising conjugated dienes, acrylonitrile-butadiene copolymers, and fluoropolymers such as PVDF (polyvinylidene fluoride). These polymers may be used alone or in combination of two or more. By containing these polymers, a good slurry property is sometimes achieved, further improving the flexibility and adhesion of the electrodes.

[0105] <Preservatives>

[0106] The adhesive composition for storage devices according to this embodiment may contain a preservative. By containing a preservative, the growth of bacteria, mold, etc., and the generation of foreign matter can sometimes be inhibited when storing the adhesive composition for storage devices. Specific examples of preservatives include compounds described in Japanese Patent No. 5477610 and the like.

[0107] 2. Slurry for energy storage equipment

[0108] One embodiment of the present invention provides a slurry for a storage device containing the aforementioned adhesive composition for storage devices. This adhesive composition can be used as a material for creating a protective film to suppress short circuits caused by dendrites generated during charging and discharging, and also as a material for creating storage device electrodes (active material layers) that improve the bonding ability between active materials, the adhesion between active materials and current collectors, and resistance to powder shedding. Hereinafter, the slurry for a storage device used to create a protective film (hereinafter also referred to as "protective film slurry") and the slurry for a storage device used to create the active material layer of the storage device electrode (hereinafter also referred to as "slurry for storage device electrode") will be described separately.

[0109] 2.1. Slurry for protective film

[0110] "Protective film slurry" refers to a dispersion liquid used to form a protective film on the surface of an electrode or a separator, or both, after being coated onto the surface of the electrode or a separator or both. The protective film slurry of this embodiment may consist solely of the aforementioned adhesive composition for energy storage devices, or may further contain inorganic fillers. Examples of inorganic fillers include those described in Japanese Patent Application Publication No. 2020-184461.

[0111] 2.2. Electrode paste for energy storage devices

[0112] "Electrode slurry for energy storage devices" refers to a dispersion liquid used to create an active material layer on the surface of a current collector after being coated onto the surface of the current collector and then dried. The electrode slurry for energy storage devices of this embodiment contains the above-mentioned adhesive composition for energy storage devices and the active material.

[0113] The following describes the components contained in the slurry for the electrode of the energy storage device according to this embodiment.

[0114] 2.2.1. Polymer (A)

[0115] The composition, physical properties, and manufacturing method of polymer (A) are as described above, therefore, the description is omitted.

[0116] The polymer component in the slurry for the electrode of the energy storage device according to this embodiment is preferably 1 to 8 parts by mass relative to 100 parts by mass of the active material, more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 6 parts by mass. If the polymer component content is within the above range, the active material in the slurry has good dispersibility, and the slurry has excellent coatability. Here, the polymer component includes polymer (A) and polymers other than polymer (A) added as needed.

[0117] 2.2.2. Active substances

[0118] As active materials for the electrode paste of the energy storage device used in this embodiment, examples include positive electrode active materials and negative electrode active materials. 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 polyphenylene oxide, and A... X B Y O Z (Where A is an alkali metal or transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, and manganese, O represents an oxygen atom, and X, Y, and Z are numbers in the range of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.50, respectively.) This refers to composite metal oxides, other metal oxides, etc. Examples of such composite metal oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and ternary nickel-cobalt-manganese oxide.

[0119] The electrode paste for the energy storage device of this embodiment can also be used when making either the positive or negative electrode, and is particularly preferred for the positive electrode.

[0120] As the positive electrode active material, it is preferably selected from at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide and olivine-type lithium phosphate compound, more preferably containing at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide and ternary lithium nickel cobalt manganese oxide, and particularly preferably containing ternary lithium nickel cobalt manganese oxide.

[0121] The battery electrode made using the battery electrode slurry of this embodiment exhibits good electrical characteristics even when using such a positive electrode active material. The reason for this is that the polymer (A) can firmly bond the positive electrode active material, and can maintain this firm bonding state during charging and discharging.

[0122] 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.

[0123] On the other hand, when manufacturing the negative electrode, the active material exemplified above preferably contains silicon and / or carbon materials, and more preferably a mixture of silicon and carbon materials. Since silicon materials have a higher lithium absorption per unit weight than other active materials, the energy storage capacity of the resulting energy storage device can be increased, resulting in improved output and energy density. On the other hand, carbon materials exhibit less volume change during charging and discharging than silicon materials. Therefore, by using a mixture of silicon and carbon materials as the negative electrode active material, the influence of volume change in silicon materials can be mitigated, further improving the adhesion between the active material layer and the current collector.

[0124] 2.2.3. Other components

[0125] In the electrode slurry of the energy storage device according to this embodiment, in addition to the above-mentioned components, polymers other than polymer (A), liquid media, conductive additives, corrosion inhibitors, cellulose fibers, and other components may be added as needed. As polymers other than polymer (A), they can be appropriately selected from the compounds exemplified in the "1.4. Other Additives" section above and used for the same purpose.

[0126] <Liquid Medium>

[0127] In the electrode slurry of the energy storage device according to this embodiment, in addition to the components introduced from the adhesive composition for energy storage devices, a liquid medium may be further added. The added liquid medium may be the same as or different from the liquid medium (C) contained in the adhesive composition for energy storage devices, and it is preferable to select from the liquid media exemplified in item "1.3. Liquid Medium (C)" above.

[0128] Regarding the content ratio of the liquid medium (including components introduced from the adhesive composition for energy storage devices) in the slurry for electrodes of the energy storage device according to this embodiment, the concentration of solid components in the slurry (referring to the proportion of the total mass of components other than the liquid medium in the slurry to the total mass of the slurry, the same below) is preferably 30 to 90% by mass, more preferably 40 to 80% by mass.

[0129] <Conductive additives>

[0130] In the electrode slurry of the energy storage device in this embodiment, in order to impart conductivity and buffer the volume change of the active material caused by the entry and exit of lithium ions, a conductive additive may be further added.

[0131] Specific examples of conductive additives include activated carbon, acetylene black, Ketjen black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotubes. Among these, acetylene black, Ketjen black, or carbon nanotubes are preferred. The proportion of the conductive additive relative to 100 parts by mass of the active material 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.

[0132] <Corrosion Inhibitor>

[0133] In the electrode slurry of the energy storage device in this embodiment, a corrosion inhibitor may be further added to suppress corrosion of the current collector according to the type of active material.

[0134] Examples of corrosion inhibitors 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. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0135] Cellulose Fiber

[0136] In the electrode slurry of the energy storage device according to this embodiment, cellulose fibers may be further added. Known cellulose fibers can be used as the cellulose fibers. Adding cellulose fibers can sometimes improve the adhesion of the active material to the current collector. It is believed that fibrous cellulose fibers can bond adjacent active materials together in a fibrous manner through line bonding or line contact, preventing the active material from falling off and improving the adhesion to the current collector.

[0137] 2.2.4. Preparation method of electrode paste for energy storage devices

[0138] The electrode slurry for the energy storage device according to this embodiment can be manufactured by any method as long as it contains the above-described adhesive composition for energy storage devices and the active substance. From the viewpoint of manufacturing a slurry with better dispersibility and stability more efficiently and inexpensively, it is preferable to add the active substance and any additives as needed to the adhesive composition for energy storage devices, and then mix them together. As a specific manufacturing method, for example, the method described in Japanese Patent No. 5999399 can be cited.

[0139] 3. Electrodes of energy storage devices

[0140] An embodiment of the present invention provides an electrode for a storage device comprising a current collector and an active material layer formed by coating the surface of the current collector with the aforementioned slurry for the storage device electrode and drying it. This storage device electrode can be manufactured by coating the surface of a current collector, such as a metal foil, with the aforementioned slurry for the storage device electrode to form a coating film, and then drying the coating film to form the active material layer. For a storage device electrode manufactured in this way, since an active material layer containing the aforementioned polymer (A), the active material, and any other components added as needed is bonded to the surface of the current collector, the adhesion is excellent, and since the expansion of the electrode during repeated charging and discharging is suppressed, the charge-discharge durability is excellent.

[0141] As a current collector, there are no particular restrictions as long as it is made of a conductive material; for example, the current collector described in Japanese Patent No. 5999399 can be cited.

[0142] 4. Energy storage devices

[0143] One embodiment of the present invention provides a storage device comprising the aforementioned storage device electrodes and further containing an electrolyte. It can be manufactured using conventional methods using components such as separators. Specific manufacturing methods include, for example, overlapping the negative and positive electrodes with a separator in between, winding or folding the battery according to its shape and storing it in a battery container, injecting electrolyte into the battery container, and sealing it. The battery shape can be suitable, such as coin-shaped, cylindrical, square, or laminated.

[0144] The electrolyte can be liquid or gel-like; any electrolyte selected from known electrolytes used in energy storage devices that effectively exhibits the function of a battery, depending on the type of active material, is acceptable. The electrolyte can be a solution obtained by dissolving an electrolyte in a suitable solvent. Examples of such electrolytes and solvents include those described in Japanese Patent No. 5999399.

[0145] The aforementioned energy storage device can be applied to lithium-ion secondary batteries, double-layer capacitors, lithium-ion capacitors, etc., which require discharge at high current densities. Among these, lithium-ion secondary batteries are particularly preferred. In the energy storage device electrodes and energy storage device of this embodiment, components other than the adhesive composition for energy storage devices can use known components for lithium-ion secondary batteries, double-layer capacitors, and lithium-ion capacitors.

[0146] 5. Examples

[0147] The present invention will now be described in detail based on embodiments, but the present invention is not limited to these embodiments. Unless otherwise specified, “parts” and “%” in the embodiments and comparative examples refer to mass.

[0148] 5.1. Examples 1-12, Comparative Examples 1-6

[0149] 5.1.1. Preparation of adhesive compositions for energy storage devices

[0150] <Example 1>

[0151] Polymer (A1) dispersion was obtained through a polymerization process as shown below. 300 parts by mass of water, a monomer mixture consisting of 1 part by mass of acrylonitrile, 5 parts by mass of methyl methacrylate, 5 parts by mass of butyl acrylate, 58 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of allyl methacrylate, 25 parts by mass of styrene, 1 part by mass of acrylic acid, 1 part by mass of methacrylic acid, 1 part by mass of acrylamide, and 1 part by mass of sodium styrene sulfonate, 0.01 parts by mass of tert-dodecyl mercaptan as a chain transfer agent, 0.2 parts by mass of sodium dodecylbenzene sulfonate as an emulsifier, 4 parts by mass of polyoxyethylene lauryl ether (manufactured by Kao Corporation, trade name "Emulgen 147"), and 0.6 parts by mass of potassium persulfate as a polymerization initiator were added to a reactor. The polymerization was carried out at 70°C for 10 hours with stirring to obtain polymer (A1) latex. The conversion rate of the polymer at this time was 98%.

[0152] Next, 80 parts by weight of the obtained latex (20 parts by weight of solids) and 230 parts by weight of N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") were added to a round-bottom flask, and a dehydration process was carried out at 85°C for 6 hours under reduced pressure in an evaporator. Since only water was removed in this dehydration process, polyoxyethylene lauryl ether remained in the adhesive composition for energy storage devices. Thus, by replacing the dispersion medium from water with NMP, the adhesive composition for energy storage devices of Example 1 was obtained. The solids concentration of the obtained adhesive composition for energy storage devices was 8% by weight.

[0153] <Examples 2-12, Comparative Examples 1-6>

[0154] In Examples 2-12 and Comparative Examples 1-6, the types and amounts of monomers were as shown in Tables 1-2 below. Otherwise, each polymer was synthesized by a single-stage polymerization in the same manner as in Example 1, and each adhesive composition for energy storage devices was obtained in the same manner as in Example 1.

[0155] 5.1.2. Physical property evaluation of adhesive compositions for energy storage devices

[0156] <Methods for Determining Polymerization Conversion Rate>

[0157] The polymerization conversion rates of the above polymers were determined as follows.

[0158] The polymerized reaction solution was extracted at a specified time and placed into a pre-measured aluminum dish (X (g)). The weight of the reaction solution (Y (g)) was measured. The solution was dried at 155°C for 15 minutes using a hot air dryer. The aluminum dish was removed, cooled, and its weight (Z (g)) was measured. The polymerization conversion rate (%) was calculated using the following formula (1) based on the measured weights X, Y, and Z.

[0159] Polymerization conversion rate (%) = ((Z-X) / Y) × 100 (1)

[0160] <Determination of Number-Average Particle Size>

[0161] The above-obtained adhesive composition for energy storage devices was diluted with NMP to a solids concentration of 0.1 wt%, and the resulting substance was used as the sample for testing. The sample for testing was then subjected to dynamic light scattering (DLS) under the following conditions to determine the number-average particle size of each polymer.

[0162] Temperature: 25℃

[0163] • NMP refractive index: 1.47

[0164] 5.1.3. Preparation of slurry for the positive electrode of lithium-ion secondary batteries

[0165] Add 1 part by weight of PVdF (manufactured by Arkema, trade name "HSV900") (solid content converted to 8% NMP solution), 2 parts by weight of polymer (A) (solid content converted to binder composition for energy storage devices as described above), 100 parts by weight of NMC811 (manufactured by Beijing DangSheng Co., Ltd., trade name "ME-83SC") as positive electrode active material, 6 parts by weight of acetylene black, and 1.8 parts by weight of NMP to a slurry with a solid content concentration of approximately 75%, and stir at 60 rpm for 1 hour. It should be noted that NMC811 is an abbreviation for ternary nickel-cobalt-manganese lithium oxide (Ni:Mn:Co = 8:1:1).

[0166] Then, NMP was added to the obtained paste to adjust the solids concentration to 68%. The mixture was then stirred and mixed at 200 rpm for 2 minutes, then at 1800 rpm for 5 minutes, and further stirred under vacuum (approximately 5.0 × 10⁻⁶). 3 The slurry for the positive electrode of a lithium-ion secondary battery was prepared by stirring at 1800 rpm for 1.5 minutes under a pressure of Pa.

[0167] 5.1.4. Fabrication and Property Evaluation of Positive Electrodes for Lithium-ion Secondary Batteries

[0168] <Fabrication of the positive electrode for lithium-ion secondary batteries>

[0169] The lithium-ion secondary battery positive electrode slurry obtained above was uniformly coated onto the surface of a current collector composed of an aluminum foil with a thickness of 20 μm using a doctor blade method, resulting in a dried film thickness of 100 μm. The film was then dried at 120°C for 20 minutes. Next, a roller press was used for pressing to achieve a film (positive electrode active material layer) density of 3.0 g / cm³. 3 Thus, the positive electrode for lithium-ion secondary batteries is obtained.

[0170] <Evaluation of Electrode Condition>

[0171] The lithium-ion secondary batteries obtained above were cut into 10cm × 10cm pieces using the positive electrode, and the number of broken bubbles on the surface was counted visually. The evaluation criteria are as follows. The evaluation results are shown in Tables 1 and 2 below. Samples in which no damage to the active material layer was observed showed reduced coating defects caused by residual emulsifier and exhibited good cycle characteristics.

[0172] (Evaluation Criteria)

[0173] ·5 points: If the number of broken bubble particles is 0, then there is no coating defect caused by residual emulsifier, which is good.

[0174] • 4 points: If the number of broken bubbles is 1 to 5, the coating is generally good and there is no poor coating caused by residual emulsifier.

[0175] • 3 points: If the number of broken bubble particles is 6 to 10, then the coating defects caused by residual emulsifier are few, which is good.

[0176] • 2 points: If the number of broken bubble particles is 11 to 15, there are some coating defects caused by residual emulsifier, making it difficult to use.

[0177] • 1 point: If the number of broken bubble particles is more than 16, the coating is poor due to residual emulsifier and the product cannot be used.

[0178] <Evaluation of Sealing Strength>

[0179] Using a knife, 10 longitudinal and 10 transverse cuts were made at 2mm intervals on the surface of the obtained lithium-ion secondary battery positive electrode, extending from the active material layer to the current collector, to create a checkerboard pattern. An 18mm wide adhesive tape (manufactured by Nichiban Corporation, trade name "Cellotape" (registered trademark), JIS Z1522:2009) was applied to the cuts and immediately peeled off. The degree of active material detachment was evaluated visually. The evaluation criteria are as follows. The evaluation results are shown in Tables 1 and 2 below.

[0180] (Evaluation Criteria)

[0181] ·5 points: 0 active substance layers were detached.

[0182] • 4 points: 1 to 5 active substance layers are detached.

[0183] • 3 points: 6 to 20 active substance layers are shed.

[0184] • 2 points: 21 to 40 active substance layers were shed.

[0185] · 1 point: More than 41 active substance layers are detached.

[0186] 5.1.5. Fabrication and Property Evaluation of Lithium-ion Secondary Batteries

[0187] <Preparation of slurry for negative electrode of lithium-ion secondary battery>

[0188] Add 1 part by weight of thickener (trade name "CMC2200", manufactured by DAICEL Co., Ltd.) (converted to solid content), 100 parts by weight of graphite (converted to solid content) as a negative electrode active material, and 68 parts by weight of water to a twin-shaft planetary mixer (PRIMIX Co., Ltd., trade name "TK Hivis Mix 2P-03"). Mix at 60 rpm for 1 hour.

[0189] Next, an amount equivalent to 2 parts by mass (solid content conversion) of SBR (trade name "TRD105A", manufactured by ENEOS Materials Co., Ltd.) was added, and the mixture was stirred for another 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 at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further stirred under vacuum at 1800 rpm for 1.5 minutes to prepare a slurry for lithium-ion secondary battery negative electrode.

[0190] <Fabrication of the negative electrode for lithium-ion secondary batteries>

[0191] The prepared lithium-ion secondary battery negative electrode slurry was uniformly coated onto the surface of a current collector composed of a 20 μm thick copper foil using a doctor blade method, resulting in a dried film thickness of 120 μm. The film was then dried at 120°C for 20 minutes. Next, a roller press was used to press the film (negative electrode active material layer) to a density of 1.9 g / cm³. 3 This leads to the negative electrode used in lithium-ion secondary batteries.

[0192] Assembly of Lithium-ion Secondary Batteries

[0193] In a glove box with an Ar-substituted dew point below -80°C, the lithium-ion secondary battery prepared above was stamped into a 16.16 mm diameter circle using the negative electrode and placed on a bipolar coin cell (manufactured by Hosen Co., Ltd., trade name "HS Flat Cell"). Next, a separator (manufactured by Celgard Co., Ltd., trade name "Celgard#2400") made of a 24 mm diameter polypropylene porous membrane was stacked on top of the negative electrode of the lithium-ion secondary battery. Then, 500 μL of electrolyte was injected to prevent air from entering. The lithium-ion secondary battery prepared above was then stamped into a 15.95 mm diameter circle using the positive electrode, stacked on top of the separator, and the outer casing of the bipolar coin cell was tightened with screws to seal it, thus assembling the lithium-ion secondary battery. The electrolyte used here was a solution obtained by dissolving LiPF6 at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0194] <Evaluation of Resistance Rise Rate>

[0195] For the lithium-ion secondary battery fabricated above, charging was initiated in a constant-temperature bath at 25°C with a constant current (1.0C). When the voltage reached 4.2V, charging continued at a constant voltage (4.2V) until the current reached 0.01C, marking the end of charging (cutoff). Then, discharging began with a constant current (0.05C) until the voltage reached 2.5V, marking the end of discharging (cutoff). The discharge capacity of the 0th cycle was calculated. Next, charging was initiated with a constant current (1.0C), and when the voltage reached 4.2V, charging continued at a constant voltage (4.2V) until the current reached 0.01C, marking the end of charging (cutoff). Then, discharging began with a constant current (1.0C) until the voltage reached 2.5V, marking the end of discharging (cutoff). The discharge capacity of the 1st cycle was calculated. This charge-discharge cycle was repeated 100 times. After 100 charge-discharge cycles, the same charge-discharge cycle as the 0th cycle was performed to evaluate the discharge capacity of the 101st cycle. The rate of increase in resistance was calculated using the following formula (2), and the evaluation was carried out according to the following criteria. The results are shown in Tables 1 to 2 below.

[0196] Resistance rise rate (%) = (Discharge capacity of the 101st cycle - Discharge capacity of the 100th cycle) / (Discharge capacity of the 0th cycle - Discharge capacity of the 1st cycle) × 100 (2)

[0197] (Evaluation Criteria)

[0198] ·5 points: Resistance rise rate is above 100% to less than 110%.

[0199] ·4 points: Resistance rise rate is above 110% to less than 120%.

[0200] • 3 points: Resistance rise rate is above 120% to less than 130%.

[0201] ·2 points: Resistance rise rate is above 130% to less than 140%.

[0202] · 1 point: Resistance rise rate is above 140% to less than 150%.

[0203] ·0 points: The resistance rise rate is above 150%.

[0204] <Evaluation of Cyclic Characteristics>

[0205] For the lithium-ion secondary battery prepared above, charging was started in a constant temperature bath at 25°C with a constant current (1.0C). When the voltage reached 4.2V, charging continued at a constant voltage (4.2V) until the current reached 0.01C, marking the end of charging (cutoff). Then, discharging was started with a constant current (1.0C) and stopped when the voltage reached 2.5V, calculating the discharge capacity of the first cycle. This charging and discharging was repeated 100 times. The capacity retention rate was calculated using the following formula (3) and evaluated according to the following criteria. The results are shown in Tables 1 to 2 below.

[0206] Capacity retention rate (%)

[0207] = (Discharge capacity in the 100th cycle) / (Discharge capacity in the 1st cycle) (3)

[0208] (Evaluation Criteria)

[0209] ·5 points: Capacity retention rate is above 95%.

[0210] • 4 points: Capacity retention rate is above 90% to less than 95%.

[0211] ·3 points: Capacity retention rate is above 85% to less than 90%.

[0212] ·2 points: Capacity retention rate is above 80% to less than 85%.

[0213] · 1 point: Capacity retention rate is above 75% to less than 80%.

[0214] • 0 points: Capacity retention rate is less than 75%.

[0215] 5.2. Examples 13-19, Comparative Example 7

[0216] In Example 13, 80 parts by weight of latex of the polymer (A3) synthesized in Example 3 (20 parts by weight of solids) and 230 parts by weight of γ-butyrolactone were added to a flask, and a dehydration process was carried out at 85°C for 6 hours under reduced pressure in an evaporator. Thus, the dispersion medium was replaced with γ-butyrolactone, and otherwise the process was carried out in the same manner as in Example 3 to obtain an adhesive composition for energy storage devices, which was evaluated in the same way as in Example 3. The solids concentration of the obtained adhesive composition for energy storage devices was 8% by weight.

[0217] In Examples 14-19, the dispersion medium was replaced with the liquid medium (C) listed in Table 3 below. Otherwise, the process was the same as in Example 3 to obtain an adhesive composition for energy storage devices, and the same evaluation was performed as in Example 3. In Comparative Example 7, the latex of the polymer (A3) synthesized in Example 3 was diluted with water to a solids concentration of 8% by mass. Otherwise, the process was the same as in Example 3 to obtain an adhesive composition for energy storage devices, and the same evaluation was performed as in Example 3.

[0218] 5.3. Examples 20-25

[0219] The slurry for the positive electrode of a lithium-ion secondary battery was prepared with the amounts of PVdF and polymer (A3) as described in Table 4 below. Otherwise, the process was carried out in the same manner as in Example 3 to obtain an adhesive composition for energy storage devices, and the same evaluation was performed as in Example 3.

[0220] 5.4. Example 26

[0221] An acrylic polymer soluble in NMP was used instead of PVdF. Otherwise, the adhesive composition for energy storage devices was obtained in the same manner as in Example 3, and the same evaluation was performed as in Example 3. The synthesis of the acrylic polymer used in Example 26 is illustrated below.

[0222] <Synthesis of Acrylic Polymers>

[0223] An acrylic polymer dispersion was obtained through a single-stage polymerization process as shown below. 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 were added to a reactor. Polymerization was carried out at 75°C for 8 hours to obtain the acrylic polymer dispersion. The polymer conversion rate at this stage was 99%.

[0224] Next, 1 part by weight of 2,6-di-tert-butyl-p-cresol was added as an anti-aging agent, and an acrylic polymer dispersion was added dropwise to 3000 parts by weight of a 0.5% calcium chloride aqueous solution. The resulting coagulant was washed with water, and a portion of the coagulant was dried at 80°C. The emulsifier content in the coagulant was analyzed. Then, the same operation was repeated. When no reduction in the residual emulsifier content in the coagulant was observed, all the remaining coagulant was dried at 80°C and recovered.

[0225] An acrylic polymer solution was prepared by adding the above-obtained acrylic polymer to NMP and stirring overnight, thereby dissolving the acrylic polymer in NMP. Here, when the total acrylic polymer solution is set to 100% by mass, the content of the acrylic polymer is adjusted to 8% by mass.

[0226] 5.5 Evaluation Results

[0227] Tables 1-2 below show the polymer composition, physical property test results, and evaluation results used in Examples 1-12 and Comparative Examples 1-6. Table 3 below shows the composition and evaluation results of the lithium-ion secondary battery positive electrode slurry used in Examples 13-19 and Comparative Example 7. Table 4 below shows the composition and evaluation results of the lithium-ion secondary battery positive electrode slurry used in Examples 20-25. Table 5 below shows the composition and evaluation results of the lithium-ion secondary battery positive electrode slurry used in Example 26. It should be noted that the numerical values ​​representing the composition shown in Tables 1-5 below represent parts by mass.

[0228] [Table 1]

[0229]

[0230] [Table 2]

[0231]

[0232] [Table 3]

[0233]

[0234] [Table 4]

[0235]

[0236] [Table 5]

[0237]

[0238] It should be noted that the polymer numbers synthesized in each example are listed in the row below the example and comparative example numbers in Tables 1 and 2 above. The monomers, emulsifiers, and polymers in Tables 1 to 5 above represent the following compounds, respectively.

[0239] <Single>

[0240] (α,β-unsaturated nitrile compounds)

[0241] AN: Acrylonitrile

[0242] MAN: Methacrylonitrile

[0243] (Unsaturated carboxylic acid esters)

[0244] MMA: Methyl methacrylate

[0245] ·BA: Butyl acrylate

[0246] ·2EHA: 2-Ethylhexyl acrylate

[0247] CHMA: Cyclohexyl methacrylate

[0248] • AMA: Allyl Methacrylate

[0249] • TENPA: Trimethylolpropane triacrylate

[0250] EDMA: Ethylene dimethacrylate

[0251] HEMA: Hydroxyethyl methacrylate

[0252] HEA: Hydroxyethyl acrylate

[0253] (Unsaturated carboxylic acids)

[0254] ·TA: Itaconic acid

[0255] AA: Acrylic acid

[0256] MAA: Methacrylic acid

[0257] (Aromatic vinyl compounds)

[0258] ST: Styrene

[0259] DVB: Divinylbenzene

[0260] (Conjugated diene compounds)

[0261] ·BD: 1,3-Butadiene

[0262] (Methacrylamide)

[0263] AAM: Acrylamide

[0264] MAM: Methacrylamide

[0265] (Compounds containing sulfonic acid groups)

[0266] •NaSS: Sodium styrene sulfonate

[0267] <Emulsifier>

[0268] (Sulfonic acid emulsifier)

[0269] ·Alkyl diphenyl ether sulfonate sodium: Trade name "Pelex SS-L", manufactured by Kao Corporation

[0270] ·Sodium dodecylbenzene sulfonate: Trade name "Neopelex G-65", manufactured by Kao Corporation

[0271] (Carboxylic acid emulsifiers)

[0272] • Semi-hydrogenated sodium butter fatty acid soap: Trade name "NS Soap", manufactured by Kao Corporation

[0273] Potassium rosinate: Trade name "Disprozin A-100", manufactured by Toho Chemical Co., Ltd.

[0274] (Nonionic surfactant)

[0275] • Polyoxyethylene lauryl ether: Trade name "Emulgen 147", manufactured by Kao Corporation

[0276] ·Polyoxyethylene alkyl ether: Trade name "Emulgen 1108", manufactured by Kao Corporation

[0277] • Polyoxyalkylene ethers: Trade name "Emulgen LS-110", manufactured by Kao Corporation

[0278] ·Polyoxyethylene distyrenated phenyl ether: Trade name "Emulgen A-90", manufactured by Kao Corporation

[0279] <Polymer>

[0280] • PVdF: Trade name "HSV900", manufactured by Arkema, polyvinylidene fluoride

[0281] In Examples 1 to 26, a slurry containing the adhesive composition for energy storage devices of the present invention and an active material was used as the positive electrode slurry for lithium-ion secondary batteries. As a result, it was confirmed that the surface condition of the active material layer formed by this slurry was good, and when the peel strength was measured, the active material layer itself did not become brittle, resulting in active material detachment or cracking, and the adhesive achieved sufficient adhesion. Furthermore, it was confirmed that the resulting lithium-ion secondary battery exhibited a reduced rate of increase in resistance and improved cycle characteristics. It is believed that the lithium-ion secondary battery positive electrode slurry, by containing an appropriate amount of nonionic surfactant (B), allows the polymer (A) to maintain its particle shape in a liquid medium (C), forming a good conductive path within the formed active material layer, thus reducing the rate of increase in resistance and improving cycle characteristics. Therefore, it can be seen that by using the adhesive composition for energy storage devices of the present invention, a positive electrode for lithium-ion secondary batteries with excellent surface condition, adhesion, and ionic conductivity can be produced, and the cycle characteristics of lithium-ion secondary batteries can be improved.

[0282] In Examples 13-19 and Comparative Example 7, a lithium-ion secondary battery positive electrode slurry containing a liquid medium other than NMP was used. As a result, it was found that when using a lithium-ion secondary battery positive electrode slurry containing a specified organic solvent, a lithium-ion secondary battery positive electrode with excellent 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 using a lithium-ion secondary battery positive electrode slurry containing water, satisfactory results were not obtained.

[0283] In Examples 20-25, lithium-ion secondary battery positive electrode slurries with appropriately varied PVdF and / or polymer (A3) content ratios were used. As a result, it was found that in any of the examples, a lithium-ion secondary battery positive electrode with excellent surface condition, adhesion, and ionic conductivity could be produced, and the cycle characteristics of the lithium-ion secondary battery could be improved.

[0284] In Example 26, a slurry for a lithium-ion secondary battery positive electrode was used, which employed an acrylic polymer soluble in NMP instead of PVdF. It is evident that under such conditions, a positive electrode for a lithium-ion secondary battery with excellent surface properties, adhesion, and ionic conductivity can be manufactured, and the cycle characteristics of the lithium-ion secondary battery can be improved.

[0285] This invention is not limited to the embodiments described above and can be modified in various ways. This invention includes configurations that are substantially the same as those described in the embodiments (e.g., configurations with the same function, method, and result, or configurations with the same purpose and effect). Furthermore, this invention includes configurations in which non-essential parts of the configurations described in the above embodiments are replaced with other configurations. Moreover, this invention also includes configurations that can achieve the same effect as those described in the above embodiments or that can achieve the same purpose. Furthermore, this invention also includes configurations in which known techniques are added to the configurations described in the above embodiments.

Claims

1. An adhesive composition for energy storage devices, comprising polymer A, nonionic surfactant B, and liquid medium C. When the total number of repeating units in polymer A is set to 100% by mass, polymer A contains: 1–50% by mass of repeating unit a1 from α,β-unsaturated nitrile compounds, and 40–80% by mass of repeating unit a2 derived from unsaturated carboxylic acid esters; The nonionic surfactant B is present in a proportion of 0.1 to 10 parts by weight relative to 100 parts by weight of polymer A. The liquid medium C is selected from at least one of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

2. The adhesive composition for energy storage devices according to claim 1, wherein, The polymer A is a polymer particle with a number-average particle size of 50 nm to 1000 nm.

3. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer A further contains 0.1 to 10% by mass of repeating unit a3 derived from unsaturated carboxylic acids.

4. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer A further contains 0.1 to 10% by mass of repeating unit a6 derived from (meth)acrylamide.

5. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer A further contains 0.1 to 10% by mass of repeating unit a7 from a compound having a sulfonic acid group.

6. A paste for electrodes of a storage device, comprising the adhesive composition for a storage device as described in claim 1 or 2, and an active substance.

7. The electrode paste for energy storage devices according to claim 6, wherein, It further contains thickeners.

8. The slurry for electrodes of energy storage devices according to claim 6, wherein, The active material is a positive electrode active material.

9. The slurry for electrodes of energy storage devices according to claim 8, wherein, The positive electrode active material contains at least one selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary lithium nickel cobalt manganese oxide, and olivine-type lithium phosphate compounds.

10. An electrode for a storage device, comprising a current collector and an active material layer formed by coating the surface of the current collector with the slurry for the storage device electrode of claim 6 and drying it.

11. An energy storage device comprising the energy storage device electrode as described in claim 10.

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