Resin composition for secondary battery, slurry composition for the secondary battery, binder for the secondary battery, electrode for the secondary battery, producing method for the secondary battery, solid electrolyte layer, and producing method for all-solid battery

Abstract

To provide a resin composition for a secondary battery capable of producing an electrode for the secondary battery and a solid electrolyte layer which are not easily destroyed even by expansion and contraction accompanying repeated charge and discharge, and capable of producing the secondary battery excellent in reliability, and also provide a slurry composition for the secondary battery, a binder for the secondary battery, an electrode for the secondary battery, a producing method for the secondary battery, a solid electrolyte layer, and a producing method for an all-solid-state battery.SOLUTION: The present invention provides a resin composition for a secondary battery, comprising: a thermoplastic binder (A); and a solvent (B), in which the thermoplastic binder (A) has a microphase-separated structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition for a secondary battery, a slurry composition for a secondary battery, a binder for a secondary battery, an electrode for a secondary battery, a method for manufacturing a secondary battery, a solid electrolyte layer, and a method for manufacturing an all-solid-state battery. [Background technology]

[0002] Lithium secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Electrodes for lithium-ion secondary batteries are fabricated by coating a current collector with a slurry composition containing a positive electrode active material or a negative electrode active material, a binder resin, etc. In recent years, silicon materials have been attracting attention as negative electrode materials for lithium-ion secondary batteries due to their advantages such as high capacity and low operating potential.

[0003] In recent years, with the aim of further improving the performance of lithium-ion secondary batteries, research has been conducted into secondary batteries that use safer inorganic solid electrolytes instead of organic electrolyte solutions. Inorganic solid electrolytes are generally non-flammable, are safer than commonly used organic solvent electrolytes, and are easy to fabricate into high-capacity batteries.

[0004] For example, Patent Document 1 discloses an all-solid-state secondary battery using an acrylic polymer as a binder. Patent Document 2 discloses an all-solid-state secondary battery using a particulate polymer containing a surfactant having a polyoxyethylene chain as a binder. Patent Document 3 discloses an all-solid-state secondary battery using a diene polymer as a binder. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5644851 [Patent Document 2] Patent No. 5652344 [Patent Document 3] International Publication No. 2013 / 146916 Summary of the Invention [Problem to be solved by the invention]

[0006] However, while anodes using silicon materials and all-solid-state batteries can produce batteries with high theoretical capacity, they have the problem that the electrodes and solid electrolyte layer repeatedly expand and contract with repeated charging and discharging, which can destroy the electrodes and solid electrolyte and make it impossible to form conductive paths.

[0007] The present invention aims to provide a resin composition for secondary batteries that can be used to prepare electrodes and solid electrolyte layers for secondary batteries that are resistant to damage even when expanded and contracted during repeated charging and discharging, thereby enabling the preparation of highly reliable secondary batteries. It also aims to provide a slurry composition for secondary batteries, a binder for secondary batteries, electrodes for secondary batteries, a method for producing a secondary battery, a solid electrolyte layer, and a method for producing an all-solid-state battery. [Means for solving the problem]

[0008] The present disclosure (1) is a resin composition for a secondary battery, which comprises a thermoplastic binder (A) and a solvent (B), and the thermoplastic binder (A) has a microphase-separated structure. The present disclosure (2) is the resin composition for a secondary battery according to the present disclosure (1), wherein the thermoplastic binder (A) is a block copolymer having a hard segment and a soft segment. The present disclosure (3) is the resin composition for a secondary battery according to the present disclosure (1) or (2), wherein the weight average molecular weight (Mw) of the thermoplastic binder (A) is 10,000 or more and 2,000,000 or less. The present disclosure (4) is the resin composition for a secondary battery according to the present disclosure (1), (2), or (3), wherein the glass transition temperature of the thermoplastic binder (A) is −80° C. or higher and 25° C. or lower. The present disclosure (5) is the resin composition for a secondary battery according to the present disclosure (2), (3), or (4), in which the structural units derived from the hard segments have a glass transition temperature of 80°C or higher and 150°C or lower, and the structural units derived from the soft segments have a glass transition temperature of -70°C or higher and -30°C or lower. The present disclosure (6) is the resin composition for a secondary battery according to the present disclosure (2), (3), (4), or (5), wherein the block copolymer has an acrylic structural unit. The present disclosure (7) is a slurry composition for a secondary battery, comprising the resin composition for a secondary battery according to the present disclosure (1), (2), (3), (4), (5), or (6) and inorganic particles (C), wherein the inorganic particles (C) contain an active material or a solid electrolyte. The present disclosure (8) is the slurry composition for a secondary battery according to the present disclosure (7), wherein the inorganic particles (C) have an average particle size of 0.05 μm or more and 30 μm or less. The present disclosure (9) is a binder for secondary batteries having a microphase-separated structure. The present disclosure (10) relates to the binder for a secondary battery of the present disclosure (9), which is a block copolymer having a hard segment and a soft segment. The present disclosure (11) is the binder for a secondary battery according to the present disclosure (9) or (10), which has a weight average molecular weight (Mw) of 10,000 or more and 2,000,000 or less. The present disclosure (12) is the binder for a secondary battery according to the present disclosure (9), (10), or (11), which has a glass transition temperature of −80° C. or higher and 25° C. or lower. The present disclosure (13) is the binder for a secondary battery according to the present disclosure (10), (11), or (12), wherein the structural unit derived from the hard segment has a glass transition temperature of 80°C or higher and 150°C or lower, and the structural unit derived from the soft segment has a glass transition temperature of -70°C or higher and -30°C or lower. The present disclosure (14) is the binder for a secondary battery according to the present disclosure (10), (11), (12), or (13), wherein the block copolymer has an acrylic structural unit. The present disclosure (15) is an electrode for a secondary battery, comprising a thermoplastic binder (A) and an active material, wherein the thermoplastic binder (A) has a microphase-separated structure. The present disclosure (16) is a method for producing a secondary battery, comprising: a step of mixing the resin composition for a secondary battery according to the present disclosure (1), (2), (3), (4), (5), or (6) with an active material to prepare a slurry composition for a secondary battery; and a step of applying the slurry composition for a secondary battery to a current collector to form an electrode film. The present disclosure (17) includes a thermoplastic binder (A) and a solid electrolyte, and the thermoplastic binder (A) is a solid electrolyte layer having a microphase-separated structure. The present disclosure (18) is a method for producing an all-solid-state battery, comprising: a step of mixing the resin composition for a secondary battery according to the present disclosure (1), (2), (3), (4), (5), or (6) with a solid electrolyte to prepare a slurry composition for a secondary battery; and a step of applying the slurry composition for a secondary battery onto a release film to form a solid electrolyte layer. The present invention will be described in detail below.

[0009] To solve the above problems, the inventors investigated the use of a binder in which crosslinks are introduced into a styrene-isobutylene polymer to provide rubber-like expansion and contraction. However, because polymers with crosslinked structures are insoluble in solvents, there was a problem that electrodes could not be formed by wet methods. Furthermore, in order to form electrodes by wet methods, the inventors investigated forming an electrode sheet using a binder without a crosslinked structure, and then crosslinking between binders by methods such as vulcanization, electron beam crosslinking, and chemical reaction. However, such methods had the problem that crosslinked structures were formed in areas where the binder was localized, making it impossible to accommodate volume expansion and contraction. Therefore, through further trial and error, the inventors discovered that by using a thermoplastic binder having a microphase separation structure, it is possible to prepare a secondary battery electrode and a solid electrolyte layer that can follow the expansion and contraction of volume and are not easily destroyed by the expansion and contraction associated with repeated charge and discharge, and thus completed the present invention.

[0010] The resin composition for a secondary battery contains a thermoplastic binder (A). The thermoplastic binder (A) has a microphase-separated structure. By using such a binder, it is possible to produce electrodes and solid electrolyte layers for secondary batteries that follow the volumetric expansion and contraction of the electrode and solid electrolyte materials and are less likely to be destroyed by expansion and contraction associated with repeated charging and discharging, thereby making it possible to produce highly reliable secondary batteries. A microphase-separated structure is a structure in which different polymer segments are microscopically phase-separated in block copolymers or graft copolymers, and a repeating structure called a microdomain structure is formed according to the length of each segment. Examples of this microdomain structure include a spherical structure in which spherical polymer segment domains are periodically dispersed in other polymer segment domains, a rod-like structure in which rod-like polymer segment domains are periodically dispersed in other polymer segment domains in a roughly parallel arrangement, and a lamellar structure in which layered polymer segment domains are periodically dispersed in other polymer segment domains in a roughly parallel arrangement. The microphase-separated structure can be confirmed, for example, by staining the thermoplastic binder (A) with ruthenium tetroxide, bromine, or the like, and observing the phase-separated structure between the stained and unstained portions under an electron microscope. In the above-mentioned method, for example, the soft segment described below is stained, and therefore, the presence or absence of the microphase-separated structure can be confirmed by confirming whether or not a microdomain structure of the soft segment is formed.

[0011] The thermoplastic binder (A) is preferably a block copolymer having a hard segment and a soft segment. In the block copolymer, the hard and soft segments are not compatible at room temperature and pressure. As a result, the binder (A) exhibits a microphase-separated structure, and the hard segments form an aggregated structure. Furthermore, the aggregation of the hard segments acts like a pseudo-crosslink, resulting in the binder (A) becoming a rubber-like elastic body. Having such a structure in the binder (A) improves the ability to respond to the volumetric expansion and contraction of the electrode and solid electrolyte materials, thereby further improving resistance to expansion and contraction associated with repeated charging and discharging.

[0012] The block shape of the block copolymer is not particularly limited, and examples thereof include linear block types such as AB diblock type, ABA triblock type, multiblock type, and random block type, branched block type, etc. Among these, the block copolymer preferably has a structure having a hard segment at one end of the copolymer and a soft segment at the other end, and an AB diblock type is more preferred.

[0013] In the block copolymer, the structural unit derived from the hard segment preferably has a glass transition temperature of 80°C or higher and 150°C or lower. By using a polymer having a glass transition temperature within the above range, the hard segment has a more rigid structure, and a strong contraction force against distortion can be obtained. The glass transition temperature is more preferably 100°C or higher and more preferably 200°C or lower. The glass transition temperature of the structural unit derived from the hard segment means the glass transition temperature of a homopolymer of the monomer component that constitutes the hard segment, and can be measured, for example, by DSC measurement or tan δ measurement using a rheometer.

[0014] Examples of the monomer component constituting the hard segment include styrene (Tg: 100°C), methyl methacrylate (Tg: 105°C), tertiary butyl methacrylate (Tg: 107°C), isobornyl methacrylate (Tg: 180°C), etc. The values in parentheses indicate the glass transition temperatures of the homopolymers. Although some of these rigid hard segment phases form microcrystals, amorphous ones are preferred. By employing an amorphous hard segment phase, crack prevention properties of the electrode layer and the solid electrolyte layer can be improved. Of the above monomer components, styrene, methyl methacrylate, and tertiary butyl methacrylate are preferably used because they are amorphous.

[0015] In the block copolymer, the glass transition temperature of the structural unit derived from the soft segment is preferably −80° C. or higher and 25° C. or lower. By using a polymer having a glass transition temperature within the above range, the soft segment is more likely to exhibit rubber elasticity. The glass transition temperature is more preferably −70° C. or higher, even more preferably −60° C. or higher, more preferably 0° C. or lower, even more preferably −30° C. or lower. The glass transition temperature of the structural unit derived from the soft segment means the glass transition temperature of a homopolymer of the monomer component that constitutes the soft segment, and can be measured, for example, by DSC measurement or tan δ measurement using a rheometer.

[0016] Examples of the monomer component constituting the soft segment include acrylic monomers such as butyl acrylate (Tg: -54°C), 2-ethylhexyl acrylate (Tg: -50°C), and ethyl acrylate (Tg: -22°C). The values in parentheses indicate the glass transition temperatures of the homopolymers. Furthermore, polytetramethylene glycol (Tg: -73°C), polypropylene glycol (Tg: -66°C), etc. can also be preferably used as the constituent component of the soft segment. Monomers with acrylated molecular ends are commercially available, and block polymers can be easily synthesized by copolymerizing these monomers with the monomer components that constitute the hard segment. Furthermore, the constituent components of the soft segment are preferably liquid or flexible at room temperature.

[0017] The block copolymer preferably contains an acrylic structural unit. The acrylic structural unit allows the block copolymer to be dissolved in various organic solvents, facilitating the wet process for producing batteries. The acrylic structural unit refers to a structural unit derived from an acrylic monomer.

[0018] In the block copolymer, the composition ratio (weight ratio) of the hard segment to the soft segment is preferably 1:9 to 5:5 (hard segment weight:soft segment weight). By using such a composition ratio, the glass transition temperature of the entire copolymer can be controlled within a suitable range, and crack prevention properties of the electrode layer and the solid electrolyte layer can be improved. The composition ratio can be determined, for example, by calculating the absorbance ratio between the absorption band attributable to the hard segment of the copolymer and the absorption band of a homopolymer of the monomer constituting the hard segment, thereby determining the content ratio of the hard segment.

[0019] The weight average molecular weight (Mw) of the thermoplastic binder (A) is preferably 10,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,000,000 or less, more preferably in the above range, whereby the phase separation structure of each block segment is easily developed and rubber elasticity is easily exhibited. The molecular weight distribution (Mw / Mn) of the thermoplastic binder (A) is preferably at least 1, more preferably at least 1.5, and is preferably at most 6, more preferably at most 4. The molecular weight distribution (Mw / Mn) is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). The weight average molecular weight (Mw) and number average molecular weight (Mn) can be measured as polystyrene-equivalent molecular weights by gel permeation chromatography (GPC). Specifically, the weight average molecular weight (Mw) and number average molecular weight (Mn) can be measured as polystyrene-equivalent molecular weights by GPC using the filtrate obtained by diluting the thermoplastic binder (A) 100 times with THF (tetrahydrofuran) and filtering the resulting diluted solution. In the GPC method, for example, a GPC HFIP-600 series (manufactured by Shodex Co., Ltd.) or the like can be used as a column.

[0020] The glass transition temperature of the thermoplastic binder (A) is preferably −80° C. or higher and 25° C. or lower. By setting the volume within the above range, it is possible to further improve the ability of the electrode and solid electrolyte materials to respond to expansion and contraction of their volumes, and to further improve the resistance to expansion and contraction that accompanies repeated charging and discharging. The glass transition temperature is more preferably −30° C. or higher and more preferably 25° C. or lower. The glass transition temperature can be measured, for example, by DSC measurement or tan δ measurement using a rheometer.

[0021] In the thermoplastic binder (A), when the microdomain structure of the microphase separation structure is a spherical structure, the average particle size of the microdomain structure is preferably 10 nm or more, more preferably 20 nm or more, and is preferably 100 nm or less, more preferably 50 nm or less. When the microdomain structure is a rod-like structure, the average minor axis of the microdomain structure is preferably 10 nm or more, more preferably 20 nm or more, and is preferably 100 nm or less, more preferably 50 nm or less. Furthermore, when the microdomain structure is a lamellar structure, the average thickness of the microdomain structure is preferably 10 nm or more, more preferably 20 nm or more, and is preferably 100 nm or less, more preferably 50 nm or less. The average particle size, average minor axis, and average thickness of the microdomains can be determined, for example, by staining the thermoplastic binder (A) with bromine or the like, observing the phase-separated structure with an electron microscope, and measuring the size of each microdomain structure.

[0022] The content of the thermoplastic binder (A) in the resin composition for a secondary battery is preferably 1% by weight or more, more preferably 5% by weight or more, and is preferably 30% by weight or less, more preferably 20% by weight or less.

[0023] Examples of methods for producing the thermoplastic binder (A) include living polymerization and a method in which the terminals of the hard segments are modified with a polysulfide compound and then the soft segment component is polymerized. Examples of living polymerization techniques include living polymerization using an organic rare earth metal complex as a polymerization initiator (see JP-A-06-93060), living anionic polymerization using an organic alkali metal compound as a polymerization initiator in the presence of a mineral acid salt such as an alkali metal or alkaline earth metal salt (see JP-A-05-507737), living anionic polymerization using an organic alkali metal compound as a polymerization initiator in the presence of an organoaluminum compound (see JP-A-11-335432), and atom transfer radical polymerization (ATRP) (see Macromolecular Chemistry and Physics, 2000, Vol. 201, pp. 1108-1114). The molecular weight distribution of copolymers obtained by living anionic polymerization tends to have a sharper peak than that of polymers obtained by free radical polymerization, and since polymerization of all monomers tends to be completed easily, unreacted monomer raw materials are less likely to remain in block copolymers of acrylic monomers.

[0024] The thermoplastic binder (A) can be produced, for example, by repeating a process of forming a desired soft segment block at the end of a desired hard segment polymer obtained by polymerizing monomer components a desired number of times, and then terminating the polymerization reaction. Specifically, the binder can be produced by a multi-stage polymerization process including a first step of polymerizing a monomer component that forms a first polymer block using a polymerization initiator composed of an organic alkali metal compound in the presence of an organoaluminum compound, a second step of polymerizing a monomer component that forms a second polymer block, and a third step of polymerizing a monomer component that forms a third polymer block, and then reacting the active end of the resulting polymer with an alcohol or the like to terminate the polymerization reaction.

[0025] Furthermore, the thermoplastic binder (A) can also be prepared, for example, by the following method. Specifically, the monomer component that forms the hard segment block is polymerized with a polysulfide compound to obtain a polymer having hard segment blocks at both ends of the polysulfide. The S-S bond is then cleaved with a weak acid or the like, and the resulting polymer is polymerized with a monomer component that forms a soft segment block, thereby producing an AB block copolymer in which the hard segment and the soft segment are bonded via sulfur. Polysulfide compounds include not only organic sulfur compounds having polysulfide bonds (-SS-, -SSS-, etc.) in the molecule, but also organic sulfur compounds having a structure in which an alkylene group, a transition metal atom, or an alkali metal atom is present between the sulfur atoms constituting the polysulfide bond. Specifically, they also include organic sulfur compounds having -SXS-, -SSXS-, etc. (X represents an alkylene group, a transition metal atom, or an alkali metal atom). Examples of the polysulfide bond include a disulfide bond, a trisulfide bond, and a tetrasulfide bond. The polysulfide compound preferably has 2 to 4 sulfur atoms constituting the polysulfide bond, and more preferably is a disulfide compound with 2 sulfur atoms.

[0026] Specific examples of the polysulfide compound include thiuram-based organic sulfur compounds, thiazole-based organic sulfur compounds, dithiocarbamate salts, and xanthogen sulfide derivatives. Examples of the thiuram-based organic sulfur compounds include thiuram-based disulfide materials such as tetrabutylthiuram disulfide, tetraisopropylthiuram disulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabenzylthiuram disulfide, and thiuram-based tetrasulfide materials such as dipentamethylenethiuram tetrasulfide. Examples of the thiazole-based organic sulfur compounds include 2,2'-dibenzothiazolyl disulfide, dibenzothiazyl disulfide, and zinc salts of 2-mercaptobenzothiazole. Examples of the dithiocarbamate salts include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dibenzyldithiocarbamate, tellurium diethyldithiocarbamate, copper dimethyldithiocarbamate, copper dibutyldithiocarbamate, nickel dibutyldithiocarbamate, ferric dimethyldithiocarbamate, and sodium diethyldithiocarbamate. Examples of the xanthogen sulfide derivatives include dimethylxanthogen disulfide, dibutylxanthogen disulfide, diisopropylxanthogen disulfide, and bis(methylthioxanthogen) disulfide.

[0027] As a method for producing the thermoplastic binder (A), in addition to the above, emulsion polymerization, suspension polymerization, bulk polymerization, interfacial polymerization, solution polymerization, etc. can be used, and among these, solution polymerization is preferred.

[0028] Examples of the polymerization initiator include dilauryl peroxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroxyperoxide, t-butyl hydroxyperoxide, cyclohexanone peroxide, disuccinic acid peroxide, potassium persulfate, and ammonium persulfate. Examples of commercially available products include Permenta H, Percumyl P, Perocta H, Percumyl H-80, Perloyl 355, Perbutyl H-69, Perhexa H, Perloyl SA, and Perloyl L (all manufactured by NOF Corporation), Trigonox 27, and Trigonox 421 (all manufactured by Nouryon).

[0029] The thermoplastic binder (A) has a microphase-separated structure and can be used as a binder for secondary batteries. The present invention also provides a binder for secondary batteries having a microphase-separated structure.

[0030] The above-mentioned slurry composition for a secondary battery contains a solvent (B). The solvent is not particularly limited, but is preferably one that has excellent coating properties, drying properties, and dispersibility of inorganic particles. The solvent is preferably a water-insoluble organic solvent, and examples thereof include alcohols such as aliphatic alcohols, glycols, terpene alcohols, and aromatic alcohols, aromatic hydrocarbons, esters, ketones, and N-methylpyrrolidone. Examples of the aliphatic alcohols include ethanol and isopropanol. Examples of the glycols include ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisobutyl ether, butyl carbitol, ethylene glycol monoethyl ether acetate, trimethylpentanediol monoisobutyrate, butyl carbitol acetate, Texanol, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, ethylene glycol ethyl ether, and ethyl carbitol acetate. Examples of the terpene alcohols include terpineol, dihydroterpineol, terpineol acetate, and dihydroterpineol acetate. Examples of the aromatic alcohols include benzyl alcohol, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, and cresol. Examples of the aromatic hydrocarbons include toluene. Examples of the esters include ethyl acetate, butyl acetate, hexyl acetate, isoamyl acetate, butyl butyrate, butyl lactate, dioctyl phthalate, and dioctyl adipate. Examples of the ketones include methyl ethyl ketone, methyl isobutyl ketone, and isophorone. Of these, butyl acetate, hexyl acetate, ethyl carbitol acetate, terpineol, terpineol acetate, dihydroterpineol, dihydroterpineol acetate, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisobutyl ether, butyl carbitol, butyl carbitol acetate, and Texanol are preferred, butyl acetate, hexyl acetate, terpineol, and ethyl carbitol acetate are more preferred, and butyl acetate, terpineol, and benzyl alcohol are even more preferred. These organic solvents may be used alone or in combination of two or more kinds.

[0031] The boiling point of the solvent (B) is preferably 110°C or higher and 240°C or lower, more preferably 120°C or higher and 210°C or lower. When the content is within the above range, evaporation does not occur too quickly, and drying can be easily performed using a fan oven, etc. Furthermore, printability can be improved, and a coated product with a smooth surface can be obtained.

[0032] The water content of the solvent (B) is preferably low, and is preferably 0.07% by weight or less. By setting the water content in this range, deterioration of the electrolyte can be prevented. The water content of the solvent (B) is more preferably 0.05% by weight or less, and even more preferably 0% by weight. The method for reducing the water content is not particularly limited, but examples thereof include a vacuum degassing method, a molecular sieve method, etc. The water content in the solvent can be measured using a Karl Fischer moisture meter.

[0033] The content of the solvent (B) in the resin composition for a secondary battery is preferably 10% by weight or more, more preferably 15% by weight or more, and is preferably 95% by weight or less, more preferably 85% by weight or less. By setting the content within the above range, it is possible to further improve the coating properties and the dispersibility of inorganic particles.

[0034] The resin composition for a secondary battery may further contain additives such as a conductive aid, a flame retardant aid, an antifoaming agent, a leveling agent, and an adhesion promoter, as long as the effects of the present invention are not impaired.

[0035] The resin composition for a secondary battery can be prepared, for example, by preparing the thermoplastic binder (A) and then adding and mixing the solvent (B) and the like. Examples of the mixing method include methods using various mixers such as a ball mill, a blender mill, and a three-roll mill.

[0036] A slurry composition for a secondary battery can be prepared by adding inorganic particles such as an active material and a solid electrolyte to the resin composition for a secondary battery. The present invention also provides a slurry composition for a secondary battery, which comprises the above-mentioned resin composition for a secondary battery and inorganic particles (C), wherein the inorganic particles (C) contain an active material or a solid electrolyte.

[0037] The slurry composition for a secondary battery contains inorganic particles (C). Examples of inorganic particles include active material particles such as positive electrode active materials and negative electrode active materials, solid electrolyte particles, graphite, carbon nanotubes, graphene, lithium metal particles, sodium particles, conductive metal particles, and sulfur particles.

[0038] Examples of the positive electrode active material include lithium nickel oxide (e.g., LiNiO2), lithium cobalt oxide (e.g., LiCoO2, LiNixCoyAlzO2, x+y+z=1), lithium manganese oxide (e.g., LiMn2O4), and composites thereof (e.g., LiNi 0.5 Mn 1.5 O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3Examples of suitable oxides include particles of oxides (lithium transition metal oxides) containing lithium and transition metal elements as constituent metal elements, such as lithium manganese phosphate (LiMnPO4) and lithium iron phosphate (LiFePO4). These may be used alone or in combination of two or more. As the material for the negative electrode active material, for example, a material that has conventionally been used as a negative electrode active material for lithium secondary batteries can be used, and examples thereof include carbon-based materials such as graphite, natural graphite, graphite carbon, and amorphous carbon, lithium transition metal oxides, lithium transition metal nitrides, silicon, and silicon compounds such as silicon oxide.

[0039] Examples of the material for the solid electrolyte include low-melting point glass such as LiO2·Al2O3·SiO2 inorganic glass, lithium sulfur glass such as Li2S-MxSy (M=B, Si, Ge, P), lithium cobalt composite oxide such as LiCoO2, lithium manganese composite oxide such as LiMnO4, lithium nickel composite oxide, lithium vanadium composite oxide, lithium zirconium composite oxide, lithium hafnium composite oxide, and lithium silicophosphate (Li 3.5 Si 0.5 P 0.5 O4), lithium titanium phosphate (LiTi2(PO4)3), lithium titanate (Li4Ti5O 12 ), Li 4 / 3 Ti 5 / 3 O4, lithium germanium phosphate (LiGe2(PO4)3), Li2-SiS-based glass, Li4GeS4-Li3PS4-based glass, LiSiO3, LiMn2O4, Li2S-P2S5-based glass and ceramics, Li2O-SiO2, Li2O-V2O5-SiO2, LiS-SiS2-Li4SiO4-based glass, ionic conductive oxides such as LiPON, lithium oxide compounds such as Li2O-P2O5-B2O3 and Li2O-GeO2Ba, Li x Al y Ti z (PO4)3-based glass, La x Li y TiOz Li-based glass x Ge y P z O4-based glass, Li7La3Zr2O 12 Li-based glass v Si w P x S y Cl z Lithium niobium oxides such as LiNbO3, lithium alumina compounds such as Li-β-alumina, 14 Examples include lithium zinc oxides such as Zn(GeO4)4.

[0040] The average particle size of the inorganic particles (C) is preferably 0.05 μm or more, more preferably 0.1 μm or more, and is preferably 30 μm or less, more preferably 10 μm or less. By setting the content within the above range, charge / discharge efficiency can be improved.

[0041] The content of the inorganic particles (C) in the slurry composition for secondary batteries is preferably 30% by weight or more and 80% by weight or less, which can sufficiently increase the strength of the electrode and active material layer after printing and improve the dispersibility of the inorganic particles.

[0042] The content of the thermoplastic binder (A) in the slurry composition for a secondary battery is preferably 1% by weight or more, more preferably 4% by weight or more, and is preferably 15% by weight or less, more preferably 10% by weight or less.

[0043] The content of the solvent in the slurry composition for a secondary battery is preferably 30% by weight or more, more preferably 40% by weight or more, and is preferably 70% by weight or less, more preferably 65% by weight or less. When preparing the slurry composition for a secondary battery, an additional solvent may be added in addition to the solvent (B) constituting the resin composition for a secondary battery, and the content of the solvent means the total amount of solvent contained in the slurry composition for a secondary battery.

[0044] The viscosity of the above-mentioned slurry composition for secondary batteries is preferably 0.1 Pa·s or more and 100 Pa·s or less when measured at 20°C using a Brookfield viscometer with the probe rotation speed set to 5 rpm. By setting the viscosity at 0.1 Pa·s or more, it becomes possible for the resulting coated product to maintain a predetermined shape after coating by die coating printing, etc. Furthermore, by setting the viscosity at 100 Pa·s or less, defects such as indelible die coating marks can be prevented, resulting in excellent printability.

[0045] The method for preparing the slurry composition for secondary batteries is not particularly limited, and examples thereof include conventionally known stirring methods, such as a method of mixing a resin composition for secondary batteries containing the thermoplastic binder (A) and the solvent (B) with inorganic particles (C), and other solvents and additives added as needed, and stirring the mixture with a three-roll mill, a ball mill, a bead mill, or the like.

[0046] A secondary battery can be produced by using the above-mentioned slurry composition for a secondary battery. Examples of the secondary battery include a nickel-cadmium battery, a nickel-metal hydride battery, a lithium secondary battery, an all-solid-state battery, and a fuel cell.

[0047] The slurry composition for a secondary battery is applied to, for example, a support film one side of which has been subjected to a release treatment, the solvent is dried, and the film is molded to produce an inorganic particle dispersion molded body. The shape of the inorganic particle dispersion molded body is not particularly limited, and may be, for example, a sheet shape. When the inorganic particle dispersion molded body is in the form of a sheet, it preferably has a thickness of 1 to 20 μm.

[0048] Examples of a method for producing the inorganic particle dispersion molded body include a method in which the slurry composition for a secondary battery is uniformly applied to a support by a coating method such as a roll coater, a die coater, a squeeze coater, or a curtain coater, and then dried and molded.

[0049] The drying method may be, for example, heat drying. The drying temperature is preferably 80°C or higher and 130°C or lower.

[0050] The support used in producing the inorganic particle dispersion molded body can be a resin film or the like that is heat-resistant, solvent-resistant, and flexible. The flexibility of the support allows the slurry composition to be applied to the surface of the support using a roll coater, blade coater, or the like, and the resulting inorganic particle dispersion molded body can be stored and supplied in a rolled state.

[0051] Examples of resins constituting the resin film include polyethylene terephthalate, polyester, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, fluorine-containing resins such as polyfluoroethylene, nylon, cellulose, and the like. The thickness of the resin film is preferably, for example, 20 to 100 μm. It is also preferable that the surface of the resin film is subjected to a release treatment, which allows the resin film to be easily peeled off in the transfer step.

[0052] For example, by using an active material as the inorganic particles (C) in the above-mentioned slurry composition for a secondary battery, an electrode for a secondary battery containing the thermoplastic binder (A) and the active material can be produced. Specifically, the resin composition for a secondary battery and an active material are mixed to prepare a slurry composition for a secondary battery, and the slurry composition for a secondary battery is applied to a current collector and dried to form an electrode film. Furthermore, a secondary battery can be produced using such an electrode film. The present invention also provides an electrode for a secondary battery, which comprises a thermoplastic binder (A) and an active material, wherein the thermoplastic binder (A) has a microphase-separated structure. The present invention also provides a method for producing a secondary battery, the method including the steps of mixing the resin composition for a secondary battery with an active material to prepare a slurry composition for a secondary battery, and applying the slurry composition for a secondary battery to a current collector to form an electrode film. The thermoplastic binder (A) constituting the secondary battery electrode is the same as the thermoplastic binder (A) constituting the secondary battery resin composition.

[0053] For example, a negative electrode for a lithium ion battery can be produced by preparing the above-mentioned slurry composition for a secondary battery using a negative electrode active material that is a mixed powder of graphite and SiO in a weight ratio of 95:5 as the inorganic particles (C), and then coating and drying the obtained slurry composition for a secondary battery on a copper foil as a current collector.

[0054] Furthermore, for example, by using a solid electrolyte as the inorganic particles (C) in the slurry composition for a secondary battery, a solid electrolyte layer containing the thermoplastic binder (A) and the solid electrolyte can be produced. Specifically, the resin composition for a secondary battery and a solid electrolyte are mixed to prepare a slurry composition for a secondary battery, and the slurry composition for a secondary battery is applied to a release film and dried to form a solid electrolyte layer. In addition, an all-solid-state battery can be fabricated using such a solid electrolyte layer. The present invention also provides a solid electrolyte layer comprising a thermoplastic binder (A) and a solid electrolyte, wherein the thermoplastic binder (A) has a microphase-separated structure. The present invention also provides a method for producing an all-solid-state battery, the method including the steps of mixing the resin composition for a secondary battery with a solid electrolyte to prepare a slurry composition for a secondary battery, and applying the slurry composition for a secondary battery onto a release film to form a solid electrolyte layer. The thermoplastic binder (A) constituting the solid electrolyte layer is the same as the thermoplastic binder (A) constituting the resin composition for secondary batteries.

[0055] For example, La 2 / 3-x Li 3xThe above-mentioned slurry composition for secondary batteries is prepared using TiO3 (LLTO), and the obtained slurry composition for secondary batteries is coated on a negative electrode Li foil and dried. A positive electrode sheet consisting of LLTO as a positive electrode, acetylene black as a conductive additive, and lithium niobium oxide as a positive electrode active material is then attached to the negative electrode, and an external electrode is installed, thereby making it possible to prepare a high-capacity all-solid-state battery. [Effects of the Invention]

[0056] According to the present invention, it is possible to provide a resin composition for a secondary battery that can produce an electrode for a secondary battery and a solid electrolyte layer that are resistant to destruction even when expanded and contracted due to repeated charging and discharging, and that can produce a highly reliable secondary battery. It is also possible to provide a slurry composition for a secondary battery, a binder for a secondary battery, an electrode for a secondary battery, a method for producing a secondary battery, a solid electrolyte layer, and a method for producing an all-solid-state battery. DETAILED DESCRIPTION OF THE INVENTION

[0057] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0058] Example 1 (Polymerization Example 1) (Preparation of polystyrene resin with thiol groups at the molecular end) In a 2 L separable flask equipped with a stirrer, a condenser, a thermometer, a hot water bath, and a nitrogen gas inlet, 100 parts by weight of styrene monomer from which the polymerization inhibitor had been removed using a stabilizer removal column, 1.1 parts by weight of tetraethylthiuram disulfide as a polysulfide compound, and 100 parts by weight of ethyl acetate as an organic solvent were mixed to obtain a monomer mixture.

[0059] The resulting monomer mixture was bubbled with nitrogen gas for 20 minutes to remove dissolved oxygen, and then the atmosphere in the separable flask was replaced with nitrogen gas. The water bath was heated to a boil while stirring. A solution of 2 parts by weight of polymerization initiator (NOF Corporation, Perloyl 355) diluted with 10 parts by weight of ethyl acetate was added in several portions. Ten hours after the start of polymerization, the mixture was cooled to room temperature to terminate the polymerization, yielding an ethyl acetate solution of sulfide-modified polystyrene resin.

[0060] To 100 parts by weight of the obtained polystyrene resin, 2 parts by weight of 1N hydrochloric acid was added, and the mixture was heated to an internal temperature of 40°C to cleave the sulfide bonds. The mixture was then washed with methanol to reduce the sodium acetate content to 0.1 moles per mole of resin. The mixture was then dried in a drying oven at 60°C for 96 hours to obtain polystyrene resin (St) having thiol groups at the molecular terminals.

[0061] (Preparation of St-BA block copolymer) 50 parts by weight of the obtained polystyrene resin and 100 parts by weight of ethyl acetate as a solvent were placed in a separable flask equipped with a reflux condenser, and the mixture was stirred at 80° C. for 6 hours to completely dissolve the polystyrene resin. To the resulting polystyrene resin solution, 100 parts by weight of butyl acrylate was added, and the mixture was reheated to an internal temperature of 80°C. Furthermore, a solution prepared by diluting 2 parts by weight of a polymerization initiator (NOF Corporation, Perloyl 355) with 10 parts by weight of ethyl acetate was added in several portions. The mixture was then dried in a drying oven at 60°C for 96 hours to obtain a St-BA block copolymer having St block segments as hard segments and BA block segments as soft segments.

[0062] 1The styrene segment content was confirmed to be 33% by weight based on the ratio of the integrated peaks of the styrene band at 7.2 ppm and the BA band at 4.0 ppm by H-NMR. The glass transition temperatures of the St block segment, BA block segment, and St-BA block copolymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The weight-average molecular weight (Mw) of the St-BA block copolymer was measured by gel permeation chromatography using a Column LF-804 (manufactured by SHOKO).

[0063] (Preparation of positive electrode layer) 100 parts by weight of Li2S-P2S5-based glass (average particle size 2.0 μm) coated with lithium niobate was blended with 3 parts by weight of polyvinylidene fluoride (PVdF) as a binder and 3 parts by weight of acetylene black as a conductive additive, and mixed with 106 parts by weight of butyl acetate. The mixture was then kneaded with a stirrer to obtain a positive electrode slurry.

[0064] The obtained positive electrode slurry was applied using a blade coater onto a support film (width 400 mm, length 30 m, thickness 38 μm) made of polyethylene terephthalate (PET) that had been previously subjected to a release treatment to form a coating film, and the formed coating film was dried at 40°C for 10 hours to remove the solvent, thereby forming an inorganic particle-dispersed sheet with a thickness of 50 μm on the support film.

[0065] (Preparation of electrolyte layer) The obtained St-BA block copolymer was used as the thermoplastic binder (A), and 5 parts by weight of the thermoplastic binder (A) was mixed with 100 parts by weight of hexyl acetate as the solvent (B) to obtain a resin composition for secondary batteries. To the obtained resin composition for secondary batteries, 95 parts by weight of a sulfide solid electrolyte (Li2S-P2S5-based solid electrolyte) was further added as inorganic particles (C), and the mixture was stirred using an ultrasonic disperser to obtain a slurry composition for secondary batteries (solid electrolyte slurry). The obtained solid electrolyte slurry was applied using an applicator to a support film made of polyethylene terephthalate (PET) that had been previously treated for release properties, and dried for 2 hours in a vacuum oven set at 100°C to obtain a solid electrolyte layer.

[0066] (Preparation of negative electrode) 50 parts by weight of anode active material (lithium titanate) and 50 parts by weight of Li2S-P2S5-based glass were mixed, and then 3 parts by weight of PVdF as a binder and 3 parts by weight of acetylene black as a conductive additive were added. 106 parts by weight of butyl butyrate was then added and kneaded with a stirrer to obtain anode slurry. The obtained negative electrode slurry was applied onto a copper foil having a thickness of 15 μm using an applicator and dried at 150° C. for 15 minutes to obtain a negative electrode.

[0067] (Fabrication of all-solid-state batteries) The obtained positive electrode layer, electrolyte layer, and negative electrode were stacked and pressed at 1 ton / cm, and then sealed with an aluminum laminate film with terminals to obtain an all-solid-state battery.

[0068] Example 2 (Polymerization Example 2) (Preparation of MMA-BA block copolymer) 6.38 g (50 mmol) of tellurium (40 mesh, metallic tellurium, manufactured by Aldrich) was suspended in 50 mL of tetrahydrofuran (THF), and 34.4 mL (55 mmol) of a 1.6 mol / L n-butyllithium / hexane solution (manufactured by Aldrich) was slowly added dropwise at room temperature. The reaction solution was stirred until the metallic tellurium completely disappeared. 10.7 g (55 mmol) of ethyl 2-bromoisobutyrate was added to the reaction solution at room temperature and stirred for 2 hours. After the reaction was completed, the solvent was concentrated under reduced pressure, followed by vacuum distillation to obtain a yellow oily substance, ethyl 2-methyl-2-n-butyltellanylpropionate. In an argon-substituted glove box, 520 μL of the 2-methyl-2-n-butyltellanyl-ethyl propionate and 1 mL of ethyl acetate were added to the reaction vessel, which was then sealed and removed from the glove box. Subsequently, while argon gas was flowing into the reaction vessel, 10 g of methyl methacrylate (MMA) and 66.5 g of ethyl acetate as a polymerization solvent were added to the reaction vessel, and the polymerization reaction was carried out at 60 °C for 20 hours to obtain a solution containing a living radical polymerized acrylic polymer. The resulting living radical polymerized acrylic polymer was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm). The resulting filtrate was fed to a gel permeation chromatograph (Waters, 2690 Separations Model) for GPC measurement. The polystyrene-equivalent molecular weight of the polymer was measured, and the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined. A GPC KF-806L (Showa Denko) column was used, and a differential refractometer was used as the detector. Subsequently, the internal temperature of the reaction solution was cooled to -30°C, and 80 g of n-butyl acrylate (BA) was added dropwise over 2 hours, and after completion of the addition, the mixture was stirred at -30°C for 5 minutes. Next, 200 g of methanol was added to terminate the polymerization reaction, and the resulting reaction solution was poured into 15 kg of methanol to precipitate a liquid precipitate. The liquid precipitate was then recovered and dried to obtain 100 g of an MMA-BA block copolymer having an MMA block segment as a hard segment and a BA block segment as a soft segment. The glass transition temperatures of the MMA block segment, BA block segment, and MMA-BA block copolymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The weight-average molecular weight of the MMA-BA block copolymer was also determined by GPC measurement using the method described above. Furthermore, the glass transition temperatures of the MMA-BA block copolymer were also measured using the method described above. 1 The total content of polymer blocks composed of methyl methacrylate units in the MMA-BA block copolymer was determined by 1 H-NMR measurement and was found to be 10% by weight.

[0069] A resin composition for a secondary battery, a slurry composition for a secondary battery, and an all-solid-state battery were produced in the same manner as in Example 1, except that the obtained block copolymer was used as the thermoplastic binder (A).

[0070] Example 3 (Polymerization Example 3) (Preparation of MMA-BA block copolymer) 6.38 g (50 mmol) of tellurium (40 mesh, metallic tellurium, manufactured by Aldrich) was suspended in 50 mL of tetrahydrofuran (THF), and 34.4 mL (55 mmol) of a 1.6 mol / L n-butyllithium / hexane solution (manufactured by Aldrich) was slowly added dropwise at room temperature. The reaction solution was stirred until the metallic tellurium completely disappeared. 10.7 g (55 mmol) of ethyl 2-bromoisobutyrate was added to the reaction solution at room temperature and stirred for 2 hours. After the reaction was completed, the solvent was concentrated under reduced pressure, followed by vacuum distillation to obtain a yellow oily substance, ethyl 2-methyl-2-n-butyltellanylpropionate. In an argon-substituted glove box, 230 μL of the 2-methyl-2-n-butyltellanyl-ethyl propionate and 1 mL of ethyl acetate were added to the reaction vessel, which was then sealed and removed from the glove box. Subsequently, while argon gas was flowing into the reaction vessel, 10 g of methyl methacrylate (MMA) and 66.5 g of ethyl acetate as a polymerization solvent were added to the reaction vessel, and the polymerization reaction was carried out at 60 °C for 20 hours to obtain a solution containing a living radical polymerized acrylic polymer. The resulting living radical polymerized acrylic polymer was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm). The resulting filtrate was fed to a gel permeation chromatograph (Waters, 2690 Separations Model) for GPC measurement. The polystyrene-equivalent molecular weight of the polymer was measured, and the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined. A GPC KF-806L (Showa Denko) column was used, and a differential refractometer was used as the detector. Subsequently, the internal temperature of the reaction solution was cooled to -30°C, and 80 g of n-butyl acrylate was added dropwise over 2 hours. After completion of the dropwise addition, the mixture was stirred at -30°C for 5 minutes. Next, 200 g of methanol was added to terminate the polymerization reaction, and the resulting reaction solution was poured into 15 kg of methanol to precipitate a liquid precipitate. The liquid precipitate was then collected and dried to obtain 100 g of an MMA-BA block copolymer having MMA block segments as hard segments and BA block segments as soft segments. The glass transition temperatures of the MMA block segments, BA block segments, and MMA-BA block copolymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The weight-average molecular weight of the resulting MMA-BA block copolymer was also determined by GPC measurement using the method described above. Furthermore, the glass transition temperatures of the MMA block segments, BA block segments, and MMA-BA block copolymer were also measured using the method described above. 1 The total content of polymer blocks composed of methyl methacrylate units in the MMA-BA block copolymer was determined by 1 H-NMR measurement and was found to be 10% by weight.

[0071] A resin composition for a secondary battery, a slurry composition for a secondary battery, and an all-solid-state battery were produced in the same manner as in Example 1, except that the obtained block copolymer was used as the thermoplastic binder (A).

[0072] (Comparative Example 1) (Polymerization Example 4) (Preparation of St polymer) A 2 L separable flask equipped with a stirrer, a condenser, a thermometer, a hot water bath, and a nitrogen gas inlet was charged with 100 parts by weight of styrene monomer, from which the polymerization inhibitor had been removed using a stabilizer removal column, and 1,000 parts by weight of water, and mixed. 10 parts by weight of a dispersant (hydroxypropyl methylcellulose) and 2 parts by weight of a polymerization initiator (lauroyl peroxide) were then added, and the mixture was dispersed with a high-speed stirrer for 10 minutes to obtain a suspension.

[0073] The resulting suspension was bubbled with nitrogen gas for 20 minutes to remove dissolved oxygen, and then the atmosphere in the separable flask was replaced with nitrogen gas. The temperature of the water bath was raised to boiling while stirring, and polymerization was carried out. Ten hours after the start of polymerization, the mixture was cooled to room temperature to terminate the polymerization, and the mixture was filtered and dried to obtain a polystyrene resin (St polymer). The resulting polystyrene resin was dissolved in ethyl acetate to a solids content of 10 wt %, yielding an ethyl acetate solution of polystyrene resin.

[0074] (Polymerization Example 5) (Preparation of BA polymer) Into a 2 L separable flask equipped with a stirrer, a condenser, a thermometer, a hot water bath, and a nitrogen gas inlet, 100 parts by weight of n-butyl acrylate, from which the polymerization inhibitor had been removed using a stabilizer removal column, and 100 parts by weight of ethyl acetate as an organic solvent were added and mixed to obtain a monomer mixture.

[0075] The resulting monomer mixture was bubbled with nitrogen gas for 20 minutes to remove dissolved oxygen, and then the atmosphere in the separable flask was replaced with nitrogen gas. The temperature of the water bath was raised to a boil while stirring. Furthermore, a solution of 2 parts by weight of a polymerization initiator (NOF Corporation, Perloyl 355) diluted with 10 parts by weight of ethyl acetate was added in several portions. Ten hours after the start of polymerization, the mixture was cooled to room temperature to terminate the polymerization, thereby obtaining an ethyl acetate solution of polybutyl acrylate resin (BA polymer).

[0076] (Preparation of Thermoplastic Binder (A)) The ethyl acetate solutions obtained in Synthesis Examples 4 and 5 were each dried in a vacuum oven, and the St polymer and BA polymer were mixed in a weight ratio of 1:1 to obtain a thermoplastic binder (A) which was a mixed resin. The glass transition temperatures of the St polymer and the BA polymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The weight average molecular weight (Mw) of the thermoplastic binder (A) was measured by gel permeation chromatography using a column LF-804 (manufactured by SHOKO Co., Ltd.).

[0077] A resin composition for a secondary battery, a slurry composition for a secondary battery, and an all-solid-state battery were produced in the same manner as in Example 1, except that the obtained thermoplastic binder (A) was used.

[0078] (Comparative Example 2) (Polymerization Example 6) (Preparation of MMA polymer) An ethyl acetate solution of polymethyl methacrylate (MMA polymer) was obtained in the same manner as in Synthesis Example 4, except that methyl methacrylate (MMA) was used instead of the styrene monomer.

[0079] (Preparation of Thermoplastic Binder (A)) The ethyl acetate solutions obtained in Synthesis Examples 5 and 6 were each dried in a vacuum oven, and the MMA polymer and BA polymer were mixed in a weight ratio of 1:4 to obtain a thermoplastic binder (A) which was a mixed resin. The glass transition temperatures of the MMA polymer and the BA polymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The weight average molecular weight (Mw) of the thermoplastic binder (A) was measured by gel permeation chromatography using a column LF-804 (manufactured by SHOKO Corporation).

[0080] A resin composition for a secondary battery, a slurry composition for a secondary battery, and an all-solid-state battery were produced in the same manner as in Example 1, except that the obtained thermoplastic binder (A) was used.

[0081] (Comparative Example 3) (Polymerization Example 7) (Preparation of St-BA random copolymer) In a 2 L separable flask equipped with a stirrer, a condenser, a thermometer, a hot water bath, and a nitrogen gas inlet, 50 parts by weight of styrene from which the polymerization inhibitor had been removed using a stabilizer removal column, 50 parts by weight of n-butyl acrylate, 1,000 parts by weight of water, and 20 parts by weight of sodium dodecyl sulfonate as a surfactant were mixed and emulsified using a high-speed stirrer to obtain an emulsion.

[0082] To the resulting emulsion, 0.2 parts by weight of potassium persulfate was added, and the temperature of the water bath was raised to 80° C. to react the monomers. Ten hours after the start of polymerization, the mixture was cooled to room temperature to terminate the polymerization, yielding a St-BA random copolymer slurry. The resulting slurry was dried in an oven at 60°C for 10 hours to yield a thermoplastic binder (A). The glass transition temperature of the thermoplastic binder (A) was measured using a differential scanning calorimeter (DSC) at a heating rate of 5°C / min. The weight-average molecular weight (Mw) of the thermoplastic binder (A) was measured by gel permeation chromatography using a column LF-804 (manufactured by SHOKO Corporation).

[0083] A resin composition for a secondary battery, a slurry composition for a secondary battery, and an all-solid-state battery were produced in the same manner as in Example 1, except that the obtained thermoplastic binder (A) was used.

[0084] (evaluation) The thermoplastic binders (A) and all-solid-state batteries obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 2.

[0085] (1) Binder structure analysis The thermoplastic binders (A) obtained in the examples and comparative examples were stained with ruthenium tetroxide, sectioned using a microtome, and the cross sections were observed using a transmission electron microscope (JEOL Ltd., "JEM-2100") to confirm the phase separation state. Those in which a periodically dispersed microdomain structure was confirmed were evaluated as "Good," and those in which a periodically dispersed microdomain structure was not confirmed were evaluated as "Poor." In Example 1, a rod-shaped microdomain structure was confirmed in which rod-shaped soft segment domains were dispersed in a periodic arrangement in the hard segment domains, approximately parallel to one another. Furthermore, in Examples 2 and 3, a spherical structure (sea-island structure) in which spherical soft segment domains were dispersed in a periodic arrangement in the hard segment domains was confirmed. On the other hand, a regular phase-separated structure was not confirmed in Comparative Examples 1 and 2, and no phase-separated structure was confirmed in Comparative Example 3.

[0086] (2) Charge / discharge characteristics For the all-solid-state batteries obtained in Examples and Comparative Examples, the initial resistance was measured, and then a charge-discharge cycle was performed 100 times under conditions of 60°C, in which constant current charge-discharge was performed at a rate of 2C from full charge to full discharge. After the cycles were completed, the resistance of the all-solid-state battery was measured, and the rate of increase in resistance from the initial resistance was calculated. An increase rate of less than 100% was evaluated as "Good", and an increase rate of 100% or more was evaluated as "Poor".

[0087] (3) Cross-sectional observation After evaluating "(2) charge / discharge characteristics," the solid-state battery was cut and the cross section of the electrolyte layer was observed using a scanning electron microscope. The battery was evaluated as "Good" if no cracks or voids were found in the electrolyte layer, and as "Poor" if cracks or voids were found in the electrolyte layer.

[0088] [Table 1]

[0089] [Table 2]

[0090] As a result of repeated charge and discharge, in Examples 1 to 3, which used a thermoplastic binder (A) having a microphase separation structure, there was almost no increase in resistance value, and no traces of cracks or voids in the electrolyte layer were observed. On the other hand, in Comparative Examples 1 to 3, which used a thermoplastic binder (A) without a microphase separation structure, the resistance value increased, and cracks and voids were observed in the electrolyte layer. From these facts, it can be seen that the all-solid-state batteries of Examples 1 to 3 are resistant to destruction even by expansion and contraction accompanying repeated charge and discharge. [Industrial Applicability]

[0091] According to the present invention, it is possible to provide a resin composition for a secondary battery that can produce an electrode for a secondary battery and a solid electrolyte layer that are resistant to destruction even when expanded and contracted due to repeated charging and discharging, and that can produce a highly reliable secondary battery. It is also possible to provide a slurry composition for a secondary battery, a binder for a secondary battery, an electrode for a secondary battery, a method for producing a secondary battery, a solid electrolyte layer, and a method for producing an all-solid-state battery.

Claims

1. A thermoplastic binder (A) and a solvent (B), The thermoplastic binder (A) has a microphase-separated structure.

2. 2. The resin composition for a secondary battery according to claim 1, wherein the thermoplastic binder (A) is a block copolymer having a hard segment and a soft segment.

3. The resin composition for a secondary battery according to claim 1 or 2, wherein the thermoplastic binder (A) has a weight average molecular weight (Mw) of 10,000 or more and 2,000,000 or less.

4. 3. The resin composition for a secondary battery according to claim 1, wherein the thermoplastic binder (A) has a glass transition temperature of −80° C. or higher and 25° C. or lower.

5. The structural unit derived from the hard segment has a glass transition temperature of 80°C or higher and 150°C or lower, and the structural unit derived from the soft segment has a glass transition temperature of -70°C or higher and -30°C or lower. The resin composition for a secondary battery according to claim 2.

6. The resin composition for a secondary battery according to claim 2 or 5, wherein the block copolymer has an acrylic structural unit.

7. A slurry composition for a secondary battery, comprising the resin composition for a secondary battery according to claim 1 or 2 and inorganic particles (C), wherein the inorganic particles (C) contain an active material or a solid electrolyte.

8. The slurry composition for a secondary battery according to claim 7, wherein the inorganic particles (C) have an average particle size of 0.05 μm or more and 30 μm or less.

9. A binder for secondary batteries with a microphase separation structure.

10. The binder for a secondary battery according to claim 9 , which is a block copolymer having a hard segment and a soft segment.

11. The binder for a secondary battery according to claim 9 or 10, having a weight average molecular weight (Mw) of 10,000 or more and 2,000,000 or less.

12. The binder for a secondary battery according to claim 9 or 10, having a glass transition temperature of −80° C. or higher and 25° C. or lower.

13. the structural unit derived from the hard segment has a glass transition temperature of 80°C or higher and 150°C or lower; The binder for a secondary battery according to claim 10, wherein the structural unit derived from the soft segment has a glass transition temperature of −70° C. or higher and −30° C. or lower.

14. The binder for a secondary battery according to claim 10 or 13, wherein the block copolymer has an acrylic structural unit.

15. A thermoplastic binder (A) and an active material are included, The thermoplastic binder (A) has a microphase separation structure.

16. 3. A method for producing a secondary battery, comprising: a step of mixing the resin composition for a secondary battery according to claim 1 or 2 with an active material to prepare a slurry composition for a secondary battery; and a step of applying the slurry composition for a secondary battery to a current collector to form an electrode film.

17. A thermoplastic binder (A) and a solid electrolyte are included, The thermoplastic binder (A) has a microphase-separated structure.

18. 3. A method for producing an all-solid-state battery, comprising: a step of mixing the resin composition for a secondary battery according to claim 1 or 2 with a solid electrolyte to prepare a slurry composition for a secondary battery; and a step of applying the slurry composition for a secondary battery onto a release film to form a solid electrolyte layer.

Images