Binder for electrode of lithium ion battery

Abstract

A binder for an electrode of a lithium ion battery includes core-shell particles including a core and a shell layer located outside the core. The core is made of rubber, and the shell layer is made of a shell-forming polymer containing at least one selected from a group consisting of methacrylic acid units and (meth) acrylate units containing a (poly) alkylene glycol chain. The content ratio of the methacrylic acid unit in the shell-forming polymer is 5-40% by weight, or the content ratio of the (meth) acrylate unit containing a (poly) alkylene glycol chain in the shell-forming polymer is 10-30% by weight.

Description

Technical Field

[0001] The present invention relates to a binder for an electrode of a lithium ion battery, an electrode of a lithium ion battery and a method for producing the same, and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are lightweight, have high energy density, and can be repeatedly charged and discharged. They are used in a wide range of applications, including power sources for personal computers and smartphones, and power sources for electric and hybrid vehicles.

[0003] In the negative electrode of a lithium-ion battery, an electrode active material layer composed of an electrode active material such as graphite and a binder such as styrene / butadiene rubber (SBR) is formed on a current collector such as a metal foil. The electrode active material layer is usually manufactured by applying a slurry prepared by mixing an electrode active material, a binder and a solvent to the current collector and drying it.

[0004] The binder used in the electrode active material layer is required to maintain the binding property (adhesion) between the electrode active materials and the binding property between the electrode active material and the current collector. Studies are being conducted to improve the binding property and enhance the characteristics of the secondary battery.

[0005] For example, Patent Document 1 describes the use of a particulate polymer containing an aliphatic conjugated diene monomer unit such as butadiene and a carboxylic acid group-containing monomer unit or a (meth)acrylic acid ester monomer unit at a specific ratio as a binder for secondary battery electrodes.

[0006] Patent document 2 describes a particulate polymer having a core-shell structure as a binder for secondary battery electrodes, wherein the core portion is composed of a polymer containing aliphatic conjugated diene monomers and aromatic vinyl monomer units, and the shell portion is composed of a polymer containing 40% by weight or more of (meth)acrylate monomer units.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: International Publication No. 2017 / 141791

[0010] Patent Document 2: International Publication No. 2017 / 056466 Summary of the invention

[0011] When a slurry containing a conventional binder is applied to a current collector, the coating property is insufficient and the surface smoothness of the formed electrode active material layer is sometimes low.

[0012] Furthermore, in order to maintain a high operating voltage in a lithium-ion battery, it is desirable that the internal resistance be low.

[0013] In view of the above-mentioned current situation, an object of the present invention is to provide a binder for lithium ion battery electrodes which has good coating properties on a current collector and can reduce the internal resistance of the lithium ion battery.

[0014] The present inventors have conducted intensive studies to solve the above problems and have found that the above objects can be achieved by using core-shell particles having a core composed of rubber and a shell layer composed of a polymer containing specific monomer units as a binder for lithium ion battery electrodes, thereby completing the present invention.

[0015] That is, the present invention relates to an electrode binder, which is an electrode binder for lithium ion batteries.

[0016] A core-shell particle comprising a core and a shell layer located outside the core,

[0017] The core is made of rubber.

[0018] The shell layer is composed of a shell-forming polymer containing at least one selected from methacrylic acid units and (meth)acrylate units containing (poly)alkylene glycol chains,

[0019] The content ratio of the methacrylic acid unit in the shell-forming polymer is 5 to 40% by weight, or the content ratio of the (poly)alkylene glycol chain-containing (meth)acrylate unit in the shell-forming polymer is 10 to 30% by weight.

[0020] According to the present invention, a lithium ion battery electrode binder having good coating properties on a current collector and capable of reducing the internal resistance of the lithium ion battery can be provided. The slurry containing the electrode binder of the present invention has good coating properties on a current collector, so an electrode active material layer with high surface smoothness can be obtained.

[0021] According to a preferred embodiment of the present invention, the binding property between the current collector and the electrode active material layer can be improved, and the charge and discharge characteristics of the lithium ion battery can be improved. DETAILED DESCRIPTION

[0022] Embodiments of the present invention will be described in detail below.

[0023] The binder for electrodes of the lithium ion battery of the present embodiment (hereinafter also referred to as “electrode binder”) contains at least core-shell particles.

[0024] The core-shell particles have a core-shell structure, including a core composed of rubber and a shell layer located outside the core layer. The shell layer is composed of a shell-forming polymer.

[0025] By using the core-shell particles of this structure as a binder for lithium ion battery electrodes, the internal resistance of the lithium ion battery can be reduced and the binding property between the current collector and the electrode active material layer can be improved.

[0026] (nuclear)

[0027] The core is a rubber particle composed of rubber. The type of rubber is not particularly limited, and the rubber is preferably a rubber containing aliphatic conjugated diene compound units and aromatic vinyl compound units, because it can improve the dispersibility of the core-shell particles in the slurry and the compatibility of the core-shell particles with the thickener, and can improve the adhesion between the collector and the electrode active material layer. The method for producing the rubber particles is not particularly limited, and it is preferably synthesized by emulsion polymerization.

[0028] The aliphatic conjugated diene compound is an aliphatic compound, and refers to a diene compound having two carbon-carbon double bonds separated by a single bond and conjugated. Specific examples of aliphatic conjugated diene compounds include isoprene, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, etc. The aliphatic conjugated diene compound can be used alone or in combination of two or more. Among them, 1,3-butadiene is preferred.

[0029] The aromatic vinyl compound is not particularly limited, and examples thereof include unsubstituted vinyl aromatic compounds such as styrene and 2-vinylnaphthalene; substituted vinyl aromatic compounds such as α-methylstyrene; cycloalkylated vinyl aromatic compounds such as 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene; cycloalkoxylated vinyl aromatic compounds such as 4-methoxystyrene and 4-ethoxystyrene; ring-halogenated vinyl aromatic compounds such as 2-chlorostyrene and 3-chlorostyrene; cyclic ester-substituted vinyl aromatic compounds such as 4-acetoxystyrene; and ring-hydroxylated vinyl aromatic compounds such as 4-hydroxystyrene. Among them, substituted or unsubstituted styrene is preferred, styrene and / or α-methylstyrene is more preferred, and styrene is particularly preferred. The aromatic vinyl compound may be used alone or in combination of two or more.

[0030] A typical example of the rubber constituting the core is styrene butadiene rubber. Styrene butadiene rubber is a copolymer of 1,3-butadiene and styrene, and is also called styrene rubber or SBR.

[0031] The rubber constituting the core may not contain vinyl monomers other than aliphatic conjugated diene compound units and aromatic vinyl compound units, and may also contain such other vinyl monomer units. Such other vinyl monomers include, for example, (meth)acrylic acids and (meth)acrylic acid alkyl esters such as acrylic acid, methacrylic acid, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, and glycidyl methacrylate; and unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile.

[0032] However, the rubber constituting the core preferably does not contain a vinyl monomer unit having a carboxyl group, such as acrylic acid, methacrylic acid, or itaconic acid.

[0033] The total proportion of the aliphatic conjugated diene compound units and the aromatic vinyl compound units in the entire rubber constituting the core is not particularly limited, and may be, for example, 80 to 100% by weight, 90% by weight or more, 95% by weight or more, 98% by weight or more, or 99% by weight or more.

[0034] When polymerizing the rubber constituting the core, a polyfunctional monomer such as divinylbenzene, allyl methacrylate, ethylene glycol dimethacrylate, or 1,3-butylene glycol dimethacrylate can be used.

[0035] Furthermore, the rubber constituting the core may be polymerized without using a chain transfer agent or in the presence of a chain transfer agent. The chain transfer agent that can be used is not particularly limited, and examples thereof include alkyl mercaptans such as n-dodecyl mercaptan, tert-dodecyl mercaptan, tert-decyl mercaptan, n-decyl mercaptan, and n-octyl mercaptan, and alkyl ester mercaptans such as 2-ethylhexyl thioglycolate.

[0036] In the rubber constituting the core, the content ratio of the aliphatic conjugated diene compound: the aromatic vinyl compound is not particularly limited, and may be, for example, in the range of 30:70 to 80:20. From the viewpoint of improving adhesion, reducing internal resistance, and maintaining capacity after charge and discharge (cycle characteristics), it is preferably 40:60 to 70:30, more preferably 45:55 to 65:35, and even more preferably 50:50 to 60:40.

[0037] The glass transition temperature (Tg) of the rubber is not particularly limited, and may be, for example, in the range of -50°C to +25°C. From the viewpoint of improving adhesion, reducing internal resistance, and maintaining capacity after charge and discharge (cycle characteristics), it is preferably -40°C to +20°C, more preferably -30°C to +15°C, further preferably -20°C to +10°C, and particularly preferably -15°C to 0°C.

[0038] The glass transition temperature of the rubber can be controlled by changing the ratio of the aliphatic conjugated diene compound unit to the aromatic vinyl compound unit in the rubber, and the type and ratio of other monomers that may be contained in the rubber. For example, the glass transition temperature of the rubber can be increased by increasing the ratio of the aromatic vinyl compound in the rubber.

[0039] The glass transition temperature can be measured using a differential scanning calorimeter (DSC).

[0040] The content of the core in the core-shell particles is not particularly limited, but is preferably 50 to 95 wt %, more preferably 60 to 90 wt %, and further preferably 65 to 80 wt %, from the viewpoint of improved adhesion, reduced internal resistance, and capacity maintenance after charge and discharge (cycle characteristics).

[0041] (Shell)

[0042] The shell layer is a polymer layer located on the surface side of the polymer particle, also called a graft layer. The shell layer is preferably graft-bonded to the core. However, the polymer forming the shell layer also includes a polymer that is not graft-bonded to the core.

[0043] The shell layer covers the surface of the core, but is not limited to covering the entire surface of the core, and may cover at least a portion of the surface of the core.

[0044] The polymer forming the shell layer (hereinafter also referred to as a shell-forming polymer) is preferably a vinyl polymer.

[0045] As the monomer constituting the above-mentioned shell-forming polymer, as long as it is a vinyl monomer, there is no particular limitation, but at least one of the (meth) acrylate units selected from methacrylic acid units and (poly) alkylene glycol chains is included. It is speculated that by making the above-mentioned shell layer have methacrylic acid units and / or (meth) acrylate units containing (poly) alkylene glycol chains, the dispersibility of the core-shell particles in the slurry and the compatibility of the core-shell particles with the thickener can be improved, and the core-shell particles and the thickener can be mixed with high uniformity. Therefore, the coating property of the slurry to the collector can be improved. At the same time, the internal resistance of the lithium ion battery can be reduced.

[0046] On the other hand, although the reason is not clear, when a carboxyl group-containing vinyl monomer other than methacrylic acid (such as acrylic acid and itaconic acid) is used, the coating property of the slurry on the current collector is insufficient, and it is difficult to obtain an electrode active material layer with high surface smoothness.

[0047] The methacrylic acid unit is used in a proportion of 5% by weight or more in the overall shell-forming polymer. If the proportion is less than 5% by weight, the effect of using the methacrylic acid unit cannot be fully obtained, and the coating property of the slurry on the collector cannot be fully improved. Preferably, it is 7% by weight or more.

[0048] The upper limit of the ratio of the methacrylic acid unit in the shell-forming polymer is not particularly limited, and from the viewpoint of polymerization stability during the manufacture of core-shell particles, it can usually be 40% by weight or less. From the viewpoint of reducing the internal resistance of the lithium ion battery, the above-mentioned content is preferably 30% by weight or less, more preferably 25% by weight or less, further preferably 20% by weight or less, particularly preferably 15% by weight or less, and most preferably 10% by weight or less. In addition, it can also be 9% by weight or less.

[0049] The expression "(poly)alkylene glycol chain" includes both an alkylene glycol chain having a polymerization degree of 1 and a polyalkylene glycol chain having a polymerization degree of 2 or more. That is, the "(poly)alkylene glycol chain" may be an alkylene glycol chain or a polyalkylene glycol chain.

[0050] The (poly)alkylene glycol chain is a monovalent group having a free terminal group. The terminal group is not particularly limited and may be a hydroxyl group or a substituent such as an alkyl group, an aryl group, or an acyl group. The number of carbon atoms of the substituent may be, for example, about 1 to 20, preferably about 1 to 10, and more preferably about 1 to 6.

[0051] The number of carbon atoms per alkylene glycol unit constituting the (poly)alkylene glycol chain is not particularly limited, but is preferably 1 to 6, more preferably 2 to 4, and even more preferably 2 to 3. Multiple types of alkylene glycol units having different numbers of carbon atoms may coexist.

[0052] Specific examples of the (poly)alkylene glycol chain include (poly)ethylene glycol chains, (poly)propylene glycol chains, (poly)ethylene glycol-(poly)propylene glycol chains, (poly)ethylene glycol-(poly)butylene glycol chains, (poly)propylene glycol-(poly)butylene glycol chains, etc. (Poly)ethylene glycol chains are particularly preferred.

[0053] The degree of polymerization of the (poly)alkylene glycol chain, that is, the number of alkylene glycol units per (poly)alkylene glycol chain is not particularly limited, and may be, for example, about 1 to 30, more preferably 1 to 20, further preferably 1 to 15, and particularly preferably 2 to 10. When the terminal group of the (poly)alkylene glycol chain is a hydroxyl group, the degree of polymerization is preferably 3 or more, more preferably 4 or more. In addition, when the terminal group of the (poly)alkylene glycol chain is the substituent, the degree of polymerization is preferably 6 or more, more preferably 8 or more.

[0054] Specific examples of the (meth)acrylates having a (poly)alkylene glycol chain whose terminal groups are hydroxyl groups include (poly)ethylene glycol (meth)acrylate (Blemmer PE-90, PE-200, PE-350, AE-90U, AE-200, AE-400, etc. manufactured by NOF Corporation), (poly)propylene glycol (meth)acrylate (Blemmer PP-500, PP-500D, PP-800, PP-1000, PP-2000D, AP-200, AP-400, AP-400D, AP-550, AP-800, AP-1000D, etc. manufactured by NOF Corporation), (poly)ethylene glycol (meth)acrylate-(poly)propylene glycol (Blemmer 50PEP-300 manufactured by NOF Corporation), (poly)ethylene glycol (meth)acrylate-(poly)butylene glycol (Blemmer 100 manufactured by NOF Corporation), and (poly)butylene glycol (Blemmer 100 manufactured by NOF Corporation). 55PET-800, 50PEP-500D, etc.), (meth)acrylate (poly)propylene glycol - (poly)butylene glycol (NOF BLEMMER 10PPB-500B, 10PPB-500BD, etc.), etc.

[0055] Specific examples of the (meth)acrylate containing a (poly)alkylene glycol chain whose terminal group is the above-mentioned substituent include methoxy (poly)ethylene glycol (meth)acrylate (BLEMMER PME-100, PME-200, PME-400, PME-1000, PME-2000, AME-400, etc. manufactured by NOF Corporation; NKESTETR M-20G, M-40G, M-90G, M-130G, M-230G, M-450G, AM-30G, AM-90G, AM-130G, AM-230G, etc. manufactured by Shin-Nakamura Chemical Co., Ltd.), methoxy (poly)propylene glycol (NKESTETR M-30PG, AM-30PG manufactured by Shin-Nakamura Chemical Co., Ltd.), lauryl (poly)ethylene glycol (meth)acrylate (BLEMMER manufactured by NOF Corporation); (PLE-1300, etc.), stearyl (meth)acrylate (poly)ethylene glycol (Blemmer PSE-1300, etc. manufactured by NOF Corporation), octyl (meth)acrylate (poly)ethylene glycol-(poly)propylene glycol (Blemmer 50POEP-800B, etc. manufactured by NOF Corporation), phenoxy (poly)ethylene glycol (meth)acrylate (NKESTER PHE-1G, AMP-30GY, etc. manufactured by Shin-Nakamura Chemical Co., Ltd.), phenoxy (poly)ethylene glycol-(poly)butylene glycol (Blemmer 43PAEP-600B, etc. manufactured by NOF Corporation), nonylphenoxy (meth)acrylate (poly)propylene glycol (Blemmer ANP-300, etc. manufactured by NOF Corporation), nonylphenoxy (meth)acrylate (poly)ethylene glycol-(poly)propylene glycol (Blemmer 75ANEP-600, etc. manufactured by NOF Corporation), etc.

[0056] These monomers may be used alone or in combination of two or more.

[0057] As the (poly)alkylene glycol chain-containing (meth)acrylate, a (poly)alkylene glycol chain-containing methacrylate is particularly preferred in order to increase the glass transition temperature of the shell-forming polymer.

[0058] The (meth) acrylate unit containing a (poly) alkylene glycol chain is used in a manner in which the proportion of the (meth) acrylate unit in the overall shell-forming polymer is 10 to 30% by weight. If the proportion is less than 10% by weight, the effect of using the (meth) acrylate containing a (poly) alkylene glycol chain cannot be fully obtained, and the coating property of the slurry on the collector cannot be fully improved. In addition, if the above proportion exceeds 30% by weight, the internal resistance of the lithium-ion battery cannot be significantly reduced. Preferably, it is 10 to 25% by weight, more preferably 10 to 20% by weight, and particularly preferably 10 to 15% by weight.

[0059] In addition to the above-mentioned methacrylic acid and the above-mentioned (meth)acrylate containing a (poly)alkylene glycol chain, the monomers forming the above-mentioned shell-forming polymer are not particularly limited, and examples thereof include (meth)acrylic acid monomers, aromatic vinyl monomers, etc. It should be noted that in the present application, "(meth)acrylic acid" is a term used to collectively refer to acrylic acid and methacrylic acid. In addition, a carboxyl group-containing vinyl monomer other than the methacrylic acid unit can be used in combination with the methacrylic acid and / or (meth)acrylate containing a (poly)alkylene glycol chain unit.

[0060] The (meth)acrylic monomer is not particularly limited, and examples thereof include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; (meth)acrylates containing aromatic rings such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; glycidyl (meth)acrylate, glycidyl alkyl (meth)acrylate; alkoxy (meth)alkyl acrylate; (meth)acrylonitrile, substituted (meth)acrylonitrile, and (meth)acrylamide. Among them, alkyl (meth)acrylates are preferred, and alkyl methacrylates are particularly preferred. The (meth)acrylic monomer may be used alone or in combination of two or more.

[0061] The aromatic vinyl compound is not particularly limited, and examples thereof include unsubstituted vinyl aromatic compounds such as styrene and 2-vinylnaphthalene; substituted vinyl aromatic compounds such as α-methylstyrene; cycloalkylated vinyl aromatic compounds such as 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene; cycloalkoxylated vinyl aromatic compounds such as 4-methoxystyrene and 4-ethoxystyrene; ring-halogenated vinyl aromatic compounds such as 2-chlorostyrene and 3-chlorostyrene; cyclic ester-substituted vinyl aromatic compounds such as 4-acetoxystyrene; and ring-hydroxylated vinyl aromatic compounds such as 4-hydroxystyrene. Among them, substituted or unsubstituted styrene is preferred, styrene and / or α-methylstyrene is more preferred, and styrene is particularly preferred. The aromatic vinyl compound may be used alone or in combination of two or more.

[0062] From the viewpoint of increasing the glass transition temperature of the shell-forming polymer and reducing the internal resistance of the lithium-ion battery, the shell-forming polymer preferably contains an alkyl methacrylate unit and an aromatic vinyl compound unit in addition to the methacrylic acid unit and / or the (meth)acrylate unit containing a (poly)alkylene glycol chain. The number of carbon atoms in the alkyl methacrylate unit is not particularly limited, but is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2.

[0063] Furthermore, in order to have good electrolyte resistance and improve the charge and discharge characteristics of lithium ion batteries, the proportion of the aromatic vinyl compound unit in the shell-forming polymer as a whole is preferably 30 to 95% by weight, more preferably 50 to 85% by weight, and further preferably 60 to 75% by weight. In addition, from the viewpoint of promoting the polymerization reaction of the shell-forming polymer, the dispersibility of the core-shell particles in the slurry, and the coating property of the slurry on the collector, the proportion of the alkyl methacrylate unit in the shell-forming polymer as a whole is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and further preferably 15 to 40% by weight.

[0064] From the viewpoint of the dispersibility of the core-shell particles in the slurry and the coating property of the slurry to the collector, the shell is preferably composed of a non-crosslinked polymer. The non-crosslinked polymer refers to a polymer that does not include a crosslinked structure and does not include a structural unit from a crosslinkable monomer, and refers to a polymer that does not belong to a rubber elastic body (such as butadiene rubber, styrene-butadiene rubber, acrylic rubber, etc.).

[0065] From the viewpoint of being easy to maintain the shape of the core-shell particles in the formed electrode active material layer and reducing the internal resistance of the lithium ion battery, the glass transition temperature (Tg) of the shell-forming polymer is preferably 60° C. or more, more preferably 80° C. or more, further preferably 90° C. or more, and particularly preferably 100° C. or more. The upper limit is not particularly limited, and may be, for example, 120° C. or less, and preferably 110° C. or less.

[0066] The glass transition temperature of the shell-forming polymer can be controlled by changing the type and ratio of the monomers constituting the polymer. For example, by using methacrylic monomers and aromatic vinyl monomers as monomers constituting the shell-forming polymer, the glass transition temperature of the polymer can be increased.

[0067] The glass transition temperature can be measured using a differential scanning calorimeter (DSC).

[0068] The content of the shell layer in the core-shell particles is not particularly limited, but is preferably 5 to 50 wt %, more preferably 10 to 40 wt %, and further preferably 20 to 35 wt % from the viewpoint of improved adhesion, reduced internal resistance, and capacity maintenance after charge and discharge (cycle characteristics).

[0069] The core-shell particles may be composed of only a core and a shell layer, but as long as the effect of the invention is achieved, an intermediate layer may be further provided between the core and the shell layer. The intermediate layer is a layer composed of a polymer, preferably graft-bonded to the core layer. When such an intermediate layer is provided, the intermediate layer covers at least a portion of the surface of the core layer, and the shell layer covers at least a portion of the surface of the intermediate layer.

[0070] (Volume average particle size of core-shell particles)

[0071] The particle size of the core-shell particles is not particularly limited, for example, the volume average particle size can be about 10 to 1000 nm. However, from the viewpoints of the dispersibility of the core-shell particles in the slurry, the miscibility of the core-shell particles with the thickener, and the reduction of the internal resistance of the lithium-ion battery, the volume average particle size is preferably 120 to 500 nm, more preferably 150 to 400 nm, and further preferably 180 to 300 nm. It should be noted that the volume average particle size of the core-shell particles can be measured in the state of the latex of the core-shell particles by using a particle size measuring device. The particle size of the core-shell particles can be controlled by the type, amount, polymerization temperature, polymerization time, etc. of the polymerization initiator, chain transfer agent, redox agent, emulsifier, etc. used during polymerization.

[0072] (Method for producing polymer particles)

[0073] The method for producing the polymer particles is not particularly limited, and for example, emulsion polymerization, miniemulsion polymerization, microemulsion polymerization, and emulsifier-free (soap-free) emulsion polymerization can be used.

[0074] The emulsifier that can be used in the emulsion polymerization is not particularly limited, and anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used. In addition, dispersants such as polyvinyl alcohol, alkyl-substituted cellulose, polyvinyl pyrrolidone, and polyacrylic acid derivatives can also be used in combination.

[0075] The anionic surfactant in the emulsifier is not particularly limited, and examples thereof include the following compounds: potassium laurate, coconut fatty acid potassium, potassium myristic acid, potassium oleate, potassium oleate diethanolamine salt, sodium oleate, potassium palmitate, potassium stearate, sodium stearate, mixed fatty acid sodium soap, semi-solidified tallow fatty acid sodium soap, castor oil potassium soap and other fatty acid soaps; sodium lauryl sulfate, higher alcohol sodium sulfate, triethanolamine lauryl sulfate, ammonium lauryl sulfate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl ether triethanolamine sulfate, polyoxyethylene alkylphenyl ether sodium sulfate, 2-ethylhexyl Alkyl sulfate ester salts such as sodium alkyl sulfate; sodium alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate; dialkyl sulfosuccinates such as sodium di-2-ethylhexyl sulfosuccinate; sodium alkylnaphthalene sulfonate; sodium alkyl diphenyl ether disulfonate; potassium alkyl phosphates; phosphate ester salts such as sodium polyoxyethylene lauryl ether phosphate; sodium salt of naphthalenesulfonic acid formalin condensate; polycarboxylic acid type polymer anions; sodium acyl (tallow) methyl taurate; sodium acyl (coconut) methyl taurate; sodium cocoyl isethionate; sodium salt of α-sulfo fatty acid ester; sodium amide ether sulfonate; oleyl sarcosine; sodium lauroyl sarcosinate; rosin acid soap, etc.

[0076] The nonionic surfactant in the above-mentioned emulsifier is not particularly limited, and examples thereof include the following compounds: polyoxyethylene alkyl allyl ethers or polyoxyethylene alkyl ethers such as polyoxyethylene nonylphenyl ether, polyoxyethylene oleyl ether, and polyoxyethylene lauryl ether, polyoxyethylene sorbitan esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan monostearate, polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, and polyethylene glycol monooleate, and oxyethylene / oxypropylene block copolymers.

[0077] The cationic surfactant in the above-mentioned emulsifier is not particularly limited, and examples thereof include the following compounds: alkylamine salts such as coconut amine acetate, stearylamine acetate, octadecylamine acetate, and tetradecylamine acetate; quaternary ammonium salts such as lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, distearyldimethylammonium chloride, alkylbenzyldimethylammonium chloride, hexadecyltrimethylammonium chloride, and behenyltrimethylammonium chloride; and the like.

[0078] The amphoteric surfactant in the emulsifier is not particularly limited, and examples thereof include the following compounds: alkyl betaines such as lauryl betaine, stearyl betaine, and dimethyl lauryl betaine; sodium lauryl diaminoethyl glycinate; amide betaine; imidazoline; lauryl carboxymethyl hydroxyethyl imidazole Betaine, etc.

[0079] These emulsifiers may be used alone or in combination of two or more. Among the emulsifiers, sodium dialkyl sulfosuccinate or a surfactant having an oxyethylene structure is preferred from the viewpoint of improving the fluidity of the obtained latex, and sodium polyoxyethylene lauryl ether phosphate is particularly preferred.

[0080] When the emulsion polymerization method is used, a known polymerization initiator, ie, 2,2'-azobisisobutyronitrile, hydrogen peroxide, potassium persulfate, ammonium persulfate, etc., can be used as a thermal decomposition type initiator.

[0081] In addition, it is also possible to use a redox initiator which uses in combination at least one of organic peroxides such as tert-butyl peroxyisopropyl carbonate, para-menthane hydroperoxide, cumene hydroperoxide, diisopropylbenzene peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, and tert-hexyl peroxide; peroxides such as inorganic peroxides such as hydrogen peroxide, potassium persulfate, and ammonium persulfate; and a reducing agent such as formaldehyde sulfoxylate and glucose; a transition metal salt such as iron (II) sulfate; a chelating agent such as disodium ethylenediaminetetraacetic acid; and a phosphorus-containing compound such as sodium pyrophosphate.

[0082] When a redox initiator is used, polymerization can be carried out even at a low temperature where the above-mentioned peroxide does not substantially undergo thermal decomposition, and the polymerization temperature can be set within a wide range, so it is preferred. Among them, organic peroxides such as cumene hydroperoxide, diisopropylbenzene peroxide, and tert-butyl hydroperoxide are preferably used as redox initiators. The amount of the above-mentioned initiator used and the amount of the above-mentioned reducing agent, transition metal salt, chelating agent, phosphorus-containing compound, etc. used when the redox initiator is used can be used within a known range. In addition, when polymerizing a multifunctional monomer, a known chain transfer agent can be used within a known range. In addition, a surfactant can be used, but this is also a known range.

[0083] As the solvent used in the emulsion polymerization, any solvent may be used as long as the emulsion polymerization can be stably carried out, and for example, water or the like can be preferably used.

[0084] The temperature during emulsion polymerization is not particularly limited as long as the emulsifier is uniformly dissolved in the solvent, and is, for example, 40 to 75°C, preferably 45 to 70°C, and more preferably 49 to 65°C.

[0085] When the core-shell particles are produced by emulsion polymerization, for example, a latex of the core-shell particles is spray-dried to obtain a powder that can be redispersed in water, and the powder can be used as an electrode binder.

[0086] The electrode binder of this embodiment may be in the form of a latex of the core-shell particles or in the form of a powder of the core-shell particles. The electrode binder is preferably in the form of a latex of the core-shell particles because of its excellent dispersibility in the slurry.

[0087] <Other ingredients>

[0088] The electrode binder of the present embodiment may also contain components such as a conductive aid, a reinforcing material, a leveling agent, a viscosity modifier, and an electrolyte additive in addition to the above-mentioned core-shell particles. These components are not particularly limited as long as they do not affect the battery reaction, and known components, such as those described in International Publication No. 2012 / 115096, may be used. In addition, these components may be used only one, or two or more may be used in combination.

[0089] (Water-based slurry)

[0090] The electrode binder of this embodiment, the electrode active material, the thickener and the aqueous medium are mixed to prepare an aqueous slurry. The aqueous slurry is applied to the surface of the current collector and dried to form an electrode active material layer on the current collector.

[0091] <Amount of core-shell particles in slurry>

[0092] The amount of the core-shell particles in the slurry can be appropriately set by a person skilled in the art, but from the viewpoint of improving the coating property of the slurry on the collector, the adhesion between the collector and the electrode active material layer, improving the charge and discharge characteristics of the lithium ion battery and reducing the internal resistance, the amount is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 parts by weight, and further preferably 0.5 to 2 parts by weight relative to 100 parts by weight of the electrode active material.

[0093] <Thickener>

[0094] Thickener is a component that can improve the dispersion stability of the electrode active material in the water-based slurry and improve the coating property of the slurry. As a thickener, a water-soluble polymer can be used, specifically, carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polycarboxylic acid, their salts, poly (meth) acrylic acid amide, etc. can be used. And, as polycarboxylic acid, polyacrylic acid, polymethacrylic acid, alginic acid, etc. can be cited. As these water-soluble polymers, only one can be used, or two or more can be used. Among them, a cellulose-based compound is preferred, and carboxymethyl cellulose or its salt is particularly preferred.

[0095] The amount of the thickener in the aqueous slurry can be appropriately set, and is, for example, preferably 0.1 to 5 parts by weight, more preferably 0.3 to 3 parts by weight, and even more preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the electrode active material.

[0096] <Negative electrode active material>

[0097] Examples of the electrode active material that can be used in the negative electrode include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials obtained by combining these.

[0098] Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

[0099] Examples of the carbonaceous material include graphitized carbon whose carbon structure is easily changed by heat treatment temperature, and non-graphitized carbon having a structure close to an amorphous structure such as glassy carbon.

[0100] Examples of graphitizable carbon include carbon raw materials made from tar pitch obtained from petroleum or coal, and specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers.

[0101] Examples of the non-graphitizable carbon include phenolic resin fired products, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin fired products (PFA), and hard carbon.

[0102] Examples of the graphite material include graphites such as natural graphite and artificial graphite.

[0103] As metal-based negative electrode active materials, for example, lithium metal, single metals that can form lithium alloys (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc., can be cited. Among them, active materials containing silicon (silicon-based negative electrode active materials) are preferred. By using silicon-based negative electrode active materials, the capacity of lithium ion batteries can be increased.

[0104] Examples of the silicon-based negative electrode active material include silicon (Si), alloys containing silicon, SiO, SiO x , a composite of a Si-containing material and conductive carbon obtained by coating or composite the Si-containing material with conductive carbon, etc. It should be noted that these silicon-based negative electrode active materials may be used alone or in combination of two or more.

[0105] Examples of the alloy containing silicon include alloy compositions containing silicon, transition metals such as aluminum and iron, and further containing rare earth elements such as tin and yttrium.

[0106] SiO x It is a compound containing Si and at least one of SiO and SiO2, and x is usually greater than or equal to 0.01 and less than 2.

[0107] As a composite of Si-containing material and conductive carbon, for example, a compound obtained by heat-treating a pulverized mixture of polymers such as SiO, polyvinyl alcohol, and any carbon raw material in an atmosphere containing organic gas and / or steam. In addition, it can also be obtained by the following well-known methods: a method of coating the surface of SiO particles by chemical vapor deposition using organic gas, etc., a method of composite particleization (granulation) of SiO particles and graphite or artificial graphite by mechanochemical method.

[0108] <Positive electrode active material>

[0109] As the electrode active material that can be used in the positive electrode, there can be mentioned compounds containing transition metals, such as transition metal oxides, transition metal sulfides, composite metal oxides of lithium and transition metals, etc. It should be noted that as transition metals, for example, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc. can be mentioned.

[0110] Here, examples of transition metal oxides include MnO, MnO2, V2O5, V6O 13 , TiO2, Cu2V2O3, amorphous V2O-P2O5, amorphous MoO3, amorphous V2O5, amorphous V6O 13 wait.

[0111] Examples of transition metal sulfides include TiS2, TiS3, amorphous MoS2, and FeS.

[0112] Examples of the composite metal oxide of lithium and a transition metal include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

[0113] As lithium-containing composite metal oxides having a layered structure, for example, there can be mentioned lithium-containing cobalt oxide (LiCoO2), lithium-containing nickel oxide (LiNiO2), Co-Ni-Mn lithium-containing composite oxides, Ni-Mn-Al lithium-containing composite oxides, Ni-Co-Al lithium-containing composite oxides, solid solutions of LiMaO2 and Li2MbO3, etc.

[0114] Examples of lithium-containing composite metal oxides having a spinel structure include lithium manganate (LiMn 2 O 4 ) and compounds obtained by replacing a portion of Mn in lithium manganate (LiMn 2 O 4 ) with other transition metals.

[0115] Examples of the lithium-containing composite metal oxide having an olivine structure include olivine-type lithium iron phosphate (LiFePO 4 ) and olivine-type lithium manganese phosphate (LiMnPO 4 ).

[0116] <Conductive additive>

[0117] The slurry may be mixed with any conductive additive. The conductive additive is not particularly limited, and known conductive additives may be used. Specifically, conductive carbon raw materials such as acetylene black, Ketjen black (registered trademark), carbon black, and graphite; and fibers and foils of various metals may be cited.

[0118] <Other polymers>

[0119] The slurry may contain any polymer other than the core-shell particles and thickener. Examples of such polymers include fluorine-containing polymers and acrylonitrile polymers.

[0120] The solid content concentration of the slurry is not particularly limited, and may be, for example, about 10 to 80% by weight, and preferably 30 to 70% by weight.

[0121] <Preparation of slurry>

[0122] The slurry can be prepared by dispersing the above components in an aqueous medium. Specifically, the slurry can be prepared by mixing the above components with the aqueous medium using a ball mill, a sand mill, a bead mill, a pigment disperser, a grinding stirrer, an ultrasonic disperser, a homogenizer, a planetary mixer, a filmix or other mixer. The mixing of the above components with the aqueous medium can usually be carried out at room temperature to 80° C. for 10 minutes to several hours.

[0123] As the aqueous medium, water can be generally used, but an aqueous solution of any compound, a mixed solution of a small amount of an organic medium and water, etc. can also be used. It should be noted that the water contained in the slurry can also include water contained in the latex when the electrode binder is a latex of core-shell particles, water contained in the thickener, etc.

[0124] (Electrodes for lithium-ion batteries)

[0125] The lithium ion battery electrode of the present embodiment comprises a current collector and an electrode active material layer formed on the current collector. The electrode active material layer comprises at least an electrode active material, a thickener and core-shell particles. The lithium ion battery electrode of the present embodiment can be obtained by applying the above-mentioned aqueous slurry on the current collector and drying it.

[0126] As the current collector, a known metal foil can be used, and examples thereof include copper foil, aluminum foil, nickel foil, and highly conductive stainless steel foil.

[0127] The core-shell particles of the present embodiment have a strong tendency to maintain the particle shape in the electrode active material layer after drying. Thus, the bonding of electrode active materials to each other or the bonding of electrode active materials to collectors can be achieved by point bonding, and as a result, the movement of lithium ions is not easily hindered due to the presence of the binder, so it is inferred that the reduction of internal resistance can be achieved.

[0128] [Coating process]

[0129] As the method for applying the water-based slurry on the collector, it is not particularly limited, and known methods can be used, specifically, a doctor blade method, an immersion method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, etc. can be cited. At this time, the slurry can be applied only on one side of the collector, or on both sides. The thickness of the slurry film on the collector before drying after coating can be appropriately set according to the thickness of the electrode active material layer obtained by drying.

[0130] [Drying process]

[0131] The method for drying the slurry film on the current collector is not particularly limited, and a known method can be used. Examples of the method include drying using warm air, hot air, or low-humidity air, vacuum drying, and drying using irradiation with infrared rays, electron beams, or the like.

[0132] After the drying step, the electrode active material layer may be subjected to a press treatment using a die press or a roll press, etc. This can improve the adhesion between the electrode active material layer and the current collector and reduce the porosity of the electrode active material layer.

[0133] In addition, the lithium ion battery electrode of the present embodiment can also be manufactured by a powder molding method. In the powder molding method, the above-mentioned slurry is first prepared, composite particles are prepared from the slurry, the composite particles are supplied to the collector, and roll-pressed and molded as desired, thereby forming an electrode active material layer on the collector.

[0134] The lithium ion battery electrode according to a preferred embodiment of the present embodiment is a negative electrode for a lithium ion battery.

[0135] (Lithium-ion battery)

[0136] The lithium ion battery of this embodiment comprises a positive electrode, a negative electrode, an electrolyte and a separator, and at least one of the positive electrode and the negative electrode (particularly the negative electrode) uses the electrode for the lithium ion battery of this embodiment. When the negative electrode is the electrode for the lithium ion battery of this embodiment, the positive electrode is not particularly limited and can be a known positive electrode.

[0137] <Electrolyte>

[0138] As the electrolyte, for example, a non-aqueous electrolyte in which a supporting electrolyte is dissolved in a non-aqueous solvent can be used. As the supporting electrolyte, a lithium salt can usually be used. As the lithium salt, for example, LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, etc. can be cited. Among them, LiPF6, LiClO4, CF3SO3Li are preferred. These can be used alone or in combination of two or more.

[0139] As a non-aqueous solvent, there is no particular limitation as long as it can dissolve the supporting electrolyte. If examples of non-aqueous solvents are given, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (MEC) can be cited; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as cyclopentane and dimethyl sulfoxide; etc. Among them, carbonates are preferred because of their high dielectric constant and wide stable potential region. The non-aqueous solvent can be used alone or in combination of two or more in any ratio.

[0140] The electrolyte solution may contain an additive. Examples of the additive include carbonate compounds such as vinylene carbonate (VC).

[0141] In addition, as electrolyte solutions other than the above, for example, polymer electrolytes such as polyethylene oxide and polyacrylonitrile; gel polymer electrolytes in which the above polymer electrolytes are impregnated with an electrolyte solution; inorganic solid electrolytes such as LiI and Li3N; and the like can be used.

[0142] <Isolator>

[0143] The separator is not particularly limited, and a microporous film made of a polyolefin-based resin (polyethylene, polypropylene, polybutylene, polyvinyl chloride) as an insulating material can be used.

[0144] <Manufacturing method of lithium-ion battery>

[0145] As a specific manufacturing method of the lithium-ion battery of this embodiment, for example, the following method can be cited: overlap the positive electrode and the negative electrode through the separator, wind and fold them according to the shape of the battery, put them into a battery container, inject electrolyte into the battery container, and seal it. Furthermore, porous metal mesh, fuses, PTC elements and other overcurrent protection elements, guide plates, etc. can also be placed as needed to prevent the pressure inside the battery from rising and overcharging and discharging. The shape of the lithium-ion battery can be any of coin-shaped, button-shaped, sheet-shaped, cylindrical, square, flat, etc.

[0146] In the following items, preferred embodiments of the present disclosure are listed, but the present invention is not limited to the following items.

[0147] [Project 1]

[0148] An electrode adhesive is an electrode adhesive for lithium ion batteries.

[0149] A core-shell particle comprising a core and a shell layer located outside the core,

[0150] The core is made of rubber.

[0151] The shell layer is composed of a shell-forming polymer containing at least one selected from methacrylic acid units and (meth)acrylate units containing (poly)alkylene glycol chains,

[0152] The content ratio of the methacrylic acid unit in the shell-forming polymer is 5 to 40% by weight, or the content ratio of the (poly)alkylene glycol chain-containing (meth)acrylate unit in the shell-forming polymer is 10 to 30% by weight.

[0153] [Project 2]

[0154] The binder for an electrode according to item 1, wherein the content ratio of the methacrylic acid unit in the shell-forming polymer is 20% by weight or less.

[0155] [Item 3]

[0156] The binder for an electrode according to item 1 or 2, wherein the shell-forming polymer further comprises an alkyl methacrylate unit and an aromatic vinyl compound unit.

[0157] [Item 4]

[0158] The binder for an electrode according to item 3, wherein the content ratio of the aromatic vinyl compound unit in the shell-forming polymer is 30 to 95% by weight.

[0159] [Item 5]

[0160] The binder for an electrode according to any one of items 1 to 4, wherein the shell-forming polymer has a glass transition temperature of 60° C. or higher.

[0161] [Item 6]

[0162] The binder for an electrode according to any one of items 1 to 5, wherein the shell-forming polymer is a non-crosslinked polymer.

[0163] [Item 7]

[0164] The binder for an electrode according to any one of items 1 to 6, wherein the rubber contains an aliphatic conjugated diene compound unit and an aromatic vinyl compound unit.

[0165] [Item 8]

[0166] The binder for an electrode according to any one of items 1 to 7, wherein the rubber has a glass transition temperature of -30°C to +15°C.

[0167] [Item 9]

[0168] The binder for an electrode according to any one of items 1 to 8, wherein the ratio of the core to the entire core-shell particles is 50 to 95% by weight.

[0169] [Item 10]

[0170] The binder for an electrode according to any one of items 1 to 9, wherein the core-shell particles have a volume average particle size of 120 nm or more.

[0171] [Item 11]

[0172] The binder for an electrode according to any one of items 1 to 10, wherein the binder for an electrode is a latex of the core-shell particles.

[0173] [Item 12]

[0174] A method for manufacturing an electrode of a lithium ion battery, comprising:

[0175] A step of preparing a slurry containing an electrode active material, a thickener, and the electrode binder according to any one of items 1 to 11, and

[0176] A step of applying the slurry to a current collector and drying the slurry.

[0177] [Item 13]

[0178] An electrode for a lithium ion battery comprises a current collector and an electrode active material layer formed on the current collector, wherein the electrode for the lithium ion battery comprises:

[0179] The electrode active material layer includes an electrode active material, a thickener, and the electrode binder according to any one of items 1 to 12.

[0180] [Item 14]

[0181] A lithium-ion battery comprising the electrode described in item 13.

[0182] Example

[0183] The present invention is further specifically described with reference to the following examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" refer to "parts by weight" and "% by weight" respectively.

[0184] (Example 1)

[0185] (Formation of the core)

[0186] 10 g of disodium hydrogen phosphate (solid content 10%) was added to 90 g of deionized water, and a solution prepared by dissolving 0.237 g of ferrous sulfate (FeSO4·7H2O) and 0.395 g of disodium ethylenediaminetetraacetate in 125.8 g of deionized water was further added, and deoxygenation was performed at -0.01 MPa for 15 minutes.

[0187] 66.7 g of NEOPELEX G-15 (manufactured by Kao Corporation: sodium dodecylbenzenesulfonate, solid content 15.0%), 11000 g of butadiene, 9000 g of styrene, and 150 g of tert-dodecyl mercaptan were placed in a 100 L pressure-resistant autoclave, and the temperature was raised to 50°C.

[0188] 140.0 g of sodium formaldehyde sulfoxylate (solid content 5%) and 7.7 g of p-menthane hydroperoxide (solid content 52%) were added to initiate polymerization.

[0189] At 15 hours after the start of the polymerization, the mixture was degassed under reduced pressure to remove butadiene remaining unused in the polymerization, thereby completing the polymerization. A latex containing styrene-butadiene rubber particles (solid content: 45.0%) was obtained.

[0190] During the polymerization, sodium formaldehyde sulfoxylate, p-menthane hydroperoxide, ferrous sulfate (FeSO4·7H2O) and disodium ethylenediaminetetraacetate were added into a 100 L pressure-resistant autoclave in any amount and at any time.

[0191] (Shell Formation)

[0192] 2333.3 g of the obtained rubber latex (solid content 45.0%) was put into an 8 L polymerizer, and 60.0 g of sodium formaldehyde sulfoxylate (solid content 5%) was added. A mixture of 300.0 g (20 parts) of styrene, 112.5 g (7.5 parts) of methyl methacrylate, 37.5 g (2.5 parts) of methacrylic acid, and 3.3 g of tert-butyl hydroperoxide (solid content 69%) was added to the above polymerizer over 120 minutes.

[0193] Sodium formaldehyde sulfoxylate and tert-butyl hydroperoxide were appropriately added, and polymerization was completed after 80 minutes to obtain a latex containing core-shell structured polymer particles with a conversion rate of 100%, a solid content concentration of 48.0% and a volume average particle size of 200 nm.

[0194] In addition, the volume average particle diameter is measured in the said latex using the nanoparticle diameter measuring apparatus NANOTRAC WAVE manufactured by Microtrac.

[0195] (Examples 2 to 18 and Comparative Examples 2 to 5)

[0196] A latex of core-shell structured polymer particles was obtained in the same manner as in Example 1 except that the volume average particle size of the core-shell particles or the type or amount of the monomers of the core and shell layers was changed as described in Table 1 or 2. The volume average particle size was controlled by adjusting the amount of the emulsifier at the start of polymerization.

[0197] (Comparative Example 1)

[0198] (Polymerization of polymer particles)

[0199] 10 g of disodium hydrogen phosphate (solid content 10%) was added to 90 g of deionized water, and a solution prepared by dissolving 0.237 g of ferrous sulfate (FeSO4·7H2O) and 0.395 g of disodium ethylenediaminetetraacetate in 125.8 g of deionized water was further added, and deoxygenation was performed at -0.01 MPa for 15 minutes.

[0200] 66.7 g of NEOPELEX G-15 (manufactured by Kao Corporation: sodium dodecylbenzenesulfonate, solid content 15.0%), 9350 g of butadiene, 10400 g of styrene, 250 g of methacrylic acid and 150 g of tert-dodecyl mercaptan were placed in a 100 L pressure-resistant autoclave and heated to an internal temperature of 50°C.

[0201] 140.0 g of sodium formaldehyde sulfoxylate (solid content 5%) and 7.7 g of p-menthane hydroperoxide (solid content 52%) were added to initiate polymerization.

[0202] At 15 hours after the start of the polymerization, the polymerization was terminated by degassing under reduced pressure to remove the remaining butadiene not used in the polymerization. A latex (solid content: 45.0%) containing styrene-butadiene rubber particles containing methacrylic acid units was obtained.

[0203] During the polymerization, sodium formaldehyde sulfoxylate, p-menthane hydroperoxide, ferrous sulfate (FeSO4·7H2O) and disodium ethylenediaminetetraacetate were added into a 100 L pressure-resistant autoclave in any amount and at any time.

[0204] (Preparation of negative electrode slurry)

[0205] Into a stirring degassing machine (manufactured by Thinky Co., Ltd., trade name "Awatori-Rentaro"), 1 part by weight (solid content conversion) of a thickener (trade name "CMC2200", manufactured by Daicel Co., Ltd.), 100 parts by weight (solid content conversion) of graphite as a negative electrode active material, and 100 parts by weight of water were added, and stirred and mixed at 2000 rpm for 5 minutes. Then, 1 part by weight (solid content conversion) of the polymer particles synthesized in each embodiment or comparative example was added, and further stirred and mixed at 2000 rpm for 5 minutes, and then deaerated and mixed at 2200 rpm for 1 minute to obtain a negative electrode slurry with a solid content concentration of 50%.

[0206] (Fabrication of Negative Electrode)

[0207] The negative electrode slurry was evenly applied on the surface of a current collector made of 17 μm thick copper foil by a doctor blade method so that the film thickness after drying was 80 μm, and vacuum dried at 80°C for 6 hours. 2 The negative electrode is obtained by pressing the negative electrode active material layer on the surface of the collector using a roller press.

[0208] (Evaluation of coating properties)

[0209] The surface of the negative electrode active material layer after drying was visually observed, and the coating properties were evaluated based on the following criteria.

[0210] ○: No streaks or spots were observed on the surface of the negative electrode active material layer.

[0211] Δ: No streaks were observed on the surface of the negative electrode active material layer, but spots were observed.

[0212] ×: Streaks and spots were observed on the surface of the negative electrode active material layer.

[0213] (Preparation of positive electrode slurry)

[0214] Into a stirring degassing machine (manufactured by Thinky Co., Ltd., trade name "Awatori-Rentaro"), 4 parts by weight of polyvinylidene fluoride (converted on a solid content basis), 4 parts by weight of acetylene black (converted on a solid content basis), 100 parts by weight of LiCoO2 (converted on a solid content basis) having a volume average particle size of 15 μm as a positive electrode active material, and 46 parts by weight of N-methylpyrrolidone were added, the mixture was stirred and mixed at 2000 rpm for 10 minutes, and then deaerated and mixed at 2200 rpm for 1 minute to obtain a positive electrode slurry having a solid content concentration of 70%.

[0215] (Fabrication of positive electrode)

[0216] The positive electrode slurry was evenly applied on the surface of a current collector made of aluminum foil with a thickness of 15 μm by a doctor blade method so that the film thickness after drying was 80 μm, and vacuum dried at 80°C for 6 hours. 2 The positive electrode is obtained by pressing the positive electrode active material layer on the surface of the collector using a roller press.

[0217] (Assembly of lithium-ion batteries)

[0218] A single-layer polypropylene separator (65 mm in width, 500 mm in length, 20 μm in thickness; produced by a dry process; porosity 60%) was prepared and cut into a 3 cm×3 cm square. In addition, an aluminum outer package was prepared as an outer package for the battery.

[0219] Then, in a glove box that has been substituted with Ar at a dew point of less than -80°C, the positive electrode prepared as described above is cut into a 2 cm × 2 cm square and arranged so that the surface on the collector side contacts the outer package of the aluminum package. Next, a square separator is arranged on the surface of the positive electrode active material layer side. Furthermore, the negative electrode prepared as described above is cut into a 2.2 cm × 2.2 cm square and arranged on the separator so that the surface on the negative electrode active material layer side faces the separator. Then, a LiPF6 solution with a concentration of 1.0 M as an electrolyte is filled (the solvent is a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3 / 7 (volume ratio), and 2 volume % (solvent ratio) of vinylene carbonate is added as an additive). Furthermore, in order to seal the opening of the outer package of the aluminum package, heat sealing at 150°C is performed to seal the outer package of the aluminum package to manufacture a laminated single cell type lithium ion secondary battery.

[0220] (Negative electrode peeling test)

[0221] The negative electrode prepared as described above was cut into a rectangle with a length of 30 mm and a width of 15 mm to prepare a test piece, and a transparent tape (transparent tape specified in JIS Z1522) was pasted on the surface of the negative electrode active material layer so that the negative electrode active material layer was facing upward, and one end of the collector was stretched and peeled off at a tensile speed of 37.5 mm / min in the vertical direction, and the stress at this time was measured. The measurement was performed 3 times, and the average value was obtained and used as the T-peel strength.

[0222] (Charge and discharge cycle characteristics)

[0223] The laminated single cell type lithium ion secondary battery prepared as described above was left to stand for 12 hours after being filled with LiPF6 solution, and was charged to 4.2V and discharged to 2.5V for 20 cycles at 25°C by a 0.2C constant current method. At this time, the capacity of the first cycle, i.e., the initial discharge capacity X1, and the discharge capacity X20 at the time of 20 cycles were measured. As the cycle characteristics, the capacity retention rate shown by the charge and discharge cycle characteristics = X20 / X1×100(%) was obtained.

[0224] (DC resistance measurement during charge and discharge)

[0225] The laminated single cell type lithium ion secondary battery prepared as described above is charged at a current of 0.2C for 2.5 hours at 25°C, and the depth of charge (charging rate (SOC) 50%) is adjusted. Stop for 1 hour, measure the open circuit voltage (OCV) after 1 hour, and calculate the DC resistance (charging DCR) based on the voltage change during the stop. In addition, the discharge DCR is charged at a current of 0.1C for 10 hours at 25°C, stop for 1 hour, and discharge at a current of 0.1C for 0.5 hours to adjust the depth of charge (charging rate (SOC) 90%). Stop for 1 hour, measure the open circuit voltage (OCV) after 1 hour, and calculate the DC resistance (discharging DCR) based on the voltage change during the stop.

[0226] Table 1 or 2 shows the evaluation results described above.

[0227]

[0228]

[0229] As shown in Tables 1 and 2, in Examples 1 to 18 using core-shell particles including a core made of rubber and a shell layer containing 5 to 40 wt % of methacrylic acid units as an electrode binder, coating properties on a current collector were good and low resistance values ​​were exhibited.

[0230] On the other hand, in Comparative Example 1 using polymer particles having no shell layer and containing methacrylic acid units in the rubber, although coating properties were good, the particles showed a higher resistance value than those in the Examples.

[0231] In Comparative Examples 2 and 3 using core-shell particles having a core-shell structure but containing no methacrylic acid unit in the shell layer or containing a low proportion of the methacrylic acid unit, the coating properties on the current collector were insufficient compared with the Examples.

[0232] In Comparative Examples 4 and 5, in which core-shell particles were prepared using a carboxyl group-containing monomer such as acrylic acid or itaconic acid instead of methacrylic acid in the shell layer, the coating properties on the current collector were also insufficient.

[0233] (Example 19)

[0234] (Formation of the core)

[0235] In the same manner as in Example 1, a latex (solid content: 45.0%) containing styrene-butadiene rubber particles was obtained.

[0236] (Shell Formation)

[0237] 2266.7 g of the obtained rubber latex (solid content 45.0%) was put into an 8L polymerizer, and 30.0 g of sodium formaldehyde sulfoxylate (solid content 5%) was added. A mixture of 117.0 g (9.75 parts) of styrene, 42 g (3.5 parts) of methyl methacrylate, 21.0 g (1.75 parts) of polyoxyethylene monomethacrylate (PEO-MMA, degree of polymerization 4.5) and 1.7 g of tert-butyl hydroperoxide (solid content 69%) was added to the above polymerizer over 60 minutes.

[0238] Sodium formaldehyde sulfoxylate and tert-butyl hydroperoxide were appropriately added, and polymerization was completed after 80 minutes to obtain a latex containing core-shell structured polymer particles with a conversion rate of 100%, a solid content concentration of 48.0% and a volume average particle size of 200 nm.

[0239] In addition, the volume average particle diameter is measured in the said latex using the nanoparticle diameter measuring apparatus NANOTRAC WAVE manufactured by Microtrac.

[0240] (Examples 20 to 23 and Comparative Examples 7 to 8)

[0241] As described in Table 3, except that the types or usage amounts of the monomers of the core part and the shell layer were changed, a latex containing polymer particles having a core-shell structure was obtained in the same manner as in Example 19.

[0242] (Comparative Example 6)

[0243] (Polymerization of polymer particles)

[0244] 10 g of disodium hydrogen phosphate (solid content 10%) was added to 90 g of deionized water, and a solution prepared by dissolving 0.237 g of ferrous sulfate (FeSO4·7H2O) and 0.395 g of disodium ethylenediaminetetraacetate in 125.8 g of deionized water was further added, and deoxygenation was performed at -0.01 MPa for 15 minutes.

[0245] 66.7 g of NEOPELEX G-15 (manufactured by Kao Corporation: sodium dodecylbenzenesulfonate, solid content 15.0%), 11000 g of butadiene, 9000 g of styrene, and 150 g of tert-dodecyl mercaptan were placed in a 100 L pressure-resistant autoclave, and the temperature was raised to 50°C.

[0246] 140.0 g of sodium formaldehyde sulfoxylate (solid content 5%) and 7.7 g of p-menthane hydroperoxide (solid content 52%) were added to initiate polymerization.

[0247] At 15 hours after the start of the polymerization, the mixture was degassed under reduced pressure to remove butadiene remaining unused in the polymerization, thereby completing the polymerization. A latex containing styrene-butadiene rubber particles (solid content: 45.0%) was obtained.

[0248] During the polymerization, sodium formaldehyde sulfoxylate, p-menthane hydroperoxide, ferrous sulfate (FeSO4·7H2O) and disodium ethylenediaminetetraacetate were added into a 100 L pressure-resistant autoclave in any amount and at any time.

[0249] The above-described evaluations were performed using the polymer particles synthesized in Examples 19 to 23 or Comparative Examples 6 to 8. Table 3 shows the results.

[0250]

[0251] As shown in Table 3, in Examples 19 to 23 using core-shell particles comprising a core composed of rubber and a shell layer containing (meth)acrylate units containing a (poly)alkylene glycol chain in a range of 10 to 30 weight % as an electrode binder, the coating property on the collector is good and a low resistance value is exhibited.

[0252] On the other hand, Comparative Example 6 using polymer particles composed only of rubber and having no shell layer had insufficient coating properties on the current collector and exhibited a high resistance value compared with the respective Examples.

[0253] In Comparative Example 7 using core-shell particles having a core-shell structure but containing no (meth)acrylate units containing (poly)alkylene glycol chains in the shell layer, the coating properties on the current collector were also insufficient and the resistance value was also high.

[0254] In Comparative Example 8 using core-shell particles containing (poly)alkylene glycol chain-containing (meth)acrylate units in the shell layer but with a low content ratio, coating properties on the current collector were insufficient.

Claims

1. An electrode adhesive, which is an electrode adhesive for a lithium ion battery, The invention comprises core-shell particles, wherein the core-shell particles comprise a core and a shell layer located outside the core, The core is composed of rubber, The shell layer is composed of a shell-forming polymer, wherein the shell-forming polymer comprises at least one selected from methacrylic acid units and (meth)acrylate units containing (poly)alkylene glycol chains, The content ratio of the methacrylic acid unit in the shell-forming polymer is 5 to 40% by weight, or the content ratio of the (poly)alkylene glycol chain-containing (meth)acrylate unit in the shell-forming polymer is 10 to 30% by weight.

2. The electrode binder according to claim 1, wherein The content ratio of the methacrylic acid unit in the shell-forming polymer is 20% by weight or less.

3. The electrode binder according to claim 1 or 2, wherein The shell-forming polymer further comprises an alkyl methacrylate unit and an aromatic vinyl compound unit.

4. The electrode binder according to claim 3, wherein The content ratio of the aromatic vinyl compound unit in the shell-forming polymer is 30 to 95% by weight.

5. The electrode binder according to claim 1 or 2, wherein The shell-forming polymer has a glass transition temperature of 60° C. or higher.

6. The electrode binder according to claim 1 or 2, wherein The shell-forming polymer is a non-crosslinked polymer.

7. The electrode binder according to claim 1 or 2, wherein The rubber contains an aliphatic conjugated diene compound unit and an aromatic vinyl compound unit.

8. The electrode binder according to claim 1 or 2, wherein The glass transition temperature of the rubber is -30°C to +15°C.

9. The electrode binder according to claim 1 or 2, wherein The ratio of the core to the entire core-shell particle is 50 to 95% by weight.

10. The binder for electrodes according to claim 1 or 2, wherein The volume average particle size of the core-shell particles is greater than 120 nm.

11. The electrode binder according to claim 1 or 2, wherein The electrode binder is the latex of the core-shell particles.

12. A method for manufacturing an electrode of a lithium ion battery, comprising: A process for preparing a slurry comprising an electrode active material, a thickener and the electrode binder according to claim 1 or 2, and A step of applying the slurry to a current collector and drying the slurry.

13. An electrode for a lithium ion battery, comprising a current collector and an electrode active material layer formed on the current collector, wherein: The electrode active material layer comprises an electrode active material, a thickener, and the electrode binder according to claim 1 or 2.

14. A lithium ion battery comprising the electrode according to claim 13.

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