JP2019053942A - Method for manufacturing electrode for electrochemical device - Google Patents

Abstract

To provide a method for manufacturing an electrode for an electrochemical device, which is superior in binding force and superior in high discharge characteristic and low-temperature input and output characteristics.SOLUTION: A method for manufacturing an electrode for an electrochemical device comprises the steps of: coating a current collector with an electrode mixture for an electrochemical device, containing a particulate polymer having a glass transition temperature of 20°C or higher, an active material and water to laminate one or more mixture layers; drying the one or more mixture layers in such a way that the surface temperature of the mixture layer never exceeds 60°C until a water content of the mixture layer becomes 10% or less; and heating the current collector so that the surface temperature of the mixture layer becomes 100°C or higher.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an electrode for an electrochemical device.

  In recent years, due to the trend of respecting a decarbonized society, the accumulation of energy and the spread of electrochemical devices as a supply source are remarkable, and they are used not only in consumer applications but also in automobile applications. Performance such as input / output characteristics is required.

  Examples of a method for producing an electrode used in an electrochemical device such as a lithium ion secondary battery and a lithium ion capacitor include an active material capable of occluding, adsorbing, desorbing and releasing ions, and styrene as a binder for the electrode. A method is known in which an electrode mixture containing a particulate polymer such as butadiene rubber or acrylic rubber latex is prepared, applied to a metal material (hereinafter referred to as a current collector), and dried.

  Electrode binders are known to greatly contribute to the binding force that binds active materials to each other or to an active material and a current collector, as well as to the input / output characteristics of electrochemical devices ( Patent Document 1).

  In general, by using a particulate polymer with a high glass transition temperature as a binder for electrodes, it is possible to reduce the surface electrical resistivity of the mixture layer, resulting in high-rate discharge characteristics and low-temperature input / output It is known that an electrode having excellent characteristics can be obtained (Patent Document 2).

  The particulate polymer having a high glass transition temperature does not function as a binder unless it is dried at a higher temperature. However, when high-temperature heat drying is performed immediately after the application of the electrode mixture, segregation of the particulate polymer occurs and a uniform electrode cannot be obtained.

International Publication WO2017 / 029902

JP2011-154981A

  An object of this invention is to provide the manufacturing method of the electrode for electrochemical devices which is excellent in binding force, and excellent in the high rate discharge characteristic and the input-output characteristic at the time of low temperature.

  In the present invention, an electrode mixture for an electrochemical device containing a particulate polymer having a glass transition temperature of 20 ° C. or higher, an active material, and water is applied to a current collector, and one or more mixture layers are laminated. A method for producing an electrode for an electrochemical device, the step of drying until the water content of the mixture layer becomes 10% or less so that the surface temperature of the mixture layer does not exceed 60 ° C., and the surface temperature of the mixture layer is The electrode for electrochemical devices obtained by providing the process of heating so that it may become 100 degreeC or more is provided.

  The electrode for an electrochemical device obtained by the production method of the present invention has excellent binding force, and by using such an electrode, an electrochemical device having excellent high rate discharge characteristics and low temperature input / output characteristics can be obtained. Can do.

  Hereinafter, the present invention will be described in detail.

  In the present invention, an electrode mixture for an electrochemical device containing a particulate polymer having a glass transition temperature of 20 ° C. or higher, an active material, and water is applied to a current collector, and one or more mixture layers are laminated. A method for producing an electrode for an electrochemical device, the step of drying until the water content of the mixture layer becomes 10% or less so that the surface temperature of the mixture layer does not exceed 60 ° C., and the surface temperature of the mixture layer is And a step of heating to 100 ° C. or higher.

  The particulate polymer of the present invention may be an aqueous copolymer latex obtained by a known polymerization method, and is not particularly limited. For example, styrene / butadiene rubber (SBR), acrylonitrile / butadiene rubber ( NBR), conjugated diene rubber latex such as methyl methacrylate / butadiene rubber (MBR), butadiene rubber (BR), acrylic rubber latex, natural rubber latex, chloroprene mainly composed of (meth) acrylic acid ester One or more rubber latex, vinyl acetate emulsion, silicone emulsion and the like can be used. Among these, conjugated diene rubber latex and acrylic rubber latex are preferable. The acrylic rubber latex referred to here is one having a structural unit derived from an aliphatic conjugated diene monomer of 0 or more and less than 10% by mass.

  As the conjugated diene rubber latex, the structural unit derived from the aliphatic conjugated diene monomer is 10 to 30% by mass, and the structural unit derived from the ethylenically unsaturated carboxylic acid monomer is 0.1 to 10% by mass. % And a monomer composition comprising 60 to 89.9% by mass of a structural unit derived from a monomer copolymerizable with an aliphatic conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer Is preferably obtained by emulsion polymerization.

  Structural unit derived from aliphatic conjugated diene monomer constituting conjugated diene rubber latex, structural unit derived from ethylenically unsaturated carboxylic acid monomer, aliphatic conjugated diene monomer and ethylene unsaturated The structural unit derived from the monomer copolymerizable with the carboxylic acid monomer will be described below.

  A structural unit derived from an aliphatic conjugated diene monomer refers to an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, an aliphatic conjugated diene monomer, and an ethylene unsaturated monomer described later. This is a structural unit derived from the aliphatic conjugated diene monomer when copolymerized with a monomer copolymerizable with a saturated carboxylic acid monomer. Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted And monomers such as linear conjugated pentadienes, substituted and side chain conjugated hexadienes. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, the use of 1,3-butadiene is particularly preferable from the viewpoint of easy production industrially and availability and cost.

  10-30 mass% is preferable with respect to the structural unit of all the monomers which comprise a copolymer, and, as for the structural unit derived from an aliphatic conjugated diene monomer, 15-25 mass% is more preferable. By adjusting so that it may become the said range, a glass transition temperature can be adjusted to the optimal range, and a mixture layer with low surface electrical resistivity can be obtained.

  The structural unit derived from an ethylenically unsaturated carboxylic acid monomer is an ethylenically unsaturated carboxylic acid monomer, the aliphatic conjugated diene monomer, an aliphatic conjugated diene monomer described later, and ethylene. It is a structural unit derived from the ethylenically unsaturated carboxylic acid monomer when copolymerized with a monomer copolymerizable with the system unsaturated carboxylic acid monomer. Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Or these anhydrides may be sufficient. These monomers can be used individually by 1 type or in combination of 2 or more types.

  The structural unit derived from the ethylenically unsaturated carboxylic acid monomer is preferably from 0.1 to 10% by weight, and from 0.2 to 9% by weight, based on the structural units of all monomers constituting the copolymer. More preferably, 0.5-5 mass% is further more preferable. By adjusting so that it may become the said range, the balance of the binding force of a mixture layer and the emulsion viscosity of a particulate polymer can be improved, and a slurry with favorable dispersibility can be obtained.

  A structural unit derived from a monomer copolymerizable with an aliphatic conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer is an aliphatic conjugated diene monomer or an ethylenically unsaturated carboxylic acid monomer. When the monomer copolymerizable with the monomer is copolymerized with the aliphatic conjugated diene monomer, the ethylenically unsaturated carboxylic acid monomer, the aliphatic conjugated diene monomer and the ethylene It is a structural unit derived from a monomer copolymerizable with an unsaturated carboxylic acid monomer. Monomers that can be copolymerized with aliphatic conjugated diene monomers and ethylenically unsaturated carboxylic acid monomers include alkenyl aromatic monomers, unsaturated carboxylic acid alkyl ester monomers, and cyanide. Vinyl monomers, unsaturated monomers containing hydroxyalkyl groups, unsaturated carboxylic acid amide monomers, polyfunctional ethylenically unsaturated monomers containing two or more unsaturated double bonds, etc. Can be mentioned.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene and the like. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, the use of styrene is particularly preferable from the viewpoint of easy production industrially and availability and cost.

  Unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate , Monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, it is particularly preferable to use butyl acrylate or methyl methacrylate from the viewpoint of easy production industrially and availability and cost.

  Examples of the vinyl cyanide monomer include monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, the use of acrylonitrile or methacrylonitrile is particularly preferable from the viewpoints of easy industrial production and availability and cost.

  Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl. Examples include methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Examples of the polyfunctional ethylenically unsaturated monomer containing two or more unsaturated double bonds include allyl methacrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth). Examples thereof include polyethylene glycol di (meth) acrylate such as acrylate, and divinyl compounds such as divinylbenzene. These can be used individually by 1 type or in combination of 2 or more types. Preferably, allyl methacrylate, ethylene glycol dimethacrylate, and divinylbenzene are used.

  In addition to the above monomers, any of the monomers used in normal emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, can be used.

  The structural unit derived from the monomer copolymerizable with the aliphatic conjugated diene monomer and the ethylenically unsaturated carboxylic acid monomer is 60% of the structural unit of all monomers constituting the copolymer. -89.9 mass% is preferable, and it is more preferable that it is 66-84.8 mass%.

  As the acrylic rubber latex, the structural unit derived from the unsaturated carboxylic acid alkyl ester monomer is 50 to 99.9% by mass, and the structural unit derived from the ethylenically unsaturated carboxylic acid monomer is 0.1. 10 mass% and structural units derived from an unsaturated carboxylic acid alkyl ester monomer and a monomer copolymerizable with an ethylenically unsaturated carboxylic acid monomer, 0 to 49.9 mass% It is preferably obtained by emulsion polymerization of the monomer composition.

  A structural unit derived from an unsaturated carboxylic acid alkyl ester monomer constituting an acrylic rubber latex, a structural unit derived from an ethylenically unsaturated carboxylic acid monomer, an unsaturated carboxylic acid alkyl ester monomer, and A structural unit derived from a monomer copolymerizable with an ethylenically unsaturated carboxylic acid monomer will be described below.

  The structural unit derived from the unsaturated carboxylic acid alkyl ester monomer means an unsaturated carboxylic acid alkyl ester monomer, an ethylenically unsaturated carboxylic acid monomer, an unsaturated carboxylic acid alkyl ester monomer described later. It is a structural unit derived from the unsaturated carboxylic acid alkyl ester monomer when copolymerized with a monomer and a monomer copolymerizable with the ethylenically unsaturated carboxylic acid monomer. Unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate , Monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, it is particularly preferable to use butyl acrylate or methyl methacrylate from the viewpoint of easy production industrially and availability and cost.

  The structural unit derived from an ethylenically unsaturated carboxylic acid monomer means an ethylenically unsaturated carboxylic acid monomer, the unsaturated carboxylic acid alkyl ester monomer, and an unsaturated carboxylic acid alkyl ester monomer described later. It is a structural unit derived from the ethylenically unsaturated carboxylic acid monomer when copolymerized with a monomer and a monomer copolymerizable with the ethylenically unsaturated carboxylic acid monomer. Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acid monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Or these anhydrides may be sufficient. These monomers can be used individually by 1 type or in combination of 2 or more types.

  The structural unit derived from the ethylenically unsaturated carboxylic acid monomer is preferably from 0.1 to 10% by weight, and from 0.2 to 9% by weight, based on the structural units of all monomers constituting the copolymer. More preferably, 0.5-5 mass% is further more preferable. By adjusting so that it may become the said range, the balance of the binding force of a mixture layer and the emulsion viscosity of a particulate polymer can be improved, and a slurry with favorable dispersibility can be obtained.

  The structural unit derived from a monomer copolymerizable with an unsaturated carboxylic acid alkyl ester monomer and an ethylenically unsaturated carboxylic acid monomer is an unsaturated carboxylic acid alkyl ester monomer or an ethylene unsaturated monomer. The unsaturated carboxylic acid alkyl when the monomer copolymerizable with the saturated carboxylic acid monomer is copolymerized with the unsaturated carboxylic acid alkyl ester monomer and the ethylenically unsaturated carboxylic acid monomer. It is a structural unit derived from a monomer copolymerizable with an ester monomer and an ethylenically unsaturated carboxylic acid monomer. Monomers that can be copolymerized with unsaturated carboxylic acid alkyl ester monomers and ethylene unsaturated carboxylic acid monomers include aliphatic conjugated diene monomers, alkenyl aromatic monomers, and cyanide. Vinyl monomers, unsaturated monomers containing hydroxyalkyl groups, unsaturated carboxylic acid amide monomers, polyfunctional ethylenically unsaturated monomers containing two or more unsaturated double bonds, etc. Can be mentioned.

  Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted And monomers such as linear conjugated pentadienes, substituted and side chain conjugated hexadienes. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, the use of 1,3-butadiene is particularly preferable from the viewpoint of easy production industrially and availability and cost.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene and the like. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, the use of styrene is particularly preferable from the viewpoint of easy production industrially and availability and cost.

  Examples of the vinyl cyanide monomer include monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile. These can be used individually by 1 type or in combination of 2 or more types. In the present embodiment, the use of acrylonitrile or methacrylonitrile is particularly preferable from the viewpoints of easy industrial production and availability and cost.

  Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl. Examples include methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like. These can be used individually by 1 type or in combination of 2 or more types.

  Examples of the polyfunctional ethylenically unsaturated monomer containing two or more unsaturated double bonds include allyl methacrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth). Examples thereof include polyethylene glycol di (meth) acrylate such as acrylate, and divinyl compounds such as divinylbenzene. These can be used individually by 1 type or in combination of 2 or more types. Preferably, allyl methacrylate, ethylene glycol dimethacrylate, and divinylbenzene are used.

  In addition to the above monomers, any of the monomers used in normal emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, can be used.

  The particulate polymer used in the present invention can be obtained by emulsion polymerization using the above monomer. Hereinafter, the emulsion polymerization according to the embodiment will be described.

  In carrying out the emulsion polymerization, in addition to the above monomers, an emulsifier (surfactant), a polymerization initiator, and, if necessary, a chain transfer agent, a reducing agent and the like can be used.

  Examples of emulsifiers (surfactants) include higher alcohol sulfates, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, and naphthalene sulfonic acid salts. Examples thereof include an anionic surfactant such as a formalin condensate, a sulfate ester salt of a nonionic surfactant, and a nonionic surfactant such as an alkyl ester type, an alkylphenyl ether type, and an alkyl ether type of polyethylene glycol. These can be used individually by 1 type or in combination of 2 or more types. The use amount of the emulsifier can be appropriately adjusted in consideration of a combination of other additives.

  Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, acetyl peroxide, Examples thereof include oil-soluble polymerization initiators such as diisopropylbenzene hydroperoxide and 1,1,3,3-tetramethylbutyl hydroperoxide. These can be used individually by 1 type or in combination of 2 or more types. In particular, use of potassium persulfate, sodium persulfate, cumene hydroperoxide, or t-butyl hydroperoxide is preferable. The amount of the polymerization initiator used is not particularly limited, but is appropriately adjusted in consideration of the combination of the monomer composition, the pH of the polymerization reaction system, and other additives.

  Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide, diisopropylxanthogendi Xanthogen compounds such as sulfide; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide; phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; Allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; α-benzyloxystyrene, α-benzine Vinyl ethers such as ruoxyacrylonitrile and α-benzyloxyacrylamide; Chain of triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, terpinolene, α-methylstyrene dimer A transfer agent is mentioned. These can be used individually by 1 type or in combination of 2 or more types. The amount of chain transfer agent used can be appropriately adjusted in consideration of combinations of other additives.

  Examples of the reducing agent include reducing sugars such as dextrose and saccharose, amines such as dimethylaniline and triethanolamine, carboxylic acids such as L-ascorbic acid, erythorbic acid, tartaric acid and citric acid, and salts thereof, sulfites and sulfites. Examples thereof include hydrogen salt, pyrosulfite, nithionate, nithionate, thiosulfate, formaldehyde sulfonate, and benzaldehyde sulfonate. In particular, L-ascorbic acid and erythorbic acid are preferable. The amount of the reducing agent used can be appropriately adjusted in consideration of combinations of other additives.

  When performing the above emulsion polymerization, and for the purpose of controlling the molecular weight and cross-linked structure of the copolymer, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptane, pentene, hexene, heptene, cyclopentene. Hydrocarbon compounds such as unsaturated hydrocarbons such as cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene, and aromatic hydrocarbons such as benzene, toluene and xylene can be used. From the viewpoint of easy recovery, it is particularly preferable to use cyclohexene or toluene.

  Furthermore, you may use additives, such as an oxygen scavenger and a chelating agent, for the reaction system which concerns on the said emulsion polymerization as needed. These additives are not particularly limited in both types and amounts used, and can be used in appropriate amounts as appropriate.

  In addition, as an embodiment of the emulsion polymerization, a predetermined amount of pure water, the monomer, an emulsifier, a polymerization initiator, a chain transfer agent, a reducing agent, and other components are added to a pressure resistant polymerization reaction vessel. It can be carried out by adjusting the temperature of the reaction system by stirring with inclined blades, turbine blades, Max blend blades, or the like.

  The temperature of the reaction system is preferably set in the range of 30 to 100 ° C., more preferably in the range of 40 to 85 ° C., from the viewpoint of safety in the tank and productivity. In this case, a polymerization initiator having an initiation temperature in the above reaction temperature range is used.

  The temperature of the reaction system can be raised at, for example, 0.25 to 1.0 ° C./min by external heating.

  Examples of the method of adding the monomer component and other components to the reaction system after reaching the above time include a batch addition method, a divided addition method, a continuous addition method, and a power feed method.

  Further, it is more preferable that the emulsion polymerization is completed after confirming that the polymer conversion rate exceeds 97%. A particulate polymer latex is thus obtained. The polymer conversion rate can be calculated from the solid content or from the amount of heat obtained by cooling the polymerization tank.

  The particulate polymer latex is preferably freed from unreacted monomers and other low-boiling compounds by a method such as heating under reduced pressure or steam distillation.

  The pH of the particulate polymer latex is preferably adjusted to 5 to 9 with ammonia, potassium hydroxide, sodium hydroxide, or the like from the viewpoint of dispersion stability and coverage on the active material. More preferably, it is adjusted to ˜8.5.

  Furthermore, additives such as a dispersant, an antifoaming agent, an anti-aging agent, an antiseptic, an antibacterial agent, a flame retardant, and an ultraviolet absorber may be used in the particulate polymer latex of the present invention. These additives are not particularly limited in both types and amounts used, and can be used in appropriate amounts as appropriate.

  The glass transition temperature of the particulate polymer used in the present invention needs to be 20 ° C. or higher, preferably 25 ° C. or higher and 60 ° C. or lower, more preferably 30 ° C. or higher and 50 ° C. or lower. When the glass transition temperature of the particulate polymer is lower than the above range, the surface electrical resistivity of the mixture layer becomes high, and the high rate discharge characteristics and the input / output characteristics at low temperature of the electrochemical device are inferior. Moreover, when the glass transition temperature is too high, the binding force of the mixture layer tends to be inferior. The glass transition temperature of the particulate polymer is measured by a differential scanning calorimeter according to the method of Examples described later.

  The number average particle size of the particulate polymer used in the present invention is not particularly limited, but is preferably 50 to 300 nm, and more preferably 70 to 250 nm, for example. The particle diameter of the particulate polymer is measured, for example, by the method of the example described later.

  The gel content (toluene insoluble content) of the particulate polymer used in the present invention is not particularly limited, but is preferably 30 to 100%, more preferably 50 to 100%, and most preferably 80 to 100%. The gel content of the particulate polymer is measured, for example, by the method of the example described later.

  Next, the electrochemical device mixture according to the present embodiment will be described.

  The electrochemical device mixture of the present embodiment includes the particulate polymer according to the present embodiment described above as a binder, and further includes an active material and water.

  As an active material, any of a positive electrode active material and a negative electrode active material may be sufficient.

  The positive electrode active material is not particularly limited. In the case of a lithium ion secondary battery, for example, transition metal oxides such as MnO2, MoO3, V2O5, V6O13, Fe2O3, Fe3O4, LiCoO2, LiMnO2, LiNiO2, and LMO2 (here, MMO Is a layered structure such as NiMn, Co, AL, etc.), LiMn2O4, LiM2O4 (where M includes Ni, Mn, Co, AL, etc.) Examples include spinel structures, composite metal oxides having an olivine structure such as LiFePO4, lithium-rich composite oxides such as Li2MnO3, transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2, and metal fluorides such as CuF2 and NiF2. It is done. These can be used alone or in combination of two or more.

  The negative electrode active material is not particularly limited, but in the case of a lithium ion secondary battery, for example, fluorocarbon, graphite, carbon fiber, resin-fired carbon, linear graphite hybrid, coke, pyrolytic vapor grown carbon, full carbon Conductive carbonaceous materials such as furyl alcohol resin calcined carbon, mesocarbon microbeads, mesophase pitch carbon, graphite whiskers, pseudo-isotropic carbon, calcined natural materials, and pulverized products thereof, polyacenic organic semiconductors, polyacetylene And a composite material containing a conductive polymer such as poly-p-phenylene and a simple metal such as silicon or tin, a metal oxide, or an alloy of the metal. These can be used alone or in combination of two or more.

  When used for a lithium ion capacitor electrode, carbon materials such as graphite, soft carbon, hard carbon and coke, polyacene organic semiconductor (PAS), and the like can be used.

  When used for an electric double layer capacitor electrode, activated carbon, activated carbon fiber, silica, alumina or the like can be used.

  The mixture for electrochemical devices of this embodiment can contain an auxiliary agent as necessary. Examples of auxiliary agents include water-soluble thickeners, dispersants, stabilizers, and conductive agents. Examples of the water-soluble thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, and casein. Examples of the dispersant include sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, and sodium polyacrylate. Examples of the stabilizer include nonionic and anionic surfactants. Examples of the conductive agent include acetylene black and carbon nanofibers. These can be used alone or in combination of two or more.

  The content of the particulate polymer in the electrochemical device mixture is preferably 0.1 to 10 parts by mass (solid content) with respect to 100 parts by mass (solid content) of the active material, 0.5 More preferably, it is -7 mass parts. When the content of the particulate polymer is 0.1 parts by mass or more, it is preferable from the viewpoint of obtaining a good adhesive force with respect to the active material, the current collector, and the like, and when it is 10 parts by mass or less, an electrochemical device is assembled. It is sometimes preferable from the viewpoint of obtaining good input / output characteristics.

  By applying the electrochemical device mixture to the current collector and drying, a mixture layer can be formed on the current collector to obtain an electrode sheet. Such an electrode sheet is used as, for example, a positive electrode plate or a negative electrode plate of a lithium ion secondary battery.

  As a method for applying the electrochemical device mixture to the current collector, for example, a known method such as a reverse roll method, a comma bar method, a gravure method, an air knife method can be used. An air dryer, a warm air dryer, a vacuum dryer, an infrared heater, a far infrared heater, or the like is used.

  In the drying step after application of the mixture for electrochemical devices in the present invention, first, the mixture layer is dried until the moisture content of the mixture layer is 10% or less so that the surface temperature of the mixture layer does not exceed 60 ° C. It is necessary to provide at least a second step of heating so that the surface temperature of the mixture layer is 100 ° C. or higher.

  In the first step, the mixture layer surface temperature must not exceed 60 ° C, preferably does not exceed 50 ° C, and more preferably does not exceed 40 ° C.

  By making the mixture layer surface temperature not exceed 60 ° C. in the first step, the input / output characteristics of the electrochemical device are improved.

  In the first step, it is necessary to dry until the moisture content of the mixture layer is 10% or less, preferably 7% or less, and more preferably 1% or less.

  When the water content of the mixture layer is 10% or less at the end of the first step, the particulate polymer is segregated on the surface of the mixture layer and the binding force of the mixture layer is reduced, and the input / output resistance is high. In addition, it is possible to prevent the particulate polymer from excessively covering the active material and increasing the input / output resistance.

  The method of measuring the moisture content of the mixture layer is not particularly limited, but the method of the examples described later, the method of scraping the mixture layer from the current collector and determining the weight and the weight after absolutely dry, or the digital moisture It can be measured by a meter, an on-line moisture meter installed during the drying process.

  In the second step, the mixture layer surface temperature needs to be 100 ° C. or higher, preferably 120 ° C. or higher, and more preferably 150 ° C. or higher.

  By setting the surface temperature of the mixture layer to 100 ° C. or higher, an electrode having a good binding force can be obtained without deteriorating input / output characteristics.

  Although the method of measuring the mixture layer surface temperature in each step is not particularly limited, it can be measured using an infrared surface thermometer or the like.

  Moreover, unless the embodiment of this invention is impaired, you may provide processes other than a 1st process and a 2nd process.

  The electrochemical device mixture according to the present embodiment is suitably used for forming an electrode of an electrochemical device such as a lithium ion secondary battery, a lithium ion capacitor, or an electric double layer capacitor.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Production of particulate polymer latex 1>
A pressure-resistant polymerization reactor was charged with 100 parts of pure water, 0.8 part of sodium dodecylbenzenesulfonate and 1.0 part of potassium persulfate, and stirring was started. Next, 10% of the monomer components shown in Table 1 and other components were charged into the polymerization reactor, the temperature was raised to 65 ° C., and the remaining monomer components were continuously added over 400 minutes. Polymerization was performed.
Thereafter, the temperature in the tank was raised from 65 ° C. to 70 ° C., held for 240 minutes, and the temperature in the tank was further raised to 75 ° C.
And after confirming that the polymerization addition rate exceeded 97%, and adding a polymerization terminator, the temperature in the tank was cooled to 35 ° C. or lower.
Then, after adjusting pH to 7.0 using sodium hydroxide aqueous solution, it hold | maintained for 30 minutes and the particulate polymer latex 1 was obtained by removing an unreacted monomer etc. by heating vacuum distillation.

<Production of particulate polymer latex 2-5>
Manufacture was performed in the same manner as the particulate polymer latex 1 except that the composition was changed to the composition shown in Table 1.

<Measurement of glass transition temperature of particulate polymer>
About 0.5 g of the particulate polymer latex was applied to a glass plate and dried at 70 ° C. for 4 hours to form a film. The film after drying is set in an aluminum pan for DSC test, and the temperature is increased from −100 to 100 ° C. at a rate of 10 ° C./min with a differential scanning calorimeter (DSC 6220: Seiko Instruments). The glass transition temperature (° C.) of the particulate polymer was determined by reading the end point of endotherm of the phase change from the obtained D S C curve. When two or more phase changes were observed, the lowest glass transition temperature was determined as the glass transition temperature of the present invention. The measurement results are shown in Table 1.

<Measurement of gel content (toluene insoluble content) of particulate polymer>
Using the particulate polymer obtained in each synthesis example and each comparative synthesis example, a film was produced in an atmosphere of a temperature of 80 ° C. and a humidity of 85%. About 1 g of the produced film was weighed to obtain Xg. This was placed in 400 ml of toluene and allowed to swell and dissolve for 48 hours. Thereafter, this was filtered through a 300-mesh wire mesh, and the toluene insoluble matter captured by the wire mesh was dried and weighed to obtain Yg. And the percentage of the dry weight of a toluene insoluble part with respect to the weight of a latex film was computed.
Gel content (%) = Y / X × 100
The measurement results are shown in Table 1.

<Method for measuring number average particle size of particulate polymer>
The number average particle diameter of the particulate polymer by the photon correlation method was measured by the dynamic light scattering method. In the measurement, FPAR-1000 (manufactured by Otsuka Electronics) was used. The measurement results are shown in Table 1.

<Production and evaluation of electrode>
An electrode was prepared by preparing an electrode mixture for an electrochemical device by the following method using the particulate polymer latex as a binder for an electrochemical device.

(Preparation of electrode mixture)
(1-1) Preparation of Negative Electrode Mixtures 1 to 5 Artificial graphite having an average particle size of about 20 μm is used as the negative electrode active material, and a carboxymethyl cellulose aqueous solution as a thickener is added to 100 parts by mass of the artificial graphite. 1 part by weight, 2 parts by weight of the particulate polymer latex 1-5 as a binder, and knead by adding an appropriate amount of pure water so that the total solid content is 45% by weight, Negative electrode mixtures 1 to 5 were prepared.

(1-2) Preparation of positive electrode mixtures 11 to 15 LiCoO2 having an average particle diameter of about 10 μm was used as a positive electrode active material, and 5 parts by weight of acetylene black as a conductive agent was increased with respect to 100 parts by mass of LiCoO2. 1 part by mass of carboxymethyl cellulose aqueous solution as the agent, 2 parts by mass of particulate polymer latex 1-5 as the binder, and a proper amount of pure so that the total solid content is 50% by mass. Water was added and kneaded to prepare positive electrode mixtures 11 to 15, respectively.

(Production of electrodes)
(2-1) Production of negative electrode (Example 1)
The negative electrode mixture 1 obtained as described above was applied to a copper foil having a thickness of 20 μm as a current collector with an applicator having a clearance of 250 μm, and as a first step, 10 Dried for minutes. During this time, the surface temperature of the mixture layer was measured with a non-contact type infrared surface thermometer, and the maximum temperature was recorded. Moreover, the moisture content of the mixture layer was measured by the method mentioned later using a part of electrode after completion | finish of a 1st process.
After completion of the first step, the electrode was dried in a hot air dryer at 115 ° C. for 120 minutes as the second step. During this time, the surface temperature of the mixture layer was measured with a non-contact type infrared surface thermometer, and the maximum temperature was recorded.
Furthermore, it roll-pressed at room temperature, and obtained the negative electrode 1 whose thickness of a coating layer is 100 micrometers.

(Examples 2 to 4, Comparative Example 1)
A negative electrode was obtained in the same manner as in Example 1 except that the negative electrode mixture 2 to 5 was used instead of the negative electrode mixture 1. In addition, the thing using the mixture 2 for negative electrodes is set to Examples 2-4, respectively, and the thing using the mixture 5 for negative electrodes is set as the comparative example 1. FIG.

(Examples 5-8, Comparative Examples 2-4)
The same method as in Example 1 except that the temperature and drying time of the hot air dryer in the first step and the hot air dryer temperature in the second step after the first step were changed to the contents shown in Table 2. A negative electrode was obtained.
Using the above negative electrode, the binding force of the mixture layer was measured by the method described later.
(2-2) Production of positive electrode (Example 11)
The positive electrode mixture 11 obtained as described above was applied to an aluminum foil having a thickness of 20 μm serving as a current collector with an applicator having a clearance of 250 μm, and as a first step, 10 in a hot air dryer at 70 ° C. Dried for minutes. During this time, the surface temperature of the mixture layer was measured with a non-contact type infrared surface thermometer, and the maximum temperature was recorded. Moreover, the moisture content of the mixture layer was measured by the method mentioned later using a part of electrode after completion | finish of a 1st process.
After completion of the first step, the electrode was dried in a hot air dryer at 115 ° C. for 120 minutes as the second step. During this time, the surface temperature of the mixture layer was measured with a non-contact type infrared surface thermometer, and the maximum temperature was recorded.
Furthermore, it roll-pressed at room temperature, and obtained the positive electrode 11 whose thickness of a coating layer is 100 micrometers.

(Examples 12-14, Comparative Example 11)
A positive electrode was obtained in the same manner as in Example 11 except that the positive electrode mixture 12 to 15 was used instead of the positive electrode mixture 11. In addition, what used the mixture 12 for positive electrodes 12-14 is set to Examples 12-14, respectively, and what used the mixture 15 for positive electrodes is set as the comparative example 11. FIG.

(Examples 15-18, Comparative Examples 12-14)
The same method as in Example 11 except that the temperature and drying time of the hot air dryer in the first step and the hot air dryer temperature in the second step after the first step were changed to the contents shown in Table 2. A positive electrode was obtained.
Using the above positive electrode, the binding force of the mixture layer was measured by the method described later.

<Measurement of moisture content of mixture layer>
The mixture layer was scraped off to about 2 g, and the weight (A (g)) was immediately weighed accurately. Thereafter, the mixture layer thus scraped off was dried at 150 ° C. for 1 hour, and the weight after drying (B (g)) was accurately weighed again. The water content of the mixture layer was determined by the following calculation formula.
Moisture content of mixture layer (%) = 100 × (A−B) / B

<Measurement of binding force of mixture layer>
Three pieces of the produced electrodes were cut out as 2 cm × 7 cm strip-shaped test pieces, and used in a room at 23 ° C. and a relative humidity of 50%, using a universal testing machine TGE-5kN manufactured by Minebea Co., Ltd., at a test speed of 100 mm / min. A 180 ° peel test was performed under the conditions. A double-sided adhesive tape was applied to the steel plate, a 2 cm × 7 cm strip-shaped electrode test piece was applied thereon, an adhesive tape was applied onto the mixture layer, and peeling was caused by pulling the adhesive tape. The measurement was performed three times and the averaged results are shown in Table 2 and Table 3. The higher the numerical value of this test, the higher the binding force of the mixture layer and the better the binding force.

(3) Battery preparation (for negative electrode evaluation)
The negative electrode is punched into a circle having a diameter of 15 mm, and a polypropylene separator having a diameter of 16 mm and a metal lithium foil having a diameter of 15 mm are laminated in this order on the mixture layer, and the capacity ratio is 1: 1 in the cell. After charging lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate so as to be 1 mol / L and filling the prepared electrolyte, the battery lid was caulked through a gasket to produce a coin cell battery.
(For positive electrode evaluation)
The positive electrode is punched into a circle having a diameter of 15 mm, and a polypropylene separator having a diameter of 16 mm and a metal lithium foil having a diameter of 15 mm are laminated in this order on the mixture layer, and the capacity ratio in the cell is 1: 1. After charging lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate so as to be 1 mol / L and filling the prepared electrolyte, the battery lid was caulked through a gasket to produce a coin cell battery.

<Measurement of high rate discharge characteristics>
Using each coin cell battery obtained by the above method, the battery was charged to 4.2 V and discharged at 0.1 C to 2.5 V. Furthermore, it charged to 4.2V and discharged to 2.5V at 2C. The capacity retention was calculated by the following formula and evaluated as follows.
High rate discharge characteristics (%) = {(discharge capacity at 2C) / (discharge capacity at 0.1C)} × 100
A: High rate discharge characteristic exceeds 90% B: High rate discharge characteristic is 85-90%
Δ: High rate discharge characteristic is less than 80 to 85% ×: High rate discharge characteristic is less than 80%

<Measurement of low-temperature discharge characteristics>
Using each coin cell battery obtained by the above method, the battery was charged to 4.2 V, and discharged to 2.5 V at 0.2 C in a thermostatic bath at 25 ° C. Furthermore, it charged to 4.2V and discharged to 2.5V at 0.2C in a -20 degreeC thermostat. The capacity retention was calculated by the following formula and evaluated as follows.
Low temperature discharge characteristics (%) = {(discharge capacity at −20 ° C.) / (Discharge capacity at 25 ° C.)} × 100
A: Low-temperature discharge characteristics exceed 75% B: Low-temperature discharge characteristics 70-75%
Δ: Low temperature discharge characteristic is less than 65 to 70% ×: Low temperature discharge characteristic is less than 65%

  Tables 2 and 3 summarize the evaluation results of the binding force, the high-rate discharge characteristics, and the low-temperature discharge characteristics of the mixture layers of Examples and Comparative Examples.

As described above, by using the electrode for an electrochemical device obtained by the production method of the present invention, it is possible to obtain an electrochemical device having excellent binding power and excellent high rate discharge characteristics and low temperature input / output characteristics. .

Claims (1)

An electrochemical device in which an electrode mixture for an electrochemical device containing a particulate polymer having a glass transition temperature of 20 ° C. or higher, an active material, and water is applied to a current collector, and one or more mixture layers are laminated. And a step of drying until the water content of the mixture layer is 10% or less so that the surface temperature of the mixture layer does not exceed 60 ° C., and the surface temperature of the mixture layer is 100 ° C. or more. The manufacturing method of the electrode for electrochemical devices which provides the process heated so that it may become.