JP5570393B2 - Electrode binder - Google Patents

Description

  The present invention relates to an electrode binder. In detail, this invention relates to the binder used for formation of the electrode of a secondary battery, an electrical double layer capacitor, or a lithium ion capacitor.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are frequently used as power sources for notebook personal computers and mobile phones. In recent years, this secondary battery has attracted attention as a large power source for electric vehicles.

  In a secondary battery, an electrode composition containing an active material is applied to a current collector and dried to form an electrode.

  In consideration of the adhesion of the active material to the current collector, a binder made of a polymer is blended in the electrode composition. Examination examples regarding this binder are disclosed in JP-A Nos. 2000-195521, 2002-110169, and 2006-107958.

JP 2000-195521 A JP 2002-110169 A JP 2006-107958 A

  When the above-mentioned binder is immersed in an electrolytic solution such as propylene carbonate, it may swell by absorbing the electrolytic solution. This swelling induces peeling of the active material from the current collector. This peeling causes a decrease in battery capacity. The swelling of the binder has a problem of reducing battery performance. There are similar problems in electric double layer capacitors and lithium ion capacitors.

  An object of the present invention is to provide a binder capable of improving the durability of a battery.

  The binder for an electrode according to the present invention is based on a polymer obtained by copolymerizing cyclohexyl (meth) acrylate and a monomer copolymerizable with cyclohexyl (meth) acrylate.

  Preferably, in this binder for electrodes, the ratio of the mass of the cyclohexyl (meth) acrylate to the total mass of the monomers used for forming the polymer is 5.0% by mass or more and 70.0% by mass or less.

  Preferably, in this electrode binder, the polymer is in the form of particles. The polymer includes a core and a shell located outside the core. The shell has a different composition than the core. The glass transition temperature of the shell is −60 ° C. or higher and 65 ° C. or lower. The glass transition temperature of this core is −60 ° C. or higher and 65 ° C. or lower.

  The electrode composition according to the present invention includes any one of the above binders, an active material, and a dispersion medium.

  The electrode according to the present invention is obtained by applying the electrode composition to a current collector and drying it.

  Another binder for electrodes according to the present invention is based on a polymer obtained by copolymerizing a (meth) acrylic monomer and a crosslinking agent copolymerizable with the (meth) acrylic monomer.

  Preferably, in this electrode binder, the crosslinking agent copolymerizable with the (meth) acrylic monomer is an unsaturated organosilane and / or N-methylolacrylamide.

  Preferably, in this electrode binder, the polymer is in the form of particles. The polymer includes a core and a shell located outside the core. The shell has a different composition than the core. The glass transition temperature of the shell is −60 ° C. or higher and 65 ° C. or lower. The glass transition temperature of this core is −60 ° C. or higher and 65 ° C. or lower.

  Another electrode composition according to the present invention includes any one of the above binders, an active material, and a dispersion medium.

  The electrode according to the present invention is obtained by applying the electrode composition to a current collector and drying it.

  In the binder according to the present invention, the absorption of the electrolytic solution is suppressed. In this binder, an increase in volume due to absorption of the electrolytic solution, that is, swelling is suppressed. For this reason, in the electrode using this binder, peeling of the active material from the current collector is prevented. According to the present invention, excellent battery performance can be effectively maintained. This binder can contribute to improving the durability of the battery.

FIG. 1 is a cross-sectional view schematically showing a secondary battery having an electrode according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a binder constituting a part of the electrode of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  The electrode which concerns on one Embodiment of this invention can be used as a positive electrode or a negative electrode of a secondary battery. This electrode can also be used as an electrode of a capacitor. This electrode is obtained by applying an electrode composition to a current collector and drying it.

  The current collector is made of a thin piece of metal. Examples of the current collector include metal foils such as copper foil and aluminum foil. When the electrode is used as a positive electrode, the current collector is preferably an aluminum foil. When this electrode is used as a negative electrode, the current collector is preferably a copper foil.

  The electrode composition includes an active material and a resin composition. When the electrode is used as a positive electrode of a secondary battery, examples of the active material include iron olivine, lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, and lithium manganese nickel composite oxide. . When this electrode is used as a negative electrode of a secondary battery, the active material includes natural graphite, amorphous carbon, graphite, graphitized mesophase spherules, carbon materials such as pitch-based carbon fibers, polyacene, PIC (Pesudo Isotropic Carbon) , FMC (Fine Mosaic Carbon), amorphous carbon, PPP (Poly (p-phenylene)) 700 ° C. fired product, mesophase microspheres 700 ° C. fired product, polyfurfuryl alcohol fired product, polysiloxane carbide and carbon steel Examples thereof include Si / Li alloy micro-dispersed therein. When this electrode is used as an electrode of a capacitor, the active material is exemplified by a carbon material having a large specific surface area. This active material is appropriately selected in consideration of electrode specifications and the like.

  The resin composition contains a binder and a dispersion medium. The binder is made of a polymer. This polymer is obtained by copolymerizing a plurality of monomers.

  The resin composition can contain water as a dispersion medium. In this case, the binder is dispersed in water. This resin composition can also contain the good solvent of the said polymer instead of water as this dispersion medium. In this case, the binder is present dissolved in this dispersion medium. Examples of such a dispersion medium include organic solvents. Examples of the organic solvent include toluene, ethyl acetate, and methyl ethyl ketone (MEK). From the viewpoint of influence on the environment, water is preferable as the dispersion medium. This resin composition is preferably an emulsion (emulsion) using water as a dispersion medium.

  As described above, the binder is based on a polymer obtained by copolymerizing a plurality of monomers. In more detail, this binder consists of a polymer obtained by copolymerizing a cyclohexyl (meth) acrylate and a monomer copolymerizable with this cyclohexyl (meth) acrylate (hereinafter referred to as another monomer).

The binder is, for example,
(1) preparing a mixture containing cyclohexyl (meth) acrylate and another monomer;
(2) It is obtained by a production method including a step of polymerizing the mixture.

  In the preparation step, distilled water, cyclohexyl (meth) acrylate, and other monomers are weighed and put into a predetermined container. Distilled water, cyclohexyl (meth) acrylate and other monomers are thoroughly stirred and mixed. Thereby, a mixture containing cyclohexyl (meth) acrylate and other monomers is prepared. In this mixture, one type of monomer may be blended as another monomer, or a plurality of different types of monomers may be blended. Other monomers are appropriately determined according to the specifications of the electrode in which the binder is used.

  In this electrode, other monomers include butadiene, butene, isobutene, (meth) acrylic acid, maleic acid, itaconic acid, (meth) acrylamide, styrene, methylstyrene, (meth) acrylonitrile, (meth) acrylate, diallyl phthalate , A monomer having a glycidyl group, a (meth) acrylate having a dicyclopentadiene skeleton, a (meth) acrylate having a tricyclodecane skeleton, a monomer having a keto group, and a monomer having two or more primary amino groups in the molecule Saturated organosilane is exemplified.

The (meth) acrylate includes acrylate and methacrylate. Examples of the (meth) acrylate include alkyl esters, hydroxyalkyl esters, monocyclic alkyl esters, alkoxy esters, alkylphenoxy esters, dialkylphenoxy esters, alkylcarbonyloxy esters, and [R ₁ -CO- ( OR ₁ ) x—R ₂ y (R ₁ and R ₂ = alkyl group, x and y = integer)] are exemplified. More specifically, as this (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate , Pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, octadecyl (meth) acrylate, behenyl (meth) acrylate, Docosyl (meth) acrylate, polyethylene oxide di (meth) acrylate, polyethylene oxide di (meth) acrylate, allyl methacrylic ester, 2-hydroxyethyl (meth) acrylate, 2 Hydroxybutyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate.

  Examples of the (meth) acrylamide include acrylamide, methacrylamide, N-methylol (meth) acrylamide, acetone acrylamide, N, N-dimethyl (meth) acrylamide, N-ethyl (meth) acrylamide, and N, N-diethyl (meth). Examples include acrylamide, N-propyl acrylamide, N-hexyl methacrylamide, N-cyclohexyl acrylamide, N-hydroxyethyl acrylamide, N-phenyl acrylamide, N-nitrophenyl acrylamide and N-ethyl-N-phenyl acrylamide.

  Examples of the monomer containing the glycidyl group include glycidyl (meth) acrylate, diglycidyl fumarate, (meth) acrylic acid-3,4-epoxycyclohexyl, 3,4-epoxyvinylcyclohexane, and (meth) acrylic acid-β. -Methyl glycidyl is exemplified.

  Examples of the (meth) acrylate having a dicyclopentadiene skeleton include dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyloxyethyl methacrylate, and dicyclopentenyl. Examples include oxyethyl methacrylate and dicyclopentanyl methacrylate.

  Examples of the monomer having a keto group include acrolein, diacetone acrylamide, diacetone methacrylate, acetoacetoxyethyl methacrylate, 4-vinylacetoacetanilide, and acetoacetylallylamide.

  The amino group contained in the monomer having two or more primary amino groups in the molecule is preferably a hydrazine type amino group, and particularly preferably an amino group having a hydrazide, semicarbazide or carbohydrazide structure. Examples of the monomer having two or more primary amino groups in the molecule include ethylenediamine, diethylenetriamine, triethylenediamine, metaxylenediamine, norbornanediamine, and 1,3-bisaminomethylcyclohexane. Monomers having two or more hydrazine-type amino groups include hydrazine and salts thereof; polycarboxylic acid hydrazides such as carbohydrazide, succinic acid dihydrazide, adipic acid dihydrazide, citric acid trihydrazide, sebacic acid dihydrazide, and isophthalic acid dihydrazide; Examples thereof include a reaction product of polyisocyanate and hydrazine such as 4,4′-ethylene disemicarbazide and 4,4′-hexamethylene disemicarbazide, and a polymer hydrazide such as polyacrylic hydrazide.

  Examples of the unsaturated organic silane include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (βmethoxyethoxy) silane, vinylacetoxysilane, vinyltriisopropoxysilane, allyltrimethoxysilane, and γ-methacryloxypropyl. Examples include methyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-acryloxypropyltrimethoxysilane. Specifically, as this unsaturated organosilane, trade names “KA1003”, “KBM1003”, “KBE1003”, “KBC1003”, “KBM1063”, “KBM1103”, “KBM1203”, manufactured by Shin-Etsu Chemical Co., Ltd., “KBM1303”, “KBM1403”, “KBM503”, “KBE503”, “KBM502”, “KBE502”, “KBM5103”, “KBM5102”, and “KBM5403” are exemplified. Further, as this unsaturated organosilane, trade names “Z-6075”, “Z-6172”, “Z-6300”, “Z-6519”, “Z-6550” manufactured by Toray Dow Corning Co., Ltd., “Z-6625”, “Z-6030”, “Z-6033”, “Z-6036”, “Z-6530” and “Z-6806” are exemplified.

  The monomer contained in the mixture prepared as described above is polymerized in the polymerization step. By this polymerization, a resin composition containing a binder is obtained. Examples of the polymerization method include emulsion polymerization and suspension polymerization from the viewpoint of easy temperature control. From the viewpoint of handling, this polymerization method is preferably emulsion polymerization. The polymerization temperature, reaction time, stirring speed, etc. are appropriately determined in consideration of the binder specifications and the like. This resin composition may be manufactured batchwise or continuously.

  In this production method, the mixture is preferably polymerized using a polymerization initiator at a temperature of 45 ° C. or higher and 95 ° C. or lower. Thereby, a resin composition in which the binder is uniformly dispersed can be obtained. According to this production method, the resin composition can be obtained as a suspension or an emulsion.

  Examples of the polymerization initiator include azobisisobutyronitrile and its hydrochloride, 2,2′-azobis (2-aminodipropane) dihydrochloride, 4,4′-azobis (4-cyanovaleric acid), and the like. Examples include azo polymerization initiators, hydrogen peroxide, water-soluble inorganic peroxides, water-soluble reducing agents and water-soluble inorganic peroxide complexes, and water-soluble reducing agents and organic peroxide complexes.

  Examples of the water-soluble inorganic peroxide include sodium persulfate, potassium persulfate, and ammonium persulfate.

  The water-soluble reducing agent is usually used as a radical redox polymerization catalyst. This reducing agent can be soluble in water. This reducing agent includes sodium sulfite, sodium hyposulfite, sodium hydrogen sulfite, sodium thiosulfate, sodium formaldehyde sulfoxylate, ferrous sulfate, ferrous ammonium sulfate, ferrous pyrophosphate, thiourea dioxide, sulfinic acid Erythorbic acid, L-ascorbic acid and its sodium salt, L-ascorbic acid and its potassium salt, L-ascorbic acid and its calcium salt, ethylenediaminetetraacetic acid and its sodium salt, ethylenediaminetetraacetic acid and its potassium salt, ethylenediaminetetraacetic acid And a complex compound of a heavy metal (for example, iron, copper, chromium, etc.), a complex compound of a salt of ethylenediaminetetraacetic acid and a heavy metal (for example, iron, copper, chromium, etc.) and a reducing sugar.

  Examples of the water-soluble organic peroxide include cumene hydroperoxide, p-cymene hydroperoxide, t-butylisopropylbenzene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, decalin hydroperoxide, t-amyl hydroperoxide, t -Hydroperoxides such as butyl hydroperoxide and isopropyl hydroperoxide are exemplified.

  The mixture may further include a chain transfer agent. This chain transfer agent can adjust the molecular weight of the copolymer obtained by polymerization of this mixture. Examples of this chain transfer agent include alkyl mercaptans such as lauryl mercaptan, n-butyl mercaptan, t-butyl mercaptan, n-dodecyl mercaptan, octyl mercaptan, alcohols having 1 to 4 carbon atoms, thioglycolic acid-2-ethylhexyl, Examples are 2-methyl-5-t-butylthiophenol, carbon tetrabromide, α-methylstyrene dimer, 2-mercaptoethanol and sodium methallylsulfonate.

  In this production method, when emulsion polymerization is selected as the polymerization method, an emulsifier is used. By using this emulsifier, an emulsion is formed. This emulsifier can disperse a monomer such as cyclohexyl (meth) acrylate contained in the above mixture in water. This emulsifier is a surfactant. In this production method, the surfactant is not particularly limited as long as it is a surfactant that does not affect the polymerization reaction. Examples of the emulsifier include a cationic surfactant, an anionic surfactant, and a nonionic surfactant. This emulsifier may be added in the preparation step of the mixture or may be added in the polymerization step.

  Examples of the anionic surfactant include sulfates such as alkyl sulfates, polyoxyalkyl ether sulfates, polyoxyethylene carboxylic ester sulfates, polyoxyethylene alkyl phenyl ether sulfates, and polyoxyethylene alkyl ether sulfates. Examples include alkali metal salts, ammonium salts and amine salts. Salts of this sulfate include polyoxyethylene octyl phenyl ether sulfate (2 to 100 addition of ethylene oxide), polyoxyethylene nonyl phenyl ether sulfate (2 to 100 addition of ethylene oxide) and polyoxyethylene Examples thereof include alkali metal salts, ammonium salts and amine salts of ethylene alkyl ether sulfates (additional mole number of ethylene oxide is 2 to 100 and carbon number of alkyl chain is 6 to 22). Examples of the anionic surfactant further include alkali metal salts, ammonium salts, and amine salts of phosphate esters such as polyoxyethylene alkylphenyl ether phosphate esters, polyoxyethylene alkyl ether phosphate esters, and higher alcohol phosphate esters. Is exemplified. As salts of the phosphoric acid ester, polyoxyethylene octylphenyl ether phosphoric acid monoester (the number of added moles of ethylene oxide is 2 to 100), polyoxyethylene octylphenyl ether phosphoric acid diester (the number of added moles of ethylene oxide is 2 to 100) ), Polyoxyethylene nonylphenyl ether phosphoric acid monoester (2 to 100 addition of ethylene oxide), polyoxyethylene nonylphenyl ether phosphoric acid diester (2 to 100 addition of ethylene oxide), polyoxyethylene alkyl ether Phosphoric acid monoester (ethylene oxide addition mole number is 2 to 100, alkyl chain carbon number is 6 to 22), polyoxyethylene alkyl ether phosphate diester (ethylene oxide addition mole number) Number 2 from 100, the number of carbon atoms in the alkyl chain of the alkali metal salt from 6 22), ammonium salts and amine salts are exemplified. Examples of the anionic surfactant further include alkali metal salts of sulfonic acids such as alkyl sulfonic acid, α-olefin sulfonic acid, succinic acid dialkyl ester sulfonic acid, α-sulfonated fatty acid, α-sulfonated fatty acid ester, ammonium Salts and amine salts are exemplified. Examples of the anionic surfactant further include alkali metal salts of dodecylbenzenesulfonic acid and fatty acids. This anionic surfactant may be used alone, or a plurality of anionic surfactants may be used in combination.

  Examples of the nonionic surfactant include a polyoxyethylene chain-containing compound having a polyoxyethylene chain in the molecule and having a surface activity. Examples of the nonionic surfactant include polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkyl ether phosphate ester, polyoxyethylene alkyl ether glycerin. Examples include boric acid esters, adducts of partial fatty acid esters of polyhydric alcohols with ethylene oxide and fatty acid amide ethylene oxide adducts. As the nonionic surfactant, a compound in which the above polyoxyethylene chain is a polyalkylene oxide chain obtained by copolymerizing ethylene oxide and propylene oxide may be used. In this case, the copolymer obtained by copolymerizing ethylene oxide and propylene oxide may be a block copolymer or a random copolymer. Examples of the nonionic surfactant include sorbitan fatty acid esters, fatty acid glycerin esters, glycerin fatty acid esters, pentaerythritol fatty acid esters, fatty acid esters of sorbitol, alkyl ethers of polyhydric alcohols, and fatty acid amides of alkanolamines. This nonionic surfactant may be used alone, or a plurality of nonionic surfactants may be used in combination.

  A polymerizable emulsifier may be used as the emulsifier. Examples of the polymerizable emulsifier include sodium vinyl sulfonate, sodium salt and ammonium salt of t-butylacrylamide sulfonic acid, sodium salt and ammonium salt of polyethylene oxide nonylpropenyl ether sulfate, polyoxyethylene alkylphenyl ether and its sulfate ester salt, Examples include polyoxyethylene alkyl ether and its sulfate ester salt and polyoxyalkylene alkenyl ether and its ammonium sulfate salt. Such a polymerizable emulsifier may be any that can be used for emulsion polymerization, and examples thereof include an anionic reactive emulsifier and a nonionic reactive emulsifier. Examples of the anionic reactive emulsifier include grades “HS-10”, “BC-10”, “KH-10” of trade names “AQUALON” manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. and trade names “New Frontier A-”. 229E ”; grades“ SE-3N ”,“ SE-5N ”,“ SE-10N ”,“ SE-20N ”, and“ SE-30N ”of the product name“ ADEKA rear soap ”manufactured by ADEKA Corporation; Grades “MS-60”, “MS-2N”, “RA-1120” and “RA-2614” of trade names “Antox” manufactured by KAISHA; grades of “ELEMINOL” manufactured by Sanyo Chemical Industries, Ltd. Examples include grades “S-120A”, “S-180A” and “S-180” of “JS-2” and “RS-30” and trade name “Latemul” manufactured by Kao Corporation. Examples of the nonionic reactive emulsifier include grades “RN-20”, “RN-30”, “RN-50” and trade names “New Frontier N-” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 177E "; trade name" NE-10 "," NE-20 "," NE-30 "and" NE-40 "of trade name" ADEKA rear soap "manufactured by ADEKA CORPORATION; trade name of Nippon Emulsifier Co., Ltd. Grades “M-20G”, “M-40G”, “M-90G” of “RMA-564”, “RMA-568” and “RMA-1114” and trade name “NK ESTER” manufactured by Shin-Nakamura Chemical Co., Ltd. And “M-230G”. This emulsifier may be used alone, or a plurality of emulsifiers may be used in combination.

  In this electrode, the aforementioned mixture may further contain an organosilane in addition to cyclohexyl (meth) acrylate and other monomers. Examples of the organic silane include amino silane, ureido silane, epoxy silane, sulfide silane, mercapto silane, ketimino silane, alkyl silane, alkoxy silane, phenyl silane, fluoro silane, and silane having an isocyanate group. Specifically, as the organosilane, trade names “KBM303”, “KBM403”, “KBE402”, “KBM602”, “KBM603”, “KBE603”, “KBM903”, “KBE903” manufactured by Shin-Etsu Chemical Co., Ltd. ”,“ KBM573 ”,“ KBM703 ”,“ KBM803 ”,“ KBE9007 ”,“ KBM5103 ”, and“ X-12-817H ”. Further, as this organosilane, trade names “Z-6011”, “Z-6020”, “Z-6023”, “Z-6026”, “Z-6032”, “Z” manufactured by Toray Dow Corning Co., Ltd. -6050 "," Z-6094 "," Z-6610 "," Z-6683 "," AZ-720 "," Z-6675 "," Z-6676 "," Z-6040 "," Z-6041 " ”,“ Z-6042 ”,“ Z-6044 ”,“ Z-6043 ”,“ Z-6920 ”,“ Z-6940 ”,“ Z-6948 ”,“ Z-6062 ”,“ Z-6911 ”, “Z-6860”, “DC-5700”, “Z-6806”, “ACS-8”, “Z-2306”, “Z-6013”, “Z-6187”, “Z-6210”, “Z -6258 "," Z-6265 "," Z-6275 "," -6288 "," Z-6321 "," Z-6329 "," Z-6341 "," Z-6366 "," Z-6383 "," Z-6582 "," Z-6586 "," Z-6721 " ”,“ Z-6597 ”,“ Z-6830 ”,“ Z-6047 ”,“ Z-6800 ”,“ Z-6333 ”,“ Z-1211 ”,“ Z-1219 ”,“ Z-1224 ”and “Z-6079” is exemplified. This organosilane may be added in the polymerization step of the mixture, or may be added after this polymerization step.

  In this electrode, the above-mentioned resin composition can be added to an acrylic emulsion, urethane emulsion, epoxy emulsion, surfactant, neutralizer, plasticizer, cross-linking agent, preservative, wetting agent, antifoaming agent, Additives such as a sticking agent, a leveling agent, and an antifreezing agent may be included. This additive may be used alone, or a plurality of additives may be used in combination. In this production method, each of these additives may be added in the polymerization step of the aforementioned mixture, or may be added after this polymerization step.

  The electrode composition of the present invention includes the resin composition thus produced and the active material described above. This electrode composition includes a binder, an active material, and a dispersion medium. As described above, the electrode composition is applied to a current collector and dried to obtain an electrode.

  The electrode composition is in a slurry or paste form.

  The method for applying the electrode composition to the current collector is not particularly limited. Examples of the coating method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and brush coating.

  The amount of the electrode composition applied to the current collector is not particularly limited. The electrode composition is preferably applied to the current collector so that a coating film having a thickness of 0.005 mm or more and 5 mm or less can be obtained by drying after application.

  The drying method is not particularly limited. Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays, electron beams, and the like.

  This electrode composition can also contain additives, such as a viscosity modifier, from the viewpoint of the applicability to the current collector, in addition to the aforementioned active material and binder. Examples of the viscosity modifier include cellulose derivatives such as acetyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose, casein, gum arabic, tragacanth gum, starch, sodium alginate, polyvinyl alcohol, polyvinyl pyrrolidone, poly (meth) such as sodium polyacrylate. Examples include acrylic acid, poly (meth) acrylic acid ester copolymer, acrylic acid-acrylamide copolymer, methacrylic acid-acrylate copolymer, polystyrene sulfonic acid, and a copolymer of polystyrene sulfonic acid and acrylic acid ester. More specifically, as the viscosity modifier, a water-soluble (meth) acrylic acid ester copolymer having a methacrylic acid content of 70% or less, such as a trade name “Toyosol RL1001” manufactured by Toyo Chemical Co., Ltd., and Henkel Japan Co., Ltd. Examples include an alkali thickening type regulator such as a trade name “KA10” manufactured by the company, and a meeting type such as a trade name “Adecanol UH438” manufactured by ADEKA Corporation.

  A lithium ion secondary battery 2 is shown in FIG. The battery 2 includes a pair of electrodes 4, an electrolytic solution 6, and a separator 8. Each electrode 4 includes a current collector 10 and a coating film 12 laminated on the current collector 10. In the battery 2, the right electrode 4a is a negative electrode, and the left electrode 4b is a positive electrode.

The electrolytic solution 6 is obtained by dissolving an electrolyte in a solvent. In this battery 2, the electrolyte is a lithium salt. As the lithium _{salt, LiClO 4, LiBF 4, LiBF} 6, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl 4, LiCl, LiBr, LiB (C 2 _{H 5) 4, CF 3 SO} 3 Li, CH 3 SO 3 Li, LiCF 3 SO 3, LiC 4 F 9 S0 3, Li (CF 3 SO 2) 2 N, Li (CF 3 SO 2) 3, LiBPh 4 And lower fatty acid lithium carboxylates. Examples of the solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, and chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. These solvents may be used alone or in combination of two or more.

  The separator 8 is disposed between the electrodes 4. In other words, the separator 8 is sandwiched between the positive electrode 4b and the negative electrode 4a. The separator 8 prevents a short circuit due to the contact between the left and right electrodes 4. As the separator 8, a film-like microporous film is usually used. The separator 8 has innumerable minute holes 14. Lithium ions can migrate between the left and right electrodes 4 through the holes 14. Examples of the material of the separator 8 include polyethylene, polypropylene, cellulose, and cellulose derivatives.

  In this battery 2, the coating film 12 of the negative electrode 4a is formed using the above-mentioned electrode composition.

  As shown in FIG. 1B, the binder 18 is in the form of particles. The binder 18 is interposed between the active material 16 and the active material 16. The binder 18 is interposed between the active material 16 and the current collector 10. The binder 18 can adhere the active material 16 to the current collector 10. The binder 18 does not have to be in the form of particles.

  Shown in FIG. 2 is a cross-sectional view of the binder 18. In FIG. 2, the center of the binder 18 is indicated by the symbol C. What is indicated by a symbol S is the surface of the binder 18. The binder 18 includes a core 20 and a shell 22. The part including the center C of the binder 18 is the core 20, and the part including the surface S of the binder 18 is the shell 22. The shell 22 is located outside the core 20. In addition, this binder 18 may be comprised from the polymer which has a single composition. The shell 22 of the binder 18 may be composed of a plurality of layers.

  The binder 18 is made of a polymer obtained by copolymerizing cyclohexyl (meth) acrylate and a monomer copolymerizable with the cyclohexyl (meth) acrylate. In other words, the polymer constituting the binder 18 has a structural unit derived from cyclohexyl (meth) acrylate. The swelling of the binder 18 when immersed in the electrolytic solution 6 is suppressed to be smaller than that of the binder not containing cyclohexyl (meth) acrylate. Since the swelling of the binder 18 is suppressed, peeling of the active material 16 from the current collector 10 is effectively prevented. Since the adhesion state of the active material 16 to the current collector 10 is maintained, excellent battery performance is maintained for a long time. The binder 18 can contribute to improving the durability of the battery 2. In this respect, the ratio of the mass of cyclohexyl (meth) acrylate to the total mass of the monomers contained in the mixture is preferably 5.0% by mass or more, more preferably 5.8% by mass or more, and 29.3% by mass or more. More preferably, 42 mass% or more is especially preferable. If the mass ratio of cyclo (meth) acrylate is excessive, the coating film 12 is cracked and the electrode 4 cannot be obtained. In this respect, the mass ratio is preferably equal to or less than 70.0 mass%, more preferably equal to or less than 65.5 mass%, still more preferably equal to or less than 58.3 mass%, and particularly preferably equal to or less than 57.8 mass%. In the case where the binder 18 is formed using a plurality of mixtures, based on the total mass of monomers contained in these mixtures and the sum of the masses of cyclohexyl (meth) acrylates contained in the respective mixtures, The mass ratio is calculated. For example, in the case where the binder 18 is composed of two kinds of mixtures (mixture a and mixture b), the sum of the total monomer mass contained in the mixture a and the total monomer mass contained in the mixture b is included in the mixture a. The ratio of the mass of cyclohexyl (meth) acrylate is calculated based on the sum of the mass of cyclohexyl (meth) acrylate and the sum of the mass of cyclohexyl (meth) acrylate contained in the mixture b.

  The binder 18 is particles made of the polymer obtained in the above-described polymerization step. As described above, the binder 18 includes the core 20 and the shell 22. In this polymerization step, the binder 18 is formed by using two types of mixed liquids and completing polymerization with another mixed liquid after the polymerization with one mixed liquid is completed. Since the binder 18 is formed in this way, the shell 22 of the binder 18 has a composition different from that of the core 20. The binder 18 may be formed by polymerization while dropping and mixing another mixed solution into one mixed solution. In this case, the binder 18 is composed of multiple layers having different polymer compositions from the center to the surface. Also in the binder 18, the shell 22 has a composition different from that of the core 20. In addition, when this binder 18 is formed using a single liquid mixture, this binder 18 consists of a polymer in which each part from the center to the surface has an equivalent composition. From the viewpoint that various characteristics can be easily imparted, the binder 18 is formed using two or more kinds of mixed liquids, in other words, the shell 22 has a composition different from that of the core 20. The ones made are preferred.

When the mass ratio of cyclohexyl (meth) acrylate is reduced, flexibility is imparted to the binder 18. The flexible binder 18 can contribute to the followability of the coating film 12 to the deformation of the electrode 4. On the other hand, when the mass ratio of cyclohexyl (meth) acrylate is increased, the swelling of the binder 18 is suppressed. The binder 18 whose swelling is suppressed can contribute to the durability of the battery 2. From such a viewpoint, after the polymerization is performed with the mixed liquid a having a small mass ratio of cyclohexyl (meth) acrylate, the polymerization is performed with the mixed liquid b having a large mass ratio of cyclohexyl (meth) acrylate, whereby a binder is obtained. 18 may be formed. The binder 18 may be formed by performing polymerization while dropping the mixed solution b into the mixed solution a. In this case, the mass ratio of cyclohexyl (meth) acrylate in the mixed solution a is preferably 46.6% by mass or less, and the mass ratio of cyclohexyl (meth) acrylate in the mixed solution b is preferably 68.6% by mass or more. . In the case where the shell 22 is formed using a plurality of mixtures, this concentration is based on the total monomer mass contained in these mixtures and the total mass of cyclohexyl (meth) acrylate contained in each mixture. Is calculated. For example, in the case where the shell 22 is composed of two kinds of mixtures (mixture b ₁ and mixture b ₂ ), the sum of the total monomer mass contained in the mixture b ₁ and the total monomer mass contained in the mixture b ₂ ; based on the sum of the mass of cyclohexyl (meth) acrylate contained in the mixture b ₂ the mass of cyclohexyl (meth) acrylate contained in the mixture b _1, the ratio of the mass of the cyclohexyl (meth) acrylate is calculated.

  In this electrode 4, the glass transition temperature of the polymer constituting the binder 18 is preferably −60 ° C. or higher and 65 ° C. or lower. By setting the glass transition temperature to −60 ° C. or higher, swelling when immersed in the electrolytic solution 6 is effectively suppressed. By setting the glass transition temperature to 65 ° C. or lower, the adhesion of the active material 16 to the current collector 10 can be maintained. When the binder 18 is composed of a plurality of layers, the glass transition temperature of the core 20 is −60 ° C. or more and 65 ° C. or less, and the glass transition temperature of the shell 22 is −60 ° C. or more and 65 ° C. or less. It is preferable.

The glass transition temperature is calculated using the following formula (1). This glass transition temperature is also referred to as an average glass transition temperature. This formula (1) represents a calculation formula for the glass transition temperature Tg of a polymer (copolymer) obtained by polymerizing n types of monomers.
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ +... W _n / Tg _n (1)
Above formula _{(1), Tg 1, Tg} 2, ··· and Tg _n represents a glass transition temperature of the respective n types of monomers. W ₁ , W ₂ ,... W _n represent the ratio (also referred to as mass fraction) of the mass of each of the n types of monomers to the total mass of the mixture. In this specification, the glass transition temperatures of these monomers are described in literature (Mitsubishi Rayon Co., Ltd., acrylic ester catalog, 1997 edition and Kyozo Kitaoka, New Polymer Library 7, Introduction to Synthetic Resins for Coatings, Polymer Publications, 168-169). , 1997) is adopted. As the glass transition temperatures of these monomers, for example, methyl acrylate (also referred to as MMA) is 100 ° C., acrylonitrile (also referred to as AN) is 100 ° C., and 2-ethylhexyl acrylate (also referred to as 2EHA) is −70 ° C. Cyclohexyl (meth) acrylate (also referred to as CHMA) is 83 ° C and methacrylic acid (also referred to as MAA) is 130 ° C.

  As described above, the electrode composition includes the active material 16 and the binder 18. From the viewpoint that the binder 18 can effectively adhere the active material 16 to the current collector 10, the blending amount of the binder 18 with respect to 100 parts by mass of the active material 16 contained in this electrode composition is 0 in terms of solid content. .2 parts by mass or more is preferable, and 1.0 part by mass or more is more preferable. In light of the fact that the binder 18 does not hinder battery performance, the amount is preferably 10 parts by mass or less, and more preferably 3 parts by mass or less.

The binder according to another embodiment of the present invention is a polymer obtained by copolymerizing a (meth) acrylic monomer and a crosslinking agent (hereinafter simply referred to as a crosslinking agent) copolymerizable with the (meth) acrylic monomer. Consists of. This binder also uses, as a base material, a polymer obtained by copolymerizing a plurality of monomers, like the above-mentioned binder. This binder is produced in the same manner as the above-mentioned binder except for the constitution of the monomer contained in the mixture prepared in the preparation step. The manufacturing method of this binder is:
(1) preparing a mixture containing a (meth) acrylic monomer and a crosslinking agent;
(2) polymerizing the mixture.

  Examples of the (meth) acrylic monomer contained in the mixture include (meth) acrylic acid, (meth) acrylate, (meth) acrylate having a dicyclopentadiene skeleton, and (meth) acrylate having a tricyclodecane skeleton. In addition, one type of monomer may be mix | blended with this mixture as a (meth) acrylic-type monomer, and the several monomer from which a kind differs may be mix | blended.

The (meth) acrylate includes acrylate and methacrylate. Examples of the (meth) acrylate include alkyl esters, hydroxyalkyl esters, monocyclic alkyl esters, alkoxy esters, alkylphenoxy esters, dialkylphenoxy esters, alkylcarbonyloxy esters, and [R ₁ -CO- ( OR ₁ ) x—R ₂ y (R ₁ and R ₂ = alkyl group, x and y = integer)] are exemplified. More specifically, as this (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate , Pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, octadecyl (meth) acrylate, behenyl (meth) acrylate, Docosyl (meth) acrylate, polyethylene oxide di (meth) acrylate, polyethylene oxide di (meth) acrylate, allyl methacrylic ester, 2-hydroxyethyl (meth) acrylate, 2 Hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and cyclohexyl (meth) acrylate.

  Examples of the (meth) acrylate having a dicyclopentadiene skeleton include dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentenyloxyethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyloxyethyl methacrylate, and dicyclopentenyl. Examples include oxyethyl methacrylate and dicyclopentanyl methacrylate.

  Examples of the crosslinking agent include (meth) acrylamide, a monomer having a glycidyl group, a monomer having a keto group, a diallyl phthalate, a monomer having two or more primary amino groups in the molecule, and an unsaturated organic silane. In addition, one type of crosslinking agent may be used for this mixture, and multiple types of crosslinking agent may be used together.

  Examples of the (meth) acrylamide include acrylamide, methacrylamide, N-methylol (meth) acrylamide, acetone acrylamide, N, N-dimethyl (meth) acrylamide, N-ethyl (meth) acrylamide, and N, N-diethyl (meth). Examples include acrylamide, N-propyl acrylamide, N-hexyl methacrylamide, N-cyclohexyl acrylamide, N-hydroxyethyl acrylamide, N-phenyl acrylamide, N-nitrophenyl acrylamide and N-ethyl-N-phenyl acrylamide.

  Examples of the monomer containing the glycidyl group include glycidyl (meth) acrylate, diglycidyl fumarate, (meth) acrylic acid-3,4-epoxycyclohexyl, 3,4-epoxyvinylcyclohexane, and (meth) acrylic acid-β. -Methyl glycidyl is exemplified.

  Examples of the monomer having a keto group include acrolein, diacetone acrylamide, diacetone methacrylate, acetoacetoxyethyl methacrylate, 4-vinylacetoacetanilide, and acetoacetylallylamide.

  The amino group contained in the monomer having two or more primary amino groups in the molecule is preferably a hydrazine type amino group, and particularly preferably an amino group having a hydrazide, semicarbazide or carbohydrazide structure. Examples of the monomer having two or more primary amino groups in the molecule include ethylenediamine, diethylenetriamine, triethylenediamine, metaxylenediamine, norbornanediamine, and 1,3-bisaminomethylcyclohexane. Monomers having two or more hydrazine-type amino groups include hydrazine and salts thereof; polycarboxylic acid hydrazides such as carbohydrazide, succinic acid dihydrazide, adipic acid dihydrazide, citric acid trihydrazide, sebacic acid dihydrazide, and isophthalic acid dihydrazide; Examples thereof include a reaction product of polyisocyanate and hydrazine such as 4,4′-ethylene disemicarbazide and 4,4′-hexamethylene disemicarbazide, and a polymer hydrazide such as polyacrylic hydrazide.

  Examples of the unsaturated organic silane include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (βmethoxyethoxy) silane, vinylacetoxysilane, vinyltriisopropoxysilane, allyltrimethoxysilane, and γ-methacryloxypropyl. Examples include methyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-acryloxypropyltrimethoxysilane. Specifically, as this unsaturated organosilane, trade names “KA1003”, “KBM1003”, “KBE1003”, “KBC1003”, “KBM1063”, “KBM1103”, “KBM1203”, manufactured by Shin-Etsu Chemical Co., Ltd., “KBM1303”, “KBM1403”, “KBM503”, “KBE503”, “KBM502”, “KBE502”, “KBM5103”, “KBM5102”, and “KBM5403” are exemplified. Further, as this unsaturated organosilane, trade names “Z-6075”, “Z-6172”, “Z-6300”, “Z-6519”, “Z-6550” manufactured by Toray Dow Corning Co., Ltd., “Z-6625”, “Z-6030”, “Z-6033”, “Z-6036”, “Z-6530” and “Z-6806” are exemplified. Note that the unsaturated organosilane is also referred to as a silane coupling agent.

  In this electrode, the above-mentioned mixture may further include another monomer copolymerizable with the (meth) acrylic monomer (hereinafter referred to as another monomer). Examples of the other monomer include butadiene, butene, isobutene, maleic acid, itaconic acid, styrene, methylstyrene, and (meth) acrylonitrile. In this case, in this mixture, one type of monomer may be blended as another monomer, or a plurality of different types of monomers may be blended.

  An electrode composition according to another embodiment of the present invention includes a resin composition containing a binder and the above-described active material obtained by polymerization. An electrode is obtained by applying this electrode composition to a current collector and drying it. This electrode can be used as an electrode of the secondary battery shown in FIG.

  Although not shown, the binder is in the form of particles. The binder is interposed between the active material and the active material. The binder is interposed between the active material and the current collector. The binder can adhere the active material to the current collector. In addition, this binder does not need to exhibit particulate form.

  As described above, the binder is composed of a polymer obtained by copolymerizing a (meth) acrylic monomer and a crosslinking agent copolymerizable with the (meth) acrylic monomer. In other words, the polymer constituting this binder has a structural unit derived from a crosslinking agent copolymerizable with a (meth) acrylic monomer. Swelling when this binder is immersed in an electrolyte solution is suppressed to be smaller than that of a binder not containing a crosslinking agent copolymerizable with a (meth) acrylic monomer. Since the swelling of the binder is suppressed, peeling of the active material from the current collector is effectively prevented. Since the active material is in close contact with the current collector, excellent battery performance is maintained over a long period of time. This binder can contribute to improving the durability of the battery. In particular, when (meth) acrylamide and / or unsaturated organosilane is selected as a crosslinking agent copolymerizable with this (meth) acrylic monomer, the swelling of the binder is effectively suppressed.

  In this electrode, N-methylol (meth) acrylamide is preferred as (meth) acrylamide. When this N-methylol (meth) acrylamide is used as a crosslinking agent copolymerizable with a (meth) acrylic monomer, the ratio of the mass of N-methylol (meth) acrylamide to the total mass of monomers contained in the mixture is: From the viewpoint that the binder can contribute to improving the durability of the battery, 0.5% by mass or more is preferable. If the mass ratio of N-methylol (meth) acrylamide is excessive, the coating film is cracked and the electrode cannot be obtained. In this respect, the mass ratio is preferably 4.0% by mass or less.

  Examples of the unsaturated organic silane include γ-methacryloxypropylmethyldimethoxysilane (trade name “KBM502” manufactured by Shin-Etsu Chemical Co., Ltd. or product name “Z-6033” manufactured by Toray Dow Corning Co., Ltd.) and γ-methacryloxypropyl. Trimethoxysilane (trade name “KBM503” manufactured by Shin-Etsu Chemical Co., Ltd. or product name “Z-6030” manufactured by Toray Dow Corning Co., Ltd.) is preferred. When γ-methacryloxypropylmethyldimethoxysilane is used as a crosslinking agent copolymerizable with a (meth) acrylic monomer, the ratio of the mass of γ-methacryloxypropylmethyldimethoxysilane to the total mass of monomers contained in the mixture Is preferably 0.5% by mass or more from the viewpoint that the binder can contribute to improving the durability of the battery. When the mass ratio of γ-methacryloxypropylmethyldimethoxysilane is excessive, the coating film is cracked and the electrode cannot be obtained. In this respect, the mass ratio is preferably 4.0% by mass or less. When γ-methacryloxypropyltrimethoxysilane is used as a crosslinking agent copolymerizable with a (meth) acrylic monomer, the weight ratio of γ-methacryloxypropyltrimethoxysilane is determined by the binder being the durability of the battery. From the viewpoint that it can contribute to improvement, 0.5% by mass or more is preferable. When the mass ratio of γ-methacryloxypropyltrimethoxysilane is excessive, the coating film is cracked and the electrode cannot be obtained. In this respect, the mass ratio is preferably 4.0% by mass or less.

  In this specification, the ratio of the mass of the crosslinking agent copolymerizable with the (meth) acrylic monomer is, when the binder is formed using a plurality of mixtures, the total mass of monomers contained in these mixtures, and Is calculated based on the total mass of the cross-linking agent copolymerizable with the (meth) acrylic monomer contained in the mixture. For example, when N-methylol (meth) acrylamide is used as a crosslinking agent copolymerizable with a (meth) acrylic monomer and the binder is composed of two types of mixture (mixture a and mixture b), it is included in the mixture a. The sum of the total mass of the monomer and the total mass of the monomer contained in the mixture b, the mass of N-methylol (meth) acrylamide contained in the mixture a, and the mass of N-methylol (meth) acrylamide contained in the mixture b. Based on the sum, the mass ratio of N-methylol (meth) acrylamide is calculated. Similarly, when an unsaturated organic silane is used as a crosslinking agent copolymerizable with the (meth) acrylic monomer, the mass ratio of the unsaturated organic silane is calculated.

  The binder is particles made of the polymer obtained in the above-described polymerization step. In this polymerization step, when the binder is formed using a single mixed solution, the binder is made of a polymer having an equivalent composition in each part from the center to the surface. In the case where this binder is formed by using two kinds of mixed liquids and polymerization by another mixed liquid after the polymerization by one mixed liquid is completed, this binder has a two-layer structure consisting of a core and a shell. And the shell has a composition different from that of the core. Furthermore, when these two kinds of mixed liquids are used, when this binder is formed by polymerization while dropping another mixed liquid into one mixed liquid, the binder is formed from the center to the surface. Is composed of a number of layers having different polymer compositions, and the shell has a composition different from that of the core. From the viewpoint that various properties can be easily provided, this binder is formed using a mixture of two or more kinds, in other words, the shell is configured to have a composition different from that of the core. Is preferred.

  In this electrode, the glass transition temperature of the polymer constituting the binder is preferably −60 ° C. or higher and 65 ° C. or lower. By setting this glass transition temperature to -60 ° C. or higher, swelling when immersed in an electrolytic solution is effectively suppressed. By setting the glass transition temperature to 65 ° C. or lower, the adhesion of the active material to the current collector can be maintained. In addition, when this binder comprises a plurality of layers, it is preferable that the glass transition temperature of the core is −60 ° C. or more and 65 ° C. or less, and the glass transition temperature of the shell is −60 ° C. or more and 65 ° C. or less. .

  As described above, the electrode composition includes an active material and a binder. From the viewpoint that the binder can effectively adhere the active material to the current collector, the blending amount of the binder with respect to 100 parts by mass of the active material contained in the electrode composition is 0.2 parts by mass or more in terms of solid content. Preferably, 1.0 mass part or more is more preferable. In light of the fact that the binder does not hinder battery performance, the amount is preferably 10 parts by mass or less, and more preferably 3 parts by mass or less.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Experiment A-Study on blending effect of cyclohexyl methacrylate]
[Example 1]
In one container, 2.2 parts by mass of an emulsifier (trade name “Aqualon HS-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was dissolved in 35 parts by mass of distilled water to obtain a solution. In this solution, 58.3 parts by weight of cyclohexyl methacrylate (also referred to as CHMA), 40 parts by weight of 2-ethylhexyl acrylate (also referred to as 2EHA) and 1.7 parts by weight of methacrylic acid (also referred to as MAA). After mixing, the mixture was sufficiently stirred to prepare an emulsion of a mixture containing CHMA, 2EHA and MAA. In a reactor, 0.5 part by mass of the above “AQUALON HS-10” was dissolved in 130 parts by mass of distilled water to obtain a mixed solution, and then the inside of the container was replaced with nitrogen. The mixed solution in the reactor was heated and adjusted to 80 ° C. In a container different from the one container, 0.5 part by mass of potassium persulfate (also referred to as KPS) as a polymerization catalyst was dissolved in 20 parts by mass of distilled water to obtain an aqueous solution. While stirring the mixed solution in the reactor, the emulsion in the one container and the aqueous solution in the other container were added to the mixed solution over 3 hours. After completion of the addition, stirring was continued for 3 hours while maintaining the warmed state. Thus, the resin composition which contains 35.6 mass% of binders of Example 1 in the solid content rate was obtained.

[Production of electrode composition]
Natural resin as an active material and carboxymethyl cellulose (also referred to as CMC) as a viscosity modifier were blended with the resin composition containing the binder of Example 1 to obtain an electrode composition. In terms of solid content, the amount of binder was adjusted to 2 parts by mass with respect to 100 parts by mass of natural graphite, and CMC was adjusted to 2 parts by mass. Natural graphite is a trade name “spherical natural graphite (average particle diameter: 24 μm, specific surface area: 4.6 m ² / g)” manufactured by Nippon Graphite Industries Co., Ltd. CMC is a trade name “Daicel 2200” manufactured by Daicel Chemical Industries, Ltd.

[Production of Electrode A]
The electrode composition was applied to a copper foil having a thickness of 25 μm. After drying, rolling and slitting were performed to obtain an electrode A.

[Example 2 and Comparative Example 1]
The binders of Example 2 and Comparative Example 1 were obtained in the same manner as in Example 1 except that the mixture was blended as shown in Table 1 below. About each binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. In Table 1, MMA represents methyl acrylate and BMA represents butyl methacrylate.

[Example 3]
In 21 parts by mass of distilled water, 1.5 parts by mass of the above “AQUALON HS-10”) was dissolved to obtain a solution. In this solution, 3.7 parts by mass of CHMA, 13.5 parts by mass of MMA, 46.5 parts by mass of 2EHA and 1.3 parts by mass of MAA were mixed, and then sufficiently stirred to obtain CHMA, MMA, 2EHA. And an emulsion (1) of the mixture a containing MAA was prepared. Separately from this emulsified liquid (1), 0.7 parts by mass of the above “AQUALON HS-10”) was dissolved in 9 parts by mass of distilled water to obtain another solution. In this solution, 2.1 parts by mass of CHMA, 19.7 parts by mass of MMA, 12.5 parts by mass of 2EHA and 0.7 parts by mass of MAA were mixed, and then sufficiently stirred, and CHMA, MMA, 2EHA. And an emulsion (2) of the mixture b containing MAA was prepared. After the mixture liquid equivalent to Example 1 was heated in the reactor and adjusted to 80 ° C., the emulsion (1) was first added over 2 hours together with the aqueous solution in which KPS equivalent to Example 1 was dissolved. Thereafter, the emulsion (2) was added over 1 hour. After completion of the addition, stirring was continued for 3 hours while maintaining the warmed state. In this manner, a resin composition containing 36.3% by mass of the binder of Example 3 in terms of the solid content was obtained. About this binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition.

[Example 4-5 and Comparative Example 2-3]
The binders of Example 4-5 and Comparative Example 2-3 were obtained in the same manner as in Example 3 except that the blends of the mixture a and the mixture b were as shown in Table 2 below. About each binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition.

[Example 6]
In 21 parts by mass of distilled water, 1.5 parts by mass of the above “AQUALON HS-10”) was dissolved to obtain a solution. In this solution, 19.3 parts by mass of CHMA, 44.4 parts by mass of 2EHA and 1.3 parts by mass of MAA were mixed and then sufficiently stirred, and an emulsion of mixture a containing CHMA, 2EHA and MAA ( 1) was adjusted. Separately from this emulsified liquid (1), 0.7 parts by mass of the above “AQUALON HS-10”) was dissolved in 9 parts by mass of distilled water to obtain another solution. In this solution, 27.5 parts by mass of CHMA, 6.8 parts by mass of 2EHA and 0.7 parts by mass of MAA were blended, and then sufficiently stirred to obtain an emulsion of mixture b containing CHMA, 2EHA and MAA ( 2) was adjusted. After the mixture liquid equivalent to Example 1 was heated in the reactor and adjusted to 80 ° C., the addition of the emulsified liquid (1) was started together with the aqueous solution in which KPS equivalent to Example 1 was dissolved. The emulsion (2) was added dropwise to the emulsion (1). Thus, the emulsions (1) and (2) were added over 3 hours while mixing. After completion of the addition, stirring was continued for 3 hours while maintaining the warmed state. Thus, the resin composition which contains 36.2 mass% of binders of Example 6 in the solid content rate was obtained. About this binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition.

[Adhesion test 1]
About the produced electrode, the evaluation regarding adhesiveness was performed based on the cross-cut test based on JIS-K-5600-5-6. The number of remaining squares out of the 100 squares was counted and ranked in three levels, “A”, “B”, and “C”. The results are shown in Tables 1 and 2 below.
A: 90 squares or more B: 80 squares or more and less than 90 squares C: Less than 80 squares

[Adhesion test 2]
The produced electrode was immersed in an electrolytic solution (a solution of LiPF ₆ dissolved in propylene carbonate (LiPF ₆ concentration: 1 mol / L)). After standing at 60 ° C. for 1 week, the area (residual area) of the non-peeled portion was measured. The ratio of the remaining area to the total area of the electrode was calculated, and was ranked into four stages of “S”, “A”, “B”, and “C”. The results are shown in Tables 1 and 2 below.
S: 80% or more A: 60% or more and less than 80% B: 40% or more and less than 60% C: Less than 40%

[Swelling test]
A 2 mm-thick coating film was prepared using the prepared electrode composition, and a 2 cm × 2 cm test piece was sampled from the coating film. After measuring the mass W0 of this test piece, this test piece was immersed in propylene carbonate. After standing at room temperature for 1 week, the mass W1 of this test piece was measured, and the swelling ratio was calculated based on the following mathematical formula. The calculation results are shown in Tables 1 and 2 below. In the table, “NG” represents a case where a coating film could not be formed.
(Swelling ratio) = ((W1-W0) / W0) × 100

[Charge / discharge cycle test]
The produced electrode was used as a working electrode. The electrode area was 4 cm ² . Lithium metal having a sufficiently large electrochemical capacity with respect to this working electrode was used as a counter electrode. Lithium metal equivalent to this counter electrode was used as a reference electrode. In this way, a monopolar cell was produced. The monopolar cell was housed in a container of sufficient size, electrolyte (obtained by dissolving LiPF ₆ in a mixture of ethylene carbonate and diethyl carbonate at 1: 1 (volume ratio) solution (LiPF ₆ concentration: 1 mol / L)) was injected to obtain a test battery. Lithium ions were inserted into the test battery at a constant current of 0.1 C to 0.01 V under a temperature condition of 60 ° C. After the insertion, lithium ions were released until the voltage became 1 V at a constant current of 0.1 C. This charging / discharging is repeated 10 times, and the ratio (retention rate) of the 10th discharge capacity (mAh) to the first discharge capacity (mAh) is calculated, and is divided into three stages “A”, “B”, and “C”. Rated. The results are shown in Tables 1 and 2 below.
A: 70% or more B: 50% or more and less than 70% C: less than 50%

  As shown in Tables 1 and 2, the binders of the examples have higher evaluations than the binders of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

[Experiment B-Study on blending effect of silane coupling agent and N-methylol (meth) acrylamide]
[Example 7]
In one container, 2.2 parts by mass of an emulsifier (trade name “Aqualon HS-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was dissolved in 35 parts by mass of distilled water to obtain a solution. To this solution, 38.5 parts by mass of MMA, 10 parts by mass of BMA, 48.6 parts by mass of 2EHA, 2 parts by mass of MAA and 0.9 parts by mass of silane coupling agent (Toray Dow Corning Co., Ltd.) Product name “Z-6033”) was mixed and sufficiently stirred to prepare an emulsion of a mixture containing MMA, BMA, 2EHA, MAA and a silane coupling agent. In a reactor, 0.5 part by mass of the above “AQUALON HS-10” was dissolved in 130 parts by mass of distilled water to obtain a mixed solution, and then the inside of the container was replaced with nitrogen. The mixed solution in the reactor was heated and adjusted to 80 ° C. In a container different from the one container, 0.5 part by mass of potassium persulfate (also referred to as KPS) as a polymerization catalyst was dissolved in 20 parts by mass of distilled water to obtain an aqueous solution. While stirring the mixed solution in the reactor, the emulsion in the one container and the aqueous solution in the other container were added to the mixed solution over 3 hours. After completion of the addition, stirring was continued for 3 hours while maintaining the warmed state. Thus, the resin composition which contains 35.6 mass% of binders of Example 7 in the solid content rate was obtained. About this binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. Using this electrode, the adhesion test 1, the adhesion test 2, the swelling test, and the discharge cycle test were performed in the same manner as in the above-described experiment A. The results are shown in Table 3 below.

[Example 8-12]
The binder of Examples 8-12 was obtained in the same manner as in Example 7 except that the mixture was blended as shown in Table 3 below. About each binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. Using this electrode, the adhesion test 1, the adhesion test 2, the swelling test, and the discharge cycle test were performed in the same manner as in the above-described experiment A. The results are shown in Table 3 below. In Table 1, Z-6030 is a trade name of a silane coupling agent manufactured by Toray Dow Corning Co., Ltd., GMA is glycidyl methacrylate, DAAm is diacetone acrylamide, AAEM is 2-acetoacetoxyethyl methacrylate, ADH is adipic acid dihydrazide. Represents.

[Example 13]
In 21 parts by mass of distilled water, 1.5 parts by mass of the above “AQUALON HS-10”) was dissolved to obtain a solution. In this solution, 10 parts by weight of MMA, 10 parts by weight of BMA, 43.4 parts by weight of 2EHA, 1.2 parts by weight of MAA and 0.4 parts by weight of Z-6033 were mixed and stirred thoroughly. , MMA, BMA, 2EHA, MAA and an emulsion (1) of a mixture a containing a silane coupling agent were prepared. Separately from this emulsified liquid (1), 0.7 parts by mass of the above “AQUALON HS-10”) was dissolved in 9 parts by mass of distilled water to obtain another solution. After adding 21.4 parts by mass of MMA, 12.7 parts by mass of 2EHA, 0.8 parts by mass of MAA and 0.1 parts by mass of Z-6033 to this solution, the mixture was sufficiently stirred to give MMA, 2EHA. The emulsion (2) of the mixture b containing MAA and a silane coupling agent was prepared. After the mixture liquid equivalent to Example 1 was heated in the reactor and adjusted to 80 ° C., the emulsion (1) was first added over 2 hours together with the aqueous solution in which KPS equivalent to Example 1 was dissolved. Thereafter, the emulsion (2) was added over 1 hour. After completion of the addition, stirring was continued for 3 hours while maintaining the warmed state. In this way, a resin composition containing 36.3% by mass of the binder of Example 13 in terms of its solid content was obtained. About this binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. Using this electrode, the adhesion test 1, the adhesion test 2, the swelling test, and the discharge cycle test were performed in the same manner as in the above-described experiment A. The results are shown in Table 4 below.

[Examples 14-17]
The binders of Examples 14-17 were obtained in the same manner as in Example 13, except that the blends of the mixture a and the mixture b were as shown in Table 4 below. About each binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. Using this electrode, the adhesion test 1, the adhesion test 2, the swelling test, and the discharge cycle test were performed in the same manner as in the above-described experiment A. The results are shown in Table 4 below. In the table, “St” represents styrene, and “BD” represents butadiene.

[Example 18]
In 21 parts by mass of distilled water, 1.5 parts by mass of the above “AQUALON HS-10”) was dissolved to obtain a solution. In this solution, 2 parts by weight of MMA, 55.5 parts by weight of 2EHA, 30 parts by weight of butyl acrylate (also referred to as BA), 1.8 parts by weight of MAA and 0.7 parts by weight of N-methylol. After blending acrylamide (also referred to as N-MAM), the mixture was sufficiently stirred to prepare an emulsion (1) of a mixture a containing MMA, 2EHA, BA, MAA and N-MAM. Separately from this emulsified liquid (1), 0.7 parts by mass of the above “AQUALON HS-10”) was dissolved in 9 parts by mass of distilled water to obtain another solution. In this solution, 8.1 parts by mass of MMA, 1.6 parts by mass of BA, 0.2 parts by mass of MAA and 0.1 parts by mass of N-MAM were mixed, and then sufficiently stirred, MMA, BA The emulsion (2) of the mixture b containing MAA and N-MAM was prepared. After the mixture liquid equivalent to Example 1 was heated in the reactor and adjusted to 80 ° C., the emulsion (1) was first added over 2 hours together with the aqueous solution in which KPS equivalent to Example 1 was dissolved. Thereafter, the emulsion (2) was added over 1 hour. After completion of the addition, stirring was continued for 3 hours while maintaining the warmed state. In this way, a resin composition containing 36.3% by mass of the binder of Example 18 in terms of the solid content was obtained. About this binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. Using this electrode, the adhesion test 1, the adhesion test 2, the swelling test, and the discharge cycle test were performed in the same manner as in the above-described experiment A. The results are shown in Table 5 below.

[Examples 19-23]
The binders of Examples 19-23 were obtained in the same manner as in Example 18 except that the blends of the mixture a and the mixture b were as shown in Table 5 below. About each binder, it carried out similarly to the case of the binder of Example 1, and manufactured the electrode composition, and produced the electrode using this electrode composition. Using this electrode, the adhesion test 1, the adhesion test 2, the swelling test, and the discharge cycle test were performed in the same manner as in the above-described experiment A. The results are shown in Table 5 below.

  As shown in Table 3, Table 4, and Table 5, the binders of the examples have higher evaluation than the binders of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

  The binder described above can be applied to various battery electrodes.

2 ... Battery 4, 4a, 4b ... Electrode 6 ... Electrolyte 8 ... Separator 10 ... Current collector 12 ... Coating film 16 ... Active material 18 ... Binder 20 ... Core 22 ... Shell

Claims (8)

Based on a polymer obtained by copolymerizing cyclohexyl (meth) acrylate and a monomer copolymerizable with cyclohexyl (meth) acrylate ,
The polymer is prepared as a mixture a and a mixture b containing the cyclohexyl (meth) acrylate and a monomer copolymerizable with the cyclohexyl (meth) acrylate. After the polymerization is performed with the mixture a, the polymerization is performed with the mixture b. Formed by being polymerized while being dropped or mixed with the mixed solution b in the mixture a,
The ratio of the cyclohexyl (meth) acrylate mass in the mixed liquid a is 46.6 mass% or less, and the mass ratio of the cyclohexyl (meth) acrylate in the mixed liquid b is 68.6 mass% or more . binder.   2. The binder for an electrode according to claim 1, wherein the ratio of the mass of the cyclohexyl (meth) acrylate to the total mass of the monomers used for forming the polymer is 5.0 mass% or more and 70.0 mass% or less. The polymer is in the form of particles,
The polymer comprises a core and a shell located outside the core;
The shell has a different composition than the core,
The glass transition temperature of this shell is −60 ° C. or more and 65 ° C. or less,
The binder for electrodes according to claim 1 or 2 whose glass transition temperature of this core is -60 ° C or more and 65 ° C or less. The electrode binder according to any one of claims 1 to 3, wherein the monomer is an unsaturated organosilane and / or N-methylol (meth) acrylamide. The binder for electrodes according to claim 4, wherein a mass ratio of the N-methylol (meth) acrylamide to a total mass of the monomers used for forming the polymer is 0.5% by mass or more and 4.0% by mass or less. The binder for an electrode according to claim 4 or 5, wherein a mass ratio of the unsaturated organosilane to a total mass of the monomers used for forming the polymer is 0.5% by mass or more and 4.0% by mass or less. A binder according to any one of claims 1 to 6, the electrode composition comprising an active material, and a dispersion medium. The electrode obtained by apply | coating the electrode composition of Claim 7 to a collector, and drying.

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