JP2005190747A - Thickening binder for secondary battery electrode and secondary battery electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thickening binder for a secondary battery electrode having high dispersion stability, high binding properties (adhesion properties) with a metallic current collector and good capacity retainability. <P>SOLUTION: The thickening binder for the secondary battery electrode is obtained by emulsion polymerization of monomer components comprising (a) 30-85 wt% aliphatic conjugated diene family monomers, (b) 15-60 wt% ethylene family unsaturated carboxylic acid monomers, (c) 0-55 wt% other monomers copolymerizable with monomers (a) and monomers (b) [wherein, (a)+(b)+(c)=100 wt%], and the secondary battery electrode is manufactured by using the thickening binder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thickening binder for a secondary battery electrode excellent in dispersion stability, binding property (adhesion) with a metal current collector, and capacity retention, and a secondary battery electrode using the same. Is.

In recent years, electronic devices have been remarkably reduced in size and weight, and accordingly, there is a great demand for reduction in size and weight for batteries serving as power sources. Various secondary batteries have been developed to satisfy these requirements, and nickel metal hydride secondary batteries and lithium ion secondary batteries have been put into practical use. As a method for manufacturing the electrode of such a secondary battery, for example, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 11-7948) and Patent Document 2 (Japanese Patent Laid-Open No. 2001-210318), An active material such as a storage alloy or graphite is kneaded with carboxymethyl cellulose as a thickener, styrene butadiene latex as a binder, and water as a dispersion medium, and this paste is used as a metal current collector. There are methods to apply and dry the body.
Here, the thickener functions to increase the dispersion stability of the active material during kneading, and the binder functions to increase the adhesion to the metal current collector. Therefore, in such a method, in order to achieve both dispersion stability and adhesion, it is necessary to use a thickener and a binder, which are essentially insulators, in a certain amount or more. This caused a decrease in capacity retention at the time.
Japanese Patent Laid-Open No. 11-7948 Japanese Patent Laid-Open No. 2001-210318

  The present invention relates to a thickening binder for a secondary battery electrode excellent in dispersion stability, binding property (adhesion) with a metal current collector and capacity retention, and a secondary battery electrode using the same. The purpose is to provide.

The present invention includes (a) 30 to 85% by weight of a structural unit composed of an aliphatic conjugated diene monomer, (b) 15 to 60% by weight of a structural unit composed of an ethylenically unsaturated carboxylic acid monomer, and (c ) 0 to 55% by weight of a structural unit consisting of the above aliphatic conjugated diene monomer and another monomer copolymerizable with an ethylenically unsaturated carboxylic acid [where (a) + (b) + (c) = 100 wt%] of the present invention relates to a thickening binder for secondary battery electrodes, the main component of which is a copolymer latex.
Further, the present invention is characterized in that it is obtained by applying a battery electrode composition obtained by mixing and dispersing an electrode active material to the thickening binder for secondary battery electrodes of the present invention to a current collector. The present invention relates to a secondary battery electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the thickening binder for secondary battery electrodes excellent in the dispersion stability, the binding property (adhesiveness) and the capacity retention ratio of the metal current collector, and the secondary battery using the same An electrode can be provided.

The present invention is described in detail below.
The thickening binder for secondary battery electrodes of the present invention comprises (a) 30 to 85% by weight of a structural unit comprising an aliphatic conjugated diene monomer, and (b) comprising an ethylenically unsaturated carboxylic acid monomer. 15 to 60% by weight of a structural unit, and (c) 0 to 55% by weight of a structural unit consisting of the above aliphatic conjugated diene monomer and another monomer copolymerizable with an ethylenically unsaturated carboxylic acid [where ( a) + (b) + (c) = 100 wt%] as a main component.
Here, the copolymer latex is usually (a) 30 to 85% by weight of an aliphatic conjugated diene monomer, (b) 15 to 60% by weight of an ethylenically unsaturated carboxylic acid monomer, and (c) ) From 0 to 55% by weight of other monomers copolymerizable with the monomer (a) to the monomer (b) [provided that (a) + (b) + (c) = 100% by weight] Obtained by emulsion polymerization.

Examples of the (a) aliphatic conjugated diene monomer used in the production of the thickening binder for secondary battery electrodes of the present invention include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene. And chloroprene, and 1,3-butadiene is preferred from the viewpoint of adhesion.
These (a) aliphatic conjugated diene monomers can be used alone or in combination of two or more.

  Examples of the (b) ethylenically unsaturated carboxylic acid monomer include itaconic acid, acrylic acid, methacrylic acid, fumaric acid, and maleic acid. In view of polymerization stability and dispersion stability, itaconic acid, acrylic acid and methacrylic acid are preferred, and methacrylic acid is most preferred. These (b) ethylenically unsaturated carboxylic acid monomers may be used alone or in combination of two or more.

(C) Other vinyl monomers copolymerizable with the above (a) monomer and (b) monomer include aromatic vinyl compounds, vinyl cyanide monomers, alkyl (meth) acrylates, Examples include vinyl acetate and acrylamide compounds.
Among these, examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and the like, and preferably styrene.
Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and preferably acrylonitrile and methacrylonitrile.

Furthermore, as alkyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl ( (Meth) acrylate, t-butyl (meth) acrylate, n-pentyl (meth) acrylate, i-pentyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (Meth) acrylates such as (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate;
Hydroxyl group-containing (meth) acrylic acid esters such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate;
Ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, Tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate , Polyfunctional (meth) acrylates such as pentaerythritol tetra (meth) acrylate;
Fluorine-containing (meth) acrylic esters such as 2,2,2-trifluoroethyl (meth) acrylate, 1H, 1H-pentadecafluoro-n-octyl (meth) acrylate;
Epoxy group-containing (meth) acrylic acid esters such as glycidyl (meth) acrylate;
2-aminoethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, 2-aminopropyl (meth) acrylate, 3-aminopropyl (meth) acrylate, 2-dimethylamino Aminoalkyl group-containing (meth) acrylic acid esters such as propyl (meth) acrylate and 3-dimethylaminopropyl (meth) acrylate;
Under the trade name, BLEMMER PE-90, PE-200, PE-350, PME-100, PME-200, PME-400, AE-350 [above, manufactured by NOF Corporation]; MA-30, MA-50, MA (Meth) acrylic having a polyoxyethylene chain such as -100, MA-150, RA-1120, RA-2614, RMA-564, RMA-568, RMA-1114, MPG130-MA [manufactured by Nippon Emulsifier Co., Ltd.] Acid esters;
Preferred are n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, (meth) acrylic acid ester having a polyoxyethylene chain, and the like.

Furthermore, as acrylamide compounds, (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, Nn-butoxymethyl (meth) acrylamide, N, N′-methylenebisacrylamide, Examples include diacetone (meth) acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.
These components (c) may be used alone or in combination of two or more.

The composition of the monomer component is as follows: (a) 30 to 85% by weight of an aliphatic conjugated diene monomer, (b) 15 to 60% by weight of an ethylenically unsaturated carboxylic acid monomer, and (c) the above It is composed of (a) a structural unit and (c) 0 to 55% by weight of another monomer copolymerizable with the structural unit, provided that (a) + (b) + (c) = 100% by weight.
The (a) aliphatic conjugated diene monomer is an essential component for the adhesion between the electrode active materials and the adhesion between the electrode active material and the metal current collector. 30-85 weight% with respect to a component, Preferably it is 40-82 weight%, More preferably, it is 50-80 weight%. When the component (a) is less than 30% by weight, the adhesion is inferior, whereas when it exceeds 85% by weight, the dispersion stability is inferior.
The amount of the (b) ethylenically unsaturated carboxylic acid monomer used is 15 to 60% by weight, preferably 18 to 55% by weight, more preferably 20 to 50% by weight, based on the total monomer components. %. When the component (b) is less than 15% by weight, the viscosity is inferior, and as a result, the dispersion stability of the active material is inferior. On the other hand, when it exceeds 60% by weight, the adhesion is poor.
Furthermore, the component (c) is mainly used for controlling the hardness according to the purpose, the swelling property of the electrolyte, etc., and its use ratio is 0 to 55% by weight, preferably 0 to 42% by weight, More preferably, it is 0 to 30% by weight.

In the emulsion polymerization of the monomer component used in the present invention, it can be usually produced using an emulsifier, a polymerization initiator and the like in an aqueous medium.
As the emulsifier, anionic surfactants, nonionic surfactants, amphoteric surfactants and the like can be used alone or in combination of two or more.
Examples of the anionic surfactant include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and sulfates of polyethylene glycol alkyl ethers.
As the nonionic surfactant, an ordinary polyethylene glycol alkyl ester type, alkyl ether type, alkylphenyl ether type, or the like is used.
Examples of amphoteric surfactants include those having a carboxylate, sulfate, sulfonate, and phosphate ester salt as the anion moiety, and an amine salt and quaternary ammonium salt as the cation moiety. Examples include betaines such as lauryl betaine and stearyl betaine, and amino acid types such as lauryl-β-alanine, stearyl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine, and the like.

In addition, by performing emulsion polymerization using a reactive emulsifier as an emulsifier, the amount of emulsifier used can be reduced, and in particular, the amount of free emulsifier in the active material paste can be reduced. A thickening binder with less adhesion and excellent adhesion can be obtained.
Examples of the reactive emulsifier include an emulsifier having an ethylenically unsaturated group as a radical reactive group, a polyoxyalkylene group, a sulfone group, a sulfuric acid group as a hydrophilic group, and an alkyl group as a hydrophobic group in one molecule.
Examples of such commercially available reactive emulsifiers include “Latemul S-180A”, “Latemul PD-104” [manufactured by Kao Corporation], “Eleminol JS-2” [manufactured by Sanyo Kasei Co., Ltd.], “Aqualon HS-10” Anionic reactions such as “Aqualon BC-10”, “Aqualon KH-10” [Daiichi Kogyo Seiyaku Co., Ltd.], “Adekaria Soap SE-10N”, “Adekaria Soap SR-10” [Asahi Denka Kogyo Co., Ltd.] Nonionic reactive emulsifiers such as “Aqualon RS-20” [Daiichi Kogyo Seiyaku Co., Ltd.], “Adekaria Soap NE-20” [Asahi Denka Kogyo Co., Ltd.], and the like.
These may be used alone or in combination of two or more.

  The above emulsifier is preferably used in an amount of 0.2 to 20% by weight based on 100% by weight of the monomer component.

Examples of the polymerization initiator include water-soluble polymerization initiators typified by persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, and cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, and the like. Oil-soluble polymerization initiators such as hydroperoxides can be used.
The amount of these water-soluble polymerization initiators and oil-soluble initiators used is 0.01 to 10% by weight with respect to 100% by weight of the monomer component.

In addition, redox polymerization initiators and the like in combination with a reducing agent can be used alone or in combination. Examples of reducing agents include ersorbic acid, sodium sorbate, potassium sorbate, ascorbic acid, sodium ascorbate, potassium ascorbate, saccharides, longgarit sodium formaldehyde sulfoxylate, sodium bisulfite, potassium bisulfite, sodium sulfite, Sulphites such as potassium sulfite, pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite, sodium pyrosulfite, potassium pyrosulfite, sodium thiosulfate, potassium thiosulfate, phosphorous acid, sodium phosphite, potassium phosphite, sulfite Phosphites such as sodium hydrogen phosphate and potassium hydrogen phosphite, pyrophosphorous acid, pyrophosphates such as sodium pyrophosphite, potassium pyrophosphite, sodium hydrogen pyrophosphite, potassium hydrogen pyrophosphite Phosphoric acid salt, mercaptan, and the like.
These reducing agents are preferably used in an amount of 0.01 to 10% by weight based on 100% by weight of the monomer component.

Further, as a more specific addition method of the initiator and the reducing agent, for example, a method of adding both to the polymerization reactor simultaneously from separate supply pipes, a polymerization system in which the initiator is present in excess of the reducing agent Examples thereof include a method of continuously adding a reducing agent therein, and a method of continuously adding an initiator into a polymerization system in which the reducing agent is present in excess of the initiator. The equivalence ratio between the initiator and the reducing agent is preferably between 100/1 and 1/100.
Furthermore, in addition to the initiator and the reducing agent, a redox catalyst can be added to the polymerization system to carry out emulsion polymerization. However, it is desirable not to use the redox catalyst from the viewpoint of charge / discharge capacity of the battery.

In emulsion polymerization of the monomer component used in the present invention, a polymerization chain transfer agent, a chelating agent, an inorganic electrolyte, and the like can be used as necessary.
Specific examples of the polymerization chain transfer agent include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-hexadecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl mercaptan; Xanthogen disulfides such as xanthogen disulfide, diethyl xanthogen disulfide, diisopropylxanthogen disulfide; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide; halogenated hydrocarbons such as chloroform, carbon tetrachloride, ethylene bromide Hydrocarbons such as pentaphenylethane and α-methylstyrene dimer; and acrolein, methacrolein, Lil alcohol, 2-ethylhexyl thioglycolate, terpinolene, alpha-terpinene, .gamma.-terpinene, and the like dipentene. These may be used alone or in combination of two or more. Of these, mercaptans, xanthogen disulfides, thiuram disulfides, carbon tetrachloride, α-methylstyrene dimer and the like are preferably used.
Examples of chelating agents include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, and inorganic electrolytes include sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and carbonate. Ammonium, sodium sulfate, potassium sulfate, ammonium sulfate and the like are used.

Examples of the polymerization method include a one-stage polymerization method, a method of polymerizing a part of the monomer, and then adding the remainder continuously or intermittently, or a method of adding the monomer continuously from the beginning of the polymerization, etc. However, it is not particularly limited, and any method may be used.
The polymerization temperature is preferably such that the temperature in the reaction vessel is between 5 ° C and 100 ° C, more preferably between 20 ° C and 90 ° C, and even more preferably between 30 ° C and 85 ° C. . The thickening binder obtained at a temperature within this range has a good balance between thickening and adhesion, and the amount of chain transfer agent remaining in the thickening binder is small and the odor is small.

  The particle size of the thickening binder of the present invention is not particularly limited, but is preferably 30 nm or more and 300 nm or less after polymerization and before adding a pH adjuster. If it is less than 30 nm, the polymerization stability may be inferior. On the other hand, if it exceeds 300 nm, the adhesion may be lowered. The particle size can be adjusted by the amount of emulsifier, water, initiator, etc. during polymerization.

  The glass transition temperature of the thickening binder (copolymer constituting the latex) of the present invention is preferably −60 to 20 ° C., and more preferably −40 to 10 ° C. When the glass transition temperature is less than −60 ° C., the dispersion stability may be inferior, and when it exceeds 20 ° C., the adhesion may be inferior. The glass transition temperature can be adjusted by the composition of the components (a) to (c).

The molecular weight of the thickening binder of the present invention (copolymer constituting the latex) is preferably 3,000 to 2,000,000 in terms of weight average molecular weight. When the weight average molecular weight is less than 3,000, the dispersion stability may be inferior, whereas when it exceeds 2,000,000, the adhesion may be inferior. The molecular weight can be adjusted by the amount of the chain transfer agent or the polymerization temperature.
The molecular weight distribution may be one group or two or more groups.

The thickening binder of the present invention is thickened by adjusting the pH to 7 or more, preferably 8 or more, using a pH regulator.
As a pH regulator, it is used in amines, aqueous ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium hydrogen carbonate, sodium carbonate, potassium carbonate, disodium hydrogen phosphate, etc. and alkaline secondary batteries described later. And known electrolytes.
The pH adjuster is preferably used after polymerization and before blending with the active material in terms of polymerization stability and dispersion stability.

The thickening binder of the present invention is mixed in an aqueous medium with various additives as necessary as a thickener and binder to the electrode active material to produce an active material paste, which is used as a current collector. Apply to make an electrode.
The amount of the thickening binder used is usually 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight as the solid content of the thickening binder with respect to 100 parts by weight of the active material. If the amount is less than 0.1 parts by weight, good adhesion cannot be obtained. On the other hand, if the amount exceeds 10 parts by weight, the overvoltage is remarkably increased and the battery characteristics are adversely affected.
The solid content concentration of the thickening binder of the present invention is not particularly limited, but is usually 10 to 65% by weight, preferably 20 to 65% by weight. As a mixing method, various kneaders, bead mills, high-pressure homogenizers, and the like can be used.

Moreover, you may use a water-soluble thickener and rubber latex as various additives used as needed.
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 rubber latex include styrene butadiene latex, methyl methacrylate butadiene latex, and acrylonitrile butadiene latex.

The average particle diameter of the secondary battery electrode active material used in the present invention is 0. 0 due to problems such as a decrease in current efficiency, a decrease in slurry stability, and an increase in interparticle resistance in the coating film of the resulting electrode. It is suitable to be in the range of 1 to 200 μm, preferably 3 to 100 μm, more preferably 5 to 50 μm.
The active material paste is applied as a coating solution on a current collector such as an aluminum foil or copper foil, heated and dried to form a battery electrode.
As a coating method, any coater head such as a reverse roll method, a comma bar method, a gravure method, and an air knife method can be used.
Although there is no restriction | limiting in particular in a drying method, A standing drying, a ventilation dryer, a warm air dryer, an infrared heater, a far-infrared heater, etc. can be used.

The thickening binder of the present invention can be used for both aqueous batteries and non-aqueous batteries.
Excellent performance can be obtained with a nickel-metal hydride battery negative electrode as an aqueous battery and an alkaline secondary battery negative electrode, a lithium ion battery negative electrode, etc. as a non-aqueous battery.

The composition for battery electrodes used in the present invention is obtained by mixing and dispersing an electrode active material in the thickening binder of the present invention.
Here, in the battery electrode composition of the present invention, the mixing ratio of (d) the thickening binder and (e) the electrode active material is (d) 0.1 to 10% by weight in terms of solid content, Preferably they are 0.2 to 3 weight%, (e) 90 to 99.9 weight%, Preferably it is 97 to 99.8 weight% [however, (d) + (e) = 100 weight%].
Moreover, the solid content concentration of the battery electrode composition is usually 20 to 80% by weight, preferably 40 to 75% by weight.

This battery electrode composition can be used for both aqueous batteries and non-aqueous batteries. Excellent performance can be obtained with a nickel-metal hydride battery positive and negative electrode as an aqueous battery and a lithium ion battery negative electrode and the like as a non-aqueous battery. As the electrode active material, a hydrogen storage alloy powder is used in an aqueous battery, particularly a nickel metal hydride battery, and a material in which a part of Ni is replaced with Mn, Al, Co or the like based on MmNi ₅ is preferably used. Here, Mm represents Misch metal which is a mixture of rare earths. The shape of the powder is a powder that has passed 100 mesh, and the particle size is about 3 to 400 μm. In a non-aqueous battery, for example, MnO ₂ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , Li _(1-x) CoO ₂ , Li _{(1-x ) · NiO 2, Li x Coy} Sn z O 2, Li (1-X) Co (1-y) Ni y O 2, TiS 2, TiS 3, MoS 3, FeS 2, inorganic, such as CuF _2, NiF ₂ Compound: Carbon materials such as carbon fluoride, graphite, vapor-grown carbon fiber and / or pulverized product thereof, PAN-based carbon fiber and / or pulverized product thereof, pitch-based carbon fiber and / or pulverized product thereof; polyacetylene, poly- Examples thereof include conductive polymers such as p-phenylene. In particular _{Li (1-x) CoO 2} , Li (1-x) NiO 2, Li x Co y Sn z O 2, Li (1-X) Co (1-y) Li-ion containing complex such as Ni _y O ₂ When an oxide is used, both positive and negative electrodes can be assembled in a discharged state, which is a preferable combination.

  Examples of the negative electrode active material include carbon fluoride, graphite, vapor-grown carbon fiber and / or pulverized product thereof, PAN-based carbon fiber and / or pulverized product thereof, pitch-based carbon fiber and / or pulverized product thereof. Preferred are carbon materials such as, conductive polymers such as polyacetylene and poly-p-phenylene, and amorphous compounds composed of compounds such as tin oxide and fluorine. In particular, when a graphite material such as natural graphite, artificial graphite, or graphitized mesophase carbon having a high graphitization degree is used, a battery having good charge / discharge cycle characteristics and high capacity can be obtained. Further, the average particle diameter of the carbonaceous material of the negative electrode active material used is 0 due to problems such as a decrease in current efficiency, a decrease in slurry stability, and an increase in interparticle resistance in the coating film of the obtained electrode. It is suitable that the thickness is in the range of 1 to 50 μm, preferably 3 to 25 μm, more preferably 5 to 15 μm.

  The battery electrode of the present invention is obtained by applying the composition for a battery electrode containing the thickening binder of the present invention to a current collector, preferably in the form of a slurry, and heating and drying as necessary. Examples of the current collector include Ni mesh, punched Ni, and Ni-plated punching metal for water-based batteries, and aluminum foil and copper foil for non-aqueous batteries. As a coating method of the battery electrode composition, any method such as a reverse roll method, a comma bar method, a gravure method, an air knife method can be used, and the drying method is left drying, a blow dryer, a hot air dryer, An infrared heater, a far infrared heater, etc. can be used. The drying temperature is usually 20 to 250 ° C, preferably 130 to 170 ° C. The drying time is usually 1 to 120 minutes, preferably 5 to 30 minutes.

In the case of assembling a battery using the battery electrode obtained as described above, as the non-aqueous electrolyte solution, one in which an electrolyte is dissolved in a non-aqueous solvent is usually used. It is not particularly restricted but includes the electrolyte, To illustrate in an alkaline secondary _{battery, LiClO 4, LiBF 4, LiAsF} 6, CF 3 SO 3 Li, LiPF 6, LiI, LiAlCl 4, NaClO 4, NaBF 4, NaI , (N-Bu) ₄ NClO ₄ , (n-Bu) ₄ NBF ₄ , KPF _{6 and the} like.
Examples of the solvent used in the electrolytic solution include ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, and phosphoric acid. Ester compounds, sulfolane compounds, and the like can be used, and ethers, ketones, nitriles, chlorinated hydrocarbons, carbonates, and sulfolane compounds are particularly preferable. Specifically, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1,2-dichloroethane, γ-butyrolactone, dimethoxyethane, methyl formate, propylene carbonate, ethylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate and mixed solvents thereof Although it can mention, it is not necessarily limited to these. As an electrolytic solution for an aqueous battery, potassium hydroxide of 5 N or more is usually used.

  Further, if necessary, a battery is configured using components such as a separator, a current collector, a terminal, and an insulating plate. Further, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, and if necessary, a paper type battery having a separator as a single layer or multiple layers, or a positive electrode, a negative electrode, and further, a separator is rolled. An example is a form of a cylindrical battery wound in a shape. Specifically, the battery electrode produced using the thickening binder for battery electrodes of the present invention can be suitably used for AV equipment, OA equipment, communication equipment, and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. Each evaluation method in Examples, Comparative Examples, Evaluation Examples, and Comparative Evaluation Examples is shown below.

Evaluation of thickening binders
Measurement of average particle size The particle size was measured using a laser particle size analysis system LPA-3000s / 3100 manufactured by Otsuka Electronics.
Measurement of glass transition temperature (Tg) A thickening agent adjusted to pH 8 with 0.5 N aqueous ammonia was applied to a glass plate and dried at 120 ° C. for 1 hour to obtain a polymer film. This was used and measured using a differential scanning calorimeter manufactured by Seiko Denshi Kogyo.

Evaluation of active material paste Add 100 parts by weight of thickening binder or comparative sample to be evaluated, needle coke pulverized product (average particle size 12 μm) and 40 parts by weight of water adjusted to pH 10 with aqueous ammonia, and mix well. An active material paste was produced and evaluated as follows.
Dispersion stability of the paste The paste after mixing was visually observed, and the case where the fluidity was good and there was no agglomerate was rated as ◯, and the other cases as x.
Bonding with copper foil Using a copper foil with a thickness of 50 μm as a base material, an active material paste obtained by a roll coater was applied at a thickness of 200 g / m ² , dried at 150 ° C. for 10 minutes, and then at room temperature. A 50 μm thick coating film was obtained by pressing. According to the cross-cut test method JIS K5400, the coating film was scratched in a cross-cut pattern, and a cellophane adhesive tape was affixed thereon and evaluated from the number of grids remaining after peeling.
For example, if the adhesion is good, all of the squares remain on the coating film, which is indicated as 100.

Evaluation of Battery Electrode 100 parts by weight of Li _1.03 Co _0.95 Sn _0.042 O _{2 having an} average particle diameter of 2 μm, 7.5 parts by weight of graphite powder, and 2.5 parts by weight of acetone black were mixed to obtain a methyl isobutyl ketone solution of fluororubber (concentration 4). % By weight) was added and mixed and stirred to obtain a coating solution.
This coating solution was applied and dried at 290 g / m ^{2 using a} commercially available aluminum foil (thickness: 15 μm) as a base material to obtain a positive electrode having a thickness of 110 μm.
Next, the copper foil coating film obtained from the active material paste was used as a negative electrode, cut into 0.9 cm × 5.5 cm, and a lithium secondary battery was assembled. The battery was charged to 4.2 V, and the cycle of discharging to 100 V at 2.5 V was repeated 300 times, and the capacity storage rate was measured from the ratio of the first discharge capacity to the 300th discharge capacity.

Example 1, Comparative Examples 1-2
400 parts by weight of water, 1 part by weight of sodium dodecylbenzenesulfonate, 1 part by weight of potassium persulfate, 1 part by weight of t-dodecyl mercaptan, and a single amount shown in Table 1 in an autoclave equipped with a stirrer and capable of adjusting temperature Body components were charged together and reacted at 60 ° C. for 12 hours to obtain a thickening binder (copolymer latex). Table 1 shows the average particle diameter and Tg.

Example 2
It is equipped with a stirrer, and 400 parts by weight of water, 2 parts by weight of Adeka Soap SR-10 manufactured by Asahi Denka Kogyo Co., Ltd., 1 part by weight of potassium persulfate, 0.5 part by weight of t-dodecyl mercaptan , Α-methylstyrene dimer 0.5 part by weight, and monomer components shown in Table 1 were charged all at once and reacted at 60 ° C. for 12 hours to obtain a thickening binder for secondary battery electrodes of the present invention ( Copolymer latex) was obtained. Table 1 shows the average particle diameter and Tg.

Evaluation Examples 1-2, Comparative Evaluation Examples 1-5
The thickening binders obtained in the above examples and comparative examples and commercially available carboxymethylcellulose (CMC) were used in the blending amounts (in terms of solid content) shown in Table 2 to evaluate the active material paste and the battery electrode. Went. The evaluation results are shown in Table 2.
However, in Comparative Evaluation Example 2, since the entire paste was solidified during mixing for paste preparation and electrode preparation was difficult, evaluation of the binding property with copper foil and capacity retention rate could not be performed.

*) PE-350: Nippon Oil & Fats Co., Ltd. Bremer PE-350 (acrylic ester having polyoxyethylene chain)

**) CMC: Carboxymethylcellulose

Examples 1 and 2 in Table 1 are copolymers within the scope of the present invention, and Comparative Examples 1 and 2 are compositions outside the scope of the present invention. As is apparent from Table 2, when the thickening binder of the present invention is used, the dispersibility and the binding property are balanced, and the capacity retention rate of the battery characteristics is excellent.
On the other hand, Comparative Example 1 is an example in which the ethylenically unsaturated carboxylic acid monomer is outside the scope of the present invention. When an attempt is made to produce a paste using this binder, Comparative Evaluation Example 1 As shown, the dispersion stability is poor.
Comparative Example 2 is an example of a binder that has been conventionally used. When a paste is produced using only this binder, the dispersion stability is poor as shown in Comparative Evaluation Example 2.
Comparative evaluation example 3 is an example in which only a thickener conventionally used is used, and is inferior in binding properties and capacity retention. Comparative Evaluation Examples 4 and 5 are examples in which a thickener and a binder that have been used in the past are used in combination. If the amount used is large, both dispersion stability and adhesion can be achieved, but the capacity storage rate is inferior. If the amount is small, it is impossible to achieve both dispersion stability and adhesion.

The thickening binder for secondary battery electrodes of the present invention is excellent in dispersion stability, binding property (adhesiveness) with a metal current collector, and capacity retention, so that either an aqueous battery or a non-aqueous battery can be used. In particular, it can exhibit excellent performance in a negative electrode of a nickel-metal hydride battery that is a water-based battery, a negative electrode of an alkaline secondary battery that is a non-aqueous battery, a negative electrode of a lithium ion battery, and the like.

Claims (5)

  (A) 30 to 85% by weight of a structural unit composed of an aliphatic conjugated diene monomer, (b) 15 to 60% by weight of a structural unit composed of an ethylenically unsaturated carboxylic acid monomer, and (c) the above aliphatic Constituent units consisting of a conjugated diene monomer and another monomer copolymerizable with an ethylenically unsaturated carboxylic acid, 0 to 55% by weight [where (a) + (b) + (c) = 100% by weight] A thickening binder for a secondary battery electrode, the main component of which is a latex copolymer.   (A) 40 to 82% by weight of the structural unit, (b) 18 to 55% by weight of the structural unit, (c) 0 to 42% by weight of the structural unit [provided that (a) + The thickening binder for secondary battery electrodes according to claim 1, wherein (b) + (c) = 100 wt%.   The thickening binder for secondary battery electrodes according to claim 1 or 2, wherein (a) is a structural unit composed of 1,3-butadiene, and (b) is a structural unit composed of methacrylic acid.   It is obtained by applying a battery electrode composition obtained by mixing and dispersing an electrode active material to the thickening binder for secondary battery electrodes according to any one of claims 1 to 3 on a current collector. Secondary battery electrode. A battery electrode composition comprising a binder for a secondary battery electrode according to any one of claims 1 to 3 and an electrode active material is applied in a slurry form to a current collector, heated, and dried. The manufacturing method of the secondary battery electrode of Claim 4.