JP2014123550A - Aqueous binder for battery electrode and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copolymer latex excellent in binding strength.SOLUTION: A copolymer latex can be obtained by performing two or more multistage polymerization of 100 pts.wt. of a monomer comprising an aliphatic conjugated diene monomer (a), an unsaturated carboxylic acid alkyl ester monomer (b) and a monomer (c) polymerizable with the aliphatic conjugated diene monomer and the unsaturated carboxylic acid alkyl ester monomer, while the final stage of the multistage polymerization can be obtained by performing polymerization of a monomer mixture comprising 0-5 pts.wt. of an aliphatic conjugated diene monomer (a) and/or an acrylic acid alkyl ester (b-1) and 10-50 pts.wt. of a monomer (c2) copolymerizable with the aliphatic conjugated diene monomer and/or the acrylic acid alkyl ester. An aqueous binder for a battery electrode contains the copolymer latex having a gel content of 94 wt.% or less.

Description

  The present invention relates to an aqueous binder for battery electrodes, and further relates to a method for producing the same.

  Secondary batteries that can be used repeatedly are remarkably widespread. Among them, lithium ion secondary batteries are lightweight and have a high energy density, and in recent years, their use for automobiles or residential power storage has expanded. In automobile or residential storage batteries, more capacity and cycle life are required than lithium ion secondary batteries used in mobile phones and laptop computers. A polymer binder is mentioned as one of the factors greatly related to the performance of the lithium ion secondary battery. The polymer binder is usually used as a binder in preparing an electrode for a lithium ion secondary battery. An electrode composition is prepared by blending an active material capable of inserting and extracting lithium (a negative electrode active material and a positive electrode active material) with a polymer binder, and the electrode composition is used as a metal substrate (hereinafter referred to as a current collector). .) The active material and the current collector are bound together by applying and drying on. The strength with which the polymer binder bonds the active materials to each other (hereinafter referred to as the binding force in the mixture layer) and the strength to bond the active material to the current collector (hereinafter referred to as the interface binding force) are the capacity of the battery. In addition, the battery electrode manufacturing process also affects productivity due to electrode peeling. For this reason, the binding force of the polymer binder (meaning binding force in the mixture layer and interfacial binding force) is important.

  Conventionally, fluorine-based polymers such as polyvinylidene fluoride have been used as the polymer binder. However, since a fluorine-based polymer such as polyvinylidene fluoride uses an organic solvent, it has been regarded as a problem that the solvent is volatilized when the electrode composition is dried, resulting in a heavy burden on the human body and the environment. For this reason, in recent years, various water-based polymer binders that do not use organic solvents have been proposed in consideration of environmental considerations, and styrene-butadiene copolymer latex is mainly used.

  As described above, since the binding force of the polymer binder is an important factor in determining the battery performance, studies on improving the binding force are being actively carried out even in aqueous binders. For example, Japanese Patent Application Laid-Open No. 11-167721 (Patent Document 1) uses a method of crosslinking a polymer when the remaining amount of monomer is 30% by weight or less, or Japanese Patent Application Laid-Open No. 10-302797 (Patent Document 2) It has been proposed to make a difference in the glass transition point.

Japanese Patent Laid-Open No. 11-167721

Japanese Patent Laid-Open No. 10-302797

  However, even in these improvement studies, sufficient binding force has not yet been obtained, and further improvement studies are required. An object of the present invention is to provide a polymer binder having an excellent binding force, thereby improving battery performance and productivity in a battery electrode manufacturing process.

  As a result of various studies, the present inventors have found that the above problems can be improved by using a battery electrode aqueous binder obtained by devising a method for producing a copolymer latex.

  That is, the aqueous binder for battery electrodes of the present invention comprises an aliphatic conjugated diene monomer (a), an unsaturated carboxylic acid alkyl ester monomer (b), and a monomer copolymerizable with these (c). Is obtained by polymerizing 100 parts by weight of a monomer composed of two or more stages of multi-stage polymerization, and the final stage is an aliphatic conjugated diene monomer (a) and / or an alkyl acrylate ester ( It is a copolymer latex obtained by polymerizing a monomer mixture composed of 0 to 5 parts by weight of b-1) and 10 to 50 parts by weight of a monomer (c2) copolymerizable therewith. And a copolymer latex having a gel content of 94% by weight or less.

  By using the aqueous binder for battery electrodes of the present invention, it is possible to obtain a strongly bonded electrode coating layer that is excellent in both the binding force in the mixture layer and the interfacial binding force. By using such an electrode, the battery A battery having good performance and productivity in the battery electrode manufacturing process can be obtained.

  The aqueous binder for battery electrodes of the present invention comprises an aliphatic conjugated diene monomer (a), an unsaturated carboxylic acid alkyl ester monomer (b), and a monomer copolymerizable with (a) and (b). It contains a copolymer latex obtained by emulsion polymerization of a monomer composition containing the monomer (c).

Examples of the aliphatic conjugated diene monomer (a) include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3. -Butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes and the like can be mentioned, and one or more can be used. 1,3-butadiene is particularly preferable.
The aliphatic conjugated diene monomer (a) is not particularly limited, but is preferably 1 to 50 parts by weight and more preferably 2 to 45 parts by weight in 100 parts by weight of the total monomer composition.

Examples of the unsaturated carboxylic acid alkyl ester monomer (b) include acrylic acid alkyl esters (b-1) having an alkyl group having 1 to 8 carbon atoms, such as methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. In addition, for example, methacrylic acid alkyl ester having an alkyl group having 1 to 4 carbon atoms such as methyl methacrylate and ethyl methacrylate, for example, maleic acid having an alkyl group having 1 to 4 carbon atoms such as dimethyl maleate and diethyl maleate Acid alkyl esters such as dimethyl itaconate, etc. Itaconic acid alkyl esters having an alkyl group having 1 to 4 carbon atoms such as monomethyl fumarate, monoethyl fumarate, dimethyl fumarate, diethyl fumarate, etc. Four Examples thereof include alkyl esters of fumaric acid having an alkyl group, for example, unsaturated monomers containing a hydroxyalkyl group such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate, and one or more of these are used. be able to. Preferably, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and methyl methacrylate are used.
The unsaturated carboxylic acid alkyl ester monomer (b) is not particularly limited, but is preferably 1 to 45 parts by weight and more preferably 2 to 40 parts by weight in 100 parts by weight of the total monomer composition.

The monomer (c) copolymerizable with the above (a) and (b) can be used without particular limitation as long as it is an ethylenically unsaturated monomer. For example, styrene, α-methylstyrene, methyl Aromatic vinyl monomers such as α-methylstyrene, vinyltoluene and divinylbenzene, for example, vinyl cyanide monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, such as acrylic Ethylenically unsaturated carboxylic acid monomers such as acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid, for example, ethylenically unsaturated acrylamide, methacrylamide, N, N-dimethylacrylamide, N-methylolacrylamide and the like Carboxylic acid amide monomers, for example, vinyl carboxylates such as vinyl acetate Examples of the tellurium include ethylenically unsaturated amine monomers such as methylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and 2-vinylpyridine. it can.
The monomer (c) copolymerizable with (a) and (b) is not particularly limited, but is 5 to 98 parts by weight, more preferably 15 to 96 parts by weight in 100 parts by weight of the total monomer composition. Can be used.

The copolymer latex in the present invention is produced by emulsion polymerization using 100 parts by weight of the above monomer mixture by multistage polymerization of two or more stages. The emulsion polymerization is preferably performed by multistage polymerization of three or more stages. Here, the final stage in the multistage polymerization is 0-5 parts by weight of the aliphatic conjugated diene monomer (a) and / or the alkyl acrylate ester (b-1), and a monomer copolymerizable therewith. (C2) It is necessary to be composed of 10 to 50 parts by weight.
When the amount of the aliphatic conjugated diene monomer (a) and / or the acrylic acid alkyl ester (b-1) in the final stage exceeds 5 parts by weight, both the interfacial binding force and the binding force in the mixture layer decrease. To do. Further, when the amount of the copolymerizable monomer (c2) in the final stage is less than 10 parts by weight, the interfacial binding force is lowered, and when it exceeds 50 parts by weight, the binding force in the mixture layer is lowered.

The copolymerizable monomer (c2) used in the final stage of the multistage polymerization includes the copolymerizable monomer (c) and the unsaturated carboxylic acid alkyl ester monomer (b). Refers to a monomer selected from monomers other than the alkyl acrylate ester (b-1), and can be used alone or in combination of two or more.
Among them, a component whose homopolymer is in a glass state at room temperature is preferable, and specific examples include styrene, methyl methacrylate, acrylonitrile and the like.

The monomer is polymerized in the presence of various chemical substances used in known emulsion polymerization including an emulsifier, a polymerization initiator, a reducing agent, and a chain transfer agent.
Examples of the emulsifier include anionic anions such as sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, and sulfate esters of nonionic surfactants. Surfactants, for example, nonionic surfactants such as polyethylene glycol alkyl ester type, alkylphenyl ether type, alkyl ether type, etc., can be mentioned, and one or more are used. Preferably, an anionic surfactant is mentioned, More preferably, alkylbenzene sulfonate and alkyl diphenyl ether disulfonate are mentioned.
The emulsifier is used in a proportion of, for example, 0.05 to 5 parts by weight, preferably 0.1 to 3 parts by weight, with respect to 100 parts by weight of monomers (total).

  The polymerization initiator is a radical polymerization initiator, for example, a water-soluble polymerization initiator such as potassium persulfate, sodium persulfate, ammonium persulfate, such as cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide. And oil-soluble polymerization initiators such as acetyl peroxide, diisopropylbenzene hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide. Preferably, the water-soluble polymerization initiator includes potassium persulfate, sodium persulfate, and ammonium persulfate, and the oil-soluble polymerization initiator includes cumene hydroperoxide.

  Examples of the reducing agent include ferrous sulfate, sulfite, bisulfite, pyrosulfite, nitrite, nithionate, thiosulfate, formaldehyde sulfonate, benzaldehyde sulfonate, such as L- Examples thereof include carboxylic acids such as ascorbic acid, erythorbic acid, tartaric acid, citric acid, and salts thereof, for example, reducing sugars such as dextrose and saccharose, and amines such as dimethylaniline and triethanolamine. Preferably, ferrous sulfate, carboxylic acids and salts thereof are used, and more preferably, ferrous sulfate and erythorbic acid are used.

Examples of the chain transfer agent include alkyl having 6 to 18 carbon atoms such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan. Mercaptans, for example, xanthogen compounds such as dimethylxanthogen disulfide, diisopropylxanthogen disulfide, for example, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, for example 2,6-di-t-butyl Phenol compounds such as -4-methylphenol and styrenated phenol, for example, allyl compounds such as allyl alcohol, such as dichloromethane, dibromometa Halogenated hydrocarbon compounds such as carbon tetrabromide, for example, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, such as triphenylethane, pentaphenylethane, acrolein, and metaacrolein. , Thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, terpinolene, α-methylstyrene dimer, and the like, and one or more can be used. Preferred are α-methylstyrene dimer and alkyl mercaptan, and more preferred are α-methylstyrene dimer and t-dodecyl mercaptan.
A chain transfer agent is used in the ratio of 0-5 weight part with respect to 100 weight part of monomers (total), for example, Preferably, 0.05-3 weight part.

In the emulsion polymerization, if necessary, as a hydrocarbon solvent, for example, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptane, such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4 Unsaturated hydrocarbons such as -methylcyclohexene, 1-methylcyclohexene, for example,
Aromatic hydrocarbons such as benzene, toluene and xylene can be used. In particular, cyclohexene and toluene, which have a moderately low boiling point and can be easily recovered and reused by steam distillation or the like after the completion of polymerization, are preferable from the viewpoint of environmental load.

  As other polymerization aids, for example, anti-aging agents, preservatives, dispersants, thickeners and the like can be added as necessary.

  The polymerization method of the copolymer latex in the present invention is not particularly limited, and batch polymerization, semi-batch polymerization, seed polymerization and the like can be used. Moreover, the addition method of various components is not particularly limited, and a divided addition method, a continuous addition method, a power feed method, and the like can be used.

  The gel content of the copolymer latex in the present invention needs to be 94% by weight or less. More preferably, it is 80 weight% or less. When it exceeds 94% by weight, the binder becomes hard and the binding force is inferior.

  Although the average particle diameter by the photon correlation method of the copolymer latex in this invention is not specifically limited, It is preferable that it is 50-200 nm. If the thickness is less than 50 nm, the viscosity of the electrode composition tends to increase and the applicability to the current collector tends to be poor. As a result, a uniform electrode coating layer cannot be obtained, and the binding force may be reduced. . If it exceeds 200 nm, the copolymer latex does not reach the details of the active material, and the binding force tends to be inferior.

The aqueous binder for battery electrodes of the present invention is used for forming electrodes of secondary batteries such as non-aqueous electrolyte secondary batteries, nickel hydride batteries, nickel cadmium batteries, and the like. The particles and the negative electrode active material or the positive electrode active material and the current collector are bound.
Specifically, the battery electrode composition is prepared by blending the battery electrode aqueous binder into the negative electrode active material or the positive electrode active material. That is, the composition for negative electrodes used for the negative electrode of a secondary battery is prepared by mix | blending the aqueous binder for battery electrodes with a negative electrode active material. Moreover, the composition for positive electrodes used for the positive electrode of a secondary battery is prepared by mix | blending the aqueous binder for battery electrodes with a positive electrode active material.

  The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium. In the case of a non-aqueous electrolyte secondary battery, for example, carbon fluoride, graphite, carbon fiber, resin-fired carbon, linear graphite, Hybrid, coke, pyrolytic gas-layer-grown carbon, furfuryl alcohol resin calcined carbon, mesocarbon microbeads, mesophase pitch carbon, graphite whiskers, pseudo-isotropic carbon, calcined natural materials, and pulverized products thereof Conductive carbonaceous materials, for example, conductive materials such as polyacenic organic semiconductors, polyacetylene, and poly-p-phenylene, and composite materials containing simple metals such as silicon and tin, metal oxides, or alloys thereof 1 type, or 2 or more types can be used.

The positive electrode active material is not particularly limited as long as it is a material capable of inserting and extracting lithium. In the case of a non-aqueous electrolyte secondary battery, for example, MnO ₂ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , Fe transition metal oxides such as _{2 O 3, Fe 3 O 4} , for _{example, LiCoO 2, LiMnO 2, LiNiO} 2, LiFePO 4, Li X Co Y Sn Z O 2 composite oxide containing lithium, such as, for example, TiS ₂ , Transition metal sulfides such as TiS ₃ , MoS ₃ , and FeS ₂ , for example, metal fluorides such as CuF ₂ and NiF ₂ , and one kind or two or more kinds can be used.

When preparing the battery electrode composition, the solid content of the copolymer latex is, for example, 0.1 to 7 weights with respect to 100 parts by weight of the negative electrode active material or the positive electrode active material. Parts, preferably 0.3 to 5 parts by weight.
If the solid content of the copolymer latex with respect to 100 parts by weight of the negative electrode active material or the positive electrode active material is less than 0.1 parts by weight, there is a tendency that good adhesion to a current collector or the like cannot be obtained, and it exceeds 7 parts by weight. When the battery is assembled as a secondary battery, the overvoltage is remarkably increased and the battery characteristics tend to be deteriorated.

  Moreover, various additives, such as a water-soluble thickener, a dispersing agent, and a stabilizer, can be added to the battery electrode composition as necessary. Examples of the water-soluble thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, and casein. Examples of the dispersant include Examples thereof include sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, and sodium polyacrylate, and examples of the stabilizer include nonionic and anionic surfactants.

  The battery electrode composition is applied to a current collector and dried to form an electrode coating layer on the current collector to obtain an electrode sheet. Such an electrode sheet is used as, for example, a positive electrode plate or a negative electrode plate of a lithium ion secondary battery.

Examples of the current collector include a metal foil such as copper and nickel as the current collector for negative electrode, and examples include a metal foil such as aluminum as the current collector for positive electrode.
As a method for applying the battery electrode composition to the current collector, a known method such as a reverse roll method, a comma bar method, a gravure method, an air knife method can be used. A warm air dryer, an infrared heater, a far infrared heater, or the like is used. The drying temperature is usually 50 ° C. or higher.

  According to such an aqueous binder for battery electrodes of the present invention, since it is excellent in both the binding force in the mixture layer and the interfacial binding force, it strongly adheres with excellent binding force between the active materials and between the current collector and the active material. An electrode coating layer can be formed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples.

<Example 1>
Preparation of Copolymer Latex (I) The substances shown in the first stage of Table 1 were added to a pressure-resistant polymerization reactor and sufficiently stirred. The internal temperature was raised to 60 ° C., and heat generation due to initiation of polymerization was confirmed. From 60 minutes to 240 minutes after the start of polymerization, the substances shown in the second row of Table 1 were continuously added at 66 ° C. Thereafter, the polymerization was continued at 66 ° C., and the substances shown in the third stage of Table 1 were continuously added at 71 ° C. from 420 minutes to 600 minutes after the start of polymerization, and the polymerization was further continued until 1020 minutes. After confirming that the polymerization conversion rate exceeded 97%, a polymerization terminator was added, and the internal temperature was cooled to 35 ° C. or lower. After adjusting the pH to about 7 using an aqueous lithium hydroxide solution, unreacted monomers and the like were removed by steam distillation to obtain a copolymer latex (i).

<Examples 2 to 10>
Preparation of copolymer latex (b) to (nu) Copolymer latex (b) to (nu) was obtained in the same manner as copolymer latex (a) except that the compositions shown in Tables 1 and 2 were used. It was.

<Example 11>
Preparation of Copolymer Latex (L) The substances shown in the first stage of Table 2 were added to a pressure-resistant polymerization reactor and stirred sufficiently. The internal temperature was raised to 66 ° C., and heat generation due to initiation of polymerization was confirmed. From 420 minutes after the start of polymerization, the substances shown in the second row of Table 2 were continuously added at 71 ° C. over 600 minutes. Thereafter, the polymerization was continued at 71 ° C. After confirming that the polymerization conversion rate exceeded 97%, a polymerization terminator was added, and the internal temperature was cooled to 35 ° C. or lower. After adjusting the pH to about 7 using an aqueous lithium hydroxide solution, unreacted monomers and the like were removed by steam distillation to obtain a copolymer latex (L).

<Example 12>
Preparation of copolymer latex (wo) A copolymer latex (wo) was obtained in the same manner as the copolymer latex (l) except that the composition and polymerization temperature were as shown in Table 2.

<Comparative Examples 1, 3, 4, 5>
Preparation of copolymer latex (wa), (yo), (ta), (re) Copolymer latex (wa) in the same manner as copolymer latex (ii) except that the composition shown in Table 3 was used. , (Yo), (ta), (le).

<Comparative example 2>
Preparation of Copolymer Latex (F) The materials shown in the first stage of Table 3 were added to a pressure-resistant polymerization reactor and sufficiently stirred. The internal temperature was raised to 66 ° C., and heat generation due to initiation of polymerization was confirmed. Polymerization was continued while maintaining the internal temperature at 66 ° C. After confirming that the polymerization conversion rate exceeded 97%, a polymerization terminator was added, and the internal temperature was cooled to 35 ° C. or lower. After adjusting the pH to about 7 using an aqueous lithium hydroxide solution, unreacted monomers and the like were removed by steam distillation to obtain a copolymer latex (f).
<Comparative Example 6>
Preparation of copolymer latex (So) A copolymer latex (So) was obtained in the same manner as in the copolymer latex (Le) except that the composition shown in Table 3 was used.

  The particle diameter and gel content of the obtained copolymer latex were measured by the methods shown below, and the results are shown in Tables 1 to 3.

Method of measuring average particle size of copolymer latex by photon correlation method The average particle size of copolymer latex by photon correlation method was measured by dynamic light scattering method. In the measurement, FPAR-1000 (manufactured by Otsuka Electronics) was used.

Method for Measuring Gel Content of Copolymer Latex A latex film was produced in an atmosphere at a temperature of 80 ° C. and a humidity of 85%. About 1 g of the prepared latex film was weighed and placed in 400 ml of toluene to swell and dissolve for 48 hours. Thereafter, this was filtered through a 300-mesh wire mesh, and the toluene insoluble matter captured by the wire mesh was dried and weighed. And the percentage of the dry weight of the toluene insoluble part with respect to the weight of a latex film was computed, and it was set as gel content (%).

Preparation of composition for negative electrode Natural graphite having an average particle diameter of 20 μm is used as a negative electrode active material, and an aqueous solution of sodium carboxymethylcellulose (Serogen EP manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener with respect to 100 parts by weight of natural graphite. (Solid content) 1 part by weight and 2 parts by weight of the copolymer latex (solid content) obtained in each of the examples and comparative examples as a binder in an appropriate amount so that the total solid content is 40% Was added and kneaded to prepare a negative electrode composition.

Preparation of Negative Electrode Each negative electrode composition was applied to a 20 μm thick copper foil serving as a current collector, dried at 130 ° C. for 5 minutes, and then roll-pressed at room temperature to form a negative electrode having a coating layer thickness of 100 μm. Obtained.

Measurement of binding force (1) Interfacial binding force The negative electrode obtained by the above method was cut into a strip of 7 cm x 2 cm, a cellophane adhesive tape was applied to the coating layer side, and the coating layer and current collector were collected by hand about 5 mm. The peeled current collector was fixed, and 100 mm / min. The stress applied to peeling when the cellophane adhesive tape was pulled in a direction perpendicular to the peeling surface was measured.
(2) Binding force in the mixture layer The negative electrode obtained by the above method was cut into a strip of 7 cm x 2 cm, a steel plate having a thickness of 1 mm was bonded to the current collector side with a double-sided tape, and a cellophane adhesive tape on the coating layer side. And 100 mm / min. With a tensile tester. The stress at the time of peeling in the 180 ° direction at a speed of was measured.
The results of the binding force obtained in (1) and (2) are shown in Tables 4 and 5.

From Table 4, all of the aqueous binders for battery electrodes of the present invention had good interfacial binding force and binding force in the mixture layer.
From Table 5, in Comparative Example 1, the amount of the aliphatic conjugated diene monomer (a) in the final stage exceeds 5 parts by weight, and the amount of the copolymerizable monomer (c2) is less than 10 parts by weight. Yes, both the interfacial binding force and the binding force in the mixture layer are inferior, but the interfacial binding force is particularly inferior.
Since Comparative Example 2 is batch polymerization, both the interfacial binding force and the binding force in the mixture layer are greatly inferior.
In Comparative Example 3, the amount of the aliphatic conjugated diene monomer (a) at the final stage and the gel content exceed the specified range of this application, and both the interfacial binding force and the binding force in the mixture layer are greatly inferior.
In Comparative Example 4, the amount of the aliphatic conjugated diene monomer (a) in the final stage exceeds 5 parts by weight, and the amount of the copolymerizable monomer (c2) exceeds 50 parts by weight, Although both the interfacial binding force and the binding force in the mixture layer are inferior, the binding force in the mixture layer is particularly poor.
In Comparative Example 5, the amount of the aliphatic conjugated diene monomer (a) in the final stage exceeds the specified range of this application, and both the interfacial binding force and the in-mixture layer binding force are inferior.
In Comparative Example 6, the gel content exceeds the prescribed range, and both the interface binding force and the binding force in the mixture layer are inferior.

  Although the above invention has been provided as an exemplary embodiment of the present invention, this is merely an example and should not be construed as limiting. Modifications of the present invention apparent to those skilled in the art are intended to be included within the scope of the following claims.

  As described above, by using the aqueous binder for battery electrodes of the present invention, it is possible to obtain a strongly adhered electrode coating layer, and it is possible to obtain an electrode with stable quality. As a result, the battery performance and the productivity in the battery electrode manufacturing process are improved, which is very useful.

Claims (4)

  100 parts by weight of a monomer composed of an aliphatic conjugated diene monomer (a), an unsaturated carboxylic acid alkyl ester monomer (b), and a monomer (c) copolymerizable therewith, Obtained by polymerization through two or more stages of polymerization, and the final stage is 0 to 5 parts by weight of an aliphatic conjugated diene monomer (a) and / or an acrylic acid alkyl ester (b-1), and It is a copolymer latex obtained by polymerizing a monomer mixture composed of 10 to 50 parts by weight of the monomer (c2) copolymerizable therewith, and the gel content is 94% by weight or less An aqueous binder for battery electrodes containing a copolymer latex.   2. The aqueous binder for battery electrodes according to claim 1, wherein the gel content of the copolymer latex is 80% by weight or less.   3. The battery electrode aqueous binder according to claim 1, wherein the copolymer latex has an average particle size of 50 to 200 nm according to a photon correlation method. 4.   100 parts by weight of a monomer composed of an aliphatic conjugated diene monomer (a), an unsaturated carboxylic acid alkyl ester monomer (b), and a monomer (c) copolymerizable therewith, Obtained by polymerization through two or more stages of polymerization, and the final stage is 0 to 5 parts by weight of an aliphatic conjugated diene monomer (a) and / or an acrylic acid alkyl ester (b-1), and A method for producing a copolymer latex for an aqueous binder for battery electrodes, wherein a monomer mixture composed of 10 to 50 parts by weight of the monomer (c2) copolymerizable therewith is polymerized.