JPH10270047A - Battery binder composition, battery electrode slurry, lithyum secondary battery electrode, lithyum secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve balance between binding and binding continuity and increase chemical stability of an electrode which uses metallic oxide as active material, by making battery binder composition contain organic dispersion medium and polymer particles which contain specific amount of nonpolar monomer originating repetitious structure unit. SOLUTION: Binder composition is generated by dispersing polymer particles which contain more than 70 wt.% of nonpolar monomer originating repetitious structure unit into organic dispersion medium. Tg of the polymer particles is less than 25 deg.C. As a nonpolar monomer, conjugate diene based monomer or mixture of conjugate diene based monomer and copolymerized nonpolar monomer is used, and as polymer for composing polymer particle, butadiene polymer or isoprene polymer is used. As organic dispersion medium, polar organic compound which is liquid at the room temperature is preferably used. It is preferable that dispersion stabilizer is used when polymer particles are dispersed into the organic dispersion medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition for a secondary battery and its use, and more particularly, to a method of dispersing polymer particles containing at least 70% by weight of a repeating structural unit derived from a nonpolar monomer in a polar organic dispersion medium. The present invention relates to a binder composition for a lithium secondary battery, a slurry for a battery obtained using the binder composition, an electrode, and a lithium secondary battery.

[0002]

2. Description of the Related Art In general, a battery electrode is prepared by dissolving a binder for a battery (hereinafter sometimes simply referred to as a binder) in a dispersion medium or dispersing the binder in a dispersion medium to form a binder composition. A battery electrode slurry (hereinafter sometimes referred to as a slurry), which is a mixture of the active materials, is applied to the current collector, and the dispersion medium or the dispersion medium is removed by a method such as drying. And the active materials are bound together. The capacity of the battery is determined by a plurality of factors such as the type and amount of the active material and the type and amount of the electrolytic solution, and the performance of the binder is also an important factor. If the binder can bind a sufficient amount of the active material to the current collector and cannot bind the active materials to each other, a large-capacity battery cannot be obtained. Drop off, and the battery capacity decreases. In other words, the binder has a strong binding property between the current collector and the active material and the active material (hereinafter sometimes simply referred to as a binding property), and a volume change of the active material due to repetition of charge and discharge. There is a demand for a binding continuity (hereinafter, sometimes simply referred to as binding continuity) such that the active material does not fall off or the active materials fall off.

An industrially used binder for a lithium secondary battery is a polyvinylidene fluoride-based polymer, which is dissolved in N-methylpyrrolidone or the like to obtain an organic dispersion medium-based binder composition. Thereafter, the active material is mixed to form a slurry, which is applied to a current collector and dried to form an electrode. However, when this binder is used, the binding property between the current collector and the active material is not always sufficient, and the active material is dropped off (insufficient binding force) due to the volume change of the active material due to repeated charging and discharging. There is a major problem in the binding durability (for example, Japanese Patent Application Laid-Open No. H6-163031). This is thought to be because the polyvinylidene fluoride-based polymer surrounds the active material in a network (fibril) shape, which has a strong binding property for binding the active materials. This is considered to be due to the fact that the bonding between the active material and the active material is not sufficiently effective. Moreover,
Polyvinylidene fluoride polymers do not have sufficient rubber elasticity, so they cannot cope with volume fluctuations of the active material due to repeated charging and discharging, and have sufficient binding continuity to prevent the active material from falling off. No effect.

Therefore, attention has been paid to the rubber elasticity of rubber, and it has been proposed to use a slurry in which an active material is mixed in a solution of uncrosslinked rubber (for example, JP-A-3-53450, JP-A-5-62668). However, when such a binder is used, the capacity may be reduced.
Further, latex rubber particles suspended in water are used as a binder (for example, see JP-A-5-21068).
And Japanese Patent Application Laid-Open No. Hei 5-74461), however, with ordinary rubber latex, the binding force between the current collector and the active material may be insufficient, and sufficient performance can still be obtained. Not. When a known rubber is used as a binder as described above, the elasticity of the rubber has a large effect on the binding durability, but the binding property between the active material and the current collector or the active material is not improved. Is not effective enough. For these reasons, a method has been proposed in which carboxymethylcellulose is mixed with and dissolved in a latex in which styrene-butadiene rubber is suspended in water, and used to enhance the binding property (Japanese Patent Application Laid-Open No. 4-342966). However, carboxymethylcellulose lowers the flexibility of the electrode, causing an imbalance in the performance with the binding durability of the rubber latex, resulting in insufficient performance. In addition, when rubber latex is used in an electrode using a metal oxide-based active material, the performance of the active material itself may be lost due to water, and a binder and a binder composition with sufficient performance have not been obtained yet. Therefore, at present, there is a need for the development of a new binder for a lithium secondary battery having excellent binding properties and binding durability and excellent battery characteristics.

[0005]

Based on such prior art, the present inventors have conducted intensive studies to obtain a new battery binder, and as a result, dispersed polymer particles having a reduced ratio of polar monomers in an organic dispersion medium. The binder composition,
It has been found that the binder composition has a good balance between the binding property and the binding durability, and furthermore provides a binder composition having excellent chemical stability of an electrode (especially a positive electrode) using a metal oxide as an active material.
The present invention has been completed.

[0006]

Thus, according to the present invention, as a first invention, a binder composition for a battery comprising polymer particles containing at least 70% by weight of a repeating structural unit derived from a nonpolar monomer and an organic dispersion medium. Is provided, as a second invention, a slurry for a battery electrode in which the composition contains an active material is provided, and as a third invention, an electrode for a lithium secondary battery using the slurry is provided. As a fourth invention, a lithium secondary battery using the electrode is provided.

[0007] 1. Battery binder composition The binder composition of the present invention is obtained by dispersing polymer particles containing 70% by weight or more of a repeating structural unit derived from a nonpolar monomer in an organic dispersion medium. 1-1. Polymer particles The polymer particles used in the present invention have a repeating structural unit derived from a nonpolar monomer of 70% by weight or more, preferably 7% by weight or more.
5% by weight or more, more preferably 80% by weight or more of polymer particles. In order to enhance the binding durability, the Tg of the polymer particles is preferably low. Therefore, the polymer particles of the present invention have a Tg of 25 ° C. or less. Preferably, it is 0 ° C or lower, more preferably -20 ° C or lower.

The polymer particles used in the present invention have a repeating structural unit derived from a non-polar monomer. It is a non-polar monomer that provides this structural unit, and the non-polar monomer in the present invention is a halogen atom, a hydroxyl group,
A group containing an atom having an electronegativity different from a carbon atom and a hydrogen atom, such as an amino group, a nitro group, a carboxyl group, a formyl group, an alkoxy group, an ester group, and a nitrile group (polar group; October 20, 1989) Published `` Chemical Dictionary ''
). Specific examples of such a non-polar monomer include a conjugated diene-based monomer and a non-polar monomer copolymerizable with the conjugated diene-based monomer. The conjugated diene-based monomer is effective for imparting binding properties and binding durability to the polymer particles. Desirable polymer particles used in the present invention are polymer particles containing a repeating structural unit derived from a conjugated diene-based monomer.
It is 0% by weight or more, preferably 80% by weight or more, and more preferably 95% by weight or more. If the proportion of the conjugated diene monomer is small, the binding strength tends to be insufficient, which is not preferable. Specific examples of the conjugated diene monomer include:
1,3-butadiene, isoprene, 2,3-dimethyl-
Examples thereof include 1,3-butadiene, 1,3-pentadiene, and piperylene, and preferably include 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene. These can be used alone or in combination of two or more. Non-polar monomers copolymerizable with conjugated diene monomers include styrene, α-methylstyrene, β-
Styrene-based monomers such as methylstyrene, pt-butylstyrene, and chlorostyrene are exemplified. These can be used alone or in combination of two or more.

The polymer particles of the present invention may have, if necessary, structural units derived from a polar monomer copolymerizable with a conjugated diene-based monomer. Are methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, Acrylic esters such as hydroxypropyl acrylate and lauryl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamido methacrylate Methacrylates such as n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxypropyl methacrylate, lauryl methacrylate; methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, isobutyl crotonate, n-crotonate Amyl, isoamyl crotonate, n-hexyl crotonate, croton 2-ethylhexyl,
(Meth) acrylic acid esters such as crotonic acid esters such as hydroxypropyl crotonic acid; Of these, alkyl (meth) acrylate is preferred, and the alkyl moiety has 1 to 6, preferably 1 to 4 carbon atoms.

Specific examples of other copolymerizable polar monomers include nitrile group-containing monomers such as acrylonitrile and methacrylonitrile; acrylamide monomers such as acrylamide, N-methylolacrylamide and N-butoxymethylacrylamide; methacrylamide, N -Methacrylamide monomers such as methylol methacrylamide, N-butoxymethyl methacrylamide; glycidyl acrylate, glycidyl methacrylate,
Glycidyl group-containing monomers such as allyl glycidyl ether; sulfonic acid group-containing monomers such as sodium styrenesulfonate and acrylamidomethylpropanesulfonic acid; methacrylic acid-based monomers such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; methoxypolyethylene Alkoxy group-containing methacrylic acid monomers such as glycol monomethacrylate; unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid; maleic acid, fumaric acid, citraconic acid, methaconic acid, glutaconic acid, itaconic acid, tetrahydrophthalic acid, Unsaturated dicarboxylic acid monomers such as crotonic acid, isocrotonic acid, and nadic acid; unsaturated acids such as monooctyl maleate, monobutyl maleate, and monooctyl itaconate Dicarboxylic acid monoester; and the like. Of these, preferred examples include styrene monomers, nitrile group-containing monomers, polycarboxylic acid monomers, unsaturated monocarboxylic acid monomers, and alkoxy group-containing methacrylic acid monomers.

Examples of the polymer which becomes the polymer particles used in the present invention include butadiene polymer, isoprene polymer, styrene-1,3-butadiene copolymer, styrene-isoprene copolymer, and styrene-1,3-butadiene-polymer. Isoprene copolymer, 1,3-butadiene-acrylonitrile copolymer, 1,3-butadiene-isoprene-
Acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate copolymer, styrene-acrylonitrile-1,3-butadiene-itaconic acid copolymer Styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer, polystyrene-polybutadiene block copolymer, styrene-1,3-butadiene-itaconic acid-
Preferred examples include homopolymers or copolymers of conjugated diene-based monomers, such as methyl methacrylate-acrylonitrile copolymer.

The polymer particles of the present invention may be single particles formed by one kind of polymer, or may be composite particles in which two or more kinds of polymers exist in a single particle. In this case, it is essential that at least one kind of polymer is a polymer having a polar monomer content of 30 mol% or less.

[0013] The polymer particles used in the present invention can be usually easily produced as a latex. The production method is, for example, a two-stage method such as emulsion polymerization, suspension polymerization, dispersion polymerization, and seed polymerization. It can be obtained by a method such as a polymerization method. The dispersants used in these polymerization methods may be those used in the synthesis of ordinary latex, and specific examples thereof include benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; lauryl sulfate Sodium, alkyl sulfates such as sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate; fatty acid salts such as sodium laurate; sodium polyoxyethylene lauryl ether sulfate;
Ethoxy sulfate salts such as sodium polyoxyethylene nonylphenyl ether tersulfate; alkane sulfonates; sodium alkyl ether phosphate; polyoxyethylene nonyl phenyl ether, polyoxyethylene sorbitan lauryl ester,
Examples include nonionic emulsifiers such as polyoxyethylene-polyoxypropylene block copolymers, and these may be used alone or in combination of two or more. The addition amount of the dispersant can be arbitrarily set, and is usually about 0.01 to 10 parts by weight based on 100 parts by weight of the total amount of the monomers. However, depending on the polymerization conditions, the dispersant may not be used.

The polymerization initiator may be one used in usual emulsion polymerization, dispersion polymerization, suspension polymerization, seed polymerization, etc., for example, persulfates such as potassium persulfate and ammonium persulfate; hydrogen peroxide; Peroxide,
There are organic peroxides such as cumene hydroperoxide and the like, which can be polymerized by a redox polymerization initiator alone or in combination with a reducing agent such as sodium acid sulfite, sodium thiosulfate, ascorbic acid,
Also, 2,2′-azobisisobutyronitrile,
2′-azobis (2,4-dimethylvaleronitrile),
Azo such as 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), dimethyl 2,2'-azobisisobutyrate, and 4,4'-azobis (4-cyanopentanoic acid) Compound; 2,2′-azobis (2-
Aminodipropane) dihydrochloride, 2,2′-azobis (N, N′-dimethyleneisobutylamidine),
Amidine compounds such as 2,2'-azobis (N, N'-dimethyleneisobutylamidine) dihydrochloride;
And the like can be used, and these can be used alone or in combination of two or more. The amount of the polymerization initiator to be used is 0.01 to 100 parts by weight of the total weight of the monomers.
10 to 10 parts by weight, preferably 0.1 to 5 parts by weight. The polymerization temperature and the polymerization time can be arbitrarily selected depending on the polymerization method and the type of the polymerization initiator to be used.
00 ° C., and the polymerization time is about 0.5 to 20 hours.

The shape of the polymer particles used in the present invention may be spherical, irregular or irregular, and is not particularly limited.
5 to 1000 μm, preferably 0.01 to 100 μm,
Particularly preferably, it is 0.05 to 10 μm. If the particle size is too large, when used as a battery binder, it is difficult to contact the electrode active material, and the internal resistance of the electrode increases. If it is too small, the necessary amount of the binder becomes too large, and the surface of the active material is covered. The particle diameter referred to here is the value of the polymer particles 100 in a transmission electron micrograph.
This is a value calculated by measuring the major axis and minor axis of each particle and calculating the average value.

The gel content of the polymer particles used in the present invention is usually at least 30%, preferably at least 60%, more preferably at least 80%. In the present invention, the gel content is calculated as a toluene-insoluble matter. Specifically, 1 g of polymer particles are dried at 100 ° C. for 24 hours, and after measuring the dry weight of the polymer particles, the polymer particles are dried at room temperature of 25 ° C. Immersed in 100 g of toluene for 24 hours, sifted through a 200-mesh sieve, dried the solid matter remaining on the sieve, weighed, and (dried weight of residual solid matter on sieve / dry weight of composite polymer particles) × 100 Is a value calculated from the calculation formula. If the gel content is too small, it may dissolve in the electrolytic solution, which is not preferable.

In order to increase the gel content, it is necessary that the polymer particles have a crosslinked structure. When crosslinking the polymer particles, the conjugated diene-based monomer is self-crosslinked when polymerized at a high temperature of about 80 ° C., so that a crosslinking agent is not necessarily required. However, the use of a crosslinking agent is preferred because the reaction is easily controlled. The amount of the crosslinking agent varies depending on the reaction conditions, the type of the polymer, and the like, but is usually 20% by weight or less based on the polymer.

Specific examples of the crosslinking agent include benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide,
2,5-dimethyl-2,5-di (peroxidebenzoate) hexyne-3,1,4-bis (tert-butylperoxyisopropyl) benzene, lauroyl peroxide, tert-butylperacetate, 2,5-dimethyl-2, 5-di (tert-butylperoxy) hexyne-3,2,5-trimethyl-2,5-di (ter
t-butylperoxy) hexane, tert-butylperbenzoate, tert-butylperphenylacetate, tert-butylperisobutyrate, tert
-Butyl per-sec-octoate, tert-butyl perpiparate, cumyl perpiparate, tert-
Peroxide-based crosslinking agents such as butyl perdiethyl acetate and azo compounds such as azobisisobutyronitrile and dimethylazoisobutyrate; dimethacrylate compounds such as ethylene diglycol dimethacrylate and diethylene glycol dimethacrylate; trimethylolpropane trimethacrylate and the like Trimethacrylate compound; polyethylene glycol diacrylate, 1,3
Cross-linking monomers such as diacrylate compounds such as -butylene glycol diacrylate; triacrylate compounds such as trimethylolpropane triacrylate; divinyl compounds such as divinylbenzene; and the like, and cross-linking agents such as ethylene glycol dimethacrylate. It is preferable to use a crosslinkable monomer such as a dimethacrylate compound or a divinyl compound such as divinylbenzene. Such a crosslinking agent is usually a monomer component 10
0.05 to 30 parts, preferably 0.5 to 10 parts, is used per 0 parts.

In the present invention, polymer particles can be used alone or in combination of two or more.

1-2. Organic Dispersion Medium The organic dispersion medium used in the present invention is not particularly limited, and may be a generally available liquid organic compound at ordinary temperature, and preferably a polar organic compound liquid at ordinary temperature. The polar organic compound referred to here is an organic substance which has a polar group as defined above and is liquid at normal temperature.

Specific examples of the polar organic dispersion medium include methanol, ethanol, propanol, isopropanol,
Alcohols such as butanol, isobutanol, s-butanol, t-butanol, pentanol, isopentanol, and hexanol; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, cyclopentanone, cyclohexanone, and cycloheptanone , Methyl ethyl ether, diethyl ether, dipropyl ether, diisopropyl ether,
Ethers such as dibutyl ether, diisobutyl ether, di-n-amyl ether, diisoamyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether and tetrahydrofuran Γ-
Lactones such as butyrolactone and δ-butyrolactone; lactams such as β-lactam; linear and cyclic amides such as dimethylformamide and N-methylpyrrolidone; methyl lactate, ethyl lactate, propyl lactate, propyl lactate, butyl lactate, and methyl benzoate And the like; a liquid substance which becomes a solvent for an electrolytic solution described later; and the like. Among them, it is preferable to use a dispersion medium having a boiling point of 80 ° C. or higher, preferably 85 ° C. or higher in the electrode manufacturing process. . of course,
Non-polar organic compounds, for example, cycloaliphatics such as cyclohpentane, cyclohexane, cycloheptane; benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene , N
-Aromatic hydrocarbons such as amylbenzene; heptane,
Aliphatic hydrocarbons such as octane, nonane, and decane; and the like can also be used as the organic dispersion medium of the present invention.

1-3. Dispersion Stabilizer In the present invention, when the above-mentioned polymer particles are dispersed in an organic dispersion medium, it is preferable to use a dispersion stabilizer. This is because the polymer particles used in the present invention have a low ratio of repeating structural units derived from polar monomers, so that the solubility parameter (hereinafter referred to as sp value) becomes small, and the organic dispersion medium
In particular, it is sometimes difficult to disperse in a polar organic dispersion medium.

As the dispersion stabilizer used in the present invention, a polymer that is soluble in an organic dispersion medium and has an affinity for polymer particles is used. Specific examples include cellulose compounds and water-soluble polymers such as polyethylene oxide, ethylene glycol and polycarboxylic acid. Among these, cellulosic compounds are particularly preferred. In the present invention, the cellulosic compound is a polysaccharide having a β-1,4-glucosidic bond and has a general cellulose skeleton represented by (C ₆ H ₁₀ O ₅ ) n, Cellulose-based compounds in which a functional group other than a hydrogen atom is bonded instead of a hydrogen atom bonded to at least a part of a hydroxyl group, or a compound containing a salt such as an ammonium salt or an alkali metal salt thereof, preferably the cellulose When the system compound is a 2% solution of the liquid organic substance contained in the binder composition, the solution viscosity is 50 centipoise (hereinafter referred to as cP) or more, preferably 50 cP or more.
0000 cP or less, more preferably 100 cP or more and 50
It is less than 00 cP.

Specific examples of the cellulose compound include a compound represented by the following formula (1).

Embedded image

(In the formula (1), R is each independently a hydrogen atom, a linear / branched / cyclic alkyl group, or a linear / branched alkyl group substituted by a carboxyl group, a hydroxyl group or an alkoxy group. Is.)

The alkyl group in the formula (1) preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, particularly preferably 1 to 3 carbon atoms. The same is true. Specific examples of such a cellulosic compound include cellulose; an alkoxy-bonded cellulose such as methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose and butylcellulose; and a hydroxyalkyl-bonded cellulose such as hydroxyethylcellulose and hydroxypropylcellulose. Type celluloses; carboxyalkyl group-bonded type celluloses such as carboxymethylcellulose, carboxyethylcellulose and carboxypropylcellulose; and the like. These cellulose compounds can be used alone or in combination of two or more. A commercially available cellulosic compound can be used, and a functional group can be introduced into celluloses according to a conventional method.

The use amount of the dispersion stabilizer is 1 to 500% by weight based on the solid content of the polymer particles. If the amount is less than 1 wt%, the stabilizing ability is insufficient, and aggregation of the polymer particles easily occurs. When the content is 500 wt% or more, the function of the polymer particles is not exhibited. Preferably it is 10 to 300 wt%, more preferably 30 to 200 wt%.

The binder composition of the present invention can be used in combination with another binder. For example, it is possible to use N-methylpyrrolidone as a dispersion medium of the binder composition of the present invention, and to add a polymer such as polyvinylidene fluoride which is soluble in the dispersion medium of the present invention.

2. Battery Electrode Slurry The slurry of the present invention is obtained by mixing the above-described binder composition of the present invention with an active material and, if necessary, an additive.

2-1. Active Material As the active material, those used in ordinary lithium secondary batteries can be used. For example, PAN-based carbon fibers such as amorphous carbon, graphite, natural graphite, and MCMB, and pitch-based carbon fibers are used as negative electrode active materials. Carbonaceous material; conductive polymer such as polyacene; LixMyNz
(However, Li represents a lithium atom, M is a metal, preferably Mn, Fe, Co, Sn, B, Al, Ti, W, S
represents at least one selected from i, Cu, V, Cr and Ni, and N represents a nitrogen atom. Further, x, y, and z are respectively 7.0 ≧ x ≧ 1.0, 4 ≧ y ≧ 0, 5
AxMyOz (where A is Li,
P or at least one selected from B, M is C
at least one selected from the group consisting of o, Ni, Al, Sn and Mn, O represents an oxygen atom, and x, y and z are each 1.10 ≧ x ≧ 0.05, 4.00 ≧ y ≧ 0.85,
5.00 ≧ z ≧ 1.5. ) And other metal oxides; TiS ₂ , Li
Metal compounds such as TiS _2; and the like are exemplified.

As the positive electrode active material, TiS ₂ , T
iS _3, amorphous _{MoS 3, Cu 2 V 2 O} 3, amorphous V ₂ O-P
₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , AxMyNzOp
(However, A is Li, M is at least one selected from Co, Ni, Fe and Mn, N is another metal that does not become M, preferably at least one selected from Al and Sn, and O is an oxygen atom. , X, y, z, and p are respectively 1.10 ≧ x ≧ 0.05, 4.00 ≧ y ≧ 0.
85, 2.00 ≧ z ≧ 0, 5.00 ≧ p ≧ 1.5) and other metal oxides. Furthermore, polyacetylene, poly-
An organic compound such as a conductive polymer such as p-phenylene can also be used.

The amount of the active material in the electrode slurry of the present invention is not particularly limited, but is usually 1 to 1000 times, preferably 2 to 500 times, more preferably 3 to 300 times by weight based on the amount of the polymer particles. Times, particularly preferably 5-2
It is blended so as to be 00 times. If the amount of the active material is too small, the active material layer formed on the current collector has many inactive portions, and the function as an electrode may be insufficient. On the other hand, if the amount of the active material is too large, the active material is not sufficiently fixed to the current collector, and easily falls off. It should be noted that a dispersion medium may be added to the electrode slurry to adjust the concentration so that it can be easily applied to the current collector. The additional dispersion medium is the same as the liquid substance.

2-2. Additives If necessary, the slurry of the present invention may contain various additives such as a viscosity modifier, a binding aid, and a conductive material for the slurry. As the additive, those arbitrarily selected can be used. For example, in addition to the above-described dispersion stabilizer, an uncrosslinked rubber having a polar group, PVDF, PTFE, or the like can also be used. A polymer having no polar group, such as ethylene / propylene rubber, polybutadiene, polyisoprene, or polystyrene, or a polymer such as plastic can be used. Among them, a cellulose compound, an uncrosslinked rubber having a polar group, and the like are preferred additives for improving battery performance.

3. Lithium secondary battery electrode The electrode of the present invention is obtained by applying the slurry to a current collector, removing the dispersion medium, and fixing the active material in a matrix formed on the current collector surface. The current collector is not particularly limited as long as it is made of a conductive material.
Metals such as copper, aluminum, and nickel are used. Although the shape is not particularly limited, the thickness is usually 0.001.
A sheet having a thickness of about 0.5 mm is used. The method of applying the slurry to the current collector is not particularly limited. For example, it is applied by doctor blade, immersion, brush coating, or the like. The amount to be applied is not particularly limited, but the thickness of the active material layer formed after removing the dispersion medium is usually 0.005 to 5
mm, preferably about 0.05 to 2 mm. The method for removing the dispersion medium is not particularly limited, but usually, the dispersion medium is removed as quickly as possible within a speed range in which stress concentration occurs and the active material layer does not crack or the active material layer does not peel from the current collector. Is adjusted so that is volatilized and removed.

4. Lithium secondary battery The lithium secondary battery of the present invention may be any one that uses the electrode of the present invention as a positive electrode and / or a negative electrode of a lithium secondary battery. Examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery. The electrolyte solution for such a lithium secondary battery may be a commonly used electrolyte solution, and an electrolyte solution that functions as a battery may be selected according to the types of the negative electrode active material and the positive electrode active material. For example, as the electrolyte, LiClO ₄ , LiB
F ₄ , CF ₃ SO ₃ Li, LiI, LiAlCl, LiP
F ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ S
Electrolytes such as O ₃ and Li (CF ₃ SO ₂ ) ₂ N which are commonly used in lithium secondary batteries. Examples of the dispersion medium for the electrolyte include ethers, ketones, lactones, nitriles, and the like. Examples include amines, amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, phosphate compounds, sulfolane compounds, and the like, and are generally ethylene carbonate, propylene carbonate, and the like. Carbonates such as diethyl carbonate are preferred.

The electrode manufactured using the slurry for a battery electrode of the present invention has a good balance between the binding property and the binding durability, so that a lithium secondary battery having excellent battery characteristics can be obtained.

[0036]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In Examples and Comparative Examples, gel content, Tg, particle size and structure, and water content were measured by the following methods or using the following instruments. (1) Gel content (%): An aggregate of 1 g of polymer particles was dried at 100 ° C. for 24 hours, and the dry weight was measured. Then, the polymer particles were immersed in 100 g of toluene at room temperature of 25 ° C. for 24 hours, sifted through a 200-mesh sieve, the solid matter remaining on the sieve was dried, and the weight was measured. It was calculated from (I). (Dry weight of residual solid on sieve / dry weight of polymer) × 100 (I) (2) Tg: Measured at a temperature rising rate of 1 ° C./min by a temperature change point of dielectric loss. (3) Particle size and structure: With a transmission electron micrograph, the major and minor diameters of each polymer particle were measured for 100 polymer particles, and the average value was determined. If necessary, the particles were stained with osmic acid, and the structure inside the particles was confirmed with a transmission electron microscope. (4) Water content: measured by the Karl Fischer method.

Example 1 (Production of polymer) 5 with a stirrer having a rated capacity of 5 liters
In a 0 Kgf / cm ² pressure-resistant autoclave, 400 parts by weight of 1,3-butadiene, 80 parts by weight of styrene, 5 parts by weight of divinylbenzene, 15 parts by weight of sodium dodecylbenzenesulfonate as an emulsifier, 1500 parts by weight of ion-exchanged water, a polymerization initiator Of azobisbutyronitrile was polymerized at 80 ° C. Monomer consumption is 99.
When the concentration reached 8%, the reaction was stopped by cooling, and the polymer particles a
Latex was obtained. The particle size of the polymer particles a in the latex state was 0.18 μm, and Tg was −75 ° C.

To 100 parts by weight of the obtained latex, 500 parts by weight of a 5% aqueous solution of hydroxyethyl cellulose (HEC) is added and stirred at 30 ° C. for 3 hours to obtain an aqueous dispersion of stabilized polymer particles. Next, 3000 parts by weight of N-methylpyrrolidone (hereinafter referred to as NMP) are mixed, and the mixture is dehydrated at 40 ° C. using an evaporator to obtain a binder composition of polymer particles a having a solid content concentration of 5% by weight and a water content of 500 ppm. The product A was obtained.

To 94 parts by weight of carbon (“KS-15” manufactured by Lonza / graphite-based carbon), the previously obtained binder composition A was added so that the solid content was 6 parts by weight.
The mixture was sufficiently mixed to obtain a negative electrode slurry. This slurry was applied to a copper foil having a width of 8 cm, a length of 20 cm, and a thickness of 18 μm,
After drying, the obtained film was roll-pressed to a thickness of 55
A negative electrode A of μm was obtained.

(Production of positive electrode) To 90 parts by weight of lithium cobaltate, 5 parts by weight (solid weight) of the previously obtained binder composition A was added, and acetylene black 5
The parts by weight were added and mixed well to obtain a positive electrode slurry. The slurry is 8 cm wide, 20 cm long and 18 thick.
The resulting film was applied to a μm aluminum foil and dried, and the obtained film was roll-pressed to obtain a positive electrode A having a thickness of 55 μm.

(Manufacture of Battery) Each of the electrodes obtained above was placed in ² cm ²
, And a polypropylene separator having a thickness of 25 μm is interposed therebetween. This is mixed with a 1: 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate by LiP.
20 cells of a battery were prepared in which an electrolyte was prepared by dissolving F ₆ at a concentration of 1 mol / liter.

(Evaluation of Battery Performance)
Each of the 0-cell batteries was subjected to the constant current method (current density: 0.1 m
(A / cm ² ), charging and discharging to 4.0 V and discharging to 3.0 V were repeated, the electric capacity was measured, and the average value of 20 cells was used as the evaluation result. As a result, the discharge capacity was 205 mAh / g at the end of 5 cycles, and 2 mA at the end of 10 cycles.
The decrease in electric capacity was extremely small at 195 mAh / g at 00 mAh / g for 50 cycles.

Example 2 (Production of a polymer) 5 with a stirrer having a rated capacity of 5 liters
In a 0 kgf / cm ² pressure-resistant autoclave, 340 parts by weight of 1,3-butadiene, 120 parts by weight of styrene, 40 parts by weight of methyl methacrylate, 40 parts by weight of acrylonitrile,
5 parts by weight of divinylbenzene, 25 parts by weight of sodium dodecylbenzenesulfonate, 1 part of deionized water
500 parts by weight and 15 parts by weight of azobisbutyronitrile as a polymerization initiator were added and polymerized at 80 ° C. When the monomer consumption reached 99.8%, the reaction was stopped by cooling to obtain a latex of polymer particles b. The particle size of this polymer was 0.17 μm, and the Tg was −43 ° C. To 100 parts by weight of the obtained latex, a 7% by weight aqueous solution of HEC is added at a solid content of 1: 1 (weight ratio) with the polymer particles, and the mixture is stirred at 30 ° C. for 6 hours. Next, NMP30
Then, water was distilled off under reduced pressure at 80 ° C. using an evaporator, and the solid content was 4% by weight and the water content was 100 p.
An NMP dispersion of pm polymer particles b was obtained. The NMP dispersion obtained here is used as a binder composition B for producing an electrode.

(Manufacture of Negative Electrode) Carbon (Lonza “K
S-15 ") The binder composition B obtained above was added to 92 parts by weight of the polymer particles b so as to be 5 parts by weight (solid content weight), and a 10% by weight NMP solution of polyvinylidene fluoride was further added. A solid content of 3 parts by weight was added and mixed well to obtain a negative electrode slurry. This slurry was applied to a copper foil having a width of 8 cm, a length of 20 cm and a thickness of 18 μm, dried, and the obtained film was roll-pressed to a thickness of 70 μm.
m of the negative electrode B was obtained.

(Preparation of positive electrode) To 90 parts by weight of lithium cobalt oxide, 7 parts by weight (solid content weight) of polymer particles b and the binder composition B obtained above were added, and 10% by weight of polyvinylidene fluoride was added. NMP solution with solid content 3
Parts by weight and thoroughly mixed. Further, 3 parts by weight of acetylene black and 50 parts by weight of NMP were added and sufficiently mixed to obtain a slurry for a positive electrode. This slurry is width 8
A positive electrode B having a thickness of 55 μm was obtained by applying the film to an aluminum foil having a thickness of 20 μm, a length of 20 cm, and a thickness of 18 μm, followed by drying.

(Production of Battery) A battery was produced in the same manner as in Example 1 using the negative electrode B and the positive electrode B.

(Evaluation of Battery Performance) The electric capacity was measured in the same manner as in Example 1. As a result, the discharge capacity is
230 mAh / g at the end of 5 cycles, 225 mAh / g at the end of 10 cycles, 222 at the end of 50 cycles
The decrease in mAh / g and electric capacity was extremely small.

Comparative Example 1 The latex of the polymer particles a obtained in Example 1 was used as a binder composition in an aqueous latex state.
A battery was manufactured in the same manner as in Example 1 and evaluated.
As a result, the battery capacity was 150 mAh at the end of 5 cycles.
/ G, 100 mAh / g at the end of 10 cycles, 50 mAh / g at the end of 50 cycles, the initial capacity was quite low, and a remarkable decrease in capacity was observed during repeated charge and discharge.

Comparative Example 2 (Production of polymer) 5 with a stirrer having a rated volume of 3 liters
In a 0 Kgf / cm ² pressure-resistant autoclave, 200 parts by weight of methyl methacrylate, 50 parts by weight of styrene, 5 parts by weight of sodium dodecylbenzenesulfonate, 5 parts by weight of divinylbenzene as a crosslinking agent, 1000 parts by weight of ion-exchanged water, and azo as a polymerization initiator After 5 parts by weight of bisisobutyronitrile was added and sufficiently stirred, the mixture was heated to 80 ° C. and polymerized. When the monomer consumption reached 99.8%, the mixture was cooled to stop the polymerization. The particle size of the polymer of this latex was 0.21 μm, and the Tg was 101 ° C. To 100 parts by weight of the obtained latex, a 7% by weight aqueous solution of hydroxyethyl cellulose was added so that the solid content was 1: 1 (weight ratio) with the polymer particles, and the mixture was stirred at 30 ° C. for 6 hours. Next, 3000 parts by weight of NMP were added, and water was distilled off under reduced pressure at 80 ° C. using an evaporator to obtain a solid content of 4%.
NMP of polymer particles c having weight% and water content of 100 ppm
A dispersion was obtained.

(Production of Battery and Evaluation of Performance) An NMP dispersion of the obtained polymer particles c was used to form an electrode in the same manner as in Example 1. However, the electrode was cut during the production of the battery and cracked. Could not be made.

Comparative Example 3 A battery was prepared and evaluated in the same manner as in Example 1 except that the polymer particles a were not added to the aqueous solution of 5% by weight of hydroxyethyl cellulose and 500 parts by weight of hydroxyethyl cellulose containing no polymer particles was used. did. As a result, the battery capacity was 190 mAh / g at the end of 5 cycles, 180 mAh / g at the end of 10 cycles, and 60 mAh / g at the end of 50 cycles, but the initial capacity was high. When the number of cycles was exceeded, a sharp decrease in capacity was observed.

Example 3 A latex of polymer particles c was obtained in the same manner as in Example 1 except that styrene was not used. The particle size of the polymer particles c in the latex state is 0.19 μm,
g was -83 ° C. Except for using the polymer particles c, a binder composition C of the polymer particles c having a solid content of 5% by weight and a water content of 300 ppm was obtained in the same manner as in Example 1. A battery was prepared in the same manner as in Example 1 except that this binder composition C was used, and the electric capacity was measured. As a result, the discharge capacity was 217 mAh / g at the end of 5 cycles, and 215 mAh at the end of 10 cycles.
/ G, at the end of 50 cycles, 220 mAh / g, an extremely small decrease in electric capacity.

Claims (5)

[Claims] 1. A battery binder composition comprising at least 70% by weight or more of polymer particles containing a repeating structural unit derived from a non-polar monomer and an organic dispersion medium. 2. The battery binder composition according to claim 1, further comprising a dispersion stabilizer. 3. A slurry for a battery electrode containing polymer particles containing a repeating structural unit derived from a nonpolar monomer in an amount of 70% by weight or more, an organic dispersion medium, and an active material. 4. An electrode for a lithium secondary battery using the slurry according to claim 2. 5. A lithium secondary battery using the electrode according to claim 3.