JPH10279608A - Polymer, battery binder made therefrom, electrode and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a battery binder composition having a good balance between binding properties and their persistence and showing excellent battery characteristics by using a polymer obtained by reacting a compound containing a cellulosic compound or its salt with a rubber having functional groups which can react with the hydroxyl groups to form ester linkages and to obtain a battery obtained therefrom. SOLUTION: The compound used is exemplified by a cellulosic compound containing repeating units of the formula (wherein R is H, an alkyl, carboxyl, hydroxyl or an alkoxyl-substituted alkyl, and at least one R is H) or an ammonium, alkali metal salt thereof and is more particularly exemplified by methylcellulose. The rubber used is one having functional groups which can react with the hydroxyl groups to form ester linkages and are desirably -COOR groups (wherein R is hydrogen, an alkyl or the like). The polymer for the binder is obtained by subjecting an organic solvent solution of e.g. a (meth)acrylic acid copolymer rubber and an organic solvent solution of a cellulosic compound in the presence of an acid catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for a battery, in particular, a binder for a secondary battery and its use.

[0002]

2. Description of the Related Art Usually, a battery electrode is prepared by dissolving a binder for a battery (hereinafter sometimes simply referred to as a binder) in a solvent or dispersing it 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 substances, is applied to a current collector, and a solvent or a dispersion medium is removed by a method such as drying to form an active material on the current collector. It is manufactured by attaching active materials to each other. 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. That is, the binder has a strong binding property between the current collector, the active material, and the active material (hereinafter, may be simply referred to as binding property).
And the continuity of the binding such that the active material does not drop off from the current collector due to the volume fluctuation of the active material due to the repetition of charge and discharge, and the active materials do not drop off (hereinafter, simply referred to as binding continuity). Is required.

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 form an organic solvent-based binder composition. 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 has not yet been obtained. Absent. When a known rubber is used as a binder as described above, the rubber 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.

[0005] For these reasons, a method has been proposed in which carboxymethylcellulose is mixed and dissolved in a latex in which styrene / butadiene rubber is suspended in water to be used by mixing and dissolving the latex (JP-A-4-342966). Such). 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. 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.

[0006]

Based on such prior art, the present inventors have conducted intensive studies to obtain a new battery binder, and as a result, a compound obtained by reacting a cellulosic compound with rubber has been obtained. The present inventors have found that the binder exhibits good battery characteristics with a good balance between adhesion and binding durability, and has completed the present invention.

[0007]

According to the present invention, a cellulose compound containing a repeating structural unit represented by the following formula (1) or a compound containing an ammonium salt or an alkali metal salt thereof is reacted with a hydroxyl group to form an ester. A polymer obtained by reacting with a rubber having a functional group capable of bonding,
A battery binder composition containing the compound, an electrode manufactured using the battery binder, and a lithium secondary battery containing the same are provided.

[0008]

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(In the formula (1), R is each independently a hydrogen atom, a linear, branched or cyclic alkyl group, or a linear or branched alkyl group substituted with a carboxyl group, a hydroxyl group or an alkoxy group. And at least one is a hydrogen atom.)

[0010] 1. Polymer The polymer of the present invention is a reaction product of a certain cellulosic compound and rubber. (Cellulose compound) The cellulosic compound used in the present invention is a cellulosic compound containing a repeating structural unit represented by the above formula (1) or a compound containing an ammonium salt or an alkali metal salt thereof. Preferably, the solution viscosity is 50 when the cellulosic compound is a 2 wt% solution of the liquid substance contained in the binder composition.
100,00 centipoise (hereinafter referred to as cP) or more
0 cP or less, preferably 100 cP or more and 50,000 c
P or less, more preferably 500 cP or more and 10,000 c
P or less. If the viscosity is too small, the molecular weight becomes too small, and the binding force becomes insufficient, which is not preferable. If the viscosity is too high, the viscosity of the slurry increases, making it difficult to apply the slurry, which is not preferable. As the cellulose compound used in the present invention, the alkyl group preferably has 1 to 6 carbon atoms,
More preferably 1 to 4 carbon atoms, particularly preferably 1 carbon atom
And the same applies to the number of carbon atoms in the alkyl portion of the alkoxy group.

Specific examples of such a cellulosic compound include cellulose; an alkoxy-bonded cellulose such as methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose and butylcellulose; and a hydroxyalkyl group-bonded cellulose such as hydroxyethylcellulose and hydroxypropylcellulose. And carboxyalkyl group-bonded celluloses such as carboxymethylcellulose, carboxyethylcellulose and carboxyethylmethylcellulose. These cellulose compounds can be used alone or in combination of two or more.

(Rubber) The rubber used in the present invention must have a functional group capable of reacting with a hydroxyl group to form an ester bond (hereinafter, may be simply referred to as a functional group). In the case of a rubber obtained by polymerizing or copolymerizing a monomer having a functional group, it can be used for the reaction as it is. When the rubber does not have a functional group, the functional group may be introduced into the terminal by introducing a functional group by a polymer reaction or by cutting the main chain by oxidation or the like. The number of functional groups is
It suffices that one or more be contained in one polymer molecule. The functional group of the rubber used in the present invention is not particularly limited as long as it chemically reacts with a hydroxyl group to form an ester bond.
Preferred specific examples include -COOH, -COOR (R
= Alkyl group, substituted alkyl group, alkenyl group or substituted alkenyl group (substituents include halogen atom, alkoxy group, etc.)), -COX (X = fluorine,
Chlorine, bromine or iodine), and particularly preferably -COOH. When such a functional group is introduced by a polymer reaction, for example, in the case of a rubber having a C ＝ C bond, a method of oxidizing C ＝ C to introduce a carboxyl group or a method of converting a (meth) acrylic acid monomer into C ＝ C In the case of a rubber having a cyano group, a method of converting into a carboxyl group can be mentioned, and in the case of a rubber having an amino group, a method of oxidizing after hydrolysis can be mentioned. Also,
In the case of rubber having a hydroxyl group, a method such as a method of oxidizing with an oxidizing agent such as hydrogen peroxide or ozone to form a carboxyl group may be mentioned. These reactions are common chemical methods, and the conditions can be arbitrarily set.

The molecular weight of rubber is a value measured by gel permeation chromatography (GPC) using a THF solvent and is a weight average molecular weight in terms of polystyrene, and is usually 500 or more and 1,000,000 or less, preferably 1,000 or less.
Not less than 200,000. Rubber used in the present invention,
One type of rubber (including a so-called block copolymer) may be used, or a plurality of types of rubber may be used. The rubber may be a cross-linked rubber as in the case of latex particles, or a non-cross-linked rubber such as raw rubber or a thermoplastic elastomer. In the present invention, other than rubber, another polymer other than rubber can be used in combination. The combined ratio of the other polymer is preferably not more than 100% by weight, preferably not more than 80% by weight, more preferably not more than 50% by weight with respect to the amount of rubber.

In the case of a crosslinked rubber, the shape and composition are not particularly limited, but may be in the form of particles or bulk like latex. In this case, particles having a uniform composition may be used, or composite polymer particles containing two or more polymers in a single particle may be used.

When the crosslinked rubber is in particulate form, it is generally manufactured as a latex. Latex can be obtained by an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, a seed polymerization method, or the like. Further, in the case of particles having a heteromorphic structure, the particles can be obtained by a two-stage polymerization method such as seed polymerization.

The dispersant used in the emulsion polymerization method includes
It may be one used in the synthesis of ordinary latex. As an emulsification / suspension stabilizer, water-soluble agents such as gelatin, maleic anhydride-styrene copolymer, polyvinylpyrrolidone, sodium polyacrylate, carboxymethylcellulose, and polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more. Polymers can also be used.

The polymerization initiator may be one used in usual emulsion polymerization, dispersion polymerization, suspension polymerization, seed polymerization and the like. The polymerization initiator is used in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the total weight of the monomers.
-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, but are usually about 50 to 200 ° C., and the polymerization time is 0.5
It is about 20 hours.

In the case of uncrosslinked rubber, the main chain may be linear or may have a branched structure (branch). In the case where the rubber is not cross-linked, it can be obtained by a usual solution polymerization method, emulsion polymerization method or suspension polymerization method.

The polymerization initiator may be one used in usual radical polymerization, anionic polymerization, cationic polymerization, anionic living polymerization, cationic living polymerization and the like. The polymerization temperature and the polymerization time can be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator to be used.
To 200 ° C., and the polymerization time is about 0.5 to 100 hours.

Examples of the monomer used as a raw material for the rubber used in the present invention include conjugated diene monomers, (meth) acrylate monomers, and monomers copolymerizable therewith.

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.

Specific examples of (meth) acrylate monomers include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, acrylic Isoamyl acid, n-acrylic acid
Acrylates such as hexyl, 2-ethylhexyl acrylate, hydroxypropyl acrylate, lauryl acrylate; methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, methacrylic acid Methacrylates such as n-amyl, isoamyl methacrylate, n-hexyl methacrylate, methacryl-2-ethylhexyl, hydroxypropyl methacrylate, lauryl methacrylate; methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, croton Acid isobutyl, crotonic acid n-
Crotonic esters such as amyl, isoamyl crotonic acid, n-hexyl crotonic acid, croton 2-ethylhexyl, and 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 the monomer which can be copolymerized with a conjugated diene monomer or a (meth) acrylate monomer include styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, chlorostyrene. Styrene-based monomers such as acrylonitrile and methacrylonitrile; acrylamide-based monomers such as acrylamide, N-methylolacrylamide and N-butoxymethylacrylamide; methacrylamide, N-methylolmethacrylamide and N-butoxymethylmethacrylamide Methacrylamide-based monomers such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether; glycidyl group-containing monomers such as sodium styrenesulfonate and acrylamide Sulfonic acid group-containing monomers such as mail propane sulfonic acid; amino group-containing methacrylic acid monomers such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; methacrylic acid-based monomers such as methoxypolyethylene glycol monomethacrylate; acrylic acid; Unsaturated monocarboxylic acid monomers such as methacrylic acid; maleic acid,
Fumaric acid, citraconic acid, metaconic acid, glutaconic acid,
Unsaturated dicarboxylic acid-based monomers such as itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid; unsaturated dicarboxylic acid monoesters such as monooctyl maleate, monobutyl maleate, and monooctyl itaconate; Among these, preferred examples include styrene-based monomers and nitrile group-containing monomers, polycarboxylic acid monomers, unsaturated monocarboxylic acid-based monomers, and alkoxy group-containing methacrylic acid-based monomers. Is a preferable example.

Examples of the rubber used in the present invention include polybutadiene, polyisoprene, styrene-1,3-butadiene copolymer, styrene-isoprene copolymer, styrene-1,3-butadiene-isoprene copolymer,
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-methyl methacrylate-acrylonitrile copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, 2-ethylhexyl acrylate-methyl acrylate-acrylic acid-methoxypolyethylene glycol Uses homopolymers or copolymers of conjugated diene monomers such as monomethacrylate and (meth) acrylate monomers, and various copolymerizable monomers with conjugated diene monomers and (meth) acrylate monomers. Preferred examples include diene rubbers represented by copolymers and the like. In addition, ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-
Styrene block copolymer, styrene-isoprene
Block copolymer, styrene-ethylene-propylene-
A block copolymer rubber such as a styrene block copolymer is also a preferred example.

When the rubber of the present invention is a crosslinked rubber, it is preferably crosslinked using a crosslinking agent. When a cross-linking agent is used, the amount of the cross-linking agent varies depending on the reaction conditions and the type of rubber, but is usually 30% by weight or less based on the uncross-linked rubber.

(Reaction) The conditions of the reaction of the present invention can be arbitrarily selected depending on the kind of the functional group capable of reacting with the hydroxyl group to form an ester bond. In the case of a rubber having a carboxyl group as a functional group, such as a copolymer rubber using (meth) acrylic acid as a raw material, the cellulose compound is dissolved in an organic solvent or dispersed in an organic dispersion medium, and then the cellulose compound is added. It can be brought into contact with a solution dissolved in an organic solvent or a dispersion dispersed in an organic dispersion medium, and can be denatured by an ester reaction, preferably using an acid catalyst such as sulfuric acid / hydrochloric acid. The organic solvent and the organic dispersion medium of the rubber can be arbitrarily selected depending on the type of the rubber, and examples thereof include substances other than water among substances that are liquid at ordinary temperature, which will be described later. The contact time between the rubber-containing liquid and the cellulosic compound-containing liquid is usually 0.5 to 25 hours, preferably 1 to 10 hours, and the temperature at the time of contact is usually 0 to 180 ° C.
It is preferably 25 to 100 ° C. (however, when the boiling point of the reaction solvent is lower than the above value, up to the boiling point). When preparing a rubber-containing liquid or a cellulosic compound-containing liquid, an auxiliary agent or the like can be appropriately used as an aid for dissolution or dispersion.

The polymer of the present invention can impart flexibility to the cellulosic compound by having a rubber structure, and can improve the drawback that the binding durability of the cellulosic compound is poor. When a mixture of one or more rubbers and one or more cellulosic compounds is used as a slurry for a battery electrode using a binder to produce an electrode, the difference in specific gravity of the components of the mixture, (part of the components of the mixture, In some cases, it is difficult to uniformly mix the active material and the binder due to the difference in surface tension between the particles, the difference in the size of the active material and the size of the particles, etc. Such a problem is solved when the polymer of the present invention in which is reacted with one compound is used as a binder. Moreover, the low binding property, which is a drawback of the cellulosic compound, can be improved by reacting with rubber, so that the amount of the binder used can be reduced and the battery can have a higher capacity. is there.

2. Battery electrode binder composition The polymer of the present invention can be used as the battery electrode binder of the present invention. After mixing the polymer of the present invention with the active material and additives in a dry state as a binder,
The electrode may be directly adhered to the current collector under pressure to form an electrode, or an appropriate liquid substance may be added to form a slurry, which may be applied to the current collector to form an electrode. Alternatively, a binder composition dissolved or dispersed in a liquid material serving as a dispersion medium is prepared, and an active material and, if necessary, an additive are mixed with the binder composition and applied as a slurry to a current collector of an electrode to manufacture an electrode. It is desirable to do.

Normal temperature (25 ° C.) usable in the present invention
And liquid substances (hereinafter sometimes simply referred to as liquid substances)
May be any as long as it can dissolve or disperse the binder or the active material of the present invention.
Water; alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, s-butanol, t-butanol, pentanol, isopentanol, and hexanol; acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, and cyclopentane Ketones such as nonone, cyclohexanone and cycloheptanone; methyl ethyl ether;
Diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, di-n-amyl ether, diisoamyl ether, methyl propyl ether, methyl isopropyl ether,
Ethers such as methyl butyl ether, ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether, and tetrahydrofuran; lactones such as γ-butyrolactone and δ-butyrolactone; lactams such as β-lactam; cyclopentane; Cyclic aliphatics such as cyclohexane and cycloheptane; benzene, toluene, o-xylene, m-
Aromatic hydrocarbons such as xylene, p-xylene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene, n-amylbenzene; aliphatic hydrocarbons such as heptane, octane, nonane, decane; dimethyl Linear or cyclic amides such as formamide and N-methylpyrrolidone; esters such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, and methyl benzoate; However, among these, the boiling point is 80 ° C
As described above, it is preferable to use a solvent or a dispersion medium having a temperature of 85 ° C. or higher from the viewpoint of the electrode manufacturing step. If necessary, the additives described in the section of the slurry described below, other storage stabilizers, and the like can be added in advance.

3. Slurry for Electrode The binder of the present invention can be used in the production of an electrode by mixing the polymer of the present invention with an active material, a liquid material and, if necessary, an additive to form a slurry.

(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 can be used as the negative electrode active material. , A carbonaceous material such as pitch-based carbon fiber; a conductive polymer such as polyacene; LixMyNz (where Li represents a lithium atom and M represents a metal, preferably Mn, Fe, Co, Sn,
B, Al, Ti, W, Si, 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 ≧ z ≧ 0.5); AxMy
Oz (where A is at least one selected from Li, P or B, M is Co, Ni, Al, Sn and Mn
O represents an oxygen atom, at least one selected from
x, y, and z are 1.10 ≧ x ≧ 0.05 and 4.0, respectively.
0 ≧ y ≧ 0.85, 5.00 ≧ z ≧ 1.5. ) And other metal oxides; metal sulfides such as TiS ₂ and LiTiS ₂ ; and the like.

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 is not particularly limited, but is usually 1 to 1000 times, preferably 2 to 500 times, more preferably 3 to 300 times, based on the weight of the polymer of the present invention. Particularly preferably, it is blended so as to be 5-200 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 solvent or 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 solvent or dispersion medium to be added is the same as the above-mentioned liquid substance.

(Additives) If necessary, various additives such as a viscosity modifier for the electrode slurry, a binding aid, and a conductive material (conductive carbon such as acetylene black) can be added. As the additive, those arbitrarily selected can be used, and examples thereof include cellulose derivatives such as carboxymethylcellulose, carboxyethylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, and carboxyethylmethylcellulose (these include salts such as ammonium salts and alkali metal salts). ), Water-soluble polymers such as polyethylene oxide, ethylene glycol, and polycarboxylic acid, uncrosslinked rubbers having a polar group, PVDF, PTFE, and the like.
Polymers such as propylene rubber, polybutadiene, polyisoprene, polystyrene, and other rubbers having no polar group, and high-molecular polymers such as plastics can be used. Among them,
Cellulose derivatives and uncrosslinked rubbers having polar groups are preferred additives for improving battery performance. Further, other additives, for example, a rubber used for modifying a cellulosic compound can be added for the purpose of being used in combination with the binder of the present invention. The amount of the additive is not particularly limited, but is preferably 0.01 to 300 parts by weight, more preferably 0.1 to 300 parts by weight, based on 100 parts by weight of the binder of the present invention.
It is 1 to 200 parts by weight.

4. 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. The shape is not particularly limited, but usually, the thickness is 0000 to 0000.
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 a blade method, a reverse roll method, a direct roll method, a knife method, a dipping method, or the like. Although the amount to be applied is not particularly limited, the thickness of the active material layer formed after removing the solvent or the dispersion medium is usually 0.005 to 5 mm,
Preferably, the amount is about 0.05 to 2 mm. The method of removing the solvent or the dispersion medium is not particularly limited, but usually, stress concentration occurs, the active material layer is cracked, or the active material layer is separated from the current collector within a speed range as fast as possible. The solvent or the dispersion medium is adjusted and removed so as to be volatilized.

5. 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 solvent for the electrolyte include ethers, ketones, lactones, nitriles, and amines. , Amides, sulfur compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds,
Examples thereof include phosphoric ester compounds and sulfolane compounds. In general, carbonates such as ethylene carbonate, propylene carbonate, and diethyl carbonate are preferred.

According to the present invention, the use of an electrode produced using a binder containing a polymer obtained by the reaction of a cellulosic compound and rubber, an active material, and the like provides excellent battery capacity and cycle characteristics. A lithium secondary battery can be manufactured.

[0037]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 (Production of rubber) In a 50 kgf / cm ² pressure-resistant autoclave equipped with a stirrer, 400 parts by weight of 1,3-butadiene, 250 parts by weight of styrene, 200 parts by weight of methyl methacrylate,
50 parts by weight of acrylic acid, 5 parts by weight of divinylbenzene as a crosslinking agent, 20 parts of sodium dodecylbenzenesulfonate
Parts by weight, 1700 parts by weight of ion-exchanged water, and 5 parts by weight of azobisbutyronitrile as a polymerization initiator were sufficiently stirred, followed by heating to 80 ° C. to carry out polymerization. 9 monomer consumption
When it reached 9.8%, the reaction was stopped by cooling, and a latex of rubber a was obtained.

Aluminum sulfate 5 was added to the obtained latex.
After adding 2000 parts by weight of a 20% aqueous solution to coagulate the rubber particles, the whole amount was filtered with a 200-mesh nylon cloth to remove water, and a coagulated product was obtained. The coagulated product was washed with dilute hydrochloric acid, further washed with water, and repeatedly washed with water until the aqueous layer became neutral. After separating the water and the coagulated rubber particles by filtration, the rubber particles were vacuum-dried at 60 ° C. for 12 hours to obtain dried rubber particles a (aggregate). Dried rubber particles a
Is dispersed in N-methylpyrrolidone (hereinafter, referred to as NMP) using a homogenizer, and the solid content concentration is 10 wt%.
NMP dispersion of rubber particles a was prepared.

(Reaction) In a reaction vessel, 100 parts by weight of an NMP dispersion of rubber particles a (10 parts by weight of rubber solids) are added, 10 parts by weight of carboxymethylcellulose are added, and the mixture is stirred at 40 ° C. for 3 hours. Next, 2 parts by weight of concentrated sulfuric acid was added, and
The reaction was carried out for 4 hours while stirring at a temperature of ° C. The reaction solution was yellow and transparent. After cooling to room temperature, 5 wt% LiOH
An aqueous solution was added to neutralize the reaction solution, the precipitated solid was filtered off, washed with water and dried to obtain a polymer a according to the present invention.
I got The weight of the dried polymer a was 18.8 parts by weight.

(Production of Binder Composition) The polymer a thus obtained was subjected to NMP using a homogenizer.
To obtain a binder composition A having 15 parts by weight (solid content weight) of gopolymer a and 85 parts by weight of NMP. (Production of negative electrode) Carbon (“KS-15” manufactured by Lonza) /
The binder composition A obtained above was added to 95 parts by weight of graphite-based carbon) and 2.5 parts by weight (solid content weight) of the polymer a, 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 obtain a negative electrode A having a thickness of 25 μm.

(Production of positive electrode) To 94 parts by weight of lithium cobaltate, 3 parts by weight (solid content weight) of polymer a and the previously obtained binder composition A were added, and 3 parts by weight of acetylene black and NMP were further added. 50 parts by weight were added and mixed well to obtain a positive electrode slurry. This slurry was applied to an aluminum 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 obtain a positive electrode A having a thickness of 55 μm.

(Manufacture of Battery) Each electrode 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 were repeated to charge to 4.0 V and discharge to 3.0 V, and the electric capacity was measured. The average value was used as the evaluation result. As a result, the discharge capacity was 215 mAh / g at the end of 5 cycles and 21 mAh / g at the end of 10 cycles.
At 0 mAh / g, 203 mAh / g in 50 cycles, the decrease in electric capacity was extremely small.

Example 2 (Production of Rubber) In a 50 kgf / cm 2 pressure-resistant autoclave equipped with a stirrer, 340 parts by weight of 1,3-butadiene, 200 parts by weight of styrene, 20 parts by weight of itaconic acid, 20 parts by weight of methyl methacrylate, and acrylonitrile 20 Parts by weight, 5 parts by weight of divinylbenzene as a crosslinking agent, 25 parts by weight of sodium dodecylbenzenesulfonate, 15 parts of ion-exchanged water
After adding 00 parts by weight and 15 parts by weight of azobisbutyronitrile as a polymerization initiator, the mixture was sufficiently stirred and heated to 80 ° C. to carry out polymerization. When the monomer consumption reaches 98%, further add 200 parts by weight of methyl methacrylate, 150 parts by weight of styrene, 10 parts by weight of itaconic acid, 5 parts by weight of divinylbenzene, and 200 parts by weight of ion-exchanged water, mix well, and polymerize. When the monomer consumption reached 99.8%, the reaction was stopped by cooling to obtain a latex of rubber particles b. NMP1000 is added to 100 parts by weight of the latex of the obtained rubber particles b.
Water was distilled off under reduced pressure at 80 ° C. using an evaporator, and NMP of rubber particles b having a water content of 100 ppm was added.
A dispersion (solid content: 5.5 wt%) was obtained.

(Reaction) NMP dispersion 100 of rubber particles b
In a reaction vessel, 200 parts by weight of a 2 wt% NMP solution of hydroxyethyl cellulose was added, and the mixture was stirred at 40 ° C. for 6 hours. Next, 1 part by weight of concentrated sulfuric acid was added with stirring, and the mixture was heated to 80 ° C.
The reaction was performed for 2 hours. After cooling to room temperature, LiOH 5w
Neutralized with a t% aqueous solution. The precipitated solid was separated by filtration, washed with water and dried to obtain a polymer b according to the present invention. The weight of the dried polymer b was 9.1 parts by weight.

(Production of Binder Composition) 50 parts by weight of the obtained polymer b was dispersed in 500 parts by weight of NMP with a homogenizer to obtain a binder composition B.

(Production of Negative Electrode) Carbon (Lonza “K
S-15 ") The previously obtained binder composition B was added to 96 parts by weight to a solid content of 4 parts by weight, and mixed well to obtain a negative electrode slurry. This slurry is 8 cm wide,
The film was applied to a copper foil having a length of 20 cm and a thickness of 18 μm and dried, and the obtained film was roll-pressed to obtain a negative electrode B having a thickness of 25 μm.

(Production of positive electrode) To 92 parts by weight of lithium cobaltate, the binder composition B obtained above was added so as to have a solid content of 4 parts by weight, and 5 parts by weight of acetylene black was further added.
NMP (50 parts by weight) was added and mixed well to obtain a positive electrode slurry. This slurry was 8 cm wide, 20 cm long,
The film was applied to an aluminum foil having a thickness of 18 μm and dried, and the obtained film was roll-pressed to obtain a positive electrode B having a thickness of 55 μm.

(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
240 mAh / g after 5 cycles, 235 mAh / g after 10 cycles, 232 mAh after 50 cycles
/ G and the decrease in electric capacity was extremely small.

Example 3 (Production of negative electrode) Carbon ("KS-15" manufactured by Lonza)
To 92 parts by weight of the binder composition A obtained in Example 1 was added 5 parts by weight (solid content weight) of the polymer a obtained in Example 1 and further, 1% by weight carboxymethyl cellulose NMP dispersion was added. A solid content of 1.5 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 obtain a negative electrode C having a thickness of 25 μm.

(Production of Battery and Evaluation of Performance) Using the obtained negative electrode C and positive electrode A as the positive electrode A of Example 1, a battery was prepared in the same manner as in Example 1, and the battery performance was evaluated. As a result, the discharge capacity was 233 mAh /
g, 230 mAh / g at the end of 10 cycles, and 225 mAh / g at 50 cycles, and the decrease in electric capacity was extremely small.

Example 4 (Production of rubber) In a 50 kgf / cm2 pressure-resistant autoclave equipped with a stirrer, 240 parts by weight of butadiene and 12 parts of styrene were added.
0 parts by weight, 2700 parts by weight of toluene, 0.1 mol / l toluene solution of n-butyllithium 1 as a polymerization initiator
0 parts by weight were added and polymerization was carried out at 60 ° C. Monomer consumption 9
At the time when it became 0%, ethylene oxide gas was introduced. After stopping the reaction with methanol, the mixture was cooled to obtain a toluene solution of a styrene-butadiene copolymer having a hydroxyl group at a terminal. The molecular weight of this rubber is Mw = 49000,
Mn = 44000. (Polystyrene equivalent, TH
GPC measurement of F solvent)

(Reaction) To 50 parts by weight of the above toluene solution (5 parts by weight of solid content), 10 parts by weight of hydrogen peroxide solution was added, and the mixture was stirred at 30 ° C. for 3 hours to oxidize the terminal hydroxyl groups and introduce carboxyl groups. did. After separating the aqueous phase, 200 parts by weight of a 5 wt% NMP solution of hydroxyethyl cellulose is added, and the mixture is stirred at room temperature for 2 hours. Next, after heating to 80 ° C., 1 part by weight of concentrated sulfuric acid was added, and the mixture was vigorously stirred for 16 hours. After cooling to room temperature, it is neutralized with a 5 wt% aqueous solution of LiOH.
The precipitated solid is filtered off. Then, after washing the solid content with water,
Polymer d was obtained. The weight of the dried polymer d is 13
Parts by weight. Treated in the same manner as in Example 1,
NMP solution (binder composition D) was obtained. .

(Manufacture of Battery and Evaluation of Performance) In the same manner as in Example 1, the battery characteristics were measured using the binder composition D. As a result, the discharge capacity was 230 at the end of 5 cycles.
mAh / g, 228 mAh / g at the end of 10 cycles,
The decrease in electric capacity was extremely small at 218 mAh / g in 50 cycles.

Comparative Example 1 (Evaluation of Battery Production and Performance) Battery characteristics were evaluated in the same manner as in Example 1, except that a 2 wt% NMP solution of hydroxyethyl cellulose was used as a binder composition. As a result, the battery capacity was 185 mAh / g at the end of 5 cycles, 170 mAh / g at the end of 10 cycles, and 3 mA at the end of 50 cycles.
Although the initial capacity was 1 mAh / g, which was a high value, an extremely severe decrease in capacity was recognized after the number of repeated charge / discharge cycles was 30 or more.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 4/02 H01M 4/02 B 4/62 4/62 Z 10/40 10/40 Z

Claims (4)

[Claims] 1. A cellulose compound containing a repeating structural unit represented by the following formula (1) or a compound containing an ammonium salt or an alkali metal salt thereof, and a rubber having a functional group capable of forming an ester bond by reacting with a hydroxyl group. A polymer obtained by reacting Embedded image (In the formula (1), each R is independently a hydrogen atom, a linear, branched or cyclic alkyl group, or a linear or branched alkyl group substituted with a carboxyl group, a hydroxyl group, or an alkoxy group. , At least one of which is a hydrogen atom.) 2. A battery binder comprising the polymer according to claim 1. 3. An electrode manufactured using the battery binder according to claim 2. 4. A lithium secondary battery containing the electrode according to claim 3.