JP2002050360A - Binder for electrode of lithium ion secondary battery and use thereof - Google Patents

Abstract

(57) [Problem] To provide a binder having excellent charge / discharge cycle characteristics of a battery. SOLUTION: A battery electrode is manufactured using a binder for a lithium ion secondary battery electrode containing a lithium salt of poly (meth) acrylic acid and a sodium salt of carboxymethyl cellulose, and a lithium ion secondary battery is manufactured using the electrode. To manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder used for a lithium ion secondary battery electrode and its use.

[0002]

2. Description of the Related Art In recent years, lithium such as coke and graphite has been absorbed and released as a negative electrode active material of a lithium ion secondary battery because of its excellent flexibility and no risk of electrodeposition of lithium metal. Possible carbon materials are being considered. A negative electrode using a carbonaceous material as an active material
Usually, a carbon powder and, if necessary, a conductive agent powder (such as acetylene black and carbon black) are dispersed in a binder composition containing a binder and a liquid substance to form a slurry, and the slurry is collected by a doctor blade method or the like. It is produced by a method of drying after coating on a metal. As the binder, a rubber-based binder such as styrene-butadiene rubber (hereinafter, referred to as SBR) is mainly used in addition to polyvinylidene fluoride (hereinafter, referred to as PVDF).

On the other hand, as a positive electrode active material, for example, Li
CoO₂, LiNiO₂, LiMn ₂O₄Etc. lithium
Containing composite metal oxides are being studied. These lithu
Positive electrodes using composite metal oxides containing
Lithium-containing composite metal oxides instead of polar carbonaceous materials
Is used to produce an electrode in the same manner as the negative electrode. Vine for positive electrode
As the hopper, PDVF, polytetrafluoroethylene
(PTFE) Other rubbers such as SBR and acrylic rubber
A binder is used.

The rubber binder is usually used in the form of a latex, dispersion or emulsion in which rubber particles are dispersed in water (aqueous binder composition). It is most common to use a sodium salt of carboxymethyl cellulose (hereinafter sometimes referred to as CMC) in combination with the aqueous binder composition. Highly polar polymers such as CMC not only function as binders themselves, but also have an appropriate viscosity for lithium ion secondary battery electrode slurries (hereinafter sometimes simply referred to as “slurries”) obtained by mixing with active materials. It is said that an excellent electrode can be obtained because the slurry can be uniformly applied to the surface of a current collector metal (hereinafter, simply referred to as a current collector) to provide the electrode. It has been proposed to use a sodium or potassium salt of polyacrylic acid in order to obtain higher adhesiveness in place of CMC (Japanese Patent Application Laid-Open No. H10-154513).

[0005]

According to the study of the present inventors, it has been found that CMC can be used without using other polar polymers having high adhesiveness.
When used alone, after the slurry is applied to the current collector in the electrode manufacturing process, at the stage of drying, the thermal decomposition starts slowly from a relatively low temperature of 120 ° C. It was found that moisture continued to be generated due to the thermal decomposition, so that moisture did not escape from the active material layer of the electrode forever. In addition, even if a known sodium or potassium salt of polyacrylic acid is used in place of CMC, sufficient charge / discharge cycle characteristics cannot be obtained because the slurry has poor paintability and it is difficult to uniformly disperse the active material. I also understood. In lithium ion secondary batteries, the presence of water in the electrodes
It is necessary to reduce as much as possible in order to reduce the performance of the battery and the safety.

[0006] Therefore, the present inventors, after the application of the slurry,
As a result of diligent research to obtain a battery in which moisture is easily removed at the drying stage and which has excellent charge / discharge cycle characteristics, a conventional binder containing CMC is used as a binder for an electrode, and lithium (poly) methacrylate is added to the conventional binder containing CMC. By adding a salt, a slurry having excellent coatability on the current collector can be obtained, and moisture can be easily removed at the stage of drying after applying the slurry, and a lithium ion secondary battery having excellent charge / discharge cycle characteristics can be obtained. This led to the completion of the present invention.

[0007]

According to the present invention, there is provided, as a first invention, a binder for a lithium ion secondary battery electrode comprising a lithium salt of poly (meth) acrylic acid and a sodium salt of carboxymethyl cellulose. And a binder for a lithium ion secondary battery electrode comprising a lithium salt of poly (meth) acrylic acid, a sodium salt of carboxymethyl cellulose, and polymer particles. As a second invention, a binder composition for a lithium ion secondary battery electrode containing the binder and water is provided. As a third invention, a lithium ion secondary battery electrode containing the binder and an active material is provided. The present invention provides a slurry for a battery, a fourth invention provides an electrode for a lithium ion secondary battery manufactured using the slurry, and a fifth invention provides a lithium ion secondary battery having the electrode. The chemical reason that the use of lithium salt of poly (meth) acrylic acid in combination with the slurry makes it easy to remove water at the stage of drying after application of the slurry is unknown, but at a relatively low temperature of about 120 ° C.
Thermal decomposition of MC is suppressed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Binder The binder of the present invention comprises CMC and a lithium salt of polyacrylic acid and / or a lithium salt of polymethacrylic acid. <Lithium salt of poly (meth) acrylic acid> Polyacrylic acid and polymethacrylic acid (hereinafter sometimes referred to as poly (meth) acrylic acid) according to the present invention are calculated by gel permeation chromatography using tetrahydrofuran. Has a weight average molecular weight in terms of monodisperse polystyrene (hereinafter, simply referred to as weight average molecular weight) of 100.
The amount is from 0 to 5,000,000, preferably from 10,000 to 3,000,000. If the weight average molecular weight is too high, the viscosity becomes too high during lithium salification, which may cause a problem in operability. Conversely, if the weight average molecular weight is too low, only a slurry having poor coatability to the current collector is obtained. May not be possible. Further, the poly (meth) acrylic acid may be cross-linked.

The lithium salt of poly (meth) acrylic acid is
It is obtained by adding a lithium source such as an aqueous solution of lithium hydroxide to an aqueous solution of poly (meth) acrylic acid. Lithium chloride increases the viscosity of the lithium poly (meth) acrylate solution. The lithium salt of poly (meth) acrylic acid used in the present invention is based on 100 parts by weight of the active material.
0.01 to 5 parts by weight, preferably 0.05 to 2 parts by weight,
More preferably, it is 0.1 to 1.5 parts by weight. If the amount of lithium salt of poly (meth) acrylic acid is too small,
If the amount is too large, the viscosity of the slurry is not appropriate and the coatability tends to be poor. If the amount of water is adjusted to adjust the viscosity of such a slurry, it becomes difficult to obtain an appropriate film thickness.

<Sodium Salt of Carboxymethyl Cellulose> The sodium salt of carboxymethyl cellulose (CMC) according to the present invention has a degree of etherification of 0.5 to 1.0.
0, preferably 0.55 to 0.9, more preferably 0.
6 to 0.85. The average degree of polymerization of CMC is 100 to
2000, preferably 200-1800, more preferably 300-1500. C with too low degree of etherification
MC is difficult to dissolve in water, and tends to make it difficult to exhibit the effects of the present invention. CMC with too high degree of etherification
When an electrode is manufactured by using, the flexibility of the electrode is deteriorated, which may adversely affect battery characteristics. If the average degree of polymerization is too small, the viscosity of the slurry tends to be insufficient to obtain sufficient paintability. Conversely, if the average degree of polymerization is too high, the viscosity of the slurry becomes too high, and the operability of application to the current collector becomes poor. become worse. CMC used in the present invention is 0.01 to 2 parts by weight, preferably 0.02 to 2 parts by weight, based on 100 parts by weight of the active material.
1 part by weight, more preferably 0.05 to 0.7 part by weight. If the amount of CMC used is too small, the viscosity of the slurry is low, resulting in poor paintability. Conversely, if the amount of CMC used is too large, the slurry is applied to the current collector and then dried (usually 120 to 120).
(160 ° C.), thermal decomposition of CMC occurs and water is generated.

<Polymer Particles> Specific examples of polymers used for the polymer particles according to the present invention include diene polymers, olefin polymers, styrene polymers, acrylate polymers, amide or imide polymers, ester polymers, Examples thereof include fluorine-based polymers, and specifically, polybutadiene, polyisoprene, isoprene-isobutylene copolymer, natural rubber, styrene-1,3-butadiene copolymer, styrene-isoprene copolymer, 1,3-butadiene-isoprene-acrylonitrile copolymer , Styrene-1,
3-butadiene-isoprene copolymer, 1,3-butadiene-acrylonitrile 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, styrene-1,3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, acrylonitrile-1,3-butadiene-
Diene polymers such as methacrylic acid-methyl methacrylate copolymer, styrene-1,3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer; ethylene -Propylene copolymer, ethylene-propylene-diene copolymer, polystyrene, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene ionomer, polyvinyl alcohol, vinyl acetate polymer, ethylene-vinyl alcohol copolymer, chlorinated polyethylene, polyacrylonitrile, chlorosulfonation Olefin-based polymers such as polyethylene;
Styrene-ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-
Acrylonitrile copolymer, styrene-acrylic acid n
Styrene-based polymers such as -butyl-itaconic acid-methyl methacrylate-acrylonitrile copolymer;

Polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, ethyl acrylate-acrylonitrile copolymer,
(Meth) acrylate-based polymers such as 2-ethylhexyl acrylate-methyl acrylate-acrylic acid-methoxypolyethylene glycol monomethacrylate; polyamide 6, polyamide 66, polyamide 11,
Amide or imide polymers such as polyamide 12, aromatic polyamide and polyimide; ester polymers such as polyethylene terephthalate and polybutylene terephthalate; fluororubber, PVDF and PTFE, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-per Fluorine-based polymers such as fluoroalkyl vinyl ether copolymer, polychlorotrifluoroethylene, and ethylene-chlorotrifluoroethylene copolymer; and the like. These polymers may be used alone or in combination of two or more.

Among the above specific examples, preferred are diene polymers and (meth) acrylate polymers. In the present invention, polymer particles in which these polymers are in the form of particles are used. As the polymer particles, a (meth) acrylic acid monomer or a (meth) acrylic monomer is further added to the outer layer of these polymer particles.
Composite polymer particles (core-shell structure) having a polymer layer such as a homopolymer or copolymer of an acrylate monomer, a copolymer of a (meth) acrylate monomer or a copolymerizable monomer with a (meth) acrylate monomer. , Composite structure, localized structure, daruma-like structure, leek-like structure, raspberry-like structure, multi-particle composite structure, etc. ("Adhesion" Vol. 34 No. 1, No. 13-
(See FIG. 6) described on page 23, particularly on page 17.)
Is a particularly preferred example.

The polymer particles used in the present invention may be an aqueous dispersion (hereinafter referred to as a latex or an emulsion) (hereinafter referred to as an emulsion).
(Collectively referred to as latex). The particle size of the polymer particles in the latex (after drying the dispersion medium, measuring the major axis and minor axis of 100 particles with an electron microscope and taking the average value) is usually 0.005 to 100 μm.
m, preferably 0.01 to 50 μm, more preferably 0.05 to 30 μm. The polymer particles used in the present invention are 0.01 to 5 parts by weight based on 100 parts by weight of the active material.
Parts by weight, preferably 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight. When the amount of the polymer particles used is small, the binding property between the current collector and the active material or between the active materials is deteriorated. On the contrary, when the amount used is too large, the battery characteristics tend to be deteriorated.

2. Binder composition The binder composition of the present invention contains the above-described binder of the present invention and water. The content of the binder of the present invention in the composition is usually 0.01 to 50% by weight, preferably 0.05 to 20% by weight, more preferably 0.05 to 1% by weight.
5% by weight. Within this range, a slurry having excellent paint properties can be obtained.

3. Battery Electrode Slurry The slurry of the present invention contains the above-described binder of the present invention and an active material. Usually, such a slurry is prepared by mixing the above-described binder composition of the present invention and an active material. In addition, a viscosity modifier or a fluidizing agent may be added to the slurry, and furthermore, carbon such as conductive graphite or activated carbon, metal powder, or the like can be added as a conductive agent. <Active Material> The active material used in the slurry of the present invention may be any material as long as it can absorb and release lithium ions. Examples of the negative electrode active material include various carbonaceous materials. Examples of the active material include metal composite oxides, particularly metal composite oxides containing lithium and at least one metal selected from the group consisting of iron, cobalt, nickel, and manganese.

More specifically, as a particularly preferred negative electrode active material, carbonaceous materials such as hard carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fiber, and polyacene are generally used. Although used, composite metal oxides and other metal oxides can also be used.

Particularly preferred cathode active materials include:
LixMO ₂ (where M represents one or more transition metals, preferably at least one of Co, Mn and Ni.
10>x> 0.05) or LixM ₂ O
₄ (where M represents one or more transition metals, preferably Mn, and 1.10>x> 0.05), for example, LiCoO ₂ , LiNiO ₂ , LiLi
xNiyCo _(1-y) O ₂ (However, 1.10>x>
0.05, 1>y> 0) and a composite oxide represented by LiMn ₂ O ₄ .

4. Lithium ion secondary battery electrode The electrode of the present invention is manufactured by applying the slurry of the present invention to a current collector such as a metal foil, drying and fixing the active material on the current collector surface. The electrode of the present invention may be either a positive electrode or a negative electrode. The current collector is not particularly limited as long as it is made of a conductive material, but is usually made of a metal such as iron, copper, aluminum, nickel, and stainless steel.
In the present invention, aluminum is particularly preferable for the positive electrode, and copper is preferable for the negative electrode. Although the shape is not particularly limited, it is usually a sheet having a thickness of about 0.001 to 0.5 mm.

The method of applying the slurry to the current collector is not particularly limited. For example, doctor blade method, dip method,
Reverse roll method, direct roll method, gravure method,
It is applied by an extrusion method, immersion method, brush painting, or the like. The amount to be applied is not particularly limited, but the thickness of the active material layer formed after drying and removing water is 0.005.
An amount of up to 5 mm, preferably 0.01 to 1 mm, is common. The drying method is not particularly limited, and examples thereof include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying conditions are usually adjusted so that water can be removed as quickly as possible within a speed range in which the active material layer is not cracked by stress concentration or the active material layer is not separated from the current collector. Further, the density of the active material of the electrode may be increased by pressing the dried current collector. As the pressing method, a method such as a die press or a roll press is used.

5. Lithium-ion secondary battery The lithium-ion secondary battery of the present invention includes an electrolyte and an electrode for a lithium-ion secondary battery of the present invention, and is manufactured according to a conventional method using components such as a separator as necessary. It is. For example, the following method can be mentioned. That is, the positive electrode and the negative electrode are overlapped via a separator, rolled or folded according to the battery shape, and put in a battery container.
Inject electrolyte and seal. Battery shape is coin type,
Any of a button type, a sheet type, a cylindrical type, a square type, a flat type and the like may be used.

The electrolyte may be any one which is usually used for a lithium ion secondary battery.
What has the function as a battery should just be selected according to the kind of positive electrode active material. As the electrolyte, for example, any of conventionally known lithium salts can be used.
₄ , LiBF ₆ , LiPF _{6 and the} like.

The solvent for dissolving the electrolyte (electrolyte solvent) is not particularly limited. Preferred specific examples are propylene carbonate, ethylene carbonate,
Carbonates such as butylene carbonate, dimethyl carbonate, and diethyl carbonate; lactones such as γ-butyl lactone; and in addition, ethers, sulfoxides, oxolanes, organic acid esters, inorganic acid esters, diglymes, Triglymes, sulfolane, oxazolidinones, sultones and the like can also be used. A single solvent or a mixed solvent of two or more solvents can be used.

[0024]

According to the present invention, when the binder of the present invention is used for manufacturing an electrode of a lithium ion secondary battery, a lithium secondary battery having excellent slurry properties, excellent battery charge / discharge cycle characteristics, and excellent safety can be obtained. Can be.

[0025]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, parts and percentages are by weight unless otherwise specified.

The evaluation conditions in the examples and comparative examples are as follows. <Evaluation of Slurry Properties> Dispersibility: 50 μm according to JIS K 5400
The degree of dispersion was measured using a crush gauge of m.
When it was less than μm, it was determined to be good. Mixability: Evaluated according to JIS K 5400. It was determined to be good when mixed evenly, and to be poor when mixed poorly. Storage stability: Storage stability for 10 days was evaluated in accordance with JIS K 5400 paint storage stability at room temperature.
If no change was observed in the slurry state, it was stable.
When the state of the slurry was changed, it was determined to be unstable. Coating property: The positive electrode slurry is coated on the following aluminum foil,
The negative electrode slurry was coated on the following copper foil with a gap of 200 μm each.
JIS K 5400 using a film applicator
The coating was performed in accordance with the above, and whether or not the coating was uniformly performed was visually evaluated. Slurries that could be applied uniformly and easily were good, and those that were difficult to apply uniformly were determined to be poor.

<Evaluation of Electrode> Production of Electrode and Coin Battery A positive electrode slurry was uniformly applied to an aluminum foil (thickness: 20 μm) and a negative electrode slurry was applied to a copper foil (thickness: 18 μm) by a doctor blade method. 1 at 150 ° C
Dry with a dryer for 5 minutes, and then 5 torr with a vacuum dryer.
After 2 hours drying under reduced pressure at r, 0.99 ° C., the active material density of the positive electrode 3.2 g / cm ³ by roll press biaxial, compressed so that the negative electrode 1.5 g / cm ^3, the thickness of the active material layer An electrode of 80 μm is obtained. This electrode was cut out into a circle having a diameter of 15 mm, and a separator made of a circular polypropylene porous membrane having a diameter of 18 mm and a thickness of 25 μm was interposed.
Stainless steel with active materials facing each other, placed so that the aluminum foil or lithium metal of the positive electrode is in contact with the bottom of the outer container, and further expanded metal is placed on the copper foil or lithium metal of the negative electrode, and polypropylene packing is installed. -Made coin-shaped outer container (diameter 20 mm, height 1.
8 mm, stainless steel thickness 0.25 mm). Here, for the negative electrode test, the positive electrode was metallic lithium,
For the positive electrode test, lithium metal is used for the negative electrode. An electrolytic solution is injected into the coin-shaped outer container so that no air remains, and the outer container is fixed with a 0.2 μm-thick stainless steel cap via a polypropylene packing, and the battery can is sealed. Then, a coin-type battery having a diameter of 20 mm and a thickness of about 2 mm is manufactured. As the electrolytic solution, a solution in which LiPF ₆ is dissolved at a concentration of 1 mol / liter in ethylene carbonate / diethyl carbonate = 50/50 (volume ratio at 20 ° C.) is used. Bending test: Ten electrode test pieces having a length of 100 mm and a width of 20 mm were bent (inwardly bent) with a stainless steel rod having a diameter of 2 mm as a core until the electrode surfaces were in contact with the active material layer of the electrode test piece inside. Later, when the same bent portion is bent in the same manner with the active material layer outside (bending outside), the number of test pieces (electrodes) in which the active material layer is cracked or the active material layer is separated from the current collector Was counted. The larger this value is, the more the electrode has many defects.

Adhesion test: The adhesion test between the current collector and the active material layer was carried out in accordance with JIS K for ten electrode test pieces.
The measurement was performed in accordance with the grid test method specified in 5400. The results were visually evaluated on a 10-point scale. The value was the average value of 10 test pieces, and the decimal part was rounded off. If this value is 8 or more, it can be determined that there is practically good binding property. Weight change measurement test: The electrode manufactured by the above method was
Further, the electrode was allowed to stand in a dryer at 150 ° C. under normal pressure for 72 hours, and the change in the weight of the electrode before and after the standing was examined using an analytical balance. When the weight change is below the detection limit, it is judged that the thermal decomposition of CMC has not occurred (（), and when the weight change is detected, CMC is detected.
Was determined to be thermally decomposed (x). In addition, CMC alone, the lithium salt of polyacrylic acid alone, and the electrode of the polymer particles alone were each manufactured and evaluated in the same manner as in the example except that the active material was 100 parts and the binder amount was 4 parts. X, the others were evaluated as ○.

<Evaluation of Battery> Charge / discharge capacity retention: A negative electrode test was performed using a coin-type battery manufactured by the above method at 25 ° C. in an atmosphere of 0 V to 1.2 V using lithium as the positive electrode. The discharge capacity at the third cycle (unit: mAh / g: per active material, the same applies hereinafter) was determined by a constant current method of 0.4 C from 3 V to 4.2 V using lithium as the negative electrode.
The discharge capacity at the 0th cycle is measured, and the ratio of the discharge capacity at the 30th cycle to the discharge capacity at the 3rd cycle is calculated as a percentage. The larger the value, the better the cycle characteristics.

In the following Examples and Comparative Examples, parts and%
Are by weight unless otherwise noted. Example 1 2 parts of polyacrylic acid (weight average molecular weight about 1,000,000)
After dissolving in 998 parts of ion-exchanged water, 12 parts of a 13% aqueous solution of lithium hydroxide was added to obtain an aqueous solution of a lithium salt of polyacrylic acid. To 100 parts of natural graphite, 0.5 parts by weight of the solid content of the aqueous solution of lithium salt of polyacrylic acid, and C
MC (Daiichi Kogyo Seiyaku Co., Ltd .: Trade name "Selogen WS-
C)), equivalent to 0.4 part solids of a 1% aqueous solution of 40%
Styrene butadiene rubber latex (styrene content 36
%) Of a solid content equivalent to 1.5 parts. Further, water was added until the total solid content in the slurry became 33.2%, and the mixture was sufficiently stirred to obtain a negative electrode slurry A. A negative electrode was manufactured using the obtained slurry A, and a battery was manufactured using the negative electrode. The above evaluation was performed for the slurry, the electrode, and the battery. Table 1 shows the results.

Example 2 Instead of the 40% styrene-butadiene rubber latex of Example 1, a 40% acrylic latex (80/5/15 (component content weight ratio) of 2-ethylhexyl acrylate / acrylic acid / methacrylonitrile) A negative electrode slurry B was obtained in the same manner as in Example 1 except that the above was used. Using the obtained slurry B, a negative electrode is manufactured,
A battery was manufactured using this negative electrode. The above evaluation was performed for the slurry, the electrode, and the battery. Table 1 shows the results.

Example 3 LiCoO ₂ was used instead of 100 parts of the natural graphite of Example _2.
A positive electrode slurry P was obtained in the same manner as in Example 2, except that 95 parts and 5 parts of conductive carbon were used, and the solid content of the slurry was 65%. A positive electrode was manufactured using the obtained slurry P, and a battery was manufactured using the positive electrode. The above evaluation was performed for the slurry, the electrode, and the battery. Table 1 shows the results.

Comparative Example 1 A solid solution of a 1% aqueous solution of CMC (trade name “Selogen WS-C”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) in 100 parts of natural graphite was 0.9.
Parts and an equivalent of 1.5 parts solids of 40% styrene butadiene rubber latex (styrene content 36%). Further, water was added until the total solid content in the slurry became 33.2%, and the mixture was sufficiently stirred to obtain a negative electrode slurry C. A negative electrode is manufactured using the obtained slurry C,
A battery was manufactured using this negative electrode. The above evaluation was performed for the slurry, the electrode, and the battery. Table 1 shows the results.

Comparative Example 2 2 parts of polyacrylic acid (weight average molecular weight: about 1,000,000)
After dissolving in 998 parts of ion-exchanged water, 12 parts of a 13% aqueous sodium hydroxide solution was added to obtain a sodium salt aqueous solution of polyacrylic acid. To 100 parts of natural graphite, 0.5 part of the solid content of the aqueous solution of the sodium salt of polyacrylic acid was added to CMC (Daiichi Kogyo Seiyaku Co., Ltd., trade name “Selogen WS”).
-C "), equivalent to 0.4 part of a solid content of a 1% aqueous solution of 40%
% Styrene butadiene latex (styrene content 36
%) Of a solid content equivalent to 1.5 parts. Further, water was added until the total solid content in the slurry became 33.2%, and the mixture was sufficiently stirred to obtain a negative electrode slurry D. A negative electrode was manufactured using the obtained slurry D, and a battery was manufactured using the negative electrode. The above evaluation was performed for the slurry, the electrode, and the battery. Table 1 shows the results.

COMPARATIVE EXAMPLE 3 Except that 0.5 parts of the solid content of the lithium salt of polyacrylic acid was not used and the amount of CMC was changed from 0.4 parts of the solid content to the equivalent of 0.9 parts of the solid content, A positive electrode slurry Q was obtained in the same manner as in Example 3. A positive electrode was manufactured using the obtained slurry Q, and a battery was manufactured using the negative electrode. The above evaluation was performed for the slurry, the electrode, and the battery.
Table 1 shows the results.

[0036]

[Table 1]

From these results, in Examples 1 to 3 using the binder containing the lithium salt of poly (meth) acrylic acid and CMC, a good slurry was obtained, and the electrode obtained using this was bent. The test gives a good electrode without cracks. The yield can be increased in an actual production line, leading to an improvement in production efficiency.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ14 AK03 AL06 AM03 AM04 AM05 AM07 CJ28 DJ08 EJ12 HJ02 5H050 AA19 BA17 CA08 CA09 CB07 CB08 DA02 DA03 DA11 EA10 EA23 EA24 FA09 GA10 HA02

Claims (6)

[Claims] 1. A binder for a lithium ion secondary battery electrode comprising a lithium salt of poly (meth) acrylic acid and a sodium salt of carboxymethyl cellulose. 2. A lithium salt of poly (meth) acrylic acid,
A binder for a lithium ion secondary battery electrode, comprising a sodium salt of carboxymethyl cellulose and polymer particles. 3. The binder according to claim 1 or 2,
A binder composition for a lithium ion secondary battery electrode containing water. 4. A slurry for a lithium ion secondary battery electrode, comprising the binder according to claim 1 and an active material. 5. An electrode for a lithium ion secondary battery produced using the slurry according to claim 4. 6. A lithium ion secondary battery having the electrode according to claim 5.