JP2013023654A - Binder for carbon coat foil coating solution, carbon coat foil coating solution, carbon coat foil, electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low resistance electrode excellent in adhesiveness of an active substance layer to a collecting body, and a low resistance to the collecting body by having a carbon coat foil layer obtained by coating the carbon coat coating solution including a binder component containing an unsaturate dicarboxylic acid as an essential component on an aluminum foil and the active substance layer, and a lithium ion secondary battery using these electrodes.SOLUTION: The present invention relates to the binder for the carbon coat foil coating solution coating on a metallic foil which is a polymer with a weight average molecular weight of 500,000-3,000,000 and obtained by polymerization of only an unsaturated dicarboxylic acid or a polymer obtained by polymerization of one or more of unsaturated monomers selected from the group consisting of (meth)acrylic acid, a hydroxyalkyl (meth)acrylate, (meth)acrylamide and N-methylol (meth)acrylamide, (meth)acrylonitrile and an alkyl (meth)acrylate, and an unsaturated dicarboxylic acid.

Description

  The present invention is composed of a binder for a carbon coating foil coating liquid, a carbon coating foil coating liquid containing these binders and a conductive auxiliary agent, a carbon coating foil coating liquid layer containing these binders and a conductive auxiliary agent, and a metal foil. The present invention relates to a carbon coated foil, an electrode for a lithium ion secondary battery using the carbon coated foil and a slurry for a lithium ion secondary battery electrode, and a lithium ion secondary battery using these electrodes.

  Carbon coated foil is obtained by coating conductive carbon on metal foil, and it is known that the resistance value can be greatly reduced as compared with a conventional metal foil alone. Carbon coated foils are expected to have low resistance, high output, and improved cycle characteristics as current collector foils for lithium ion secondary batteries and electric double layer capacitors.

  The lithium-ion secondary battery market is expanding with the spread of notebook computers, mobile phones, power tools, and electronic / communication equipment. Furthermore, recently, from the viewpoint of environmental problems, demand for lithium ion secondary batteries for electric vehicles and hybrid vehicles is also increasing. In particular, these require high output, high capacity lithium ion secondary batteries, and long life. It is said that. In order to realize these, it is essential to reduce the internal resistance of the battery.

In general, a lithium ion secondary battery includes a positive electrode using a metal oxide such as lithium cobaltate as an active material, a negative electrode using a carbon material such as graphite as an active material, a separator made of a porous sheet such as polypropylene or polyethylene, and a six-flux. The electrolyte is composed of an electrolyte solution in which an electrolyte such as lithium phosphate (LiPF ₆ ) is dissolved in a carbonate-based solvent. For details on each electrode, the positive electrode layer is formed by applying slurry for a lithium ion secondary battery positive electrode composed of a metal oxide and a binder to an aluminum foil or the like in the positive electrode, and the negative electrode is a lithium secondary battery negative electrode composed of graphite and a binder. It is obtained by coating the slurry for copper on a copper foil or the like to form a negative electrode layer.

  In general, when a lithium ion secondary battery electrode slurry is applied to a copper foil, an aluminum foil, etc. to produce a lithium ion secondary battery electrode, an organic solvent system is used as a binder for the lithium ion secondary battery electrode slurry. Polyvinylidene fluoride (PVDF) using N-methylpyrrolidone (NMP) as a solvent, and water-based styrene-butadiene rubber latex (SBR) using carboxymethyl cellulose (CMC) as a thickener.

  Conventionally, PVDF systems used as binders for lithium ion secondary battery electrode slurries have low binding properties between active materials and between active materials and metal foils. As a result, the capacity of the lithium ion secondary battery is reduced (see, for example, Patent Document 1).

  In addition, the SBR system has been used for a wide range of applications as a binder for an aqueous lithium ion secondary battery electrode because of its good binding property between active materials and between an active material and a metal foil (see, for example, Patent Document 2). ). However, this binder has problems of low mechanical stability and low swelling resistance against the electrolyte solvent. Furthermore, this binder has a problem that the battery capacity and charge / discharge cycle characteristics are deteriorated in a lithium ion secondary battery used at a high temperature.

  As a technique for solving the binding property between the active material and the metal foil, a precoat layer containing a latex binder and an aqueous dispersant is formed on the metal foil, and the active material and the latex binder are formed on the precoat layer. There is a proposal of a nonaqueous electrolyte secondary battery characterized in that it is an electrode obtained by applying an aqueous slurry containing an adhesive and an aqueous dispersant to form a mixture layer and then drying (for example, a patent) Although the binding property between the active material in the electrode and the metal foil is improved, there is a problem that the resistance of the current collector increases and the capacity of the lithium ion secondary battery decreases.

  Moreover, there is a proposal of a binder for a lithium ion secondary battery negative electrode obtained by (co) polymerizing a water-soluble monomer (mixture) containing itaconic acid as an essential component (see, for example, Patent Document 4). Is a binder having a weight average molecular weight of about 2,000 to 100,000, the dispersion of the conductive auxiliary agent is insufficient, and the adhesiveness with the metal foil (especially aluminum foil) is low, and the active material is liable to fall off. There is a problem that the cycle characteristics deteriorate. Therefore, this binder is not suitable as a binder for a carbon coat foil coating solution.

Japanese Patent No. 3966570 Japanese Patent No. 3562197 JP 2009-238720 A JP 2010-177061 A

  The present invention solves the problems of the prior art, has excellent adhesion without peeling off the active material in the current collector applied to the metal foil (particularly aluminum foil), and has a resistance between the active material and the metal foil. A carbon coating foil coating liquid layer containing a binder and a conductive assistant, a carbon coating foil coating liquid containing these binder and a conductive assistant, and a binder for a carbon coating foil coating liquid having a low charge-discharge cycle characteristic; To provide a carbon coat foil composed of metal foil, a lithium ion secondary battery electrode using these carbon coat foil and slurry for lithium ion secondary battery electrodes, and a lithium ion secondary battery using these electrodes Objective.

  The inventor provides a current collector by providing a carbon coat foil coating liquid layer obtained by coating a carbon coat foil coating liquid in a current collector composed of an active material and a metal foil. Binder for carbon coating foil coating solution that has excellent adhesion without peeling off the active material, has low resistance between the active material and the metal foil, and has charge / discharge cycle characteristics, and includes these binder and conductive aid Carbon coat foil coating solution, carbon coat foil obtained by coating these carbon coat foil coating solutions on metal foil, lithium ion secondary battery electrode using lithium ion secondary battery electrode, and these electrodes As a result of earnest studies for the purpose of obtaining a lithium ion secondary battery using a polymer, a polymer obtained by polymerizing only unsaturated dicarboxylic acid or (meth) acrylic coated on a metal foil One or more unsaturated monomers and unsaturated dicarboxylic acids selected from hydroxyalkyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, (meth) acrylonitrile and alkyl (meth) acrylate Is a polymer obtained by polymerizing a binder, and a weight average molecular weight of 500,000 to 3,000,000, a binder for a carbon coating foil coating solution to be coated on a metal foil, and a solid content of these binder and carbon coating foil coating solution Carbon coating foil coating liquid containing a conductive auxiliary that is 30 to 80% by mass, carbon coated foil coating liquid layer containing these binder and conductive auxiliary agent, and carbon coated foil composed of a metal foil, these carbon Lithium ion secondary battery electrode obtained by using coated foil and lithium ion secondary battery electrode slurry, and these It found that the lithium ion secondary battery obtained by using the electrode obtained, and have completed the present invention.

  That is, the present invention is a polymer obtained by polymerizing only unsaturated dicarboxylic acid, or (meth) acrylic acid, hydroxyalkyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, It is a polymer obtained by polymerizing one or more unsaturated monomers selected from (meth) acrylonitrile and alkyl (meth) acrylate and an unsaturated dicarboxylic acid, and has a weight average molecular weight of 500,000 to 3,000,000. The present invention relates to a binder for a carbon coating foil coating solution that is applied to a metal foil.

  The present invention relates to a binder for a carbon-coated foil coating solution, wherein the unsaturated dicarboxylic acid is itaconic acid.

  The present invention is a carbon coat foil coating solution containing a binder for a carbon coat foil coating solution, wherein the carbon coat foil coating contains 30 to 80% by mass of a conductive auxiliary agent based on the solid content of the carbon coat foil coating solution. Concerning the working fluid.

  The present invention relates to a carbon coat foil obtained by applying a carbon coat foil coating liquid to a metal foil, that is, a carbon coat foil coating liquid layer and a metal foil containing a binder for a carbon coat foil coating liquid and a conductive auxiliary agent. It is related with the carbon coat foil comprised from.

  The present invention relates to an electrode for a lithium ion secondary battery obtained by using a carbon coated foil obtained by applying the carbon coated foil coating solution to a metal foil and a slurry for a lithium ion secondary battery electrode.

  The present invention relates to a lithium ion secondary battery obtained using the electrode for a lithium ion secondary battery.

  According to the present invention, a polymer obtained by polymerizing only unsaturated dicarboxylic acid, or (meth) acrylic acid, hydroxyalkyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, ( It is a polymer obtained by polymerizing one or more unsaturated monomers selected from (meth) acrylonitrile and alkyl (meth) acrylate and an unsaturated dicarboxylic acid, and has a weight average molecular weight of 500,000 to 3,000,000. A carbon coating foil coating solution containing a binder for a carbon coating foil coating solution to be applied to a metal foil and a conductive aid of 30 to 80% by mass with respect to the solid content of the carbon coating foil coating solution; Using a slurry for secondary battery electrodes, a layer of carbon coat foil coating solution is provided in a current collector composed of an active material and metal foil (especially aluminum foil). And providing a lithium ion secondary battery having excellent charge and discharge cycle characteristics by having excellent adhesion without peeling off the active material in the current collector and reducing the resistance between the active material and the metal foil. Can do.

  Hereinafter, the components constituting the present invention will be described in detail.

  The binder for a carbon coating foil coating solution to be applied to the aluminum foil according to the present invention is a polymer obtained by polymerizing only unsaturated dicarboxylic acid as an unsaturated monomer, or (meth) acrylic acid, (meta ) Polymerizing one or more unsaturated monomers selected from hydroxyalkyl acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, (meth) acrylonitrile and alkyl (meth) acrylate and unsaturated dicarboxylic acid. It contains the polymer obtained by this.

  Examples of the unsaturated dicarboxylic acid used in the present invention include itaconic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, and allylmalonic acid. The purpose of using the unsaturated dicarboxylic acid is to improve the binding properties between the conductive assistants, the conductive assistant and the active material, and the conductive assistant, the active material and the aluminum foil. Among them, itaconic acid is preferable because it has a great effect of improving the binding property.

  (Meth) acrylic acid, hydroxyalkyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, (meth) acrylonitrile or alkyl (meth) acrylate (hereinafter these monomers are collectively referred to as (meth) The purpose of using acrylic acid, etc.) is to improve the handling properties such as the dispersibility of the conductive assistant when blended with the conductive assistant in the binder and the stability over time after blending, and the resistance to electrolyte. Because.

  Specific examples of hydroxyalkyl (meth) acrylate include, for example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, and 2-hydroxypropyl acrylate. Of these, 2-hydroxyethyl methacrylate is preferable in terms of improving the adhesion to the aluminum foil and improving the resistance to electrolytic solution. Specific examples of the alkyl (meth) acrylate include, for example, methyl methacrylate, ethyl methacrylate, -n-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, or isobornyl methacrylate. And alkyl acrylates such as alkyl methacrylate such as ethyl acrylate, n-butyl acrylate, t-butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and isobornyl acrylate. Of these, isobornyl methacrylate is preferable in terms of improving adhesion to the aluminum foil and resistance to electrolytic solution.

  It is preferable that the content of the monomer unit derived from itaconic acid when itaconic acid is copolymerized with these (meth) acrylic acids, etc. is 50 to 100% by mass with respect to the total amount of the solid content of the binder. More preferably, it is -100 mass%, and it is further more preferable that it is 80-100 mass%. When the content of the monomer unit derived from itaconic acid is less than 50% by mass, the binding properties between the conductive assistants, the conductive assistant and the active material, and the conductive assistant, the active material, and the aluminum foil tend to decrease. is there. When the content of the monomer unit derived from (meth) acrylic acid or the like is more than 50% by mass, handling properties such as dispersibility of the conductive assistant when blending the conductive assistant into the binder and stability over time after blending, Electrolytic solution resistance tends to decrease.

  In addition, if necessary, not only the (meth) acrylic acid but also monomers other than these can be further copolymerized with itaconic acid. Examples of other monomers that can be copolymerized with itaconic acid include dimethylacrylamide, diethylacrylamide, vinylpyrrolidone, vinylformamide, vinylacetamide, vinylpyrrolidone, maleic acid, and crotonic acid.

  The binder for carbon coat foil coating liquid of the present invention can be obtained by radical polymerization by a known method. As the polymerization initiator used for radical polymerization, known ones can be used. For example, hydrogen peroxide, potassium persulfate, ammonium persulfate, tertiary butyl hydroperoxide, azobis- (2-amidinopropane) Examples thereof include hydride chloride, lauroyl peroxide, a, a′-azobisisobutyronitrile, ketone hydroperoxide and the like. These polymerization catalysts can be used as so-called redox catalysts either alone or in an appropriate combination with a reducing agent. Examples of the reducing agent include amine, ferrous salt, sodium thiosulfate, sodium sulfite, sodium hyposulfite, sodium bisulfite, sodium formaldehyde sulfoxylate, tartaric acid and its salts, ascorbic acid and its salts, erythorbic acid and its salts, etc. can give. Especially, the redox initiator which uses ammonium persulfate and sodium bisulfite as a reducing agent from the point which is excellent in polymerizability is preferable. Moreover, a chain transfer agent, a crosslinking agent, etc. can also be used in the range which is not contrary to the meaning of the present invention.

  The weight average molecular weight of the binder for a carbon coating foil coating solution of the present invention is preferably 500,000 to 3,000,000, more preferably 600,000 to 2.8 million, and even more preferably 70 to 250. When the weight average molecular weight of the binder for the carbon coating foil coating solution is lower than 500,000, the binding properties between the conductive assistants, the conductive assistant and the active material, and the conductive assistant, the active material, and the aluminum foil are lowered. If it becomes a tendency and becomes higher than 3 million, the viscosity of the carbon coating foil coating solution tends to be high, and the coating property tends to be low.

  The carbon-coated foil coating solution of the present invention is composed of the carbon-coated foil coating solution binder and a conductive aid, and is obtained by, for example, adding a solvent such as water to disperse the conductive aid. It is done. The content of the binder for the carbon coating foil coating solution with respect to the solid content of the carbon coating foil coating solution is preferably 20 to 70% by mass, more preferably 30 to 60% by mass, and 40 to 50% by mass. % Is more preferable. When the content of the binder for the carbon coating foil coating solution is less than 20% by mass, the active material in the current collector is easily peeled. When the content is more than 70% by mass, the resistance between the active material and the metal foil is high. Tend to be. The solid content concentration of the carbon-coated foil coating solution is preferably 5 to 50% by mass, more preferably 7 to 30% by mass, and even more preferably 10 to 20% by mass. When the solid content concentration of the carbon coating foil coating solution is less than 5% by mass, the coating film tends to repel, and when it exceeds 50% by mass, the coating property tends to be lowered.

  Conductive aids include carbon materials such as carbon black such as acetylene black and ketjen black, cokes such as coke, petroleum coke, pitch coke, and coal coke, polymer charcoal, carbon fiber, carbon nanotube, and other carbon-based conductive materials. Auxiliaries are used. In particular, acetylene black is preferable because it has excellent conductivity and is relatively inexpensive.

  Moreover, it is preferable that content of the conductive support agent with respect to solid content of a carbon coat foil coating liquid is 30-80 mass%, It is more preferable that it is 40-70 mass%, It is 50-60 mass%. More preferably. When the content of the conductive auxiliary is less than 30% by mass, the resistance between the active material and the metal foil is increased, and when the content is more than 80% by mass, the active material in the current collector tends to be easily peeled off.

  The carbon coat foil of the present invention is obtained by coating the carbon coat foil coating solution on a metal foil such as an aluminum foil, and is composed of a carbon coat foil coating solution layer and a metal foil. Examples of coating methods include gravure method, reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, bar method, dipping method, and squeeze method. In addition, the gravure method is preferable in that it is possible to easily realize that the excess coating liquid is scraped off with a doctor blade and the coating liquid in the cell of the gravure plate is applied to the substrate.

The positive electrode active material used in the electrode slurry for a lithium ion secondary battery of the present invention is not particularly limited as long as it is a positive electrode active material that can be used in a normal lithium ion secondary battery. LiCoO ₂ ), Ni—Co—Mn lithium composite oxides, Ni—Mn—Al lithium composite oxides, Ni—Co—Al lithium composite oxides containing nickel, One or more kinds of chalcogen compounds such as spinel type lithium manganate (LiMn ₂ O ₄ ), olivine type lithium iron phosphate, TiS ₂ , MnO ₂ , MoO ₃ , V ₂ O ₅ are used in combination.

  The negative electrode active material used in the electrode slurry for the lithium ion secondary battery of the present invention may be any material that intercalates lithium ions. For example, carbon fiber, metallic lithium, lithium alloy, polyacetylene, polypyrrole, etc. 1 of organic polymers, pyrolytic carbons, glassy carbon, organic polymer material sintered body obtained by sintering organic polymer material in vacuum or inert gas at 500 ° C. or higher, carbon fiber, etc. Species or multiple types are used in combination.

  Examples of the binder used in the electrode slurry for the lithium ion secondary battery of the present invention include polyvinylidene fluoride, styrene butadiene resin, butadiene resin, styrene acrylic resin, and acrylic resin. Moreover, the same thing as what is used for the said carbon coat foil coating liquid can be used for a conductive support agent, and acetylene black is especially preferable at the point which is excellent in electroconductivity and is comparatively cheap. Examples of the organic solvent used in the electrode slurry for a lithium ion secondary battery include n-methylpyrrolidone, N, N-dimethylacetamide, and N, N-dimethylformamide.

  The electrode of this invention is manufactured by apply | coating the slurry for lithium ion secondary battery electrodes to the carbon coat foil which is a collector, and drying. The carbon coated foil of the present invention can be applied to both positive and negative electrodes. The slurry application method of the present invention may be a general method such as reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dip method. Method and squeeze method.

  The application of the slurry for the lithium ion secondary battery electrode to the current collector may be performed on one side or both sides. When applying to both sides of the current collector, either side by side or both sides may be applied simultaneously. May be. Moreover, you may apply | coat to the surface continuously or intermittently. The thickness, length and width of the coating layer can be appropriately determined according to the size of the battery.

  As a method for drying the slurry of the present invention, a general method can be used. In particular, it is preferable to use hot air, vacuum, infrared rays, far-infrared rays, electron beams and low-temperature air alone or in combination. The drying temperature is preferably in the range of 80 to 350 ° C, more preferably in the range of 100 to 250 ° C, and still more preferably in the range of 120 to 200 ° C. When the drying temperature is lower than 80 ° C, the drying becomes insufficient, and when the drying temperature is higher than 350 ° C, the binder may be decomposed.

The electrode material used for manufacturing the electrode of the present invention is not particularly limited as long as it is metallic such as iron, copper, aluminum, nickel, and stainless steel. Also, the shape of the electrode material is not particularly limited, but it is usually preferable to use a sheet having a thickness of 0.001 to 0.5 mm. The electrode of the present invention can be pressed as necessary. As a pressing method, a general method can be used, but a mold pressing method and a calendar pressing method are particularly preferable. Although a press pressure is not specifically limited, 0.2-10 t / cm < ² > is preferable.

  The battery of the present invention is produced according to a known method using the positive electrode and / or negative electrode of the present invention and components such as an electrolyte and a separator. As the electrode, a laminate or a wound body can be used. As the exterior body, a metal exterior body or an aluminum laminate exterior body can be used as appropriate. The shape of the battery may be any shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, and a flat shape.

Any known lithium salt may be used as the electrolyte in the battery electrolyte, and may be selected according to the type of active material. For _{example, LiClO 4, LiBF 6, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, CF 3 Examples include SO ₃ Li, CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, and lower fatty acid lithium carboxylate.

  The solvent for dissolving the electrolyte is not particularly limited as long as it is usually used as a liquid for dissolving the electrolyte. Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), etc. can be used. Preferably, a cyclic carbonate and a chain carbonate are used in combination. These may be used individually by 1 type and may be used in combination of 2 or more type.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples and comparative examples, “parts” and “%” indicate parts by mass and mass%, respectively, unless otherwise specified. Binder for carbon coating foil coating solution obtained in Examples and Comparative Examples, carbon coating foil and lithium ion secondary obtained by coating carbon coating foil coating solution containing these binder and conductive additive on aluminum foil The performance evaluation test of the lithium ion secondary battery electrode obtained using the battery electrode slurry and the lithium ion secondary battery obtained using these electrodes was performed by the following method.

(Current collector peel strength test)
The carbon coating foil coating solution obtained below was applied to an aluminum foil by a gravure method so as to have a thickness of 1 μm, dried at 120 ° C. for 5 minutes to form a carbon coating layer, and then an electrode slurry was formed thereon. The test piece was coated to a thickness of 200 μm before drying, heated and dried at 120 ° C. for 5 minutes, and then allowed to stand at 23 ° C. and 50% RH for 24 hours or longer. In the peel strength test, the coated surface of the test piece and the SUS plate were bonded using a double-sided tape, and 180 ° peeling was performed (peel width 25 mm, peel rate 100 mm / min). The peel strength is mN, and the peel strength is 50 mN / mm or more.

(Charge / discharge high temperature cycle characteristics)
The cycle test of the battery was CC-CV charge (upper limit voltage 4.2 V, current 1 C, CV time 1.5 hours, CC discharge (lower limit voltage 3.0 V, current 1 C), and all were performed at 60 ° C. The maintenance rate was the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle, and the charge / discharge cycle was 70% or more.

(Synthesis of binder A)
A separable flask having a condenser, a thermometer, a stirrer, and a dropping funnel was added with 50 parts of 25% aqueous sodium hydroxide and 50 parts of itaconic acid to obtain a uniform mixed solution. Nitrogen was introduced into the separable flask, and the internal temperature was adjusted to 60 ° C. with a constant temperature water bath. 60 minutes after the introduction of nitrogen, 1 part of a 2% ammonium persulfate aqueous solution and 1 part of a 2% sodium bisulfite aqueous solution were added as polymerization initiation catalysts to initiate the polymerization. The product obtained by the reaction for 24 hours was pulverized, washed and re-dried to obtain a binder A having a weight average molecular weight of 500,000. The weight average molecular weight was measured using a gel permeation chromatography apparatus Shodex GPC-101 (manufactured by Showa Denko KK), a 0.1N NaNO ₃ aqueous solution as an eluent, and a measurement sample concentration of 0.05% by mass. did. Hereinafter, the weight average molecular weight was also measured for the binders B to J by the same method.

(Synthesis of Binder B)
The same operation as in the synthesis of Binder A was performed except that 0.25 part of 2% ammonium persulfate aqueous solution of polymerization initiation catalyst and 0.25 part of 2% sodium bisulfite aqueous solution were changed to 0.25 part. Binder B having a weight average molecular weight of 3 million was obtained.

(Synthesis of binder C)
The same operation as the synthesis of Binder A was performed except that 30 parts of itaconic acid and 20 parts of methacrylic acid were used instead of 50 parts of itaconic acid. Binder C having a weight average molecular weight of 600,000 was obtained.

(Synthesis of binder D)
The same operation as the synthesis of Binder A was performed except that 40 parts of itaconic acid and 10 parts of 2-hydroxyethyl methacrylate were changed to 50 parts of itaconic acid. A binder D having a weight average molecular weight of 1,000,000 was obtained.

(Synthesis of binder E)
The same operation as the synthesis of Binder A was performed except that 40 parts of itaconic acid and 10 parts of acrylamide were changed to 50 parts of itaconic acid. Binder E having a weight average molecular weight of 1,500,000 was obtained.

(Synthesis of binder F)
The same operation as the synthesis of Binder A was performed except that 48 parts of itaconic acid and 2 parts of N-methylolacrylamide were changed to 50 parts of itaconic acid. A binder F having a weight average molecular weight of 2.5 million was obtained.

(Synthesis of binder G)
The same operation as in the synthesis of Binder A was performed except that 45 parts of itaconic acid and 5 parts of acrylonitrile were used instead of 50 parts of itaconic acid. A binder G having a weight average molecular weight of 700,000 was obtained.

(Synthesis of binder H)
The same operation as the synthesis of Binder A was performed except that 48 parts of itaconic acid and 2 parts of isobornyl methacrylate were changed to 2 parts instead of 50 parts of itaconic acid. A binder H having a weight average molecular weight of 600,000 was obtained.

(Synthesis of Binder I)
The same operation as the synthesis of Binder A was performed except that 25 parts of acrylic acid-2-hydroxyethyl and 25 parts of acrylamide were used instead of 50 parts of itaconic acid. Binder I having a weight average molecular weight of 2 million was obtained.

(Synthesis of binder J)
The same operation as the synthesis of Binder A was performed except that 50 parts of acrylic acid was used instead of 50 parts of itaconic acid. A binder J having a weight average molecular weight of 100,000 was obtained.

(Binder K)
The same operation as the synthesis of Binder A was performed except that the reaction time was changed from 24 hours to 4 hours. A binder K having a weight average molecular weight of 100,000 was obtained.

(Binder L)
SBR having a weight average molecular weight of 3 million and a nonvolatile content of 40% by mass were used as the binder L.

(Binder M)
A urethane resin having a weight average molecular weight of 300,000 and a non-volatile content of 37% by mass were used as the binder M.

(Creation of carbon coating foil coating solution A)
Carbon coat foil coating liquid A was prepared by adding 400 parts of water to a mixture of 50 parts of binder A and 50 parts of acetylene black as a conductive additive and further mixing. In addition, the solid content density | concentration of the produced carbon coat foil coating liquid A was 20 mass%.

(Creation of carbon coating foil coating solutions B to M)
Except for changing the binder A to binders B to M, the same operations as in the preparation of the carbon coating foil coating solution A were performed to obtain carbon coating foil coating solutions B to M.

(Creation of carbon coated foils A to M)
Carbon coat foil coating liquids A to M were applied to an aluminum foil so as to have a thickness of 1 μm by a gravure method, and dried at 120 ° C. for 5 minutes to obtain carbon coat foils A to M.

Example 1
The production of the positive electrode will be described. 90 parts of LiCoO ₂ , 5 parts of acetylene black as a conductive assistant, and 5 parts of polyvinylidene fluoride as a binder are mixed with 100 parts of N− with respect to the total amount of active material, conductive assistant and binder. Methylpyrrolidone was added and further mixed to prepare a positive electrode slurry. This was coated on the carbon-coated foil A by a doctor blade method so that the slurry for positive electrode was 200 μm in a state before drying, was heated and dried at 120 ° C. for 5 minutes, and a positive electrode was obtained through a pressing process.

  The production of the negative electrode will be described. 94 parts of graphite, 1 part of acetylene black as a conductive additive, 5 parts of polyvinylidene fluoride as a binder were mixed, and further 100 parts of N-methylpyrrolidone was added and further mixed to prepare a slurry for negative electrode. This was applied to a Cu foil having a thickness of 10 μm as a current collector so that the thickness after the roll press treatment was 120 μm, dried at 100 ° C. for 5 minutes, and a negative electrode was obtained through a pressing process.

The adjustment of the electrolytic solution will be described. LiPF ₆ was dissolved to a concentration of 1.0 mol / L in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70 to prepare an electrolytic solution.

  The creation of the battery will be described. Conductive tabs were attached to the positive electrode and the negative electrode, and a laminate type battery was obtained using these, a separator including a polyolefin-based porous film, and an electrolytic solution.

  Table 1 shows the evaluation results of the carbon coated foil, the electrode slurry, and the lithium ion secondary battery produced using these.

(Examples 2 to 8)
Except for using the carbon coated foils B to H, the same operation as in Example 1 was performed to obtain a lithium ion secondary battery. The evaluation results are shown in Table 1.

(Comparative Examples 1-5)
A lithium ion secondary battery was obtained by performing the same operation as in Example 1 except that the carbon coated foils I to M were used. The evaluation results are shown in Table 1.

(Comparative Example 6)
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that the positive electrode slurry was applied to an aluminum foil not coated with the carbon coating foil coating solution. The evaluation results are shown in Table 1.

  From comparison between Examples 1-8 and Comparative Examples 1-6, by using the carbon coating foil coating solution for lithium ion secondary battery electrode of the present invention, it is excellent in current collector peel strength and charge / discharge high temperature cycle characteristics. It can be seen that a lithium ion secondary battery is obtained.

Claims (6)

Polymers obtained by polymerizing only unsaturated dicarboxylic acids, or (meth) acrylic acid, hydroxyalkyl (meth) acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, (meth) acrylonitrile and (meth) ) A polymer obtained by polymerizing at least one unsaturated monomer selected from alkyl acrylate and unsaturated dicarboxylic acid, and coated on a metal foil having a weight average molecular weight of 500,000 to 3,000,000. Binder for carbon coating foil coating solution. The binder for carbon coat foil coating liquid according to claim 1, wherein the unsaturated dicarboxylic acid is itaconic acid. It is a carbon coat foil coating liquid containing the binder for carbon coat foil coating liquid of Claim 1 or 2, Comprising: 30-80 mass% of conductive support agents are included with respect to solid content of a carbon coat foil coating liquid. Carbon coating foil coating solution. The carbon coat foil comprised from the carbon coat foil coating liquid layer and the metal foil containing the binder for carbon coat foil coating liquid of Claim 1 or 2, and a conductive support agent. The electrode for lithium ion secondary batteries obtained using the carbon coat foil of Claim 4, and the slurry for lithium ion secondary battery electrodes. The lithium ion secondary battery obtained using the electrode for lithium ion secondary batteries of Claim 5.