JP2013048043A - Coating liquid, conductive coating film, electrode plate for power storage device and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating liquid having excellent electrolyte resistance and oxidation resistance, exhibiting high adhesion to a collector such as an aluminum foil or a copper foil, and capable of forming a conductive electrode film having a high surface resistance.SOLUTION: The coating liquid used for forming a conductive coating film on the surface of a collector configuring the electrode plate for a power storage device contains (A) a polymer acid, (B) a native polyvinyl alcohol and/or a denatured polyvinyl alcohol having a saponification degree of 75 mol% or higher, (C) a conductive material, and (D) a polar solvent.

Description

  The present invention provides a coating liquid used for forming a conductive coating film disposed between a current collector and an electrode active material layer (hereinafter also referred to as an “electrode layer”), and a coating liquid used therefor. The present invention relates to a conductive coating film, a member for an electrode plate, an electrode plate for a power storage device, and a power storage device. More specifically, a coating that can form an electroconductive coating film between the current collector and the electrode layer that has excellent electrolytic solution resistance and oxidation resistance and can improve the adhesion between the current collector and the electrode layer. The present invention relates to a liquid, and a conductive coating film, an electrode plate member, an electrode plate for a power storage device, and a power storage device obtained using the same.

  In recent years, electronic devices and communication devices have been rapidly reduced in size and weight, and there is an increasing demand for reduction in size and weight of power storage devices such as secondary batteries used as power sources for driving these devices. ing. In response to these demands, secondary batteries having a high energy density and a high voltage as typified by lithium ion secondary batteries have been developed instead of conventional alkaline storage batteries. And along with the spread of these secondary batteries, power storage devices aiming at further higher capacity and members for constituting the same have been proposed (Patent Documents 1 and 2).

  On the other hand, it is desired to increase the size of the power storage device for applications such as electric vehicles and hybrid vehicles, but there are many problems for practical use. For example, in the case of a lithium ion battery, it is possible to secure safety corresponding to an increase in electrolyte, which is a flammable substance, and secure input / output characteristics that can be put to practical use. Therefore, along with the improvement of safety, higher capacity and higher output are issues to be solved in the future for power storage devices.

  In order to increase the capacity and output of the power storage device, it is effective to reduce the internal resistance. For that purpose, it is important to control the charge transfer phenomenon at the interface of each layer such as the electrode layer, the current collector, and the electrolyte layer (Non-Patent Documents 1 and 2), and various proposals have been made.

  For example, at the graphite negative electrode interface of a lithium ion battery, a surface resistance film called SEI film formed by decomposition of the electrolyte solution or decomposition of the lithium-based compound that is a supporting salt has a significant effect on maintaining the performance of the battery. It has been known. It is known that the addition of catechol carbonate and its derivatives to the electrolyte reduces the thickness of the SEI film and reduces the film resistance (Non-Patent Document 2).

  In addition, the positive electrode current collector made of aluminum constituting the lithium ion battery is passivated by forming a barrier film (passive film) on the surface thereof in an electrolyte containing fluorine. Although this passive film affects the cycle characteristics of the lithium ion battery, conductivity can be imparted to the passive film by applying an ultrafine carbon dispersion to the heat-treated current collector (Non-patent Document 3). ).

  Furthermore, with regard to safety improvement, all-solid-state lithium ion batteries using nonflammable electrolytes have attracted attention as power storage devices with safety. However, the all-solid-state lithium ion battery has a drawback that the output performance is not yet sufficient. In recent years, in order to solve this drawback, attempts have been made to interpose an oxide solid electrolyte as a buffer layer between an electrode layer and an electrolyte layer, and it has been reported that output performance has been greatly improved (Non-patent Document). 4).

  Further, in a power storage device including a solid electrolyte, a fluorine-based polymer whose conductivity is close to that of a liquid electrolyte is used. However, the fluoropolymer has a drawback that it does not adhere well to the current collector metal. For this reason, the proposal which coats an electrical power collector with acid-modified polyolefin is made | formed in order to solve this fault and to maintain also the outstanding cycling characteristics (patent document 3).

  However, in these proposals, problems to be solved are limited to problems under specific conditions, and most of them are limited and individual solutions. The reason seems to be that there are still many unclear points in the phenomenon of charge transfer and ion transfer at the interface between layers in the power storage device (Non-patent Document 3). Under these circumstances, the present inventors consider practicality as the first point, expand the viewpoint, and regard the phenomenon between each structural unit in the power storage device as one system including an interface. I came to think that it is necessary to examine the validity of the system and to solve the problem.

  An electrode plate can be given as a main “system including an interface” constituting the power storage device. The electrode plate is an electrode member in which unit members such as an electrode layer and a current collector are integrated, and is a member that greatly affects the performance of the power storage device. With regard to the electrode plate, it has been proposed to increase the area of the thin film in order to extend the charge / discharge cycle life and increase the energy density. For example, for a lithium ion battery, a paste-like coating solution prepared by dispersing and dissolving a positive electrode active material powder such as a metal oxide, sulfide, halide, etc., a conductive material, and a binder in an appropriate solvent is used. Patent Documents 4 and 5 disclose positive plates obtained by applying a coating film on the surface of a current collector made of a metal foil such as the above.

  Capacitors using an electric double layer formed at the interface between the polarizable electrode plate and the electrolyte are used as memory backup power supplies, and are applied to applications that require high output such as power supplies for electric vehicles. Is also attracting attention. Since a capacitor has a large output, both high capacitance and low internal resistance are required. A polarizable electrode plate for a capacitor is manufactured by applying and drying a coating liquid, which is a mixture of a binder and a conductive material, on a current collector, in the same manner as a negative electrode plate of a battery.

  As a binder to be contained in a coating liquid used for manufacturing an electrode plate of a power storage device, for example, a fluorine-based resin such as polyvinylidene fluoride, or a silicone / acrylic copolymer is used. The negative electrode plate and the polarizable electrode plate are obtained by applying a paste-like coating solution prepared by adding a binder material dissolved in an active material such as a carbonaceous material to a current collector. . The binder used for the preparation of the coating liquid needs to be electrochemically stable with respect to the non-aqueous electrolyte. Furthermore, it is necessary not to elute into the electrolyte solution of a battery or a capacitor, not to swell greatly by the electrolyte solution (electrolytic solution resistance), and to be soluble in some solvent.

  On the other hand, a protective film is formed on the surface of a current collector made of aluminum or the like by applying various resin solutions. However, since the formed protective film has insufficient durability against the organic solvent, there is a problem that the resistance to electrolytic solution is insufficient. In addition, the conductive coating film formed by applying and drying the coating liquid usually has insufficient adhesion and flexibility to the current collector and a large contact resistance to the current collector. Furthermore, there has been a problem in that the conductive coating film is peeled off, dropped off, cracked, or the like during the assembly or charging / discharging of the battery or capacitor.

  Further, the positive electrode plate of the lithium ion battery is subjected to extremely strong oxidation conditions. On the other hand, the negative electrode plate is subjected to extremely strong reducing conditions. For this reason, the coating film formed on the current collector surface also suffers from deterioration and destruction due to these severe conditions, and the development of a coating film having high oxidation resistance is desired. .

  Conventional batteries and capacitors have problems of poor adhesion between the electrode layer and the current collector (substrate) as described above, and high resistance at the interface between the electrode layer and the substrate. Although various coating liquids have been proposed, the poor adhesion may be improved by the conductive coating film formed by these coating liquids, but the resistance to electrolytic solution and oxidation resistance may be improved. Sexuality is insufficient. For this reason, the actual situation is that the resistance between the electrode layer and the current collector is further increased, and the problem has not been solved.

JP 2006-310010 A JP 2007-95641 A JP-A-11-297332 JP 63-10456 A JP-A-3-285262

Takeshi Abe, Zenpachi Okumi: “Interfacial Charge Transfer Reaction in Lithium Ion Batteries”, Surface Science, 27, 10, 609-612, 2006 Hideya Yoshitake, Tatsumi Ishihara, Masayuki Yoshio: “Control of Lithium-ion Battery Graphite Negative Electrode Interface”, Surface Technology, Vol. 53, No. 12, pp. 887-889, 2002 Nishina Ikuo, Tachibana Kazuhiro, Endo Takashi, Ogata Takeaki: “Effects of Passive Film Formed on Aluminum Current Collector in Lithium Ion Secondary Battery System”, Battery Technology, Vol. 15, p. 28- Page 40, 2003 Kazunori Takada: “High output of all-solid-state lithium ion battery”, IEICE Technical Report, 107, 493, 43-47, 2008

  The present invention has been made in view of such problems of the prior art, and the problem is that it is excellent in electrolytic solution resistance and oxidation resistance, and is used for collecting current such as aluminum foil and copper foil. An object of the present invention is to provide a coating liquid capable of forming a conductive electrode film having high adhesion to a body and low surface resistivity.

  The subject of the present invention is a conductive coating having excellent electrolytic solution resistance and oxidation resistance, high adhesion to a current collector such as an aluminum foil or copper foil, and low surface resistivity. An object of the present invention is to provide a film, a member for an electrode plate provided with the conductive coating film, an electrode plate for a power storage device, and a method for manufacturing the electrode plate for the power storage device.

  Furthermore, an object of the present invention is to provide a power storage device having characteristics such as excellent charge / discharge efficiency (cycle characteristics), large discharge capacity, and low internal resistance.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that a conductive coating film containing polymer acid, unmodified polyvinyl alcohol having a saponification degree of 75 mol% or more and / or modified polyvinyl alcohol, and a conductive material as essential components. Was found to be effective. And the suitable structure as a coating liquid for forming an electroconductive coating film in the electrode plate of such an electrical storage apparatus was discovered, and it came to complete this invention.

That is, according to this invention, the coating liquid shown below is provided.
[1] A coating solution used for forming a conductive coating film on the surface of a current collector constituting an electrode plate for a power storage device, comprising (A) a polymer acid and (B) a saponification degree of 75 mol. % Or more of unmodified polyvinyl alcohol and / or modified polyvinyl alcohol, (C) a conductive material, and (D) a polar solvent.
[2] The coating solution according to [1], wherein the polymer acid is a homopolymer of a carboxyl group-containing vinyl monomer and / or a copolymer of a carboxyl group-containing vinyl monomer and a carboxyl group-free vinyl monomer. .
[3] The coating solution according to [1] or [2], wherein the polymer acid is at least one selected from the group consisting of polyacrylic acid, polyitaconic acid, and polymaleic acid.
[4] The modified polyvinyl alcohol is carboxy group-modified polyvinyl alcohol, carbonyl group-modified polyvinyl alcohol, silanol group-modified polyvinyl alcohol, amino group-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, and acetoacetyl group-modified. The coating liquid according to any one of [1] to [3], which is at least one selected from the group consisting of polyvinyl alcohol.
[5] The conductive material is at least one selected from the group consisting of acetylene black, ketjen black, graphite, furnace black, single-walled or multi-walled carbon nanofibers, and single-walled or multi-walled carbon nanotubes [1] ] To [4].
[6] The content of the polymer acid with respect to 1 part by mass of the conductive material is 0.1 to 3 parts by mass, and the total of the unmodified polyvinyl alcohol and the modified polyvinyl alcohol with respect to 1 part by mass of the conductive material. The coating liquid according to any one of [1] to [5], in which the content is 0.1 to 3 parts by mass and the solid content concentration is 0.02 to 40% by mass.
[7] The total content of the unmodified polyvinyl alcohol and the modified polyvinyl alcohol with respect to 1 part by mass of the polymer acid is 0.1 to 1 part by mass, according to any one of [1] to [6]. Coating liquid.
[8] The coating solution according to any one of [1] to [7], further including a crosslinking agent.

Moreover, according to this invention, the electroconductive coating film shown below is provided.
[9] A conductive coating film formed by the coating liquid according to any one of [1] to [8].
[10] The conductive coating film according to [9], wherein the film made of the coating solution is heat-treated at 80 to 250 ° C., and the dry film thickness thereof is 0.1 to 10 μm.
[11] The above [9] or [10], wherein the surface resistivity measured in accordance with JIS K 7194 is 3,000Ω / □ or less when formed on a glass plate with a dry film thickness of 4 μm. Conductive coating film.

Furthermore, according to this invention, the member for electrode plates shown below is provided.
[12] An electrode plate member comprising: a current collector; and the conductive coating film according to any one of [9] to [11] disposed on a surface of the current collector.

Moreover, according to this invention, the electrode plate for electrical storage apparatuses shown below and its manufacturing method are provided.
[13] An electrode plate for a power storage device, comprising: the electrode plate member according to [12]; and an electrode active material layer disposed on a surface of the conductive coating film.
[14] The electrode plate for a power storage device according to [13], wherein the current collector is an aluminum foil, and the positive electrode active material is contained in the electrode active material layer.
[15] The electrode plate for a power storage device according to [13], wherein the current collector is a copper foil, and the negative electrode active material is contained in the electrode active material layer.
[16] The electrode plate for a power storage device according to [13], wherein the current collector is an aluminum foil and is a polarizable electrode plate.
[17] A step of applying the coating liquid according to any one of [1] to [8] to the surface of the current collector to form a conductive coating film, and on the surface of the conductive coating film Forming an electrode active material layer on the substrate.
[18] After applying the coating liquid to the surface of the current collector, the polar solvent contained in the coating liquid is removed by heating, or while removing the polar solvent, the temperature is 1 at 80 to 250 ° C. The method for producing an electrode plate for a power storage device according to [17], wherein the heat treatment is performed for 2 to 60 minutes.

Furthermore, according to the present invention, the following power storage device is provided.
[19] A power storage device comprising the electrode plate for a power storage device according to any one of [13] to [16].
[20] The power storage device according to [19], which is a secondary battery or a capacitor.

  Although the coating liquid of the present invention uses a polymer (specific polyvinyl alcohol) having a low environmental load as a binder, it is between the current collector and the electrode layer constituting the electrode plate for the power storage device. And forming a conductive electrode film that is excellent in electrolytic solution resistance and oxidation resistance, has high adhesion to a current collector such as aluminum foil and copper foil, and serves as an undercoat layer with low surface resistivity. Can do. As a result, it is possible to provide an electrode plate member in which an electrode layer excellent in adhesion, oxidation resistance, and electrolytic solution resistance is provided on the surface of a current collector such as an aluminum foil or a copper foil. . Furthermore, since the contact resistance between the current collector and the electrode layer is also improved, an electrode plate for a power storage device such as an electrode plate for a battery or a polarizable electrode plate for a capacitor having excellent characteristics, and a power storage device including the same Can be provided.

  Next, the present invention will be described in more detail with reference to preferred embodiments. Polyvinyl alcohol contained as a resin binder in the coating liquid of the present invention is a polymer with a low environmental load. For this reason, the coating liquid of this invention has little influence with respect to an environment compared with the conventional coating liquid. The inventors have found that polyvinyl alcohol having a saponification degree of 75% or more is preferably selected and used. The inventors of the present invention have developed a slurry composition obtained by adding a conductive material such as a carbon-based filler and a polymer acid having a resin curing function to such a specific polyvinyl alcohol. As a result, the present inventors have found that it is particularly useful as a coating liquid for forming a conductive coating film for use in the present invention. More specifically, the coating liquid of the present invention is applied to the surface of the current collector to form a conductive coating film (thin film), and this thin film is used as the undercoat layer of the electrode layer. It has been found that the remarkable effects mentioned above can be obtained.

  For example, the present inventors use a conductive coating film formed by applying the above coating liquid on the surface of a current collector as an undercoat layer, and a battery or a capacitor is formed on the surface of the conductive coating film. When the electrode layer is formed, the resistance between the electrode layer and the current collector is not increased at all, but rather the resistance is lowered and the adhesion between the electrode layer and the current collector can be remarkably improved. As a result, the present invention has been completed.

  In the present invention, unmodified polyvinyl alcohol and / or modified polyvinyl alcohol (hereinafter also simply referred to as “PVA”) having a saponification degree of 75% or more is used as the resin binder. By using such specific PVA, in addition to reducing the load on the environment, the following effects can be obtained. As conventional resin binders, for example, polyvinylidene fluoride, polytetrafluoroethylene, acrylic resin, polyimide resin, polyamideimide resin, silicone / acrylic resin, styrene-butadiene copolymer rubber, and the like are used. In the case of using these conventional resin binders, for example, a complicated and expensive treatment for improving the adhesion between the electrode layer and the current collector, such as a chemical conversion treatment on the surface of the current collector, is essential. It was. On the other hand, when the coating liquid of the present invention is used, such a complicated and expensive process is unnecessary. And even if it does not perform such a process, the further outstanding adhesiveness and low resistance can be achieved. As a result, a highly efficient and long-life power storage device is provided.

(1) Coating liquid The coating liquid of this invention is a coating liquid used in order to form an electroconductive coating film on the surface of the electrical power collector which comprises the electrode plate for electrical storage apparatuses. The coating solution of the present invention includes (A) a polymer acid, (B) unmodified polyvinyl alcohol and / or modified polyvinyl alcohol having a saponification degree of 75 mol% or more, (C) a conductive material, and (D) A polar solvent. The details will be described below.

  Conventionally, polymers having a hydroxyl group or an amino group in the molecule, such as cellulose, starch, chitin, chitosan, alginic acid, PVA, polyallylamine, and polyvinylamine, exhibit excellent adhesion to metal materials such as aluminum. It is known that a film can be formed. However, this film has a problem that it swells with a polar solvent such as water or N-methylpyrrolidone (NMP) and easily peels from the surface of the metal material. In addition, when said polymers are used as a binder of the coating liquid for manufacturing an electrode plate, the adhesiveness with respect to the electrical power collector of the electroconductive coating film formed will become favorable. However, there is a problem that durability of the battery such as ethylene carbonate and propylene carbonate with respect to the electrolytic solution is low.

  The present inventors paid attention to PVA that has a particularly low environmental load among the above-mentioned polymers, and studied to improve the organic solvent resistance and oxidation resistance of a film formed by this PVA. As a result, a coating solution prepared by adding PVA with a high degree of saponification to a polar solvent together with a polymer acid can form a film having excellent adhesion, organic solvent resistance, and oxidation resistance on the surface of a metal material. I found out. In addition, when heated after applying the above coating solution, the polymer acid acts as a crosslinking agent for PVA by heating, and the fastness of the formed film is improved, and the solubility and swelling in organic solvents and electrolytes are also improved. Was found to be significantly reduced.

  One of the main effects of the conductive coating film formed from the coating solution of the present invention is that it has excellent resistance to electrolytic solution and oxidation. These effects are considered to be the effects obtained by forming the conductive coating film of the present invention with a coating solution containing PVA having a high degree of saponification and a polymer acid. Since PVA is produced by saponifying polyvinyl acetate, PVA of various saponification degrees exists. PVA having a high degree of saponification, that is, PVA into which many hydroxyl groups have been introduced tends to have a crystal structure. For this reason, when PVA with a high degree of saponification is used, a tough film can be formed. Furthermore, when a polymer acid is added to PVA having a high degree of saponification that can form such a tough film, the polymer acid crosslinks and reinforces the PVA molecules. Therefore, it is possible to form a conductive coating film having extremely high fastness and having high oxidation resistance and electrolytic solution resistance.

(Polymer acid)
The coating liquid of the present invention contains a polymer acid. The “polymer acid” in the present specification refers to a polymer having a plurality of acidic groups such as carboxyl groups and phosphoric acid groups, and a polymer obtained by polymerizing a plurality of carboxylic acid compounds and phosphoric acid compounds. The acidic group may be a free acid or may form a salt. The polymer acid may be a homopolymer or a copolymer. As the polymer acid, a homopolymer of a carboxyl group-containing vinyl monomer and a copolymer of a carboxyl group-containing vinyl monomer and a carboxyl group-free vinyl monomer are preferable. More preferred polymer acids include homopolymers such as phthalocyanine polycarboxylic acid, phytic acid, hexametaphosphoric acid, polyphosphoric acid, acrylic acid, methacrylic acid, itaconic acid, maleic acid, and copolymers thereof; styrene / maleic acid copolymer Examples thereof include polymers, isobutylene / maleic acid copolymers, vinyl ether / maleic acid copolymers, pectinic acid, polyglutamic acid, polymalic acid, polyaspartic acid, acrylic acid / maleic acid / vinyl alcohol copolymer, and the like. Of these, polyacrylic acid, polyitaconic acid, and polymaleic acid are particularly preferable.

(PVA)
The polyvinyl alcohol contained in the coating liquid of the present invention is at least one of unmodified polyvinyl alcohol and modified polyvinyl alcohol. Unmodified polyvinyl alcohol is a known resin obtained by saponifying polyvinyl acetate. In the present invention, polyvinyl alcohol having a saponification degree of 75% or more, preferably 80 to 100% is used. In the present invention, it is preferable to use unmodified polyvinyl alcohol having a polymerization degree of 300 to 5,000 and a saponification degree of 90 to 100%. Commercially available products of such unmodified polyvinyl alcohol include “Kuraray Poval” (manufactured by Kuraray Co., Ltd.), “Gosenol” (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.), and “Denka Poval” (manufactured by Denki Kagaku Kogyo Co., Ltd.). , "J-Poval" (manufactured by Nippon Vinegar Poval Co., Ltd.) and various grades.

  Modified polyvinyl alcohol is obtained by introducing a functional group other than a hydroxyl group and an acetic acid group into the above-mentioned unmodified polyvinyl alcohol. Specific examples of the modified polyvinyl alcohol include carboxyl group-modified polyvinyl alcohol, carbonyl group-modified polyvinyl alcohol, silanol group-modified polyvinyl alcohol, amino group-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, and acetoacetyl group-modified. A polyvinyl alcohol etc. can be mentioned. These modified polyvinyl alcohols can be used singly or in combination of two or more. Commercially available products of these modified polyvinyl alcohols are as follows: “Goselan” (sulfonic acid group-modified polyvinyl alcohol), “Gosefimer K” (cationic modified polyvinyl alcohol), “Gosefimer Z” (acetoacetyl) Group-modified polyvinyl alcohol), “Gosenal” (carboxyl group-modified polyvinyl alcohol) (manufactured by Nippon Synthetic Chemical Industry); “D polymer” (carbonyl group-modified polyvinyl alcohol), “A series” (carboxyl group-modified polyvinyl alcohol) Examples of various grades such as “Kuraray C polymer” (cation modified polyvinyl alcohol) (manufactured by Kuraray Co., Ltd.) and the like can be mentioned.

(Conductive material)
The coating liquid of the present invention contains a conductive material. Specific examples of the conductive material include acetylene black, ketjen black, graphite, furnace black, single-layer or multilayer carbon nanofiber, single-layer or multilayer carbon nanotube, and the like. These conductive materials can be used singly or in combination of two or more. By using these conductive materials, the electrical contact of the formed conductive coating film is further improved. Therefore, a power storage device with low internal resistance and high capacity density can be manufactured.

(Polar solvent)
The coating liquid of the present invention contains a polar solvent. A conventionally well-known thing can be used as a polar solvent. Specific examples of polar solvents include water; alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol; carbonates such as ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, and butylene carbonate; formamide N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-diethylformamide, vinylformamide, vinylacetamide, acetamide, N-methylacetamide, N-ethylacetamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, vinylpyrrolidone, piperidone, N-methylpiperidone Amides such as N-ethylpiperidone, hexamethylphosphoric triamide, 1,3-dimethyl-2-imidazolidinone, methyl oxazolidinone, ethyl oxazolidinone; sulfoxides such as dimethyl sulfoxide; sulfones such as tetramethylene sulfone be able to.

  Among these, water, methyl alcohol, ethyl alcohol, isopropyl alcohol, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3- Dimethyl-2-imidazolidinone and dimethyl sulfoxide are preferred. These polar solvents can be used singly or in combination of two or more. As these polar solvents, commercially available products may be used as they are or after purification as necessary.

(composition)
The amount of PVA contained in the coating liquid of the present invention is preferably 0.1 to 3 parts by mass, and 0.3 to 2 parts by mass when the conductive material is 1 part by mass. Is more preferable. The amount of the polymer acid contained in the coating liquid of the present invention is preferably 0.1 to 3 parts by mass, and 0.3 to 2 parts by mass when the conductive material is 1 part by mass. More preferably. In addition, the solid content concentration of the coating liquid is preferably 0.02 to 40% by mass, and more preferably 0.02 to 35% by mass, when the entire coating liquid is 100% by mass. It is preferably 0.1 to 35% by mass.

  The content of PVA when the total coating liquid is 100 parts by mass is preferably 1 to 40 parts by mass, more preferably 1 to 20 parts by mass, and 1 to 10 parts by mass. Is particularly preferred. Moreover, it is preferable that it is 1-40 mass parts, and, as for content of a polymer acid when the whole coating liquid is 100 mass parts, it is more preferable that it is 1-20 mass parts. Further, the content of the conductive material when the entire coating liquid is 100 parts by mass is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, 2 to 15 parts by mass is particularly preferable.

  When there is too little content of PVA and a polymer acid, the intensity | strength of the electroconductive coating film formed, the adhesiveness with respect to a collector, and electrolyte solution resistance may be insufficient. On the other hand, when there is too much content of PVA and a polymer acid, it may become difficult to obtain a uniform coating liquid. Moreover, when there is too little content of an electroconductive material, the electroconductivity of the electroconductive coating film formed may be insufficient. On the other hand, when there is too much content of an electroconductive material, since content of another component is relatively insufficient, the performance of the electroconductive coating film formed may fall.

  The content of PVA (total of unmodified polyvinyl alcohol and modified polyvinyl alcohol) relative to 1 part by mass of the polymer acid is preferably 0.1 to 1 part by mass. When the content of PVA with respect to 1 part by mass of the polymer acid is less than 0.1 parts by mass, the electrolytic solution resistance of the formed conductive coating film may be lowered. On the other hand, when the content ratio of PVA with respect to 1 part by mass of the polymer acid is more than 1 part by mass, the oxidation resistance of the formed conductive coating film may be lowered.

(Crosslinking agent)
The coating liquid of the present invention may contain a crosslinking agent other than the above-described polymer acid. By containing a crosslinking agent, the formed conductive coating film can be reinforced. Specific examples of the crosslinking agent include naturally occurring organic acids such as succinic acid and citric acid; polybasic acids such as butanetetracarboxylic acid, phosphonobutanetricarboxylic acid, pyromellitic acid and trimellitic acid; ethylene glycol diglycidyl Epoxy compounds such as ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether; isocyanate compounds such as toluylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, phenyl diisocyanate; and phenols of these isocyanate compounds Blocks blocked with blocking agents such as alcohols, alcohols, active methylenes, mercaptans, acid amides, imides, amines, imidazoles, ureas, carbamic acids, imines, oximes, sulfites, etc. Click isocyanate compound; glyoxal, glutaraldehyde, can be cited aldehyde compounds such as dialdehyde starch.

  Further specific examples of the crosslinking agent include (meth) acrylate compounds such as polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and hexanediol diacrylate; methylol compounds such as methylolmelamine and dimethylolurea; zirconyl acetate, zirconyl carbonate, and titanium lactate. Organic acid metal salts such as: aluminum trimethoxide, aluminum tributoxide, titanium tetraethoxide, titanium tetrabutoxide, zirconium tetrabutoxide, aluminum dipropoxide acetylacetonate, titanium dimethoxide bis (acetylacetonate), titanium dibutoxide Examples thereof include metal alkoxide compounds such as bis (ethyl acetoacetate).

  Further specific examples of the crosslinking agent include vinylmethoxysilane, vinylethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-amino. Silane coupling agents such as propyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, imidazolesilane; silane compounds such as methyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane; carbodiimide compounds Etc. When these crosslinking agents are contained, the content of the crosslinking agent is preferably 0.01 to 200% by mass of PVA used as a resin binder.

(Other resin components)
A resin component such as a homopolymer (polyvinylpyrrolidone) having vinylpyrrolidone as a constituent monomer, a copolymer having vinylpyrrolidone as an essential constituent monomer, chitosan, or a derivative thereof may be added to the coating liquid of the present invention. it can. These resin components can be used individually by 1 type or in combination of 2 or more types. By containing these resin components in the coating liquid, the dispersibility of the conductive material in the coating liquid can be improved. Furthermore, since these resin components also function as film-forming components, it is possible to form a conductive coating film having better characteristics.

(Preparation method etc.)
To prepare the coating liquid of the present invention, first, PVA as a resin binder, conductive material, polymer acids, and resin components used as necessary are added to a polar solvent so as to have a predetermined ratio. . And if these components are mixed and disperse | distributed, the coating liquid of this invention can be prepared. When mixing and dispersing the components, a conventionally known disperser such as a homogenizer, a bead mill, a ball mill, a sand mill, or a roll mill, or a kneader such as a planetary mixer can be used as necessary.

  In addition, as for PVA and polymer acid, a commercial item may be used as it is, and what was refine | purified as needed may be used. Moreover, the order which adds PVA and a polymer acid to a polar solvent is not specifically limited, Either PVA and a polymer acid may be added previously, or both may be added simultaneously. When the PVA and the polymer acid are dissolved in the polar solvent, the PVA and the polymer acid may be stirred under room temperature conditions, but may be stirred under heating conditions as necessary. In addition, it is preferable to dissolve by heating to 80 ° C. or higher.

  The coating liquid of the present invention is preferably subjected to physical processing before coating using a conventionally known physical processing means. Examples of the physical processing means include processing means using a bead mill, ball mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer and the like.

  For example, in the case of processing means using a bead mill, a ceramic vessel is filled with zirconia beads (diameter 0.03 to 3 mm) so as to have a filling rate of 50 to 95%, and the rotor circumferential speed is 5 to 20 m / s. What is necessary is just to perform distributed processing by a type | formula or a continuous circulation type.

  Furthermore, it is preferable to prepare the coating solution so that the surface resistivity of the conductive coating film to be formed is 3,000 Ω / □ or less. In order to set the surface resistivity of the conductive coating film within the above numerical range, for example, the content ratio of the conductive material may be adjusted as appropriate. The surface resistivity of the conductive coating film can be measured according to JIS K 7194 by forming a conductive coating film having a dry film thickness of 4 μm on a glass plate.

(2) Conductive coating film, electrode plate member, and electrode plate for power storage device When the above-described coating solution is used, an electrode plate for power storage device such as a secondary battery or a capacitor is useful as a constituent material of the present invention. A conductive coating film can be formed. The conductive coating film has, for example, a dry film thickness of preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm, and particularly preferably 0. It can form by heat-processing, after apply | coating so that it may become 1-2 micrometers. In addition, it is preferable that the conditions of heat processing shall be 80-250 degreeC and 1 second-60 minutes. By conducting the heat treatment under such conditions, it is possible to sufficiently crosslink PVA as the resin binder, and to form a conductive coating film with further improved adhesion to a current collector and the like and resistance to electrolytic solution.

  When the conductive coating film of the present invention is formed on a glass plate with a dry film thickness of 4 μm, the surface resistivity measured according to JIS K 7194 is preferably 3,000 Ω / □ or less. , Preferably 2,000 Ω / □ or less. When a conductive coating film having a surface resistivity exceeding 3,000 Ω / □ is applied to the electrode plate, the internal resistance increases, making it difficult to obtain a highly efficient and long-life battery or capacitor.

  The surface resistivity of the conductive coating film can be measured according to the method shown below. First, after applying a coating solution on a glass plate, heat treatment is performed at 200 ° C. for 1 minute to form a conductive coating film having a dry film thickness of 4 μm. In accordance with JIS K 7194, the surface resistivity of the formed conductive coating film is measured by a four-probe method. In addition, a brand name "Lorester GP" and "MCP-T610" (made by Mitsubishi Chemical Analytech) can be used for a measurement. The measurement conditions may be 25 ° C. and relative humidity 60%.

  When a conductive coating film is formed on the surface of the current collector, a positive electrode layer for a battery, a negative electrode layer for a battery, or a polarizable electrode layer for a capacitor is formed on the surface of the conductive coating film. Thus, an electrode plate for a power storage device having a low resistance between the electrode layer and the current collector and a small environmental load can be obtained.

  The electrode member of the present invention includes a current collector and the above-described conductive coating film disposed on the surface of the current collector. In addition, an electrode plate for a power storage device of the present invention comprises the above electrode plate member and an electrode active material layer disposed on the surface of the conductive coating film. That is, the electrode plate for a power storage device of the present invention comprises an undercoat layer formed of a conductive coating film formed using the coating liquid of the present invention between a current collector and an electrode active material layer (electrode layer). It is arranged as. Therefore, PVA as a resin binder, a polymer acid, and a conductive material are contained as essential components in the conductive coating film constituting the electrode plate for a power storage device.

(3) Method for Manufacturing Electrode Plate for Power Storage Device The method for manufacturing the electrode plate for power storage device of the present invention is a step of forming a conductive coating film by applying the above-mentioned coating liquid to the surface of a current collector (first step) One step) and a step (second step) of forming an electrode active material layer on the surface of the formed conductive coating film. Examples of the current collector include a positive electrode current collector made of a metal foil such as aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony; and a negative electrode current collector made of a metal foil such as copper. Can do. As the positive electrode current collector, an aluminum foil that has corrosion resistance to an electrolytic solution, is lightweight, and can be easily machined is preferable. The thickness of the metal foil (current collector) is preferably 5 to 30 μm, and more preferably 8 to 25 μm. The surface of the current collector is preferably pretreated with a coupling agent such as silane, titanate or aluminum.

  In the first step, a coating solution is applied to the surface of the current collector by various coating methods. The coating solution is preferably applied so as to have a dry thickness of 0.1 to 10 μm, more preferably 0.1 to 5 μm, and more preferably 0.1 to 2 μm. It is particularly preferred. If it is less than 0.1 μm, it may be difficult to apply uniformly. On the other hand, if it exceeds 10 μm, the flexibility of the conductive coating film to be formed may be lowered. Specific examples of various coating methods include gravure coating, gravure reverse coating, roll coating, Mayer bar coating, blade coating, knife coating, air knife coating, comma coating, slot die coating, slide die coating, dip coating, and the like. it can.

  After applying the coating liquid, for example, if the polar solvent contained in the coating liquid is removed by heating or heat treatment is performed while removing the polar solvent, a conductive coating film that functions as an undercoat layer is formed. be able to. The heat treatment conditions are preferably 80 to 250 ° C. and 1 second to 60 minutes. By heat-treating under such conditions, PVA as a resin binder can be sufficiently cross-linked, and the adhesion of the formed conductive coating film to the current collector and the resistance to electrolytic solution can be further improved. In addition, when the conditions of heat processing are less than 80 degreeC or less than 1 second, the adhesiveness with respect to the electrical power collector of the electroconductive coating film formed, and electrolyte solution resistance may become inadequate.

In the second step, an electrode active material layer (electrode layer) is formed on the surface of the formed conductive coating film. Thereby, the electrode plate for electrical storage devices can be obtained. In order to further improve the homogeneity of the electrode layer, it is preferable to press the electrode layer using a metal roll, a heating roll, a sheet press machine or the like. The conditions for the press treatment are preferably 500 to 7,500 kgf / cm ² . If it is less than 500 kgf / cm ² , the homogeneity of the electrode layer may be difficult to improve. On the other hand, if it exceeds 7,500 kgf / cm ² , the electrode plate for a power storage device including the current collector tends to be easily damaged.

  The electrode plate for a power storage device of the present invention obtained as described above is composed of a conductive material moderately dispersed between the current collector and the electrode layer, and PVA which is a resin binder crosslinked with a polymer acid. An undercoat layer having excellent adhesion, oxidation-reduction resistance, and solvent resistance and having flexibility is formed and disposed. The undercoat layer has the characteristics as described above.

(4) Secondary battery If the electrode plate (positive electrode plate and negative electrode plate) for power storage devices of the present invention is used, a secondary battery such as a nonaqueous electrolyte secondary battery can be produced. For example, when a lithium-based non-aqueous lithium ion battery is manufactured, a non-aqueous electrolyte solution in which a lithium salt as a solute is dissolved in an organic solvent or an ionic liquid is used. Specific examples of the lithium salt include inorganic lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, LiBr; LiB (C ₆ H ₅ ) ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO _{2 CF 3) 3, LiOSO 2} CF 3, LiOSO 2 C 2 F 5, LiOSO 2 C 3 F 7, LiOSO 2 C 4 F 9, LiOSO 2 C 5 F 11, LiOSO 2 C 6 F 13, LiOSO 2 C 7 organic lithium salt F ₁₅ or the like, and the like.

  Examples of the organic solvent include cyclic esters, chain esters, cyclic ethers, chain ethers and the like. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, γ-valerolactone, and the like.

  Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, butyl propyl carbonate, and propionic acid alkyl ester. , Malonic acid dialkyl ester, acetic acid alkyl ester and the like.

  Examples of cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkylalkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, and the like. Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether. it can.

  An ionic liquid is a liquid consisting only of ions based on a combination of an organic cation and an anion. Examples of organic cations include dialkylimidazolium cations such as 1-ethyl-3-methylimidazolium ion; trialkylimidazolium cations such as 1,2-dimethyl-3-propylimidazolium ion; dimethylethylmethoxyammonium ion and the like. Tetraalkylammonium ions, alkylpyridinium ions such as 1-butylpyridinium ion, dialkylpyrrolidinium ions such as methylpropylpyrrolidinium ion, dialkylpiperidinium ions such as methylpropylpiperidinium ion, and the like. These organic cations can be used singly or in combination of two or more.

Examples of the anions that are pairs of these organic cations include AlCl ₄ ⁻ , PF ₆ ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , PF ₃ (CF ₃ ) ₃ ⁻ , BF ₄ ⁻ , and BF ₂ (CF ₃ ). ₂ ⁻ , BF ₃ (CF ₃ ) ⁻ , CF ₃ SO ₃ ⁻ (TfO; triflate anion), (CF ₃ SO ₂ ) ₂ N ⁻ (TFSI; trifluoromethanesulfonyl), (FSO ₂ ) ₂ N ⁻ (FSI) Fluorosulfonyl), (CF ₃ SO ₂ ) ₃ C ⁻ (TFSM) and the like. The other configuration of the secondary battery is the same as that of a conventionally known secondary battery.

(5) Capacitor If the electrode plate for a power storage device (polarizable electrode plate) of the present invention is used, a capacitor such as an electric double layer capacitor or a lithium ion capacitor can be produced. The conductive coating film constituting the polarizable electrode plate contains PVA, polymer acid, and conductive material.

  The coating liquid used when manufacturing a polarizable electrode plate for a capacitor preferably has a PVA content of 1 to 40 parts by mass, with a solid content per 100 parts by mass of the coating liquid. Part is more preferable, and 1 to 10 parts by mass is particularly preferable. When there is too little content of PVA, a coating film component may fall off easily from the conductive coating film formed. On the other hand, when there is too much content of PVA, an electroconductive material will be covered with PVA and internal resistance of the polarizable electrode plate obtained may increase.

  As the polymer acid, those having a high content of acidic groups such as carboxyl groups and phosphoric acid groups are preferable from the viewpoint of crosslinkability to PVA. The amount of the polymer acid contained in the coating solution is preferably 100 to 1000 parts by mass and more preferably 100 to 500 parts by mass per 100 parts by mass of PVA. When the content of the polymer acid is less than 100 parts by mass, adhesion of the formed conductive coating film to the current collector and resistance to electrolytic solution may be insufficient. On the other hand, when the content of the polymer acid exceeds 1000 parts by mass, the insolubility and non-swellability of the formed PVA cross-linked product (cross-linked polymer) in the electrolyte solution tend to decrease, and it is economically disadvantageous. Tend to be.

  As the conductive material to be contained in the coating liquid used when manufacturing a polarizable electrode plate for a capacitor, conductive carbon such as acetylene black, ketjen black, carbon black, carbon nanofiber, and carbon nanotube is preferable. By using such a conductive material, the electrical contact of the formed conductive coating film can be further improved, the internal resistance of the capacitor can be lowered, and the capacitance density can be increased. The amount of the conductive material contained in the coating liquid is preferably 0.1 to 30 parts by mass, and more preferably 2 to 15 parts by mass with respect to 100 parts by mass of the coating liquid.

  It is preferable to process the coating liquid used when manufacturing the electrode plate for capacitors, if necessary, by physical processing means before coating. Examples of the physical processing means include processing means using a bead mill, ball mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer and the like. In addition, when mixing each component, the conductive material is first treated using a mixer such as a crusher, planetary mixer, Henschel mixer, omni mixer, etc., and then a solution of PVA or polymer acid is added. And the method of mixing uniformly is also preferable. By adopting this method, a uniform coating solution can be easily obtained. Moreover, the polarizable electrode plate for capacitors which has a more favorable characteristic can be obtained by using a uniform coating liquid.

  As a material constituting the current collector, a material having electrical conductivity and electrochemical durability is preferable. In particular, from the viewpoint of heat resistance, a current collector made of a metal material such as aluminum, titanium, tantalum, stainless steel, gold, or platinum is preferable, and a current collector made of aluminum or platinum is more preferable. The shape of the current collector is not particularly limited, but a sheet-like material having a thickness of about 0.001 to 0.5 mm is usually used.

  When the coating liquid is applied to the surface of the current collector and dried, a conductive coating film can be formed. Examples of the application method of the coating liquid include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, and a spray coating method.

  Although the viscosity of a coating liquid changes also with the kind of coating machine and the shape of a coating line, it is 10-100,000 mPa * s normally, Preferably it is 50-50,000 mPa * s, More preferably, it is 100-20,000 mPa. -S. The amount of the coating liquid to be applied is not particularly limited, but the thickness of the conductive coating film formed after drying and removing the polar solvent is usually 0.05 to 100 μm, preferably 0.1 to 10 μm. Is the amount. The drying method and conditions are the same as in the case of manufacturing an electrode plate for a battery.

  An electric double layer capacitor or a lithium ion capacitor can be manufactured in accordance with a conventional method using the above-mentioned polarizable electrode plate, electrolytic solution, and separator. Specifically, a laminate obtained by laminating polarizable electrode plates via a separator is wound or folded in accordance with the capacitor shape and placed in a container. Next, a capacitor can be manufactured by sealing after injecting the electrolyte into the container.

As the electrolytic solution, a nonaqueous electrolytic solution obtained by dissolving an electrolyte in an organic solvent is preferable. Any conventionally known electrolyte can be used as the electrolyte for the electric double layer capacitor. Specific examples of such an electrolyte include tetraethylammonium tetrafluoroborate, triethylmonomethylammonium tetrafluoroborate, and tetraethylammonium hexafluorophosphate. Specific examples of the electrolyte for the lithium ion capacitor include lithium salts such as LiI, LiClO ₄ , LiAsF ₆ , LiBF ₄ , and LiPF ₆ .

  The organic solvent (electrolytic solution solvent) for dissolving these electrolytes is not particularly limited as long as it is used as a general electrolytic solution solvent. Specific examples of the electrolyte solvent include carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile. These electrolytic solution solvents can be used singly or in combination of two or more. Of these, carbonates are preferred because of their high withstand voltage. The concentration of the electrolytic solution is usually 0.5 mol / L or more, preferably 0.8 mol / L or more.

  As the separator, there can be used known ones such as a microporous film or non-woven fabric made of polyolefin such as polyethylene or polypropylene; a porous film generally made of pulp called electrolytic capacitor paper; Alternatively, a separator in which inorganic ceramic powder and a resin binder are dispersed in a solvent may be applied and dried on the electrode layer. Further, a solid electrolyte or a gel electrolyte may be used instead of the separator. In addition, about other materials, such as a container, what is used for a normal capacitor can be used.

  EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the text, “part” or “%” is based on mass unless otherwise specified.

(1) Preparation of coating liquid (Example 1)
Add 5 parts of acetylene black to 40 parts of 12.5% polyacrylic acid aqueous solution, stir and mix with a dissolver, then disperse for 1 hour with a bead mill (0.8 mm diameter zirconia beads, filling rate 70%). A liquid was obtained. To the obtained dispersion, 50 parts of 10% unmodified polyvinyl alcohol (unmodified PVA) aqueous solution (trade name “Kuraray Poval 117”, manufactured by Kuraray Co., Ltd., saponification degree 99 mol%, polymerization degree 1700) and 5 parts of ion-exchanged water were added. In addition, the mixture was stirred and mixed for 30 minutes to prepare a coating solution.

(Examples 2 to 20, Comparative Examples 1 to 3, Reference Example 1)
A coating solution was prepared in the same manner as in Example 1 except that the composition of each component was as shown in Table 1. The meanings of the abbreviations in Table 1 are as shown below.
-AB: Acetylene black-KB: Ketjen black-FB: Furnace black-CNT: Carbon nanotubes-PMA: pyromellitic acid-TMA: trimellitic acid-MeOH: methyl alcohol-IPA: isopropyl alcohol-NMP: N-methyl- 2-pyrrolidone

(2) Production of conductive coating film (Example 21)
The coating liquid of Example 1 was applied on one side of an aluminum foil (current collector) having a thickness of 20 μm using a comma roll coater. After heat treatment at 110 ° C. for 2 minutes using an oven, heat treatment was further performed at 180 ° C. for 2 minutes. As a result, the solvent was removed and the polymer component was crosslinked to form a conductive coating film having a dry film thickness of 1 μm on the current collector.

(Examples 22 to 40, Comparative Examples 4 to 7, Reference Example 2)
A conductive coating film was formed on the current collector in the same manner as in Example 21 except that the coating solution shown in Table 2 was used. In Comparative Example 7, a coating solution obtained by dispersing 5 parts of acetylene black in 5 parts of an NMP solution of polyvinylidene fluoride (for convenience, indicated as “PVDF solution” in Table 2) was used.

(Evaluation of adhesion)
Using a cutter, 11 parallel lines perpendicular to the produced conductive coating film were drawn at 1 mm intervals to form 100 squares within a range of 1 cm ² . The mending tape was peeled off after applying the mending tape on the mesh, and the number of cells not peeled off without being attached to the mending tape was measured, and the average value of 10 times was calculated. The results are shown in Table 2. The number of squares that did not peel was used as an index of the adhesion of the conductive coating film to the current collector.

(Evaluation of electrolyte resistance)
The same as above, in a LiPF ₆ solution (electrolyte) obtained by dissolving 1 mol of LiPF ₆ as a supporting salt in 1 L of a mixed solvent of ethylene carbonate: propylene carbonate: dimethoxyethane = 1: 1: 2 (volume ratio) The conductive coating film on which the cells were formed by the above procedure was immersed at 70 ° C. for 72 hours. The state of the conductive coating film after immersion was visually observed, and the electrolytic solution resistance (dissolution / swellability) of the conductive coating film was evaluated according to the following criteria. The results are shown in Table 2.
A: Neither dissolution, swelling, or peeling is observed.
○: Slightly swollen, but no peeling is observed.
X: While dissolving or swelling, peeling is recognized.

(Evaluation of oxidation resistance)
The conductive coating film was immersed in a 6% aqueous hydrogen peroxide solution, heat-treated at 80 ° C. for 3 hours, washed with water and air-dried. The surface of the conductive coating film (dried coating film) was rubbed with the belly of the index finger, and the oxidation resistance of the conductive coating film was evaluated according to the following criteria. The results are shown in Table 2.
(Double-circle): It does not peel after heat processing, and it does not peel even if it rubs the surface of a dry coating film strongly with the belly of an index finger, and carbon on the surface does not fall off.
◯: Not peeled after heat treatment, and does not peel even when the surface of the dried coating is rubbed strongly with the index finger. However, some of the carbon on the surface falls off.
X: It peels after heat processing, or it does not peel after heat processing, but it peels, if the surface of a dry coating film is rubbed strongly with an index belly.

(Measurement of surface resistivity)
Each of the coating liquids shown in Table 2 was applied onto the glass plate using a comma roll coater, followed by heat treatment at 200 ° C. for 1 minute to form a conductive coating film having a dry film thickness of 4 μm on the glass plate. In accordance with JIS K 7194, the surface resistivity of the formed conductive coating film was measured by the four-probe method. For measurement, trade names “Lorestar GP” and “MCP-T610” (manufactured by Mitsubishi Chemical Analytech) were used. Moreover, it measured on 25 degreeC and 60% of relative humidity conditions.

(3) Production of battery (Example 41)
<Preparation of positive electrode plate>
90 parts of LiCoO ₂ powder having a particle diameter of 1 to 100 μm, 5 parts of acetylene black as a conductive assistant, and 50 parts of a 5% NMP solution (PVDF solution) of polyvinylidene fluoride as a binder were mixed. A planetary mixer was used and stirred and mixed at 60 rpm for 120 minutes to obtain a slurry-like positive electrode solution containing a positive electrode active material.

The positive electrode solution obtained using a comma roll coater was applied to the surface of the conductive coating film obtained in Example 21, and then dried in an oven at 110 ° C. for 2 minutes. Furthermore, it dried for 2 minutes in 180 degreeC oven, the solvent was removed, and the positive electrode composite layer by which the positive electrode active material layer with a dry film thickness of 100 micrometers was formed on the electroconductive coating film was obtained. The obtained positive electrode composite layer was pressed under the condition of 5,000 kgf / cm ² to make the film thickness uniform. Subsequently, aging was performed in a vacuum oven at 80 ° C. for 48 hours to sufficiently remove volatile components (solvent, unreacted polybasic acid, etc.) to obtain a positive electrode plate.

<Preparation of negative electrode plate>
The coating liquid of Example 1 was applied on one side of a 15 μm thick copper foil (current collector) using a comma roll coater. After heat treatment at 110 ° C. for 2 minutes using an oven, heat treatment was further performed at 180 ° C. for 2 minutes. As a result, the solvent was removed and the polymer component was crosslinked to form a conductive coating film having a dry film thickness of 1 μm on the current collector.

  90 parts of carbon powder obtained by pyrolyzing carbon coke at 1200 ° C., 5 parts of acetylene black as a conductive auxiliary agent, and 50 parts of 5% NMP solution (PVDF solution) of polyvinylidene fluoride as a binder were mixed. A planetary mixer was used and stirred and mixed at 60 rpm for 120 minutes to obtain a slurry-like negative electrode solution containing a negative electrode active material.

A negative electrode solution obtained using a comma roll coater was applied to the surface of the conductive coating film, and then dried in an oven at 110 ° C. for 2 minutes. Furthermore, it dried for 2 minutes in 180 degreeC oven, the solvent was removed, and the negative electrode composite layer by which the negative electrode active material layer with a dry film thickness of 100 micrometers was formed on the electroconductive coating film was obtained. The obtained negative electrode composite layer was pressed under the condition of 5,000 kgf / cm ² to make the film thickness uniform. Next, aging was performed in a vacuum oven at 80 ° C. for 48 hours to sufficiently remove volatile components (solvent, unreacted polybasic acid, etc.) to obtain a negative electrode plate.

<Production of battery>
Positive electrode plate and negative electrode plate obtained via a separator made of a porous film of (sponge-like) polyolefin (polypropylene, polyethylene, or a copolymer thereof) having a three-dimensional pore structure wider than the positive electrode plate Was wound in a spiral to obtain an electrode body. The obtained electrode body was inserted into a bottomed cylindrical stainless steel container also serving as a negative electrode terminal. Next, a LiPF ₆ solution (electrolytic solution) obtained by dissolving 1 mol of LiPF ₆ as a supporting salt in 1 L in a mixed solvent of ethylene carbonate: propylene carbonate: dimethoxyethane = 1: 1: 2 (volume ratio). The solution was poured into the container. As a result, an AA size battery with a rated capacity of 500 mAh was assembled.

(Examples 42 to 47, Comparative Example 8)
Instead of the coating liquid and coating film of Example 1 used for the production of the positive electrode plate and the negative electrode plate used in Example 18, the conductive coating film, coating liquid, and current collector shown in Table 3 were used. A positive electrode plate and a negative electrode plate were produced in the same manner as in Example 41 except that the body was used. And the battery was assembled like the above-mentioned Example 41 using the produced positive electrode plate and negative electrode plate.

(Measurement of charge / discharge capacity retention rate)
Using a charge / discharge measuring device, each cell was charged at a temperature of 25 ° C. with a charging current of 0.2 CA at a current value of 0.2 CA. (1) After charging from the charging direction to a battery voltage of 4.1 V, (2) Pause for 10 minutes, (3) Then, after discharging to 2.75 V at the same current, (4) 100 cycles of charge and discharge cycles of resting for 10 minutes were repeated. The ratio of the charge / discharge capacity value at the 100th cycle to the charge / discharge capacity value at the first cycle was calculated as “charge / discharge capacity maintenance rate (%)”. The results are shown in Table 3.

(4) Production of capacitor (Example 48)
The coating liquid of Example 1 was applied on one side of an aluminum foil (current collector) having a thickness of 20 μm using a comma roll coater. After heat treatment at 110 ° C. for 2 minutes using an oven, heat treatment was further performed at 180 ° C. for 2 minutes. As a result, the solvent was removed and the polymer component was crosslinked to form a conductive coating film having a dry film thickness of 0.5 μm on the current collector. A planetary mixer was charged with 100 parts of high-purity activated carbon powder having a specific surface area of 1500 m ² / g, an average particle diameter of 10 μm, and 8 parts of acetylene black as a conductive material. An NMP solution of polyvinylidene fluoride was added and mixed for 60 minutes so that the solid concentration was 45%. The electrode solution was obtained by diluting with NMP so that the solid content concentration was 42% and mixing for another 10 minutes. An electrode solution obtained using a doctor blade was applied onto the conductive coating film. It dried for 30 minutes at 80 degreeC using the ventilation drying machine. Thereafter, pressing was performed using a roll press machine to obtain a polarizable electrode plate for a capacitor having a thickness of 80 μm and a density of 0.6 g / cm ³ .

  Two sheets of the obtained polarizable electrode plate were cut out into a circle having a diameter of 15 mm. After the two polarizable electrode plates cut out were dried at 200 ° C. for 20 hours, the surfaces of the electrode layers were placed facing each other, and a laminate was obtained by sandwiching a cellulose-made circular separator having a diameter of 18 mm and a thickness of 40 μm. . The obtained laminate was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. The electrolyte was injected so that no air remained in the container, and a stainless steel cap with a thickness of 0.2 mm was put on the outer container through a polypropylene packing, and the container was sealed by fixing the cap, A coin-type capacitor having a diameter of 20 mm and a thickness of about 2 mm was manufactured. As the electrolytic solution, a solution in which tetraethylammonium tetrafluoroborate was dissolved in propylene carbonate at a concentration of 1 mol / L was used.

(Examples 49 to 53, Reference Example 3)
A capacitor was manufactured in the same manner as in Example 48 except that the coating solution shown in Table 4 was used.

(Measurement and evaluation of capacitance)
The capacitance of the manufactured capacitor was measured at a current density of 20 mA / cm ² . In addition, it means that the performance as a capacitor is so favorable that an electrostatic capacitance is large. The capacitance of the capacitor was evaluated according to the following criteria. The results are shown in Table 4.
A: The capacitance is 20% or more larger than the capacitance of the capacitor of Reference Example 3.
○: The capacitance is 10% or more and less than 20% larger than the capacitance of the capacitor of Reference Example 3.
X: The capacitance is equal to or less than the capacitance of the capacitor of Reference Example 3.

(Evaluation of internal resistance)
The internal resistance of the manufactured capacitor was measured at a current density of 20 mA / cm ² . In addition, it means that the performance as a capacitor is so favorable that internal resistance is small. The internal resistance of the capacitor was evaluated according to the following criteria. The results are shown in Table 4.
A: The internal resistance is 20% or more smaller than the internal resistance of the capacitor of Reference Example 3.
○: The internal resistance is 10% or more and less than 20% smaller than the internal resistance of the capacitor of Reference Example 3.
X: The internal resistance is equal to or less than the internal resistance of the capacitor of Reference Example 3.

  As is clear from the results shown in Table 4, if a polarizable electrode plate including the conductive coating film of the present invention is used, a capacitor having a large capacitance and a small internal resistance can be produced.

  As described above, by using the coating liquid of the present invention, a conductive coating film excellent in adhesion, solvent resistance, and oxidation resistance can be formed on the surface of a metal material such as an aluminum material. . In addition, the formed coating film has excellent adhesion to a current collector made of aluminum foil, copper foil, etc., and also has excellent resistance to electrolyte, and contact resistance with the current collector. Has also been improved. For this reason, if the coating liquid of this invention is used, the electroconductive coating film which has the outstanding characteristic, the member for electrodes, the electrode plate for electrical storage apparatuses, and an electrical storage apparatus can be manufactured.

Claims (20)

A coating liquid used for forming a conductive coating film on the surface of a current collector constituting an electrode plate for a power storage device,
(A) a polymer acid;
(B) unmodified polyvinyl alcohol and / or modified polyvinyl alcohol having a saponification degree of 75 mol% or more;
(C) a conductive material;
(D) A coating solution containing a polar solvent.   The coating solution according to claim 1, wherein the polymer acid is a homopolymer of a carboxyl group-containing vinyl monomer and / or a copolymer of a carboxyl group-containing vinyl monomer and a carboxyl group-free vinyl monomer.   The coating liquid according to claim 1 or 2, wherein the polymer acid is at least one selected from the group consisting of polyacrylic acid, polyitaconic acid, and polymaleic acid.   The modified polyvinyl alcohol is carboxy group-modified polyvinyl alcohol, carbonyl group-modified polyvinyl alcohol, silanol group-modified polyvinyl alcohol, amino group-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, and acetoacetyl group-modified polyvinyl alcohol. The coating liquid according to claim 1, which is at least one selected from the group consisting of:   The conductive material is at least one selected from the group consisting of acetylene black, ketjen black, graphite, furnace black, single-walled or multi-walled carbon nanofibers, and single-walled or multi-walled carbon nanotubes. The coating liquid as described in any one. The content of the polymer acid with respect to 1 part by mass of the conductive material is 0.1 to 3 parts by mass,
The total content of the unmodified polyvinyl alcohol and the modified polyvinyl alcohol with respect to 1 part by mass of the conductive material is 0.1 to 3 parts by mass,
Solid content concentration is 0.02-40 mass%, The coating liquid as described in any one of Claims 1-5.   The coating liquid according to any one of claims 1 to 6, wherein a total content of the unmodified polyvinyl alcohol and the modified polyvinyl alcohol is 0.1 to 1 part by mass with respect to 1 part by mass of the polymer acid.   The coating liquid as described in any one of Claims 1-7 which further contains a crosslinking agent.   The electroconductive coating film formed with the coating liquid as described in any one of Claims 1-8.   The conductive coating film according to claim 9, wherein the film made of the coating solution is formed by heat treatment at 80 to 250 ° C. and has a dry film thickness of 0.1 to 10 μm. When formed on a glass plate with a dry film thickness of 4 μm,
The conductive coating film according to claim 9 or 10, wherein the surface resistivity measured in accordance with JIS K 7194 is 3,000 Ω / □ or less.   The member for electrode plates provided with a collector and the electroconductive coating film as described in any one of Claims 9-11 arrange | positioned on the surface of the said collector. The electrode plate member according to claim 12,
An electrode plate for a power storage device, comprising: an electrode active material layer disposed on a surface of the conductive coating film. The current collector is an aluminum foil;
The electrode plate for a power storage device according to claim 13, wherein the electrode active material layer contains a positive electrode active material. The current collector is a copper foil;
The electrode plate for a power storage device according to claim 13, wherein the electrode active material layer contains a negative electrode active material. The current collector is an aluminum foil;
The electrode plate for a power storage device according to claim 13, which is a polarizable electrode plate. Applying the coating liquid according to any one of claims 1 to 8 to the surface of the current collector to form a conductive coating film;
And a step of forming an electrode active material layer on the surface of the conductive coating film.   After applying the coating solution to the surface of the current collector, the polar solvent contained in the coating solution is removed by heating, or while removing the polar solvent, at 80 to 250 ° C. for 1 second to 60 The method for manufacturing an electrode plate for a power storage device according to claim 17, wherein the partial heat treatment is performed.   An electrical storage apparatus provided with the electrode plate for electrical storage apparatuses as described in any one of Claims 13-16.   The power storage device according to claim 19, wherein the power storage device is a secondary battery or a capacitor.