JPH11250916A - Material for covering current collector, current collector, electrode for lithium ion secondary battery, its manufacture, and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve binding persistence and a cycle characteristic by using a current collector coated with a specific polymer containing no conductive material on its surface, applying a slurry containing an active material to the current collector, then compressing it under a specific condition after drying it. SOLUTION: This current collector has a layer made of a current collector surface coating material mixed with one or two or more kinds of polymers and having the tensile strength of 0.1-500 Kgf/cm<2> , the elongation of 50-4,000%, and the volume natural resistance value of 10<6> Ωcm or above. A slurry containing an active material, a binder and a liquid material is applied and dried to the current collector to form an electrode, then the electrode is compressed in thickness to the compression ratio of 0.2-0.8 against the thickness before compression. A polymer containing 10-100 wt.% of uncrosslinked rubber, an uncrosslinked granular polymer, or crosslinked granular polymer is used for the polymer, thereby the binding property between the current collector and the active material can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for coating a surface of a current collector used for an electrode of an electrochemical element, particularly a lithium ion secondary battery, a current collector whose surface is coated with a polymer, and the current collector The present invention relates to a method for producing a lithium-ion secondary battery electrode using the same, and a battery using the same.

[0002]

2. Description of the Related Art In recent years, portable terminals such as notebook computers, portable telephones, and electronic organizers have rapidly become widespread. As a result, electrochemical devices such as secondary batteries and capacitors used for these power supplies (currently, in particular, lithium-ion secondary batteries are frequently used) are being reduced in size, weight, performance, and cost. Down is strongly demanded. In order to satisfy these needs, electrochemical elements are being improved from all angles, and are effective in reducing size, weight, performance, and cost. Is being developed.

[0003] Metals are frequently used in current collectors used for electrodes of electrochemical elements such as nickel-metal hydride batteries, lithium ion secondary batteries, and non-aqueous electrolyte capacitors. For example, in the case of a lithium ion secondary battery (hereinafter, sometimes simply referred to as a battery), a current collector used for a positive electrode and a negative electrode is usually made of a metal such as aluminum, copper, iron, nickel, titanium, and stainless steel. ing. The electrode is manufactured by applying a slurry containing an active material, a binder and a liquid material to a current collector made of such a metal, drying the liquid material and applying an active material layer. The manufactured electrode is further combined with a separator,
After being bent at 80 degrees or wound finely and densely, it is inserted into an outer can and an electrolytic solution is added to manufacture a battery. Therefore, it is important for the electrode that the active material and the active material, and the active material and the current collector are firmly bound even in such a battery manufacturing process. In addition, since the volume of the active material expands and contracts repeatedly as the battery is repeatedly charged and discharged, the active material and the active material, and the active material and the current collector, are also firmly bound by the charge and discharge. is important. It is the binder contained in the active material layer that binds such active materials to each other and the active material and the current collector. Therefore, the binding property of the binder often determines the life and productivity of the battery. That is, when the binding property is low and the active material is easily separated from the current collector, the productivity of the battery is reduced, or even if the battery can be manufactured, the deterioration of the battery comes early.

[0004] A polyvinylidene fluoride (hereinafter sometimes referred to as PVDF) polymer, which is widely used industrially as an electrode binder for a lithium ion secondary battery, is a polymer such as N-methylpyrrolidone. After dissolving in a liquid material to form a binder composition, the active material is mixed to form a slurry, applied to a current collector, and dried to form a positive electrode and a negative electrode. However, when this binder is used, the binding property between the current collector and the active material is not always sufficient, so that the defective rate at the time of manufacturing the electrode is high, and even if a battery can be manufactured, the active material due to repeated charge and discharge It has been pointed out that a large problem (insufficient binding stability) that the active material falls off from the current collector due to the volume fluctuation (for example, Japanese Unexamined Patent Publication No.
-163031). This is because the polyvinylidene fluoride-based polymer has a strong binding property for binding between active materials, but is not sufficient for binding between the current collector and the active material (that is, binding continuity). This is probably due to the lack of any significant effect. It has also been proposed to use latex polymer particles suspended in water as a binder (for example, JP-A-4-51459, JP-A-5-21068, JP-A-5-74461, etc.). However, even in this case, when the slurry is applied or dried, a phenomenon in which the binder is concentrated on the electrode surface occurs, so that the binding property (binding continuity) between the current collector and the active material is insufficient. (JP-A-5-89871),
Sufficient performance has not yet been obtained.

[0005] As a method of improving the binding durability,
In addition to considering improving the binder and active material itself,
Attempts have been made to increase the amount of binder to increase the binding to the current collector, or to roughen the surface of the current collector by etching or mechanical polishing to improve the binding by the anchor effect. However, if the amount of the binder is increased, the amount of the active material in the electrode is reduced accordingly, and not only does the battery capacity decrease, but also if the amount of the binder is too large, the binder covers the active material surface and the battery performance deteriorates. There is also. In addition, the method of roughening the surface of the current collector increases the cost and is not suitable because the reproducibility during mass production is uneasy. For this reason, there has been proposed a method of increasing the binding property between the active material and the current collector by coating the surface of the current collector in contact with the active material layer with a thin film made of a polymer in which a conductive material is mixed (Japanese Patent Application Laid-Open (JP-A) No. 2002-157572). No. 63-12264, JP-A-63-1812
No. 58, JP-A-6-260164, JP-A-8-260164
JP-A-329928, JP-A-9-35707, etc.). In such a technique, a layer (binding layer) between the current collector surface and the active material layer is devised so that electricity easily flows between the current collector surface and the active material layer. That is, in the method of coating the surface of the current collector of the electrode with a binder such as PVDF as disclosed in JP-A-8-329928, graphite or metal powder is dispersed in the binder to reduce the internal resistance of the binding layer. And JP-A-6-26016
In the example of JP-A No. 4 (1999) -2004, the polyamide resin is applied to the positive electrode current collector in an island shape instead of being applied over the entire surface to ensure conductivity. Further, as described in Japanese Patent Application Laid-Open No. 9-35707, a multilayer structure in which a current collector is coated with an acrylate polymer in which a conductive agent such as graphite is mixed is formed on the surface of the current collector to conclude charge-discharge cycle characteristics. Attempts have been made to balance the wearability.

However, in the known method of dispersing and mixing a conductive agent such as graphite or metal powder into a polymer, if the amount of the conductive agent is small, the electrical conductivity in the binder layer tends to be insufficient, and the conductive agent is not sufficiently energized. When the number is too large, there is also a problem that the amount of the polymer used in the binder layer becomes too small, and the binder layer itself becomes difficult to bind. Furthermore, in order to firmly form a binder layer in which such a conductive agent is dispersed and mixed on a current collector, it is necessary to apply a sufficient thickness so that the conductive agent does not peel off. It is necessary to reduce the amount of active material per unit, and in any case, the battery performance is reduced.

[0007] As described above, the known method using a binding layer is such that a sufficient current flows between the current collector and the active material layer, that is, in order for electricity to flow, the binding layer must be made of a conductive material. Since this method was developed based on the idea that the conductive material must be used, there were many problems caused by including a conductive material.

As another method, a slurry containing a metal composite oxide as an active material is applied to a positive electrode having aluminum or its alloy as a current collector, dried, and then strongly compressed to form a metal current collector. It has been proposed that an active material is press-fitted into the inside to provide mechanical coupling and electrical contact and obtain high-rate discharge performance (Japanese Patent Application Laid-Open No. 7-335199). However, in such a method, since the binder comes into direct contact with the current collector in the end, it is greatly affected by the binding property of the active material layer to the current collector, and the binding to the expansion and contraction of the electrode due to repeated charge and discharge. Wearability is not significantly improved. In addition, there is a concern that the active material having the optimum particle size may be pulverized and crushed by a strong compression force at the time of press-fitting, thereby causing deterioration of battery performance. Since crushing and crushing do not always occur evenly, there is also a problem that there is no reproducibility of manufacturing batteries having the same performance in mass production.

As described above, a lithium ion secondary battery excellent in the binding property between the current collector and the active material and the charge / discharge cycle characteristics (hereinafter, may be simply referred to as cycle characteristics) has not yet been obtained. It was the current situation.

[0010]

Based on such prior art, the present inventors have improved the binding property between the current collector and the active material (hereinafter, sometimes referred to as binding durability), As a result of intensive studies to obtain a lithium ion secondary battery exhibiting cycle characteristics, the current collector surface was coated with a specific polymer containing no conductive agent, and the current collector contained an active material and the like. After applying and drying the slurry and compressing it under specific conditions, it was found that an electrode for a lithium ion secondary battery having excellent binding durability and cycle characteristics was obtained, and the present invention was completed.

[0011]

Thus, according to the present invention, first, a current collector surface coating material obtained by mixing one or more kinds of polymers and having a tensile strength of 0.1 kgf /
cm ^{2 to} 500 kgf / cm ² , elongation 50% to 4,000
%, And a current collector surface coating material having a volume resistivity of 10 ⁶ Ωcm or more is provided. A second current collector having a layer made of the current collector surface coating material is provided. A slurry containing an active material, a binder, and a liquid material is applied to a current collector, dried to form an electrode, and then compressed. The electrode has a compression ratio of 0.1 to the thickness before compression. 2-0.
A method for producing a lithium ion secondary battery electrode characterized by being compressed to 8 is provided, and fourthly, a lithium ion secondary battery containing an electrode produced by the method is provided.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Current collector surface coating material The current collector surface coating material of the present invention (hereinafter, simply referred to as a coating material) is a current collector surface coating material obtained by mixing one or more kinds of polymers. Strength 0.1 ~ 500
Kgf / cm ² , preferably 0.5 to 400 Kgf / c
m ² , more preferably 0.5 to 300 kgf / cm
² , and the elongation is 50 to 4000%, preferably 80 to
3000%, more preferably 100-2000%, and the volume resistivity is usually 10 ⁶ Ωcm or more, preferably 1 Ωcm or more.
It is not less than 0 ⁷ Ωcm. Polymers with insufficient tensile strength are easily broken when coated on the current collector, and polymers with too large a tensile strength value are too tough and the active material is pressed into the coating material by compression of the active material layer described later. I can't do it. Further, the polymer having a small elongation is easily peeled when the current collector is bent, and when the elongation is too large, the coating on the surface of the current collector becomes uneven in the active material layer compression step described below, which is not preferable. . A high volume resistivity value means a high insulating property, which means that a conductive substance such as carbon is not contained in the polymer. In the polymer composition containing a conductive material, the tensile strength and elongation become insufficient, and in the active material layer press-bonding step described later, a crack or chipping of the coating material or the active material layer bonded to the coating material may occur. There is not preferred. In particular, inorganic materials that are not compatible with the polymer, such as carbon and metal powder, make the coating material layer inhomogeneous, and this tendency is increased.

All of the above methods for measuring tensile strength and elongation use a dumbbell-shaped No. 3 test piece according to the method of JIS K 6301 (3. Tensile test). JIS K 63
01 is a rule of the vulcanized rubber physical test method, but in the present invention, all polymers are measured by this method without being limited to vulcanized rubber. In the measurement, the particulate polymer dispersed in the liquid dispersion medium is measured after sufficiently evaporating and drying the liquid dispersion medium. Unlike the conventional coating material in which a conductive agent is contained in advance, the present invention does not need to hold the conductive agent, so that the amount of the polymer can be reduced.

Preferred polymers to be the coating material of the present invention include diene polymers, olefin polymers, styrene polymers, acrylate polymers, polyimide polymers, ester polymers, cellulose polymers, and thermoplastic polymers. More specifically, polybutadiene, polyisoprene, isoprene-isobutylene copolymer, natural rubber, styrene-1,3-butadiene copolymer, styrene-isoprene copolymer,
1,3-butadiene-isoprene-acrylonitrile copolymer, styrene-1,3-butadiene-isoprene copolymer, 1,3-butadiene-acrylonitrile copolymer, 1,3-butadiene-methyl methacrylate copolymer, Styrene-acrylonitrile-1,3-butadiene-methyl methacrylate copolymer, styrene-acrylonitrile-1,3-butadiene-itaconic acid copolymer,
Styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer, styrene-1,
3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, acrylonitrile-1,3-
Butadiene-methacrylic acid-methyl methacrylate copolymer, styrene-1,3-butadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer Diene-based polymers such as coalescence;
Ethylene-propylene copolymer, ethylene-propylene-diene copolymer, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene ionomer, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, chlorinated polyethylene, chlorosulfonated Olefin polymers such as polyethylene; styrene
Ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-isoprene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonitrile copolymer, styrene-n-butyl acrylate Styrene polymers such as -itaconic acid-methyl methacrylate-acrylonitrile copolymer; polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, 2-ethylhexyl acrylate-methyl acrylate Acrylate polymers such as acrylic acid-methoxypolyethylene glycol monomethacrylate; polyamide 6, polyamide 66, polyamide 11, polyamide 12, aromatic polyamide, poly Polyamide or polyimide acid polymers such as amides; Ester condensation polymers such as polyethylene terephthalate and polybutylene terephthalate; Cellulosic polymers such as hydroxyethylcellulose, hydroxypropylcellulose, carboxymethyl and ethylcellulose; Polystyrene-polybutadiene block copolymers, ethylene- Propylene block copolymer, ethylene-propylene-diene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-isoprene block copolymer, styrene -Ethylene-propylene-styrene block copolymer, methyl methacrylate polymer, vinyl alcohol polymer, vinyl acetate polymer Thermoplastic elastomers; is like. Among these polymers of uncrosslinked rubber, uncrosslinked particulate polymer or crosslinked particulate polymer 10 wt% to 100 wt% content to have a polymer, is preferably used.

The particulate polymer is dispersed in a liquid medium as particulate polymers having various shapes, and may be in any form such as a latex, an emulsion, and a non-aqueous polymer dispersion. When a material containing a particulate polymer in a ratio of 10 to 100% by weight in the polymer is used as the coating material, it has a remarkable effect on the binding stability between the current collector and the active material layer, and is used as an electrode. Time 180
It shows excellent performance in the bending test. Polymer particle size when used as a particulate polymer is 0.01 to 10 μm
m, preferably 0.03 to 7 μm, more preferably 0.05 to 5 μm. For example, a homopolymer or copolymer of a conjugated diene monomer or a (meth) acrylate monomer, or a copolymer using a conjugated diene monomer or a (meth) acrylate monomer and various copolymerizable monomers. Preferable examples include coalescence and the like. Further, the homopolymer or copolymer of a (meth) acrylic acid-based monomer or a (meth) acrylate-based monomer, ) Particulate composite polymers (core-shell structure, composite structure, localized structure, daruma) in which a polymer layer such as an acrylic acid monomer or a copolymer of a monomer copolymerizable with a (meth) acrylate monomer is formed. Structures, such as scallop-like structures, leek-like structures, raspberry-like structures, and multi-particle composite structures ("Adhesion" Vol. 34 No. 1 No. 1 To 2
Those having the description on page 3 and particularly having FIG. 6) described on page 17) are mentioned as particularly preferred examples.

2. Current Collector The current collector of the present invention is not particularly limited as long as it is made of a conductive material, and is usually made of a metal such as iron, copper, aluminum, nickel, titanium, and stainless steel (metal foil,
Metal net, ex-band metal, punching metal, etc.) can be arbitrarily selected and used depending on the use of each of the positive electrode and the negative electrode. Although the shape is not particularly limited,
For example, when it is used for a small lithium ion secondary battery or the like, a foil film-like material having a thickness of about 0.001 to 0.5 mm is usually used.

As a method of coating the surface of the current collector (either one surface or both surfaces) with a coating material, a polymer is previously molded by a method such as extrusion molding, injection molding, or inflation molding. A method of bonding, a method of powder coating a coating material in a powder form, or a method by a dry process such as plasma or vacuum deposition can also be adopted. In addition, the polymer is dissolved in an organic or inorganic liquid medium at a predetermined concentration by heating, if necessary,
Alternatively, there is also a method of dispersing, coating and drying the current collector surface, and this method is the simplest and preferable. The organic or inorganic liquid medium used for dissolving or dispersing the coating material is not particularly limited, but is preferably water or an organic liquid medium having a boiling point at normal pressure of 30 to 350 ° C.

Specific examples of these liquid media include:
For example, in addition to water, it is an organic liquid medium such as a hydrocarbon compound, a nitrogen-containing organic compound, an oxygen-containing organic compound, a chlorine-containing organic compound, and a sulfur-containing organic compound. For example, (1) As the hydrocarbon compound, aromatic hydrocarbon compounds such as benzene, toluene and xylene; n-butane, n-pentane, n-
Saturated hydrocarbon organic compounds such as hexane, n-heptane, n-octane, isooctane, cyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, nonane, decane, decalin, dodecane, gasoline and industrial gasoline; 2) Nitrogen-containing organic compounds include nitroethane, 1-nitropropane, 2-nitropropane, acetonitrile, triethylamine, cyclohexylamine, pyridine, monoethanolamine, diethanolamine, forphorin, N, N
And nitrogen-containing organic compounds such as -dimethylformamide and N-methylpyrrolidone. (3) Examples of the oxygen-containing organic compound include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, secondary butyl alcohol, amyl alcohol, isoamyl alcohol, methyl isobutyl carbinol, and 2-ethyl. Butanol, 2-
Compounds having a hydroxyl group such as ethylhexanol, cyclohexanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, ethylene glycol, hexylene glycol, glycerin; propyl ether, isopropyl ether, butyl ether, isobutyl ether, n-amyl ether, isoamyl ether, Aliphatic saturated ethers such as methyl butyl ether, methyl isobutyl ether, methyl n-amyl ether, methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether, ethyl butyl ether, ethyl isobutyl ether, ethyl n-amyl ether, and ethyl isoamyl ether; Aliphatic unsaturated ethers such as allyl ether and ethyl allyl ether; anisole, phenene Lumpur, phenyl ether,
Aromatic ethers such as benzyl ether; cyclic ethers such as tetrahydrofuran, tetrahydropyran and dioxane; ethylene glycol monomethyl ether;
Ethylene glycols such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; organic acids such as formic acid, acetic acid, acetic anhydride, and butyric acid; butyl formate, amyl formate, and propyl acetate , Isopropyl acetate, butyl acetate, sec-butyl acetate,
Amyl acetate, isoamyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, butylcyclohexyl acetate,
Organic acid esters such as ethyl propionate, butyl propionate, amyl propionate, butyl butyrate, diethyl carbonate, diethyl oxalate, methyl lactate, ethyl lactate, butyl lactate and triethyl phosphate; acetone, ethyl ketone, propyl ketone, butyl ketone; Ketones such as methyl isopropyl ketone, methyl isobutyl ketone, methyl isobutyl ketone, diisobutyl ketone, acetylacetone, diacetone alcohol, cyclohexanone, cyclopentanone, methylcyclohexanone, cycloheptanone; and others such as 1,4-dioxane, isophorone, furfural And oxygen-containing organic compounds of the formula (1).
(4) Examples of the chlorine-containing organic compound include chlorine-substituted hydrocarbons such as tetrachloroethane, trichloroethylene, perchloroethylene, dichloropropane, amyl chloride, dichloropentane, and chlorobenzene.
(5) Examples of the sulfur-containing organic compound include thiophene, sulfolane, dimethyl sulfoxide and the like. Among these, an organic liquid medium having a boiling point at normal pressure of 60 to 200 ° C is preferable.

Examples of the coating method include an extrusion coater, a reverse roller, a doctor blade, a dipping method, and a casting method, but other general coating methods may be used. When a multilayer film of a coating material is formed, the above methods can be appropriately combined. Examples of a drying method after the application of the polymer (particularly when an organic or inorganic liquid medium is used) include a method of drying by applying hot air, a method of vacuum drying, and a method of leaving the film in a high-temperature and low-humidity environment. The drying temperature can be arbitrarily set depending on the drying method. However, it is preferable to set the temperature to a temperature lower than the boiling point of the organic or inorganic liquid medium itself, since there is no uneven coating.

The polymer coated on the surface of the current collector by the method of the present invention preferably has a uniform thickness, and the average thickness is 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more. 7 μm or less, more preferably 0.5 μm
It is not less than μm and not more than 5 μm. If the film thickness is in this range,
A good balance between the binding durability and the charge / discharge cycle characteristics can be obtained. If the average film thickness of the polymer is too large, the binding durability is good, but the charge / discharge cycle characteristics deteriorate, which is not preferable. Conversely, if the average film thickness of the polymer is too small, the binding durability will be poor. As will be described later, the active material layer usually has a binder. However, in the present invention, the active material can be held on the current collector even without the binder. Is also possible.

3. Method for Producing Electrode An electrode produced by the method of the present invention is obtained by providing a layer containing an active material on the current collector of the present invention, and usually uses a slurry containing an active material, a binder, and a liquid material. This is applied to the current collector by a method to be described later, dried to form an electrode, and then compressed, and the thickness of the electrode is reduced by a compression ratio with respect to the thickness (1.0) before compression. 0.8-0.2,
Preferably 0.75 to 0.25, more preferably 0.7
To a thickness of ~ 0.3. If the compression is insufficient, the active material does not penetrate sufficiently into the coating material, and the energization and the durability of the binding are not sufficient. Conversely, if the compression is excessive, the energization and the binding are sufficient but the active material is crushed and the active material is crushed. The packing density of the material layer becomes too high, so that the electrolyte is hardly immersed, and the battery performance may be reduced. The compression method is not particularly limited, and examples thereof include a flat plate press, a roll press, and a calender press. The compression conditions may be determined according to the compression ratio, the compression method, the thickness of the active material layer, the type of the binder, and the like. To achieve the above-mentioned thickness, the compression force in the case of a flat plate press or the like is 50 kgf / cm. ^{2 to} 300,
000 kgf / cm ² , preferably 100 kgf / cm ²
１００100,000 Kgf / cm ² , and in the case of a roll press or a calender press, the compression force (linear pressure) is 50 Kg.
f / cm to 10,000 kgf / cm, preferably 10
The compression temperature is 0 Kgf / cm to 5,000 Kgf / cm, and the compression temperature can be arbitrarily selected in the range of 0 to 400 ° C, preferably 10 to 200 ° C.

The polymer used as the coating material of the present invention is an insulating substance. In an electrode obtained by simply applying a slurry to a current collector and drying the current collector, the surface is coated with an active material layer and a polymer. It is difficult to conduct electricity with the body. Therefore, the active material layer is strongly compressed, and the active material in the active material layer is pressed into the layer made of the coating material, so that the active material comes into contact with or close to the current collector, thereby enabling current to flow. In this step, if there is no insulating coating material layer containing a polymer having a tensile strength or elongation within the above range, the active material will not be destroyed in an uneven manner in the compression step, or the active material will not be destroyed. Only insufficient compression is possible. Conversely, the coating material layer of the present invention serves as a cushion,
This compression makes it possible to conduct electricity. At the same time, the active material penetrates into the layer made of the coating material having excellent binding durability by compression, so that an electrode having excellent binding durability can be manufactured by the anchor effect.

The active material used in the production method of the present invention comprises:
Any substance may be used as long as it can occlude and release lithium ions.Examples of the negative electrode active material include various carbonaceous materials, metal composite oxides, and lithium nitride metal compounds. Metal composite oxide,
Particularly, a metal composite oxide containing lithium and at least one metal of iron, cobalt, nickel, and manganese is exemplified. The binder used to hold the active material on the current collector may be any binder as long as it is used as a binder for a lithium ion secondary battery, and specifically, a butadiene polymer, an isoprene polymer, and the like. Diene rubbers obtained using the diene of
Using styrenes such as styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-butadiene-isoprene copolymer, styrene-ethylene-butylene terpolymer, and styrene-ethylene-propylene terpolymer. Butadiene-acrylonitrile copolymer, butadiene-isoprene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene copolymer, styrene-acrylonitrile-
Butadiene-methyl methacrylate copolymer, styrene-
Acrylonitrile-butadiene-itaconic acid copolymer,
Styrene-acrylonitrile-butadiene-methyl methacrylate-fumaric acid copolymer, styrene-butadiene-
Nitrile group-containing rubber containing nitrile group such as itaconic acid-methyl methacrylate-acrylonitrile copolymer; rubber having a saturated main chain such as acrylic rubber, copolymer rubber obtained by using ethylene and propylene; polystyrene-polybutadiene Styrene block copolymers such as block copolymers; fluororubber, polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, poly Fluorinated polymers such as chlorotrifluoroethylene, polyvinyl fluoride, ethylene-chlorotrifluoroethylene copolymer, etc .; polyalkylene resins such as polyethylene and polypropylene; polystyrene resins; Acrylic resins such as an acid; carboxymethyl cellulose, carboxyethyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, (including salts such as their ammonium salts and alkali metal salts) cellulose compound such as carboxymethyl ethyl cellulose; and the like,
These composite polymers can also be used.

These binders are mixed with an active material and a liquid material to form a slurry according to a conventional method, applied to a current collector through a layer made of the coating material of the present invention, dried, and bound.

The liquid material used for dissolving or dispersing these active materials and binders is room temperature (2
0 ° C.) It is preferably a substance which is liquid at normal pressure and has a boiling point of 50 to 400 ° C., for example, water, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, s-butanol, t-butanol, Alcohols such as pentanol, isopentanol and hexanol; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, cyclopentanone, cyclohexanone and cycloheptanone; methyl ethyl ether, diethyl ether, dipropyl ether; Diisopropyl ether,
Ethers such as dibutyl ether, diisobutyl ether, di-n-amyl ether, diisoamyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether and tetrahydrofuran Γ-
Lactones such as butyrolactone and δ-butyrolactone; lactams such as β-lactam; cyclopentane;
Cycloaliphatics such as cyclohexane and cycloheptane;
Benzene, toluene, o-xylene, m-xylene, p
-Aromatic hydrocarbons such as xylene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene and n-amylbenzene; aliphatic hydrocarbons such as heptane, octane, nonane and decane; dimethylformamide, N Linear or cyclic amides such as -methylpyrrolidone; esters such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, and methyl benzoate;

The slurry used in the production of the electrode may contain various additives such as a viscosity modifier, a binding aid, and a conductive agent (such as conductive carbon) in addition to the above-described active material, binder, and liquid material. An agent may be added. The usage ratio of the binder and the active material is usually 1 to 1000 times, preferably 2 to 500 times, more preferably 3 to 300 times, particularly preferably 5 to 200 times the weight of the active material relative to the binder. Mix as follows.
The amount of the liquid material used when the active material and the binder are mixed to form a slurry is not particularly limited, and may be any ratio depending on the ease of application to the current collector, the thickness of the coated film, and the like. can do.

In the lithium ion secondary battery electrode manufactured by the method of the present invention, the above-mentioned slurry is applied to the current collector according to the present invention in a conventional manner, dried, and then the active material layer is compressed by the above-described method. Made at least. The method of applying the slurry to the current collector is not particularly limited. For example, it is applied by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, dipping, brushing, or the like. The amount to be applied is not particularly limited, either, but the amount is such that the thickness of the active material layer formed after drying and removing the dispersion medium is usually 0.005 to 5 mm, preferably 0.05 to 2 mm. The drying method is not particularly limited, and examples thereof include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying conditions are usually adjusted so that the dispersion medium is volatilized as quickly as possible within a speed range in which stress concentration does not occur and the active material layer is cracked or the active material layer does not peel off from the current collector.

4. Battery The battery of the present invention is a lithium ion secondary battery. Lichi
The electrolyte used for the lithium ion secondary battery is
In addition, as a battery according to the type of anode active material and cathode active material
What is necessary is just to select the one exhibiting the function of. For example, electrolysis
The quality can be any of conventionally known lithium salts,
LiClO_Four, LiBF₆, LiPF₆, LiCF_ThreeS
O_Three, LiCF_ThreeCO_Two, LiAsF₆, LiSbF₆, L
iB_TenCl_Ten, LiAlCl_Four, LiCl, LiBr,
LiB (C_TwoH_Five)_Four, CF_ThreeSO_ThreeLi, CH_ThreeSO_ThreeL
i, LiCF_ThreeSO_Three, LiC_FourF₉S0_Three , Li (CF_ThreeS
O_Two)_TwoN, lithium lower fatty acid carboxylate, etc.
It is.

The electrolyte solvent is not particularly limited as long as it is a commonly used solvent, but carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; γ-butyl Lactones such as lactone; trimethoxymethane,
Ethers such as 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; sulfoxides such as dimethylsulfoxide; 1,3-dioxolane and 4-methyl-1,3-dioxolane; Oxolanes; nitrogen-containing compounds such as acetonitrile and nitromethane; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate; triester phosphate, dimethyl carbonate, diethyl carbonate, and carbonic acid Inorganic acid esters such as diester carbonate such as dipropyl; diglymes; triglymes; sulfolanes; oxazolidinones such as 3-methyl-2-oxazolidinone; 1,3-propane sultone;
Sulfones such as butane sultone and naphtha sultone; alone or in combination of two or more.

The lithium ion secondary battery of the present invention contains the above-mentioned electrolytic solution and the electrode of the present invention, and is manufactured by using a component such as a separator according to a conventional method. For example, the following method can be mentioned. That is, the positive electrode and the negative electrode are overlapped with a separator interposed therebetween, and are wound or folded according to the battery shape, placed in a battery container, filled with an electrolytic solution, and sealed using a sealing plate or a safety valve. Further, if necessary, an over-current prevention element such as an ex-band metal, a fuse, or a PTC element, a lead plate, and the like may be inserted to prevent an increase in the pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

[0031]

The electrode manufactured using the current collector whose surface is coated with the coating material of the present invention has a very strong binding property between the current collector and the active material, and can be bent even at 180 degrees. Since the active material layer does not peel off from the current collector and has good electrical conductivity, a battery having good charge / discharge cycle characteristics can be obtained particularly when used for a lithium ion secondary battery. The same effect can be obtained when a current collector whose surface is coated with the coating material of the present invention is used for an electrode of a nickel-metal hydride secondary battery or a capacitor.

[0032]

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

(Measurement of Tensile Strength and Elongation of Polymer Used for Coating Material) The dumbbell-shaped No. 3 type test piece was measured according to the method of JIS K 6301 (3. Tensile test).

(Measurement of Thickness) The thickness of the current collector, the coating material layer, the electrode, etc. is 0.1 μm or more. The thickness including the four corners and the center of the test piece is measured using a contact micrometer. The locations were measured and their average values were taken. Those having a thickness of 0.1 μm or less were measured using an electron microscope. (Measurement of particle size of particulate polymer) Polymer particles 50 dispersed in water or an organic dispersion medium in a transmission electron micrograph.
The longest diameter of each of the dried particles was measured, and the average value was determined.

(Electrode bending test) Length 100 mm,
Fifty test pieces having a width of 20 mm were bent with the active material layer of the electrode inside and a stainless steel rod having a diameter of 2 mm as a core until the electrode surfaces were in contact with each other (inward bending). The test piece (electrode) was similarly bent with the material layer on the outside (outside bending), and the number of cracks in the active material layer and the number of test pieces (electrodes) from which the active material layer was separated from the current collector were counted. The larger this value is, the more the specimen has many defects.

(Measurement of Volume Specific Resistance) JIS K6
It was measured according to 911 (volume resistivity of plastic). (Binding Persistence Test) The binding property between the current collector and the active material layer was determined using JIS K 5400 for ten electrode test pieces.
The evaluation was made according to the cross-cut test method specified in the above. Result is,
It was visually evaluated on a 10-point scale, the average value was used, and the decimal part was rounded off. If this value is 8 or more, it can be determined that there is practically good binding property. (Compression ratio) The thickness of the electrode before and after compression was measured by the method described above, and was calculated by the following equation. (Thickness of electrode after compression) / (thickness of electrode before compression) = compression ratio

(Evaluation of Cycle Characteristics) The battery performance was measured by charging a 20-cell battery manufactured by the same method to 4.0 V by a constant current method (current density: 0.2 mA / cm ² ), and up to 2.8 V. The charge / discharge for discharging was repeated, and the electric capacity was measured. Using the average value of 20 cells as a measured value, a charge / discharge capacity retention ratio expressed as a ratio (%) of the electric capacity at the end of 50 cycles to the electric capacity at the end of 5 cycles was determined, and this was used as an evaluation standard of cycle characteristics. did. The higher this value, the better the cycle characteristics.

Examples 1 to 47 and Comparative Examples 1 to 18 <Coating of Current Collector> A coating material comprising the polymer shown in Table 1 was dissolved or dispersed in the liquid medium of Table 1 to obtain a 1% by weight solution or dispersion. And This solution or dispersion is uniformly applied by a doctor blade method on the surfaces of the aluminum foil (thickness: 20 μm) serving as a positive electrode current collector and the copper foil (thickness: 18 μm) serving as a negative electrode current collector, in contact with the active material layer. 100 ° C, 1
After drying in a dryer for 5 hours, 5 mmHg in a vacuum dryer,
It dried under reduced pressure at 120 degreeC for 2 hours. The thicknesses of the coating material layers are shown in Table 2 for the positive electrode and Table 3 for the negative electrode.

[0039]

[Table 1]

Description of abbreviations in the column of polymer in Table 1 BR: butadiene rubber "Ni" manufactured by Zeon Corporation
pol BR-1220L "SBR: Styrene-butadiene rubber manufactured by Zeon Corporation
Brand name "Nipol 1502" NBR: acrylonitrile-butadiene rubber Nippon Zeon Co., Ltd. brand name "Ni
pol 1043 ”IR: Isoprene rubber“ Ni
pol IR-2200 "SEBS: Styrene-ethylene-butylene-styrene block copolymer Shell Co. product name" Clayton G
1657 ”HNBR: hydrogenated acrylonitrile-butadiene rubber“ Zetpol 1020 ”(trade name, manufactured by Zeon Corporation) EPDM: ethylene-propylene-diene copolymer
Idemitsu DSM product name “Keltan 312” ACM: acrylic rubber Product name “Ni
pol AR32 "SBS: Styrene-Butadiene-Styrene Block Copolymer" Califlex KX1 "manufactured by Shell
55P "CHR: epichlorohydrin rubber manufactured by Zeon Corporation, trade name" Gechron 1100 "Particulate SB: styrene butadiene-based latex manufactured by Zeon Corporation trade name" Nipol LX430 ", in which water is replaced by methyl lactate. Average particle size = 0.1
5 μm. Particulate NB: Acrylonitrile-butadiene latex "Nipol LX51" (trade name, manufactured by Zeon Corporation)
3 ", average particle size = 0.14 μm. Particulate AC: acrylate-based latex manufactured by Nippon Zeon Co., Ltd. The dispersion medium of the trade name “Nipol LX811” is obtained by replacing water with N-methylpyrrolidone (NMP). Average particle size = 0.11 μm. Particulate MB: methyl methacrylate-butadiene-based latex “Crosslen 2M-33” (trade name, manufactured by Takeda Pharmaceutical Co., Ltd.)
The dispersion medium of "A" is prepared by converting 80% by weight of NMP and ethanol 2 from water.
What was replaced with a 0% by weight mixture. Average particle size 0.16μ
m. PNB: Polynorbornene rubber "NORSOREX" manufactured by Zeon Corporation

<Production of Electrode> The positive electrode slurry was LiCoO
₂ 60 parts by weight of conductive carbon, 5 parts by weight of particulate AC 2 parts by weight in Table 1 as a binder, N- methylpyrrolidone (hereinafter, NMP hereinafter) 40 parts by weight was prepared by mixing in a ball mill. The negative electrode slurry is high purity natural graphite 6
0 parts by weight, 4 parts by weight of the particulate SB shown in Table 1 as a binder, and 45 parts by weight of methyl lactate were mixed by a ball mill. The slurry of the positive electrode and the negative electrode was uniformly applied to the previously obtained coated current collector by a doctor blade method. This was dried in a dryer at 120 ° C. for 15 minutes, and further dried in a vacuum dryer at 5 mmHg and 120 ° C.
And dried under reduced pressure for 2 hours to prepare an electrode having a thickness of the active material layers of the positive electrode and the negative electrode of 200 μm. This was further compressed by a biaxial roll press at 120 ° C. at a compression ratio shown in Table 2. The electrode thus obtained was subjected to a bending test and a binding durability test. The results are shown in Table 2 for the positive electrode,
Table 3 shows the negative electrode.

[0042]

[Table 2]

[0043]

[Table 3]

<Production of Battery and Evaluation of Battery Performance> The positive electrode and the negative electrode shown in Table 2 (positive electrode) and Table 3 (negative electrode) were each cut out into a circle having a diameter of 15 mm, and a diameter of 18 mm and a thickness of 25 mm.
With a separator made of a porous polypropylene membrane of μm in between, the active materials are opposed to each other, placed so that the aluminum foil of the positive electrode is in contact with the bottom of the outer container, and expanded metal is put on the copper foil of the negative electrode, It was housed in a stainless steel coin-shaped outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with a polypropylene packing. An electrolyte in which LiPF ₆ was dissolved at a concentration of 1 mol / liter as an electrolyte was injected into a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 so that no air remained. A stainless steel cap with a thickness of 0.2 mm is fixed on the outer container via a polypropylene packing, and the battery can is sealed, and the diameter is 20 mm and the thickness is about 2 m.
m coin type batteries were manufactured for each condition. The cycle characteristics of the battery thus obtained were evaluated as a charge / discharge capacity retention rate. Table 4 shows the results.

[0045]

[Table 4]

Comparative Example 19 A positive electrode was prepared in the same manner as in Example 8, except that aluminum powder (average particle size: 3 μm) was added to the toluene solution containing the coating material H shown in Table 1 in the same weight part as the coating material H. Was prepared, and a bending test and a binding durability test were performed. As a result, the result of the bending test was 32. The binding durability test was 5. This result indicates that although the effect of improving the binding durability was recognized as compared with the positive electrode using no coating material at all, peeling was confirmed in many electrodes, reproducibility was insufficient, and it was not practically feasible. I have to say that it was a satisfactory result.

Comparative Example 20 The same procedure as in Example 23 was carried out except that the same weight parts as the coating material H were added to the toluene solution containing the coating material H shown in Table 1 and graphite powder capable of absorbing and releasing lithium ions was added. A negative electrode was prepared by the method, and a bending test and a binding durability test were performed. As a result, it was 41 in the bending test. The binding durability test was 6. The result is
Compared to a negative electrode that does not use a coating material at all, although an effect of improving the durability of binding is recognized, peeling was confirmed in many electrodes, reproducibility was insufficient, and inadequate results from the viewpoint of practicality I have to say that it was.

Claims (6)

[Claims] 1. A current collector surface coating material obtained by mixing one or more kinds of polymers, and having a tensile strength of 0.1 kgf.
/ Cm ^{2 to} 500 kgf / cm ² , elongation 50% to 4,000
0% and a material for coating the surface of the current collector having a volume resistivity of 10 ⁶ Ωcm or more. 2. The current collector surface coating material according to claim 1, wherein the polymer is an uncrosslinked rubber, an uncrosslinked particulate polymer, or a crosslinked particulate polymer. 3. A current collector having a layer comprising the current collector surface coating material according to claim 1. 4. A collector containing an active material, a binder and a liquid material is applied to the current collector according to claim 3, dried to form an electrode, and then compressed to reduce the thickness of the electrode before compression. A method for producing a lithium-ion secondary battery electrode, comprising compressing to a compression ratio of 0.2 to 0.8 with respect to the thickness. 5. A lithium ion secondary battery electrode produced by the method according to claim 4. 6. A lithium ion secondary battery comprising the electrode according to claim 5.