Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-04-23
2002-07-23
Kalafut, Stephen (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C029S623500, C429S231800
Reexamination Certificate
active
06423105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an electrode for a battery. In particular, the present invention relates to a process for producing an electrode for a battery, wherein an electrode active material layer can be firmly formed on both surfaces of a current collector for the electrode.
2. Description of the Background
Electrodes used in lithium ion secondary batteries are presently formed by applying a coating containing an electrode active material to both surfaces of a current collector of the electrode and drying the coating. In particular, a coating for the cathode contains a cathode active material and a binder, wherein the cathode active material is suitably dispersed therein in such a manner that it is not broken. The cathode coating is first applied to one surface of a metal foil as the electrode current collector and, after drying, it is also applied to the other surface thereof in the same manner as above, and then dried. Thus, the electrode active material layers are formed on both surfaces of the current collector for the electrode. Finally, the current collector for the electrode having the electrode active material layers formed on both surfaces thereof is cut into pieces, which is then used as the electrodes.
In the case where the coating film is formed on such a metal foil in the prior art, the adhesion between the metal foil and the electrode active material layer is insufficient to causing this problem, it has the electrode active material layer to peel off. In addressing this problem, it has been proposed, for example, to increase a resin content of an electrode coating, and to add an acid. Also, Japanese Patent Unexamined Published Application (hereinafter referred to as “J. P. KOKAI”) No. Hei 2-68855 discloses and specifically describes that the adhesion is improved by using an acid.
However, when such an acid is used another problem occurs. Specifically, when the electrode active material layer is formed on one surface (hereinafter referred to as “surface A”) of the electrode current collector and then the same layer is formed on the other surface (hereinafter referred to as “surface B”) thereof, the adhesion of the current collector to surface B is much decreased as compared with the adhesion of that to surface A. Therefore, the electrode thus prepared exhibits the peeling off of the electrode active material layer, particularly from the back surface (surface B) of the electrode current collector. When such peeling occurs, the capacity of the battery produced therefrom is lowered, or the electrode active material layer thus peeled off is interposed between a separator and, for example, a cathode electrode, and it breaks the separator to cause the short circuit of the cathode electrode and the anode electrode, disadvantageously. Such a product is, therefore, not practically usable as a battery element.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a process for producing an electrode for a battery by successively applying an electrode coating containing an electrode active material, a binder, a solvent and an acid to both surfaces of an electrode current collector to obtain excellent adhesion between the electrode active material layer and the electrode current collector and to avoid peeling-off of the electrode active material layers from both surfaces of the electrode current collector.
In particular, the above object and others are provided by a process for producing an electrode for a battery by successively applying an electrode coating containing an electrode active material, a binder, a solvent and an acid to both surfaces of an electrode current collector, wherein after applying the electrode coating to one surface of the electrode current collector and drying it, the other surface thereof is cleaned with water prior to the application of the electrode coating thereto.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is predicated upon the surprising discovery that the above-described object can be effectively attained by a process for applying an electrode coating containing an electrode active material, a binder, a solvent and an acid to both surfaces of an electrode current collector successively, wherein after applying the electrode coating to one surface of the electrode current collector and drying it, the other surface thereof is cleaned with water prior to the application of the electrode coating thereto. The present invention has been completed on the basis of this finding.
In more detail, the electrode coating used in the present invention contains an electrode active material, a binder, a solvent and an acid.
The electrode active materials usable herein are not particularly limited and those used hitherto as the electrode active materials are usable.
The materials used as the electrode active materials are various, and they are selected suitably depending on the use for the cathode or anode. Carbonaceous materials are those usually used as the cathode active materials. The carbonaceous materials are those used hitherto and not particularly limited. They are, for example, amorphous carbon, acetylene black, petroleum coke, coal coke, artificial graphite, natural graphite, graphite carbon fibers and difficultly graphitizable carbon.
The anode active materials are those used hitherto. Various cathode active materials, are usable without particular limitation. Various cathode active materials, such as lithium cobaltate and lithium manganate are usable.
The electrode coating in the present invention contains usually about 10 to 75% by weight, based on the solid content of the electrode coating, and preferably about 25 to 55% by weight, of the electrode active material.
Any binder may be useable so long as it is conventionally used in this technical field, without particular limitation. The binder includes, for example, polyacrylonitrile (PAN), polyethylene terephthalate, polyvinylidene fluoride (PVDF) and polyvinyl fluoride.
The binder is used in an amount of about 1 to 40 parts by weight, preferably about 2 to 25 parts by weight, and particularly about 5 to 15 parts by weight, per 100 parts by weight of the electrode active material.
The solvent is not particularly limited and any of those used hitherto for the preparation of electrode coatings can be used. The solvent includes, for example, N-methylpyrrolidone (NMP), pyrrolidone, N-methylthiopyrrolidone, dimethylformamide (DMF), dimethylacetamide and hexamethylphosphamide. They are used either alone or in the form of a mixture of them.
The solvent is used in such an amount that the solid content (nonvolatile matter content) of the electrode coating is about 10 to 80% by weight, preferably about 30 to 60% by weight and particularly preferably about 35 to 45% by weight.
The acid may be either an organic acid or an inorganic acid. As the acids, weak acids are preferred, and weak organic acids are particularly preferred. Preferred examples of the weak organic acids include oxalic acid, formic acid and maleic acid, and hydrates of these acids.
The acid is used in an amount of usually about 0.001 to 5 parts by weight, preferably about 0.01 to 3 parts by weight, per 100 parts by weight of the electrode active material.
When the electrode active material has a low electric conductivity, an electric conductor can be used, if necessary. As the electric conductors, the above-described carbonaceous materials are usable. In this cases the electric conductor is used in an amount of usually about 1 to 25 parts by weight, preferably about 3 to 15 parts by weight and particularly preferably about 5 to 10 parts by weight, per 100 parts by weight of the active material.
Metal foils are preferably used as the electrode current collectors in the present invention. The metal materials for the electrode current collectors are not particularly limited, and various metal materials used hitherto for this purpose are usable. Such metal materials are, for example, copper, alumi
Iijima Tadayoshi
Satoh Jun-ichi
Alejandro Raymond
Kalafut Stephen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
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