Metal working – Method of mechanical manufacture – Electrical device making
Patent
1997-09-12
2000-11-07
Maples, John S.
Metal working
Method of mechanical manufacture
Electrical device making
429206, H01M 204
Patent
active
061430412
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improvement of a manufacturing method of a button type alkaline cell. It is to provide a button type alkaline cell, having a good self-discharge characteristic, manufactured by combining a negative electrode can made from a raw material of steel on which Ni is provided at one surface thereof and Cu is provided at the other surface thereof and which is fabricated by using a die whose part abutting at least with the Cu surface is ceramics, with other components of the cell such as a positive electrode compound, a negative electrode compound, a separator, a positive electrode can, a gasket and an alkaline electrolyte. It is to provide, specifically, a button type alkaline cell containing a very little amount of mercury or no mercury at all and a manufacturing method thereof.
BACKGROUND ART
Hitherto, a button type alkaline cell is manufactured by fabricating a negative electrode can by using metallic molds such as a die, a punch and a blank holder made from tool steel, high speed steel or cemented carbide and by combining it with other components such as a positive electrode compound, a negative electrode compound, a separator, a positive electrode can, a gasket and a alkaline electrolyte.
As raw materials of the negative electrode can of the button type alkaline cell, an Ni--SUS--Cu clad material or a material in which Ni is plated on the side opposite from Cu which becomes the inner surface of the negative electrode can on a laminated material of Cu and SUS or Cu and a deep drawing steel is used. The negative electrode can is fabricated by working the raw material using a die made from tool steel or cemented carbide. The button type alkaline cell is manufactured by combining this negative electrode can with the other components such as the negative electrode compound mainly composed of zinc, the positive electrode compound mainly composed of silver oxide, the separator, the electrolyte, the positive electrode can and the gasket.
However, the button type alkaline cell using the negative electrode can manufactured by using the prior art die, in which tool steel or cemented carbide is used for the part which contacts with the Cu surface, generates gas from the Cu surface when the negative electrode zinc contacts with the alkaline electrolyte and when part of the electrolyte decomposes. It is because Fe of the tool steel, Co or Ni used as a binder of the cemented carbide or W which is the base material of the cemented carbide is transferred and adheres on the Cu surface, i.e. the inner surface of the negative electrode can, during working of the negative electrode can, though it is a very small amount. The generation of gas leads to the exhaustion of the negative electrode compound within the button type alkaline cell, thus deteriorating the self-discharge characteristic of the cell.
Although the gas may be suppressed from generating by containing mercury within the negative electrode compound because the degree of generation of gas may be reduced as the mercury covers the Cu surface, there is apprehension that the environment might be contaminated by the mercury contained within the disposed cells.
Although it has been attempted to reduce the amount of mercury by fully cleaning the negative electrode can or by adding indium and bismuth in order to reduce the amount of mercury contained within the button type alkaline cell and to maintain the effect of suppressing the generation of gas (e.g. Japanese Patent Laid-Open Nos. Hei. 8-31428, Hei. 8-130021 and others), it is difficult to prevent the gas from generating from the inner surface of the negative electrode can.
SUMMARY OF THE INVENTION
Then, according to the present invention, a negative electrode can having an inner surface of Cu is formed and worked by a die whose part abutting at least with the Cu surface is ceramic. More preferably, the negative electrode can is worked by using a die coated with ceramic. While there is a number of types of ceramics which can be used as the coating for the die, zi
REFERENCES:
patent: 4442186 (1984-04-01), Urry
patent: 4861688 (1989-08-01), Miura et al.
patent: 4882238 (1989-11-01), Yoshioka et al.
Ishizaki Morio
Nozawa Mutsuo
Takahashi Kazuyuki
Tanno Koji
Ishizaki Press Ind. Co. Ltd.
Maples John S.
SII Micro Parts Ltd.
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