Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-04-30
2001-06-12
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S241000, C029S002000
Reexamination Certificate
active
06245463
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ground plate for a substrate of a secondary battery electrode alternatively known as an electrode current collector, and a substrate of a secondary battery electrode produced therefrom, and a secondary battery electrode and a secondary battery produced thereof.
THE BACKGROUND ART
In a nickel-cadmium secondary battery serving as a high output battery, an electrode comprising a substrate having a layer of sintered porous metal with a large surface area is used so as to generate a large current. The substrate having a layer of sintered porous metal is produced by pressing nickel powder onto a perforated steel sheet, that is, a ground plate, which is plated by nickel with a thickness of 60 to 80 &mgr;m, or by applying slurry of nickel powder to it and thereafter sintering the same at a temperature of 900 to 1100° C. in an anti-oxidizing atmosphere. In the above-mentioned temperature range, there is generated necking caused by the solid phase diffusion at the contacting portions of nickel powders with each other, and nickel powders are sintered. At the same time bonding is caused at the contacting portions between the perforated steel sheet with a nickel-plated layer and the nickel powders due to the solid phase diffusion of nickel. Thus, the substrate of a secondary battery electrode is produced by bonding the sintered porous nickel layer, which is composed of the nickel powders bonded to each other at the necking portions to form a network themselves and have about 80% of porosity, to the steel sheet or the ground plate.
However, the substrate of a secondary battery electrode of such structure, that the sintered porous metal is bonded to the ground metal plate only by the solid phase diffusion, has not enough bonding strength, so that the sintered porous metal often peels off from the ground metal plate when the substrate is rolled up and fixed into a cylindrical battery container. This peeling-off occurs particularly in the center portion of the rolled-up substrate where the roll-up radius is too small, which causes problems as shown in
FIG. 1
(
a
) such that an active material falls off due to the peeling-off of the sintered porous metal from the ground metal plate, or the fallen active material and sintered porous metal crash through the separator, to cause a short circuit.
So far, several measures have been taken to increase the bonding strength of the sintered porous metal to the ground metal plate which constitute a substrate of a secondary battery electrode and to improve the strength of the sintered porous metal. Those are as follows:
1) A layer containing metal fiber is formed near the ground metal plate as a core material in order to increase the strength of the sintered metal (Laid Open Japanese Patent No. Sho 64-24364).
2) A layer added by cobalt or the like is formed near the ground metal plate as a core material in order to enhance the solid phase sintering and increase the strength of the sintered metal (Laid Open Japanese Patent No. Hei 5-174831).
3) A surface of the ground metal plate is roughened by etching in order to increase the contacting area thereof with the sintered metal (Laid Open Japanese Patent No. Hei 4-162360).
4) TD nickel plate is used as the ground metal plate in order to increase the anti-peeling strength of it with yttoria particle contacting nickel particle (Laid Open Japanese Patent No. Sho 61-130405).
However, these improvement skills remain within a solid phase sintering technology, and they cannot drastically increase the bonding strength of the sintered porous metal to the ground metal plate constituting a substrate of a secondary battery electrode.
The object of the present invention is to provide an electrode current collector (a ground plate for a substrate) of a secondary battery electrode and a substrate, and a secondary battery electrode and a secondary battery using the same, having sufficient bonding strength so as not to cause peeling-off of the sintered porous metal from the ground metal plate when the electrode is rolled up and fixed into a cylindrical battery container.
DISCLOSURE OF THE INVENTION
According to the present invention, a substrate having sufficient bonding strength so as not to cause the peeling-off of a sintered porous metal from a ground metal, can be produced by means of generating a small quantity of a liquid phase when the sintered porous metal is heat-bonded to the ground metal plate.
In the electrode current collector or ground plate for a substrate of a secondary battery electrode of the present invention, a metal layer having a melting point lower than that of a steel sheet is formed on at least one side of the steel sheet.
Also, a nickel layer is formed on at least one side of a steel sheet, and further a layer (if metal having a melting temperature lower than that of the nickel layer is formed on the nickel layer.
A nickel-phosphorus layer is preferable as a layer of the metal having a low melting point, and it is also preferable that a boronized layer is formed on at least one side of a steel sheet.
Also, the ground plate of the present invention has a nickel layer, formed on at least one side of a steel sheet, and further a boronized layer is formed on the nickel layer.
It is also preferable that such a ground plate has a large number of pores having small diameters.
A producing method of a ground plate for a substrate of a secondary battery electrode of the present invention is characterized in that a metal layer having a melting point lower than that of a steel sheet is formed at least on one side of the steel sheet having a large number of pores with small diameters.
Also, it is characterized in that a nickel layer is formed at least on one side of a steel sheet having a large number of pores with small diameters, and further a metal layer whose melting temperature is lower than that of nickel is formed on the nickel layer.
Further also, it is possible to form a nickel layer on a steel sheet having a large number of pores with small diameters, and further to be boronized after that.
It is preferable in the above-mentioned producing methods that the metal layer having a low melting temperature is composed of nickel-phosphorus alloy.
Further, a porous layer is formed on a ground plate for a substrate of a secondary battery electrode of the present invention.
It is preferable in the above-mentioned substrate of a secondary battery electrode that the porous layer is prepared by sintering nickel powder.
A producing method of a substrate of a secondary battery electrode of the present invention is characterized in that a porous layer is formed on a ground plate by forming a layer of metal powder having a melting point higher than that of a metal layer having a low melting point, heating it at a temperature between not less than the melting temperature of the metal layer having a low melting point and less than that of a steel sheet or the metal powder, and sintering the metal powder, and the porous layer is bonded to the ground plate at the same time.
Also, it is characterized in that a porous layer is formed on a ground plate by forming a layer of powdered metal that can be eutectically alloyed with boron, heating it at a temperature between not less than the melting temperature of the eutectically alloyed metal and less than that of a steel sheet or the metal powder, and sintering the metal powder, and the porous layer is bonded to the ground plate at the same time.
A secondary battery electrode of the present invention is characterized in that the above--mentioned substrate of an electrode has an active material impregnated therein, and a secondary battery of the present invention comprises the above-mentioned secondary battery electrode.
REFERENCES:
patent: 2724733 (1955-11-01), Hagspihl et al.
patent: 4003753 (1977-01-01), Hall
patent: 4105832 (1978-08-01), Sugalski
patent: 4228224 (1980-10-01), Heredy et al.
patent: 4293089 (1981-10-01), McCormick et al.
patent: 4460666 (1984-07-01), Dinkler et al.
Matsuo Satoru
Oomura Hitoshi
Tashiro Hirohumi
Yazaki Katsuhito
Browdy and Neimark
Chaney Carol
Toyo Kohan Co. Ltd.
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