Chemistry: electrical current producing apparatus – product – and – Means externally releasing internal gas pressure from closed... – Blowout type
Reexamination Certificate
1998-08-12
2001-04-03
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Means externally releasing internal gas pressure from closed...
Blowout type
C429S053000
Reexamination Certificate
active
06210825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to especially safety valve elements for battery use, battery case lids provided with safety valves and batteries produced by employing such safety valve elements and battery case lids.
DESCRIPTION OF RELATED ART
Conventionally, batteries which use an alkali metal such as lithium, sodium or potassium as an active material on negative electrode thereof sometimes suffer from rupture when the pressure in the batteries becomes abnormally elevated. To prevent the occurrence of such a rupture, safety valves which can release the pressure outside when the pressure in the battery reaches an excessive level have been requested and accordingly various safety valves having different mechanisms have been proposed. To assure the safety in which even when the battery ruptures by a chance, broken pieces or contents of the battery do not scatter outside and cause no damage especially to personnel, the batteries must be operated at a low pressure of not more than 30 kgf/cm
2
.
The dry-cell type battery which uses an alkali metal as the active material negative electrode is further required to have a high sealability. A Japanese laid-open publication SHO 63-285859 discloses a safety valve which can release the inner pressure of such a battery to the outside. In this battery, a part of the wall of the battery vessel is made thin by cold rolling using a press until the thickness of the rolled part becomes half of the original thickness of the part. Accordingly, when the inner pressure reaches a predetermined elevated inner pressure, the thinned wall part is ruptured and the inner pressure is released to the exterior of the battery vasel.
To release the inner pressure at a low pressure of not more than 30 kgf/cm
2
, the thinned wall part must be made considerably thin. Accordingly, during the press working to obtain the extremely thin wall part, fine or minute cracks may occur, and once such cracks occur, the sealability of the vessel is spoiled. Although the thinned wall part is hardened with such a press working, the hardening does not occur uniformly. Accordingly, the release valve disclosed in Japanese laid-open publication SHO 63-285859 also suffers from a drawback that even when the thinned wall part is pressed to have a uniform thickness, the thinned wall part does not always rupture at the selected predetermined pressure.
Furthermore, although an etching method has been proposed to make a part of the wall of the battery vessel thin, it is extremely difficult to control the thickness of the thinned wall part after etching and the thinned wall part is apt to suffer from pin holes. Accordingly, thinned wall parts of all battery vessels must be subject to a pin hole test for detecting the presence of pin holes.
In this manner, with the above-mentioned method, it is extremely difficult to provide the thinned wall part which has a uniform thickness so that especially on the condition that the safety valves are to be operated to release pressure at a low pressure of not more than 30 kgf/cm
2
, a reliable reproductivity of the pressure releasing operation cannot be achieved.
To resolve the drawbacks of the above-mentioned methods, Japanese laid-open publication HEI 5-314959 discloses a method in which one metal plate having a perforated opening and the other thin metal plate are clad with each other to produce a thinned wall part having a uniform thickness and such a method provides a valve operating pressure which is not more than 30 kgf/cm
2
and has a reliable reproductivity on a pressure releasing operation.
In this method, however, since the perforated metal plate and the thinned metal plate are heated in a vacuum furnace and heat-sealed with each other under pressure, the materials for these metal plates must meet a condition that they can be heat-sealed under pressure. Namely, the materials for these metal plates are restricted to the same metals or metals having similar physical properties such as a similar melting point. In Japanese laid-open publication HEI 5-314959, stainless steel, iron, nickel and the like are proposed as preferable materials for these metal plates.
Furthermore, to heat seal these metal plates under pressure to obtain a uniform adhering strength, an oxide film formed on the surface of these metal plates must be removed by buffing or the like and then the metal plates must be heated at a high temperature of approximately 1000° C. so the method necessitates a sophisticated operation and facilities. Furthermore, these thin metal plates are usually produced by a cold rolling so that they are subjected to hardening by working. Since the above-mentioned metal plates are hardened by working, they are annealed at a high temperature during the heat sealing under pressure so that the mechanical strength of these metal plates differs before and after the heat sealing operation. Accordingly, the properties of the materials before heat sealing, the heating temperature and the heating time have to be strictly controlled to make the mechanical strength (the limit strength which causes a rupture as the inner pressure is elevated) of the metal plates constant after heat sealing.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide safety valve elements which rupture precisely at a predetermined pressure in a low pressure range and can be manufactured readily.
It is another object of the present invention to provide battery case lids which are provided with such safety valve elements.
It is still another object of the present invention to provide batteries which incorporate such safety valve elements and such battery case lids.
The safety valve element according to the present invention comprises a metal substrate which is provided with a perforated opening and a metal foil which is stacked on the metal substrate to close the perforated opening. The safety valve element may preferably be provided with a plurality of perforated openings. The metal substrate may be made of one selected from a group consisting of a steel plate, stainless steel plate, copper plate and aluminum plate. The metal foil may be made of one selected from a group consisting of a steel foil, stainless steel foil, copper foil, aluminum foil, nickel foil, and nickel-iron alloy foil.
The battery case lid which is provided with the safety valve element may preferably be produced by forming a perforated opening on the metal substrate, pressure welding the metal foil to the metal substrate so as to close the perforated opening and molding the metal substrate into a case lid form.
The battery may preferably be provided with either the safety valve element or the battery case lid provided with the above-mentioned safety value.
REFERENCES:
patent: 93-314959 (1993-11-01), None
patent: 7130346 (1995-05-01), None
patent: 96-17416 (1996-01-01), None
Isobe Yoshihiko
Saijo Kinji
Takada Akiyoshi
Takagi Akira
Yoshida Kazuo
Browdy and Neimark
Maples John S.
Toyo Kohan., LTD
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