Chemistry: electrical current producing apparatus – product – and – Means externally releasing internal gas pressure from closed... – Blowout type
Reexamination Certificate
2000-01-06
2002-08-27
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Means externally releasing internal gas pressure from closed...
Blowout type
C429S059000, C429S062000
Reexamination Certificate
active
06440599
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application is the national stage under 35 U.S.C. 371 of PCT/JP98/01802, filed Apr. 20, 1998.
FIELD OF THE INVENTION
The present invention relates to a closed battery capable of bursting at a prescribed pressure, especially at a low pressure, to rapidly release the internal pressure and at the same time to break a current, when the battery temperature or the battery internal pressure is elevated.
RELATED ART
Recently, with increasing requirement for electronic devices that are made into much smaller size and lighter weight with high performance, the use of non-aqueous batteries with high energy density has become popular. Batteries which use an alkaline metal such as lithium, sodium, or potassium as an active material for the negative electrode thereof employ a battery container of a completely closed structure, since the alkaline metal easily acts with water.
Such a completely closed battery has the advantage of reasonable storability, however, its high sealability sometimes causes rupture of the battery itself due to the abnormally elevated internal pressure thereof in a case where the battery is exposed to high temperature, or short circuit is formed inside or outside of the battery to cause a large flow of the current, or hydrogen gas is generated in the battery due to water contamination penetrated in the manufacturing process thereof. In such a case, the device that accommodates such a rupturing battery will be broken and moreover, there may be a danger of the broken device and battery harming the user. Accordingly, there is a need for some pressure releasing mechanism before the internal pressure of the battery is increased to such a high extent.
So far, several methods for releasing the internal pressure of a battery have been proposed and some of them have been used in practice. For instance, Japanese laid-open publication HEI 2-304861 discloses a safety valve for a battery, which comprises a valve chest provided at a part of a container of the battery and having a valve through hole to be communicated with the inside of the battery and an outlet to be communicated with the outside, the valve chest comprising a valve member at least whose surface opposed to the valve through hole is made of rubber, and an elastic member for pushing the above mentioned rubber surface of the valve member to the valve through hole. This safety valve holds the sealability of the battery by closing the valve through hole with the rubber-made valve member, and prevents the internal pressure of battery from rising in excess of a prescribed pressure by permitting the valve through hole to be opened when the internal pressure rises to the pressure prescribed for the elastic member.
Such a conventional safety valve has been widely used in Ni—Cd type batteries, however, it has not yet been used in the non-aqueous batteries which employ alkaline metals as the active material for the negative electrode, since even if the elastic member presses the valve member to the valve through hole to thereby close the battery, it is impossible to obtain such a high sealability as required for the non-aqueous batteries.
One of the methods for releasing the internal pressure of a battery which requires high sealability is disclosed in Japanese laid-open publication SHO 63-285859. In this method, a container of the battery is provided with a thinned portion at a part of its wall. This thinned portion is formed by cold rolling a sheet of the container using a press device until the thickness of the rolled portion of the sheet becomes half of the initial thickness thereof. Thus, the battery is provided with good sealability with regard to this thinned wall portion because it is only transformed from a part of the continuous wall of the container.
Another pressure releasing mechanism of this type is disclosed in Japanese laid-open publication HEI-6-215760. This releasing mechanism comprises a valve diaphragm fitted in an open end of the cylindrical container of a battery having a bottom and disposed above the electrode element of the battery, and a lead for current cutoff disposed above the valve diaphragm. In this structure, when the internal pressure of the battery is elevated, the valve diaphragm is expanded to break the lead for current cutoff to cut the current.
According to the method as disclosed in Japanese laid-open publication SHO-63-285859, it is necessary to obtain an extremely thin wall portion of the container so that the thin portion can be ruptured at a relatively low pressure. However, when the wall portion is made too thin, there may be formed fine or minute cracks during press-forming, thus impairing the sealability of the battery container.
Further when metals are processed by cold working, their workability will be inevitably harden. The hardening of the metals does not always take place uniformly, and therefore, there arises a problem that the operating pressure for such pressure releasing mechanism cannot regularly be controlled. There is also proposed a half-etching method for making thinner a part of the wall of a battery container, however, it is extremely difficult to control the remaining thickness of the thinned portion after etching, and also difficult to obtain a good yield. Another problem is that the half-etched portion cannot be free from the formation of pinholes, and therefore, all the products need to be inspected.
On the other hand, according to the method as disclosed in Japanese laid-open publication HEI-6-215760, it is necessary to accurately control the depth of a cut off portion formed in the lead, which causes problems of difficulty for cut off forming and unstable cut off of the current at a prescribed pressure. Another problem is that the current is not reliably cut off at a prescribed pressure.
SUMMARY OF THE INVENTION
With the view to solving the conventional drawbacks as mentioned above, it is the object of the present invention to provide a closed battery incorporating a valve chip which can stably and accurately burst at a prescribed pressure, especially at a low pressure, so as to rapidly release the internal pressure thereof and can be manufactured easily.
In order to solve the above-mentioned problems, the present invention provides a closed battery which comprises an electrode element consisting of a positive electrode, a negative electrode, and a separator; an electrolyte; a battery container accommodating said electrode element together with said electrolyte; and a closing member fitted in the inner periphery of an open end portion of said battery container to close the open end portion of the battery container, wherein said closing member consists of a metal substrate, a valve element which is provided in said metal substrate and defined by a break line so as to serve as a releasing chip such that when the internal pressure of the battery is elevated, the valve element is bent from a bending fulcrum so as to provide the metal substrate with an opening portion for releasing the internal pressure, and a metal foil which is adhered to the inner surface of the metal substrate.
According to the present invention, when the internal pressure of a battery is elevated due to short circuit, overcharge, reverse charge or the like, a valve chip, consisting of a metal substrate in which a valve element is provided for releasing the internal pressure of the battery and a metal foil which has a uniform and accurate thickness and is laid over the metal substrate so as to close a through hole which is usually closed with the valve element, operate to deform itself and push and raise the valve element up, and when the internal pressure reaches a prescribed pressure, the metal foil stably and accurately burst to cut the electric connection and at the same time discharge the internal gas within the battery so that an abrupt rising of the internal temperature or explosion of the battery can previously be prevented.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is now explained in conjunction with preferred embodim
Isobe Yoshihiko
Saijo Kinji
Takada Akiyoshi
Yoshida Kazuo
Yoshimoto Nobuyuki
Browdy and Neimark
Chaney Carol
Dove Tracy
Toyo Kohan Co. Ltd.
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