Chemistry: electrical current producing apparatus – product – and – Means externally releasing internal gas pressure from closed...
Reexamination Certificate
1999-08-17
2001-09-04
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Means externally releasing internal gas pressure from closed...
C429S056000, C429S057000, C429S058000, C429S066000, C429S082000, C429S116000, C429S163000, C429S171000
Reexamination Certificate
active
06284403
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the field of sealed batteries and more particularly to explosion-proof, safety features of a closure assembly incorporated in hermetically sealed secondary batteries such as lithium ion secondary batteries.
BACKGROUND OF THE INVENTION
There has been a rapid increase in portable, cordless electric appliances of audiovisual equipment, office equipment such as personal computers, and communications equipment in recent years. Since non-aqueous electrolyte secondary batteries typically represented by high-capacity alkaline rechargeable batteries or lithium ion secondary batteries are ideally suited as a drive power source for such equipment, research is being conducted to develop a sealed non-aqueous electrolyte secondary battery of high energy density and excellent load characteristics.
One example of prior art closure assemblies for sealed batteries is shown in
FIG. 19
to FIG.
21
. In these figures, reference numeral
110
,
120
,
130
represent a metal cap, a metal spacer, and an upper metal foil, respectively. The center of the upper metal foil
130
is warped to form a dent
131
, and a thin part
132
is formed by impressing on one side relative to this dent
131
, as shown in
FIG. 21. 140
is a dish-like insulating gasket having a bottom, and
150
is a belt-like lower metal foil. The lower metal foil
150
has a bulge
151
in its center, a slit
152
in the form of letter C surrounding the bulge
151
, and punched holes
153
at both ends of the slit
152
, as shown in
FIG. 20. 160
is a metal case in the form of a cup which has a gas vent
161
in its center and is joined to a lead terminal that is connected to one electrode. The closure assembly for sealed batteries constructed as described above is mounted airtightly to an open end of an outer case of the battery. In the case of the closure assembly for sealed batteries described above, the upper and lower metal foils
130
,
150
are electrically connected only through a welding point S in their respective centers, and the breaking strength of an uncut portion formed by the slit
152
in the lower metal foil determines the pressure at which this electrical connection is broken. Specifically, when the internal pressure of the battery which acts on the upper metal foil
130
through the punched holes
153
builds up to a predetermined value, the pressure concentrates on the warped portion
131
of the upper metal foil
130
, pushing same upwards and thereby inverting the dent into a bulge as shown by a phantom line in FIG.
19
. The welding point S of the lower metal foil
150
is thus pulled up, splitting apart the uncut portion of the slit
152
and thereby disconnecting the upper metal foil
130
and lower metal foil
150
. The contact between the lower metal foil
150
connected to an electrode through the metal case
160
and the upper metal foil
130
connected to the metal cap
110
through the metal spacer
120
is broken whereby electric current supply is stopped. A further build-up of internal pressure leads to rupture of the thin part
132
in the upper metal foil
130
, through which the gas within the battery is released to the outside.
In the event of failure, over-charging or inappropriate use of the charger and alike, pressure can build up within the battery to an excessive level due to an abnormal increase of gas generated by chemical reaction within the battery.
The battery can eventually explode or damage the equipment to which it is applied. To avert such possibility, explosion-proof features are normally provided in this and other types of batteries to release gas to the outside in case of build-up of pressure within the battery beyond some predetermined limit.
Furthermore, since there is a risk of ignition upon rapid heating of the battery in non-aqueous electrolyte secondary batteries, safety features are also provided by which power supply is stopped prior to emission of the gas in case the internal pressure of the battery exceeds a predetermined limit.
In the prior art closure assembly for sealed batteries described above, due to difficulty in controlling the machining precision of the thin part
132
in the upper metal foil
130
, there exists variation in the thin part
132
. As a result, the breaking pressure at the point of letting out the internal gas cannot be fixedly determined. The breaking pressure at the point when power supply is stopped is not constant either, because of the variation in dimensions of the warped portion
131
in the upper metal foil
130
and uncut portion of the slit
152
due to difficulty in controlling the machining precision. Improvement in the reliability of the explosion-proof, safety features is thus strongly desired. Furthermore, since the upper and lower metal foils
130
,
150
are thin films, minute cracks that can cause leakage are inevitably formed in the welding point S where the upper and lower metal foils
130
,
150
are laser-welded. Moreover, a considerable space in upward and downward directions is required in order to allow the warped portion
131
of the upper metal foil
130
to be inverted, by which the dimensions of the entire closure assembly cannot be further reduced.
An object of the present invention is to solve the aforementioned problems, i.e., to improve the reliability of safety features of sealed batteries for averting explosion. Another object of the invention is to make the closure assembly thinner while improving its leakage-proof performance.
SUMMARY OF THE INVENTION
In order to accomplish the above objects, the present invention according to a first feature thereof provides a closure assembly for sealed batteries characterized in that a pressure receiving sheet that consists of a resin sheet or a metal foil and is arranged in the closure assembly has a pressure receiving portion defined in one part of the pressure receiving sheet, and the periphery of said pressure receiving portion is restricted by other elements constituting the closure assembly that are positioned above and below the pressure receiving sheet, so that, upon an abnormal increase in pressure within the battery, the pressure receiving portion of the pressure receiving sheet expands and eventually ruptures for releasing gas within the battery to the outside.
With the above construction, it is easier to control the thickness and area of the pressure receiving portion of the pressure receiving sheet at a predetermined value than to control the thickness of the thin part in the upper metal foil at a predetermined value in the prior art example. There is thus less variation in the breaking pressure, and the reliability of the explosion-proof safety features for releasing gas upon an abnormal build-up of internal pressure can be improved.
The present invention according to a second feature thereof provides a closure assembly for sealed batteries characterized in that an insulating resin gasket in the closure assembly is shaped in a dish-like form having a bottom and is provided with a thin part in the bottom thereof, said thin part being defined to be a pressure receiving portion, and the periphery of said pressure receiving portion of the insulating resin gasket is restricted by other elements constituting the closure assembly that are positioned above the periphery of the pressure receiving portion, so that, upon an abnormal increase in pressure within the battery, the pressure receiving portion of the insulating resin gasket expands and eventually ruptures for releasing gas within the battery to the outside.
With the above construction, similarly to the first feature of the present invention, the reliability of the explosion-proof safety features for releasing gas upon an abnormal build-up of internal pressure can be improved, and, the construction can be simplified since the resin sheet in the first feature of the present invention is omitted.
The present invention according to a third feature thereof provides a closure assembly for sealed batteries characterized by having an insulating resin
Kobayashi Hideyuki
Masumoto Kenjin
Mizutani Seiichi
Tsurutani Shinji
Yoshio Hideaki
Brouillette Gabrielle
Jordan and Hamburg LLP
Martin Angela J.
Matsushita Electric - Industrial Co., Ltd.
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