Electricity: circuit makers and breakers – Special application – Frangible or destructible type
Reexamination Certificate
2000-08-22
2002-05-21
Friedhofer, Michael (Department: 2832)
Electricity: circuit makers and breakers
Special application
Frangible or destructible type
C200S334000, C429S053000, C429S056000, C429S057000
Reexamination Certificate
active
06392172
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure-sensitive breaker for a battery, and more particularly, to a pressure-sensitive breaker for a battery used to ensure safety when the internal pressure in a battery case rises.
2. Description of the Related Art
In a chargeable lithium ion secondary battery or the like, when any abnormality is caused by overcharging or overdischarging of the battery, a large quantity of gas may be generated due to decomposition, evaporation, or the like of an electrolytic solution, and the pressure inside the closed battery case may rise. This may deform and burst the battery case, or cause leakage of the electrolytic solution.
As a countermeasure thereto, a pressure-sensitive breaker for a battery is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 7-335272, in which overcharging or overdischarging of a battery can be prevented by cutting off the electric path of the battery in response to deformation of the battery case.
FIGS. 8
to
10
show the above-described conventional pressure-sensitive breaker for a battery. In the pressure-sensitive battery breaker, a ceramic substrate
21
is closely attached to a side face of a battery case
28
a
of a rectangular battery
28
, such as a lithium ion secondary battery.
The battery
28
is covered with the battery case
28
a
on the periphery, as shown in
FIG. 8. A
first electrode
25
and a second electrode
26
project from the left side face of the battery case
28
a
in the figure, and a third electrode
27
projects from the right side face. Electromotive force is generated between the second and third electrodes
26
and
27
.
The ceramic substrate
21
made of a fragile material and having a rectangular outline is placed on the upper surface of the battery case
28
a
. A conductive pattern
22
is formed by printing on the upper surface of the ceramic substrate
21
, and a V-shaped groove
23
is formed across the full width on the lower surface of the ceramic substrate
21
. A portion of the ceramic substrate
21
at the groove
23
is easily broken.
A pair of terminals
24
are provided to attach the battery
28
and the ceramic substrate
21
into a unit. Each of the terminals
24
is formed by bending an elastic metal plate of phosphor bronze, stainless steel, or the like, and comprises legs
24
a
and
24
b
bifurcated in elastic contact with the conductive pattern
22
, a leg
24
c
in elastic contact with the lower surface of the battery
28
, and a louver portion
24
d
in which the first or third electrode
25
or
27
projecting from the left or right side face of the battery case
28
a
is fitted. The terminals
24
are substantially angularly U-shaped overall.
When attaching the pressure-sensitive battery breaker to the battery
28
, as shown in
FIGS. 8 and 9
, the ceramic substrate
21
is placed on the upper surface of the battery case
28
a
, and the terminals
24
are fitted thereon from the right and left sides in the figure by using an assembly jig (not shown), so that the battery
28
and the ceramic substrate
21
are pressed and clamped by the bifurcated legs
24
a
and
24
b
. Moreover, the first and third electrodes
25
and
27
are fitted into the louver portions
24
d
and are electrically connected to the conductive pattern
22
via the terminals
24
.
That is, the ceramic substrate
21
is attached to the side face of the battery
28
by the terminals
24
, and an electric path is formed between the first and third electrodes
25
and
27
.
A description will be given of the operation of the conventional pressure-sensitive battery breaker with such a configuration. The battery
28
equipped with the pressure-sensitive battery breaker is incorporated in a portable device or the like (not shown), and the first and second electrodes
25
and
26
are used as power terminals of the portable device or the like.
When overcharging or overdischarging is performed, as described above, pressure inside the battery
28
rises, and the battery case
28
a
expands and deforms.
The ceramic substrate
21
is broken at the groove
23
due to deformation of the battery case
28
a
, as shown in
FIG. 10
, thereby cutting the conductive pattern
22
.
The electric path between the first and third electrodes
25
and
27
is thereby cut off, the supply of electric power to the battery
28
is terminated, and expansion of the battery case
28
a
stops, whereby the battery
28
is prevented from bursting.
In a case in which such a conventional pressure-sensitive battery breaker is used in a low-profile and light-weight polymer lithium secondary battery or the like which has been recently sold commercially, since the battery case of the polymer lithium secondary battery is made of a flexible film formed of a laminate of aluminum foil and plastic, it is bent and deformed when the ceramic substrate
21
made of a fragile material is attached to the side face of the flexible battery case and tightly clamped by the terminals
24
. This may crack the ceramic substrate
21
at the groove
23
and cut off the electric path between the first and third electrodes
25
and
27
.
Furthermore, since the louver portions
24
d
of the terminals
24
are fitted on the first and third electrodes
25
and
27
when attaching the ceramic substrate
21
to the battery
28
, a special assembly jig is required. This decreases assembly efficiency.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a pressure-sensitive breaker for a battery with high assembly efficiency, which can be used in a polymer lithium secondary battery having a battery case formed of a laminated film or the like without any problem.
In order to achieve the above object, according to an aspect of the present invention, there is provided a pressure-sensitive breaker for a battery including a battery having a battery case for holding a power-generating element therein, a battery pack for accommodating the battery, and an element made of a fragile material, wherein a recess is formed at a position on the inner surface of the battery pack opposing a side face of the battery case, a first terminal is provided to be connected to an external electrode of the battery pack and a second terminal is provided to be connected to one electrode of the battery, a conductive portion is formed on the surface of the element, both ends of the conductive portion are connected to the first and second terminals so as to form an electric path between the first and second terminals, the element is deformed toward the recess and is broken due to bending of the side face of the battery case toward the recess caused when the internal pressure in the battery rises above a predetermined value, and the electric path is cut off by the breaking of the element.
In this case, the recess is formed on the inner surface of the battery pack, the electric path is formed of the conductive portion on the surface of the element, and both ends of the conductive portion are connected to the first and second terminals. The element is deformed toward the recess and is broken due to bending of the side face of the battery case toward the recess caused when the internal pressure in the battery rises above a predetermined value, and the electric path is cut off by the breaking of the element. Therefore, even if the battery has a low profile, when the side face of the battery case is bent, the element can be easily broken to cut off the electric path. This makes it possible to provide a high-performance and safe pressure-sensitive breaker for a battery which does not cause bursting of the battery, leakage of the electrolytic solution, and the like even when an abnormality occurs inside the battery.
Preferably, the element is supported over the recess so as to be stretched between shoulder portions disposed on both sides of the recess.
Since the battery case is deformed, the element is broken from the center
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Friedhofer Michael
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