Pressure sensitive current breaker for a cell

Details Pressure sensitive current breaker for a cell Pressure sensitive current breaker for a cell

2000-02-22

2002-06-11

Bradley, P. Austin (Department: 2832)

Chemistry: electrical current producing apparatus, product, and

Means externally releasing internal gas pressure from closed...

C429S056000, C200S512000, C200S061080

Reexamination Certificate

active

06403250

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure sensitive current breaker for a cell, which is used for ensuring the safety when a pressure inside a cell case is increased.
2. Description of the Related Art
There has been widely employed a rechargeable lithium ion secondary cell in which an organic solvent system electrolyte is filled and sealed inside a cell case as a power supply for portable equipment, such as portable telephones and personal computers.
However, overcharging during recharging such a cell, or recharging with an excessive current against the specified current will produce abnormality in the cell to generate gas inside the cell case. Therefore, the generated gas raises the pressure and temperature inside the case, swells the case to finally create cracks, and effuses the internal electrolyte, which on some occasion has caused negative influence over the equipment incorporating the cell.
And, even if the abnormality does not reach that degree, to continue using the cell in such abnormality as mentioned above will promote to swell the cell, which leads to such a hazard that the cell case ruptures, and the cell with such abnormality created has to be discontinued in use.
A technique that removes such obstacles will be described with reference to
FIG. 8
,
FIG. 9
which illustrate the conventional pressure sensitive current breaker that is used for a circular cell. The pressure sensitive current breaker includes a cell cover
3
attached to a cell case
1
through a gasket
2
by caulking the surrounding thereof so as to seal the inside of the cell case
1
, and, under the cell cover
3
, an actuator
4
capable of displacing upward.
The cell cover
3
has an air vent
3
a
formed thereon, and when the actuator
4
ruptures due to a pressure increase inside the cell case
1
, the inner high pressure gas is made to run out through the air vent
3
a.
And, the actuator
4
has an annular safety valve
4
a
formed by the drawing, etc. The annular safety valve
4
a
has a protrusion
4
b
projecting downward on the center of the actuator, and a radial groove
4
c
formed on the lower side thereof to surround the protrusion
4
b
. The actuator
4
is made thin in the area where this groove
4
c
is formed, whereby the actuator
4
can be ruptured by the pressure increase inside the cell case
1
.
And, an insulating plate
5
is provided underneath the actuator
4
. The insulating plate
5
has a hole
5
a
through which the protrusion
4
b
of the safety valve
4
a
is inserted, and additionally a vent hole
5
b
formed.
A lead fixing member
6
is provided to underlie the insulating plate
5
. The lead fixing member
6
is provided with a hole
6
a
communicating with the hole
5
a
of the insulating plate
5
, and a vent hole
6
b
communicating with the vent hole
5
b
of the insulating plate
5
.
Through the holes
5
a
,
6
a
of the insulating plate
5
and the lead fixing member
6
is inserted the protrusion
4
b
of the safety valve
4
a
, and on the front of the protrusion
4
b
is attached a thin lead
7
made of a metal plate.
This thin lead
7
has a junction portion
7
a
welded by the spot welding or the like on the front of the protrusion
4
b
, whereby the actuator
4
is electrically made conductive with the lead
7
. And, the other end of the lead
7
is connected to a generating element
8
illustrated on the lower part in the drawing, and a current path is configured across the generating element
8
and the cell cover
3
.
When the pressure inside the cell case
1
is raised by an abnormality of the cell, the pressure increased gas is flown into the vent holes
5
b
,
6
b
, as in the arrow A shown in
FIG. 9
, which produces a force to push up the rear side of the safety valve
4
a.
This force displaces the safety valve
4
a
upward, and exerts a concentrated stress on the junction portion
7
a
of the lead
7
. This concentrated stress breaks the junction portion
7
a
to cut off the electric connection between the lead
7
and the actuator
4
, thus disconnecting the current path of the cell.
This current path disconnection cuts off the flow of currents inside the cell, so that the pressure increase inside the cell case
1
can be restricted. If the cutoff of the current path does not suppress the pressure increase inside the cell and the inner pressure is further increased, the further increased inner pressure of the cell is exerted on the radial groove
4
c
formed on the safety valve
4
a
, the actuator
4
formed thin by the groove
4
c
is ruptured. Therefore the pressure increased gas runs out through the air vent
3
a
, thus preventing the blowout of the cell.
Portable equipment such as portable telephones using this type of a conventional cell has advanced miniaturization, and along with this, there has been an increased demand for the miniaturization of a cell used in such portable equipment.
However, in the conventional pressure sensitive current breaker for a cell, the size of the actuator
4
has to be made as large as the actuator
4
can operate without a difficulty, even when the pressure increase inside the cell is low. Therefore, it is difficult to miniaturize the conventional pressure sensitive current breaker, and it has been difficult to miniaturize the cell.
Further, when the lead
7
is ruptured by the pressure increase inside the cell, the junction portion
7
a
is drawn and stretched by the actuator
4
and broken as it is torn, since the lead
7
is formed by a thin plate.
Accordingly, long burrs like beards are produced on the ruptured face of the junction portion
7
a
after the rupture, and on the ruptured face of a ruptured hole
7
b
made after the rupture of the junction portion
7
a
. Because of the burrs, there has been a possibility that the current path between the actuator
4
displaced up and the lead
7
is not completely cut off.
The present invention has been made in view of the foregoing circumstances, and provides a high-performance pressure sensitive current breaker for a cell that allows the miniaturization and reliably cuts off the current path even when a pressure increase inside the cell is low.
SUMMARY OF THE INVENTION
In order to accomplish the foregoing object, the pressure sensitive current breaker for a cell according to one aspect of the invention includes a cell case containing a generating element inside thereof, a cell cover that hermetically seals the cell case, a diaphragm portion formed on the cell cover to expand inward inside the cell case, an external electrode having a terminal part connected to the generating element and exposed outside and a lead part that is easy to break, and an insulating retaining member that embeds the external electrode therein and has an opening to expose the lead part. In the pressure sensitive current breaker thus constructed, the lead part is placed overlying the diaphragm portion to face each other, the lead part located in the opening is formed integrally with an insulator to swell out toward the diaphragm portion, a current path between the generating element and the terminal part of the external electrode is made through the lead part, and when a pressure inside the cell case rises over a specific value, the insulator is pressed by a displacement of the diaphragm portion, and thereby the lead part is ruptured and the current path is cut off.
According to another aspect of the invention, the pressure sensitive current breaker is configured such that the terminal part and the lead part are integrally formed in the external electrode.
According to another aspect of the invention, the pressure sensitive current breaker is configured such that the lead part is embedded into the insulator to be integrated.
According to another aspect of the invention, the pressure sensitive current breaker is configured such that the retaining member is provided with a coupling part to couple the insulator, and the insulator and the retaining member are separated by cutting the coupling part.
According to another aspect of

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