Cell current cutoff mechanism

Details Cell current cutoff mechanism Cell current cutoff mechanism

1999-08-30

2001-08-14

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Means externally releasing internal gas pressure from closed...

C429S054000, C429S055000, C429S056000, C429S061000, C429S072000, C429S082000

Reexamination Certificate

active

06274264

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current cutoff mechanism of a cell, particularly relates to a current cutoff mechanism of a cell used for securing safety when pressure inside a cell case is increased
2. Description of the Related Art
Heretofore, a sealed lithium ion secondary cell inside the case of which an electrolyte including an organic solvent for example is injected and which can be charged are widely used for a power source for portable equipment such as a mobile telephone and a personal computer
However, if such a cell is excessively charged when it is charged again or is charged with larger current than defined current, abnormality occurs in the cell, gas is generated in a cell case, pressure and temperature in the cell case rise, the cell case is swollen, further a crack is formed, an inside electrolyte leaks outside and the leaked electrolyte sometimes has an adverse effect on equipment in which the cell is built.
If the use of the above cell is continued in the above abnormal state even if the above leaked electrolyte does not have an adverse effect on the equipment, the swell of the cell progresses, the cell case may burst and the use of the abnormal cell is required to be stopped promptly.
A conventional type current cutoff mechanism of a cell for preventing the burst of such a cell will be described as a circular cell shown in
FIGS. 10 and 11
below. First, in a cell case
1
, a cell lid
3
attached by riveting the periphery of the cell lid via a gasket
2
or welding in order to seal the inside of the cell case
1
and an actuator
4
which can be displaced above and below in the lower part of the cell lid
3
are respectively arranged.
An air vent
3
a
is formed in the cell lid
3
and when the actuator
4
in the lower part is displaced and cleaves its way upward air in a part between the cell lid
3
and the actuator
4
is emitted outside from the air vent
3
a.
In the actuator
4
, a circular relief valve
4
a
is formed by drawing and in the relief valve
4
a
, a projection
4
b
protruded downward in the drawings is formed in the center and a radial groove
4
c
is formed on the surface around the projection
4
b.
An insulating plate
5
is arranged below the actuator
4
and in the insulating plate
5
, a hole
5
a
for inserting the projection
4
b
of the relief valve
4
a
and an air vent
5
b
are formed.
A lead fixing member
6
is arranged below the above insulating plate
5
and in the lead fixing member
6
, a hole
6
a
for communicating with the above hole
5
a
of the insulating plate
5
and an air vent
6
b
communicating with the air vent
5
b
of the insulating plate
5
are respectively provided.
The projection
4
b
of the relief valve
4
a
is inserted into the respectively holes
5
a
and
6
a
of the above insulating plate
5
and the lead fixing member
6
and a thin lead
7
made of a metallic plate is attached to the end of the projection
4
b.
The thin lead
7
is provided with a junction
7
a
bonded to the end of the projection
4
b
by welding, and the actuator
4
and the lead
7
are electrically connected. The other end of the lead
7
is connected to a generating element
8
in the lower part in the drawings and a conductive path is formed between the generating element
8
and the cell lid
3
.
If an abnormality occurs inside the cell and pressure inside the cell case
1
is increased, the pressure of gas is increased and the gas flows from the air vents
5
b
and
6
b
as shown by an arrow A in FIG.
11
. The application force which pushes up the rear of the relief valve
4
a
is applied.
When concentrated stress is applied to the junction
7
a
of the lead
7
by application force applied to the relief valve
4
a
and the concentrated stress is larger than the shearing stress of the junction
7
a
, the junction
7
a
is disconnected from the lead
7
, electrical connection between the lead
7
and the actuator
4
is cut off and the conductive path of the above cell is cut off.
The flow of current inside the cell is cut off by the above cutoff of the conductive path, the increase of pressure inside the cell case
1
is prevented and the cell can be prevented from bursting beforehand.
Portable equipment using such a conventional type cell (such as a mobile telephone) has become more and more miniaturized and the need has increased for the miniaturization and the thinning of the cell used for such portable equipment.
However, as the above conventional type current cutoff mechanism is formed by one plate though the lead
7
is thin, the application force of the actuator
4
varies widely depending upon variation in the thickness of the lead
7
and it is difficult to securely disconnect the junction
7
a
from the lead
7
when the internal pressure of the cell is increased up to a predetermined value.
As the junction
7
a
is disconnected as if it were torn off when the internal pressure of the cell is increased and the junction
7
a
is disconnected from the lead
7
, a burr like a beard is made on the section of a disconnected hole
7
b
of the junction
7
a
after the junction is disconnected from the lead and it is difficult to precisely and completely cut off the conductive path between the actuator
4
displaced upward and the lead
7
.
SUMMARY OF THE INVENTION
The present invention is made to solve the above problems and the object is to provide a high performance current cutoff mechanism of a cell wherein the miniaturization and the thinning are enabled and when pressure inside the cell is increased up to a predetermined value, a conductive path inside the cell can be securely cut off.
A current cutoff mechanism according to the present invention of a cell as first arrangement for solving the above problems is provided with a cell case in which a generating element is housed, a cell lid for airtightly shielding the inside of the cell case, a diaphragm connected to the cell lid, displaced according to the internal pressure of the cell case and provided with a convex portion in a part and an internal electrode provided with a fitted part for fitting the above convex portion of the diaphragm at the base, and is characterized in that the convex portion of the diaphragm is press-fitted into the above fitted part, a conductive path is formed between the cell lid and the generating element via the diaphragm and the internal electrode and when the internal pressure of the cell case is increased over a predetermined value and the diaphragm is displaced, the convex portion of the diaphragm is pulled out from the fitted part and the above conductive path is cut off.
A current cutoff mechanism according to the present invention as second arrangment for solving the above problems is characterized in that plural slits radially extended from the center of the base are formed, each triangular tongue is provided in a part between these plural slits, these plural tongues are protruded approximately in a conic shape, the above fitted part is formed by the tops of these plural tongues and the convex portion of the diaphragm is press-fitted into the fitted part.
A current cutoff mechanism according to the present invention as third arrangment for solving the above problems is characterized in that the above convex portion is formed so that the end is wider than the base fitted into the fitted part.
A current cutoff mechanism according to the present invention as fourth arrangment for solving the above problems is characterized in that the above fitted part is formed in the shape of a bag having a hollow part whose entrance is narrow and the inside is wider than the entrance and the wider end of the convex portion is press-fitted into the hollow part of the fitted part.


REFERENCES:
patent: 4943497 (1990-07-01), Oishi et al.
patent: 5705290 (1998-01-01), Azema
patent: 5738952 (1998-04-01), Abe
patent: 5821008 (1998-10-01), Harada et al.

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