Sealed alkaline storage battery with safety vent unit

Details Sealed alkaline storage battery with safety vent unit Sealed alkaline storage battery with safety vent unit

2001-03-07

2004-02-10

Ruthkosky, Mark (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Means externally releasing internal gas pressure from closed...

Elastic, resilient or spring biasing valve means

Reexamination Certificate

active

06689506

ABSTRACT:

This application is based on application No. 66169 filed in Japan on Mar. 10, 2000 and application No. 52005 filed in Japan on Feb. 27, 2001, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
This invention relates to a safety vent apparatus of a sealed alkaline storage battery.
Sealed alkaline storage batteries such as nickel cadmium storage batteries and nickel hydride storage batteries are rechargeable batteries which use alkaline aqueous solutions as electrolyte.
As shown in
FIG. 1
, an alkaline storage battery
10
is a cylindrical metal external battery case
30
with a closed bottom end containing an electrode unit
12
together with electrolyte L and sealed at the open end of the external case
30
with a closing lid
80
.
As shown in
FIG. 1
, the electrode unit
12
is formed by rolling a positive electrode plate
14
, a negative electrode plate
16
, and a gas permeable separator
18
intervening between the two electrode plates, into a spiral shape. The positive electrode plate
14
and the negative electrode plate
16
are formed by applying each of the active materials, nickel oxide and cadmium compounds to conducting electrode plates.
A positive electrode collector
20
is electrically connected to the upper end of the positive electrode plate
14
, and the closing lid
80
is disposed above, and electrically connected to, the positive electrode collector
20
.
The closing lid
80
is provided with a sealing plate
40
which is electrically connected to the positive electrode collector
20
and has a gas release hole
42
opened at its center, a safety vent unit
60
to close the gas release hole, and a positive electrode cap
70
to hold the safety vent unit
60
in a compressed state between the cap
70
and the sealing plate
40
. The sealing plate
40
is caulked into the open end of the battery case
30
via an insulating gasket
76
to tightly close off and seal the external battery case
30
.
In the sealed alkaline storage battery
10
, when gas is generated internally as a result of conditions such as over-charge or over-discharge and the battery's internal pressure exceeds a given pressure, the safety vent unit
60
, is activated and gas and electrolyte inside the battery are vented to the outside to prevent battery case deformation, etc.
In general, gas generated inside a battery due to over-charging is consumed inside the battery. However, if charging is continued unchecked, the rate of gas generation can exceed the rate of gas consumption resulting in internal pressure rising above equilibrium values. Therefore, when internal battery pressure rises abnormally, battery case deformation and closing lid protrusion are prevented by venting gas via the safety vent unit described above.
The safety vent unit
60
is made up of a rubber ventage plate
62
and a spring
64
to power the ventage plate
62
. In this safety vent unit
60
, when internal battery pressure exceeds a given value, the spring
64
is compressed, the ventage plate
62
moves to open the gas release hole
42
, and gas and electrolyte are ejected to the outside through the gas release hole
42
in the sealing plate
40
and gas venting holes
78
provided in the positive electrode cap
70
.
Here, the activation pressure to begin operation of the safety vent unit is the pressure which begins to distort the spring in that unit.
FIG. 2
shows the relation of the change in spring length to the amount of pressure applied to the safety vent unit (internal battery pressure). As shown by line a in
FIG. 2
, when activation pressure is set low, gas generated inside the battery can be vented at an early stage of internal pressure increase. This allows the previously mentioned dangers of battery case deformation and closing lid protrusion to be avoided at an early stage. However, since the gas generated inside a battery is due to electrolysis of water in the electrolyte, the quantity of electrolyte decreases as gas is vented. As a result, this can bring about loss in battery capacity after the safety vent has returned to its normal position. In contrast, when activation pressure is set high as shown by line b in
FIG. 2
, gas is not ejected even though the internal battery pressure is increased. This can invite the dangers of battery case deformation and closing lid protrusion.
Consequently, activation pressure is set to a suitable value which does not bring about loss in battery capacity and avoids the dangers associated with high internal battery pressure.
However, even when activation pressure is set to a suitable value, the rate of gas generation can be high during malfunctions such as extremely large charging current flow through the battery. In this case, even if the safety vent unit activates, if spring compression is small, the rate of gas ejection by the safety vent unit cannot approach the rate of gas generation.
SUMMARY OF THE INVENTION
The object of the present invention to provide a sealed alkaline storage battery which can eject large quantities of material such as gas and electrolyte, when internal pressure exceeds a given value, by setting the spring compressive load to length change (deformation) ratio to an optimum value.
To resolve the issues described above, the sealed alkaline storage battery of the present invention is provided with a sealing lid. The sealing lid is made up of a sealing plate electrically connected to an electrode unit, having a positive electrode plate, a negative electrode plate, and an intervening separator, which is contained in an external battery case having a cylindrical shape and a bottom; a safety vent unit which closes a gas release hole established through the sealing plate; and a positive electrode cap which accommodates the safety vent unit in a compressed state between the sealing plate and the cap. The safety vent unit is provided with a ventage plate to close the gas release hole and a spring to spring-load the ventage plate against the gas release hole. The ratio of compressive load per length change (deformation) of the spring is 50 N/mm or lower.
Since the ratio of compressive load per length change (compressive load/spring deformation) of the safety vent unit spring of the sealed alkaline storage battery described above is ≦50 N/mm, the distance the ventage plate can move when internal battery pressure exceeds a given value, can be large. Therefore, large quantities of material such as gas and electrolyte can be ejected outside the battery by widely opening the ventage plate from the gas release hole. As a result, external battery case deformation or rupture, due to a rise in internal battery pressure, can be prevented.


REFERENCES:
patent: 4207384 (1980-06-01), Peters
patent: 4788112 (1988-11-01), Kung
patent: 5455125 (1995-10-01), Matsumoto
patent: 5521021 (1996-05-01), Alexandres et al.
patent: 5554455 (1996-09-01), Inoue et al.
patent: 5567539 (1996-10-01), Takahashi
patent: 5747187 (1998-05-01), Byon
patent: 6255013 (2001-07-01), Marukawa et al.
patent: 6326100 (2001-12-01), Han et al.
patent: 757394 (1997-02-01), None
patent: 408339793 (1996-12-01), None
patent: 9-27310 (1997-01-01), None
patent: 2001052005 (2001-11-01), None

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