Note: Descriptions are shown in the official language in which they were submitted.
CA 02572931 2006-12-21
SAFETY STRUCTURE FOR A PLASTIC BATTERY CASE
BACKGROUND OF 'fHE Ily'VEN'CYON
Field of the Inygntion
The present invention relates to a safety strncture for a plastic battery
case, and
more particularly to a safety design for a plastic battery case for safely
releasing the
internal pressure thereof.
Description of the Prior Art
Due to the great brake-through in material technique, lithium secondary
battery,
as a high capacity power supply (sucb as LipePO4 type lithium secondary
battery),
has been used on power devices, such as electric bicycle, electric wbeelchair,
and etc.
The power storage and supply capacity of such a high capacity non-aqueous
electrolyte type lithium secondary battery are greater than that of a
conventional
lithium battery. The battery case of the abovementioned lithium secondary
battery is
usually a metal case made of ahtminum. Since the battery case is filled with
electrode
board and non-aqueous electrolyte, and in order to ensure a long term and
stable
sealing performance, the open end of the battery case should be sealed with a
sealing
plate by laser welding.
If the abovementioned lithium secondary battery is overcharged and
consequently the interior current value exceeds the normal value, or the
battery is
misused and cause short circuit, the non-aqueous electrolyte in the battery
case will be
fully decomposed and produce a great deal of gas. When the gas pressure inside
the
CA 02572931 2006-12-21
battery case exceeds the maximum pressure limit, the battery case will be
ruptured
and gas will be gushed out of the battery case instantly, causing damage to
the
powered device the battery and causing electrolyte contamination.
Therefore, the aluminum sealing plate of the conventional non-aqueous
electrolyte lithium secondary battery is usually defined with an air hole
sealed with a
thin aluminum safety valve. When the intemal gas pressure of the battery case
exceeds a predetermined value, the gas will break through the aluminum valve,
thus
releasing the pressure from the battery case.
It is to be noted that the safety valve is located on the surface of the
sealing
plate, considering the battery as a whole, the safety valve is located
comparatively far
away from mid portion of the electrode board, and since the air hole is
limited by the
size of the sealing plate, the inner diameter of the air hole will not be
large. The gas
will take a long time to break through the safety valve. The normal condition
is that,
when the internal pressure of the battery case increases, the mid portion of
the battery
case will be inflated and ruptured instantly, however, the safety valve
doesn't work.
Obviously, such a conventional safety valve is unable to solve the safety
problem of
the battery case.
1lierefore, as shown in Fig. 1, a safety mechanism for an aluminum rectangular
battery case was made and was disclosed in US Pat. No. 6,964,690, in the
elongated
side surface of the battery case 10 is formed a plurality of cutting grooves
11.
Between a groove bottom surface of the cutting groove 11 and an inner surface
of the
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battery case 10 is provided a thin-walled casily-rupturable portion designed
to rupture
at an instant when an internal pressure of the battery case reaches a
predetermined
value, thus releasing the gas pressure from the battery case.
For such a safety mechanism design of cuttfng the cutting grooves in the metal
battery case, when the internal pressure of the battery case increases, the
easily-rupturable portion will be ruptured. It is to be noted that a great
deal of gas
pressure impacts the sma11 easily-rupturable portion in a very short time, the
resultant
ruptured grooves in the battery case will be very large, and as a result, the
gas and the
non-aqueous electrolyte will be gushed out of the battery case via the
ruptured
grooves, and the electrode board inside the battery case will be exposed out
of the
ruptured portion, This is a very large threat to a powered device.
The safety structure of the present invention is such that, when the internal
pressure of the battery case increases, the strong impact force caused by the
unusual
gas pressure increase is buffered and then is released through small slits.
SUMMARY OF THE INVENTION
The primary objective of the present invention is to provide a plastic
integrally
formed battery case, in the inner surface of the battery case is formed a
plurality of
grooves whose open side face the interior of the battery case. When the
internal
pressure of the battery case is too high, the closest grooves will bulge
instantly, and
the bulged working portion wiil not be ruptured right away. When the thickness
of the
working portion is thinned to zero, a smaIl slit will appear. At this moment,
the gas
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can be released from the slit, thus preventing a great deal of gas from
gushing out of
the battery case in an instant and contaminating the powered device.
The secondary objective of the present invention is to provide a plastic
integrally formed battery case, in the inner surface of the battery case is
formed a
plurality of grooves whose open side face the interior of the battery caseõ
the open
side of the groove is opposite the direction of the gas pressure, thus
facilitating the
collection of pressure, and making it easier for the thinnest working portion
to bulge
outward.
BRIEF DESCRIPTI4N OF THE DRAWINTGS
Fig. 1 is a perspective view of showing a conventional safety structure for an
aluminum rectartgular battery disclosed in US Pat. No. 6,964,690;
Fig. 2 is an exploded view of a circular plastic battery case and a core
assembly
in accordance with the present invention;
Fig. 3 is a longitudinal cross sectional view in acoordance with the present
imention of showing a circular plastic battery case;
Fig. 4 is a transverse cross sectional view in accordance with the present
invention of showing a circular plastic battery case;
Fig. 5 is a longitudinal cross sectional view in accordance with the present
invention of showing that the working portion in Fig. 4 is being bulged;
Fig. 6 is a longitudinal cross sectional view in accordance with the present
invention of showing that the working portion in Fig. 4 is bulgbd and
ri,ptured to
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release the gas;
Fig. 7 is an exploded view of a circular plastic battery case with
longitudinal
and transverse grooves and a core assembly in accordance with the present
invention;
Fig. 8 is a longitudinal cross sectional view in accordance with the present
invention of showing that the longitudinal and transverse working portions in
Fig. 7 is
bulged and ruptured to release the gas;
Fig. 9 is an exploded view of a rectangular plastic battery case and a core
assembly in accordance with the present invention; and
Fig. 10 is a longitudinal cross sectional view in accordance with the present
invention of showing that the working portion in Fig. 9 is bulged and ruptured
to
release the gas.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be more clear from the following description when
viewed together with the accompanying drawings, which show, for purpose of
illustrations only, the preferred embodiment in accordance with the present
invention.
Referring to Figs. 2, 3 and 4, a safety structure for a plastic battery case
in
accordance with a preferred embodiment of the present invention comprises at
least
one groove formed in a battery case, wherein:
The battery case 20 is a circular plastic unitary structure in which is
defined a
receiving space 21 with an open end for acconYmodation of a core assembly 40,
a
leakage-proof washer 60, and non-aqueous electrolyte 50. A connecting flange
22 is
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formed around the peripheral edge of open end of the receiving space, a cover
23 is
fixed to the connecting flange 22 by screws 24 to seal the open end, thus
creating an
airtight receiving space 21.
In the inner surface of the receiving space 21 of the battery case 20 is
formed at
least one groove 30 whose open side 31 faces the interior of the battery case
20, and
between the bottom of the groove 30 and the outer surface of the battery case
20 is a
working portion 32 which is the thinnest portion of the wall of the battery
case 20.
When unusual factors (including: overcharge, short circuit of the electrode
plate,
overload) occur and consequently the non-aqueous electrolyte is decomposed
into
high pressure gas, the worldng portion can substantially bulge outward and
then
become thinner and consequently form a slit to release the gas from the slit.
The battery case of the present invention is made of plastic material, in the
inner surface of the battery case is fomed at least one groove, and when the
intemal
pressure of the battery case exceeds a predetermined value, the working
portion of the
groove will bulge outward and become thinner and consequently form a slit for
releasing the pressure. And such a pressure-releasing process can prevent the
battery
from explosion, and ensure that the internal pressure can be released safely.
The
operation of the embodiment is explained as follows:
Referring to Figs. 2, 3 and 4 again, the battery case 20 is a unitary
structure
made of plastic material, in the inner surface of the battery case 20 is
formed a
plurality of grooves 30, and between the bottom of the gmoves 30 and the outer
wall
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of the battery casa 20 is a working portion 32 which is the thinnest portion
of the wall
of the battery case 20. The number of the grooves 30 is based on the size of
the
battery case 20. For example, a 20 cm diameter circular battery case 20 can be
axially
formed in its inner surface with four grooves 30, and the grooves 30 are
equidistantly
arranged.
Referring then to Figs. 4, 5 and 6, when unusual factors occur and
consequently
the non-aqueous electrolyte is decomposed into high pressure gas 70, the gas
pressure
will make the battery case 20 bulge outward. It is to be noted that the
location where
the unusual factors take place may be located at one of the inner sides of the
battery
case 20 only, and the pressure on this inner side of the battery case 20 is
the greatest.
The worlcing portion 32 of the groovcs 30 located closest to the bigh pressure
point
will bulge instantly. The battery case 20 is made of plastic material, and the
plastic
surface of the battery case 20 has certain flexibility, so that the bulged
worlciiig
portion 32 will not be rupttued right away. The rupture time is prolonged, and
then a
small slit 33 will appear when the thickness of the working portion 32 is
thinned to
zero. At this moment, the gas 70 will be released from the battery via the
slit 33.
It has to be mentioned that the battery case of the present invention is made
of
plastic material, and as compared with the conventional metal battery case,
the plastic
battery case makes it easier for the battery to pass the free-fa11 test.
It is to be noted that, as shown in Fig. 4, each of the grooves 30 is V-shaped
in
cross section, and the open side 31 of the grooves 30 faces the interior of
the battery
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case 20. When the unusual gas pressure is applied to the inner surface of the
battery
case 20, the open side 31 of the grooves 30 is opposite the direction of the
gas
pressure for facilitating the collection of pressure, and making it easier for
the thinnest
worldng portion 32 to bulge toward the radial direction of the battery and
consequently form a slit 33. And thus the pressure can be released safely.
'Therefore, it
is very important that the open side 31 of the grooves 30 opens toward the
interior of
the battery case 20.
In addition, the location of the grooves 30 is the position where the gas 70
inside the battery case 20 is to be released. With the structural design, the
grooves 30
can be arranged at a predetermined position, so that the position where the
gas 70 to
be released can be anticipated, thus preventing the powered device from being
contaminated and damaged. In addition to the longitudinal direction as shown
in Fig.
7, the direction in which the grooves 30 are ananged can also be arrranged in
transverse direction. For example, as shown in Fig. 8, the battery case can be
formed
with longitudinal grooves 30 and transverse grooves 30a, and it has the same
pressure
releasing effect.
In addition to being used on circular battery case, the safety structure
design of
the present invention is also suitable for use in a rectangular battery case.
With
reference to Fig. 9, the grooves 30 and the working portion 32 are formed in
the
rectangular battery case. And as shown in Fig. 10, which is an illustrative
view of
showing that the worldng portion 32 of the rectangular battery 20a is bulged
and
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CllptUred.
It can be seen from the above description that the battery case of the present
invention is formed in its inner surface thereof with at least one groove, and
since the
plastic battery case is flexible, when the internal pressure of the battery
case exceeds a
predetermined value, the worldng portion of the groove will bulge outward and
become thinner and consequently form a slit to release the pressure. In other
words,
the safety pressure release is achieved by the flexible inflation of the
plastic material,
so that the strong impact force caused by the unusual gas pressure increase is
buffered
and then is released.
While we have shown and described various embodiments in accordance with
the present invention, it is clear to those sldlled in the art that further
embodiments
may be made without departing from the scope of the present invention.
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