Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1998-07-14
2001-01-16
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S163000, C429S177000, C029S623100
Reexamination Certificate
active
06174620
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a prismatic sealed battery obtained by coupling a cover member to an opening portion of a prismatic outer case and welding the cover member and the opening portion, and to a method of manufacturing the prismatic sealed battery.
Recently, because of an increasing demand of portable OA devices and communication devices, there is a great demand for prismatic sealed batteries as power supplies. In particular, nickel metal hydride rechargeable batteries and lithium ion rechargeable batteries, the prismatic sealed batteries are small in size and can be mounted in the above devices with high volume efficiency.
In general, the prismatic sealed battery has an outer case
1
A provided with an opening portion
3
A, as shown in
FIG. 1. A
cover member
2
A is coupled to the opening portion
3
A of outer case
1
A, and a coupling portion between these members is hermetically welded by a laser beam L.
When the laser beam L is radiated on the lateral side of the outer case
1
A and scanned along the coupling portion between the outer case
1
A and cover member
2
A, the scan direction of laser beam L is controlled in the X- and Y-directions along the outer peripheral surface of outer case
1
A in FIG.
1
.
In a case where the laser beam L is incident on the lateral side of outer case
1
A and scanned in the X- and Y-directions for welding, however, it is difficult to treat a corner portion R of outer case
1
A and a corner portion r of cover member
2
A. Specifically, if the laser beam L is scanned linearly in the X- and Y-directions, the laser beam L is not incident perpendicular to the outer periphery of the outer case
1
A and cover member
2
A at the corner portions R and r of outer case
1
A and cover member
2
A.
For example, when the radius of curvature of corner portion R, r is set at about 2.0 mm, an angle &thgr; between the direction of radiation of laser beam L and a plane normal to a tangential line (including a surface to be welded) of the corner portion, R, r is 45° at maximum. At this time, the area of radiation of laser beam L increases 1. 41 times (=1/cos 45°).
Consequently, the radiation energy density (fluence: J/cm
2
) of laser beam L decreases by about 40%, compared to the case where beam L is incident perpendicular to the surface to be welded. In general, the allowance in a laser welding process with respect to a variation in the fluence is ±10%. Under the above condition, the depth of weld penetration also decreases and the strength of bonding deteriorates. As a result, cracks may occur at the welded portion.
In particular, in a case where the outer case
1
A and cover member
2
A is formed of aluminum or aluminum alloy in order to reduce weight, cracks will easily occur and the yield of manufactured products will considerably deteriorate. In order to achieve good welding, the condition, cos &thgr;>0.9, needs to be satisfied. Therefore, it is desirable to meet the condition, &thgr;<25°.
In a case where the outer case
1
A and cover member
2
A are formed of steel or stainless steel, the radius of curvature of the entire outer case including corner portions R, r is set to a small value, e.g. about 1.0 to 1.3 mm. Thereby, a deviation in angle of radiation of the laser beam L on the outer periphery of the corner portion R, r is decreased, and the strength of bonding is prevented from deteriorating.
In the case of using aluminum or aluminum alloy, however, if the radius of curvature of the corner portion R, r is decreased, the stress will concentrate at the corner portion R, r when the pressure in side the outer case
1
A increases, and the rigidity thereof decreases. Since the strength of the aluminum or aluminum alloy itself is low, the radius of curvature of the corner portion R, r needs to be increased. Because of this, a deviation in angle of radiation of the laser beam L increases and the depth of welding penetration at the welded portion decreases. As a result, the welding strength decreases.
If the scan direction of the laser beam L is turned in accordance with the curvature of the corner portion R, r, such problem will not arise. However, if the scan direction of the laser beam L is turned along the corner portion R, r, the control for scanning the laser beam L becomes intricate and the cost of the scan device increases. Furthermore, a process time increases. Therefore, this measure is not practical.
On the other hand, the cross section of the outer case
1
A of the prismatic sealed battery, which is parallel to the opening portion
3
A, is formed prismatic (including a curve of the corner portion R), and the wall thickness (i.e. thickness of material forming the outer case) of a long-side portion
4
A is equal to that of a short-side portion
5
A.
If the wall thickness is not sufficient, the rigidity of the outer case
1
A decreases. Thus, if a gas is produced by a chemical reaction of an electrolyte while a power generating element in the secondary battery is being charged, the internal pressure of the outer case
1
increases and, as indicated by solid-line arrows in
FIG. 3
, the inner surface of the long-side portion
4
A of outer case
1
A is pressurized in the direction of expansion and deformed.
Consequently, a bending moment is applied at the corner portions R, as indicated by broken-like arrows, and the short-side portions
5
A are deformed inward by the bending moment and the entire outer case
1
A is deformed.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a prismatic sealed battery and a method of manufacturing the same, wherein when an outer case and a cover member are welded, a decrease in depth of weld penetration at corner portions due to a large variation in radiation angle of a laser beam is prevented.
Another object of the invention is to provide a prismatic sealed battery and a method of manufacturing the same, wherein an outer case is not easily deformed due to a rise in internal pressure.
According to the present invention, there is prismatic sealed battery comprising:
a metallic outer case having an opening portion and a first corner portion at an outer periphery of the opening portion;
a power generating element stored within the outer case and having a positive electrode and a negative electrode opposed to each other, with a separator interposed;
a metallic cover member coupled to an end face of the opening portion of the outer case, provided with a second corner portion corresponding to the first corner portion of the outer case, and welded to the outer case, with a coupled portion between the cover member and the outer case irradiated with a laser beam; and
an electrode element electrically connected to the power generating element.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 6007944 (1999-12-01), Bechtold et al.
Homma Katsuhisa
Kato Masahiro
Okada Naotada
Kabushiki Kaisha Toshiba
Kalafut Stephen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wills M.
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