Fluid handling – Destructible or deformable element controlled – Destructible element
Reexamination Certificate
2001-03-07
2003-06-03
Buiz, Michael Powell (Department: 3753)
Fluid handling
Destructible or deformable element controlled
Destructible element
C137S068250, C220S089200, C429S056000
Reexamination Certificate
active
06571816
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a cell safety valve in which a thin valve plate is formed in an opening hole in a sealing plate for sealing a cell such that if an internal cell pressure exceeds a predetermined value this valve plate may break so as to release a gas in the cell out of the cell, and a method for manufacturing the same.
(2) Description of the Related Art
Recently, besides LiCoO
2
and other lithium-containing composite oxides used as the positive electrode material, non-aqueous electrolyte cells using as the negative electrode material, such materials as lithium-aluminum alloy and carbon materials, which are capable of intercalating and deintercalating lithium ions, are attracting public attention as being capable of improving capacity.
When such a non-aqueous electrolyte cell is mishandled, e.g., put in fire, recharged, or discharged under abnormal conditions, a great amount of gas may be produced in the cell. Unless the gas in the cell is released out quickly, it may burst or ignite problematically. To prevent such a problem, such a cell is provided with a safety valve for releasing the gas in the cell out of it quickly at the time of abnormality. As such a safety valve, the following valves have been proposed:
(1) a valve that, as described in Japanese Unexamined Patent Application No. 11-250885 (see FIGS.
1
through
4
), in an opening hole
21
a
in a ring-shaped base material
21
, a cladding material
22
(with a thickness of about 10% of that of the base material) formed by two sheets of aluminum-based materials and constituting a valve plate is welded or pressure-welded to form a safety valve
23
, which is in turn mounted to a sealing plate
24
(one that is a so-called cladding-material-spec safety valve);
(2) a valve that, as described in Japanese Unexamined Patent Application No. 11-250885 (see FIGS.
5
and
6
), a break groove
26
is formed at around the middle of an opening hole
25
a
in a sealing plate
25
; and
(3) a valve that, as described in Japanese Unexamined Patent Application No. 11-273640 (see FIGS.
7
and
8
), a dome-shaped thin valve plate
29
is formed starting from the lower end of an opening hole
28
a
in a sealing plate
28
.
Those conventional safety valves, however, have had the following problems.
Problems of Type (1) Safety Valve
This safety valve
23
may have irregularities in strength of welding or pressure welding of the base material
21
and the cladding material
22
, which may in turn damage the cladding material
22
when the safety valve
23
is mounted to the sealing plate
24
, thus causing leakage of an electrolyte or increasing the cell-to-cell difference in the operating pressure of the safety valve.
Problems of Type (2) Safety Valve
This safety valve, although it reduces the cell-to-cell difference in the safety-valve's operating pressure, may have irregularities in the open area of a valve plate
27
upon the breaking of the safety valve, so that in case the open area is small, amount of gas production may be more than the amount of gas release. This may prevent the safety valve from having its own functions sufficiently, thus causing the cell to ignite or burst problematically.
Problems of Type (3) Safety Valve
This safety valve, although it can release a lot of gas produced quickly due to an enlarged open area of the valve plate
29
, has the thin valve plate
29
formed from the lower end of the opening hole
28
a
, so that the valve plate
29
may be damaged by a jig etc. to produce cracks etc. if it had vibration or shock on it during assembly of the cells, thus causing the leakage of the electrolyte.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide such a cell safety valve and a method for manufacturing the same that can ensure a sufficient open area during the operation of the safety valve while reducing the cell-to-cell difference in the operating pressure of the safety valve.
It is another object of the present invention to provide such a safety valve and a method for manufacturing the same that can prevent an electrolyte from leaking.
To achieve the above-mentioned objects, a cell safety valve according to a first aspect of the invention has its thin valve plate formed on a sheet-shaped sealing plate for sealing the cells such that if the internal cell pressure exceeds a predetermined value, the valve plate may break to release the gas in the cell to the outside, wherein the valve plate has a dome-shaped dome portion formed thereon and also at its middle or near it has a break groove for facilitating the breakage thereof.
Since thus the valve plate has the break groove at its middle or near it for facilitating the breakage thereof, if the internal cell pressure rises abnormally, the valve plate breaks surely starting from the break groove; in addition, as the valve plate has the dome-shaped dome portion formed thereon, after the valve plate has thus started breaking starting from the break groove, the peripheries of the dome portion also break by increased stress due to the gas. Therefore, even with some irregularities in the thickness of the valve plate, the cell-to-cell difference can be reduced in the operating pressure of the safety valve.
A second aspect of the invention is characterized in that the cell safety valve according to the first aspect of the invention, wherein the above-mentioned dome portion is provided one.
A third aspect of the invention is characterized in that the cell safety valve according to the second aspect of the invention, wherein the above-mentioned break groove is formed in the periphery of the above-mentioned dome portion.
The break groove is thus formed in the periphery of the dome portion, to further facilitate the breaking of the valve plate, thus reducing the cell-to-cell difference in the operating pressure of the safety valve.
A forth aspect of the invention is characterized in that the safety valve according to the first aspect of the invention, wherein the above-mentioned dome portion is provided two or more.
The dome portion is thus provided two or more, to ensure a sufficient open area during the operation of the safety valve.
A fifth aspect of the invention is characterized in that the safety valve according to the forth aspect of the invention, wherein the above-mentioned break groove is formed in the periphery of at least one of the above-mentioned two dome portions or more.
Such a configuration gives almost the same actions and effects as those of the third aspect of the invention.
A sixth aspect of the invention is characterized in that the safety valve according to the first aspect of the invention, wherein the above-mentioned valve plate as a whole is disposed between an imaginary plane flush with the outside surface of the above-mentioned sealing plate and an imaginary plane flush with the inside surface of the above-mentioned sealing plate.
In such a configuration, the valve plate does not come in direct contact with the jig etc., so that even in case of a vibration or shock during the assembly of the cells, it does not cause the jig etc. to damage the valve plate, thus inhibiting the electrolyte from leaking.
A seventh aspect of the invention is characterized in that the safety valve according to the first aspect of the invention, wherein the above-mentioned dome portion bulges in a direction toward the outside of the cell so as to form a dome shape.
Such a configuration further ensures the operations of the safety valve.
An eighth aspect of the invention is characterized in that the safety valve according to the first aspect of the invention, wherein the thickness of the above-mentioned valve plate is regulated to 0.1 through 10% of that of the above-mentioned sealing plate.
The thickness of the valve plate is thus regulated because a valve plate thickness of less than 0.1% of the sealing plate thickness is so thin that may cause leakage of the electrolyte, while a valve plate thickness of more than 10% of the sealing plate is so thick that excessively i
Fujii Shigeki
Marubayashi Hironori
Morishita Takuma
Tobita Yosihiro
Armstrong Westerman & Hattori, LLP
Buiz Michael Powell
Krishnamurthy Ramesh
Sanyo Electric Co,. Ltd.
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