Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Plural cells
Reexamination Certificate
2001-03-01
2003-10-14
Gulakowski, Randy (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Plural cells
C429S160000, C429S178000, C029S623100
Reexamination Certificate
active
06632562
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and a structure for connecting a plurality of cells in series for forming a battery module having a desired output voltage.
DESCRIPTION OF RELATED ART
In order to form a battery module having a desired output voltage by connecting a plurality of cells in series, it is known in the art to employ connectors. Generally, a cell for constituting a battery module includes a negative electrode in the form of metallic cell case which covers the cell entirely except for one end surface thereof. The opening on one end of the cell case is closed with a sealing assembly including a positive electrode plate made of metal. When connecting two cells in series, a connector is interposed between the positive electrode plate of one cell and the cell case constituting the negative electrode of the other cell, and electrically connected at predetermined locations to both of them. The connector is spot-welded to the cells, and therefore it connects the two cells not only electrically but also couples them mechanically together.
Spot welding usually includes applying electric current across a pair of welding electrodes which tightly hold a portion to be welded, so as to melt the portion held between the welding electrodes. In welding two cells together with a connector, however, the connector is interposed between the cells and cannot be held between the pair of welding electrodes, as a result of which electric current flows through the surfaces of the connector or the electrode plate across the welding electrodes, and in cases where the connector is thick or has a low specific resistance, the welding becomes difficult. That is, in accordance with the prior art method of connecting cells, since materials having a large thickness or a low specific resistance cannot be used for the connector, the electric resistance in the joint between two cells is large, and accordingly the loss at the joints where large current flows becomes large. Moreover, the mechanical strength of the connector is low, making the mechanical connection between adjacent cells low.
The inventors of the present application have previously proposed an improved structure for connecting cells and a welding method for reducing electrical connection resistance while enhancing mechanical connection strength, whereby the problems found in prior art are resolved. (Japanese Laid-open Patent Application No. 10-106533).
FIG. 5
is a longitudinal cross sectional view showing this cell connecting structure. A connector
1
includes a flat bottom plate
3
abutted on a positive electrode plate
2
of one cell B
1
, and a cylindrical wall
7
oupled to a cell case
4
of the other cell B
2
which doubles as the negative electrode thereof. A plurality of projections
8
and
9
for the welding purpose are formed each in circles on the cylindrical wall
7
and on the bottom plate
3
. The drawing shows the cells before welding. The connector
1
is welded to the electrode plate
2
of one cell B
1
through the projections
9
and joined thereto, while it is welded to the cell case
4
of the other cell B
2
through the projections
8
and joined thereto.
Projection welding involves generation of heat by local concentration of electric current at the joints between two members to be welded together contacting each other in a very small area such as the projections
8
,
9
, where the electric resistance becomes largest. The contacting area melts by the heat and the two members are welded together. The portions to be welded need not be held tightly between the welding electrodes as in the spot welding. The connector
1
in the above-described connecting structure is welded respectively to the two cells B
1
, B
2
by such projection welding, and therefore the choice of the material for the connector
1
need not depend on its thickness or specific resistance, and also, the welding strength can be improved. Moreover, since the electrode plate
2
and the cell case
4
are welded to the connector
1
at a plurality of locations on matching circles, the electric current flows the shortest distance through the joint between the cells. Thus the cells are coupled with high mechanical strength as well as with low electric resistance.
The cell connecting structure offers such advantages as described above, but still has problems to be resolved in practical application. That is, the projection welding in accordance with the above-described method includes at least two welding steps, one for welding the bottom plate
3
of the connector
1
to the electrode plate
2
of one cell B
1
, and one for welding the cylindrical wall
7
of the connector
1
to the cell case
4
of the other cell B
2
.
As the number of the cells to be connected increases, so does the number of the connector
1
. The connector
1
has a considerably complex structure: It has a circular shape having a stepped bottom and a cylindrical wall projecting over the outside of the cell case
4
of cell B
2
for detouring the gasket
10
of cell B
1
, and has an opening
12
in its center at the bottom for passing the cap-shaped positive electrode terminal
11
of cell B
1
therethrough. Furthermore, although not shown, the cylindrical wall
7
of the connector
1
is formed with cut-outs for providing resiliency so that it makes tight engagement with the cell case
4
of cell B
2
when coupled thereto, and the bottom plate
3
is also formed with cut-outs for preventing wasted current during the projection welding. Thus the connecting structure described above has high costs because of the large numbers of welding processes and components such as the connector
1
, which has such a complex shape as described above and cannot be obtained at low cost.
Another problem is that, since the cylindrical wall
7
of the connector
1
is coupled over the cell case
4
, the resultant battery module wherein a plurality of cells are connected has protruding portions at each joint of adjacent cells because of the increased outer diameter, leading to the problem of dimensional precision of an outer tube for covering the battery module. Furthermore, electric resistance at the joint between adjacent cells becomes large by the length of the electric current path passing through the connector
1
.
In view of the problems in prior art as described above, it is an object of the present invention to provide a method and structure for connecting cells, whereby a reduction in cost is achieved, protruding portions are eliminated from the cell case of each cell, and the electric resistance at the joints between adjacent cells is reduced.
SUMMARY OF THE INVENTION
In order to achieve the above object, the present invention provides a cell connecting structure for coupling together two adjacent cells in a battery module wherein a plurality of cells are arranged coaxially in series and connected electrically. Each of the cells includes a cylindrical cell case having an open end and a bottom surface on the other end doubling as one electrode of the cells, and a sealing assembly for sealing the open end of the cylindrical cell case. The cell connecting structure of the invention includes a cell case of a first cell, and a sealing assembly, having a specific structure, of a second cell. The sealing assembly includes an electrode plate formed with a concavity in a central portion thereof, a valve body housed in the concavity, a valve body holding plate welded to an upper peripheral edge of the concavity for sealing the concavity, a connection electrode formed in an annular shape and protruded outwards in a direction along the axis of the cells at a location near outer peripheral edge of the electrode plate, and a plurality of projections formed on the connection electrode. The plurality of projections on the connecting electrode of the second cell are directly welded to the bottom surface of the cell case of a second cell.
According to the cell connecting structure of the invention, two adjacent cells among the plurality of cells arranged in series are
Iwasaki Mizuo
Nakatsuka Saburo
Crepeau Jonathan
Gulakowski Randy
Jordan and Hamburg LLP
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