Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
2001-03-13
2003-11-25
Gulakowski, Randy (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S244000
Reexamination Certificate
active
06653017
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to nonaqueous electrolyte secondary cells which comprise a can and a rolled-up electrode unit accommodated in the can and serving as a secondary cell element and which are adapted to deliver electric power generated by the electrode unit from a pair of electrode terminals provided on the can.
BACKGROUND OF THE INVENTION
In recent years, attention has been directed to lithium secondary cells or batteries having a high energy density for use as power sources for portable electronic devices, electric motor vehicles, etc. Cylindrical lithium secondary cells of relatively large capacity, for example, for use in electric motor vehicles comprise, as shown in
FIGS. 11 and 12
, a cylindrical cell can
1
having a cylinder
11
and lids
12
,
12
welded to the respective ends of the cylinder, and a rolled-up electrode unit
4
encased in the can
1
. A pair of positive and negative electrode terminal assemblies
9
,
9
are attached to the lids
12
,
12
, respectively. The two electrodes of the rolled-up electrode unit
4
are connected to the terminal assemblies
9
,
9
, whereby the electric power generated by the electrode unit
4
can be delivered to an external device from the pair of terminal assemblies
9
,
9
. Each lid
12
is provided with a gas vent valve
13
.
As shown in
FIG. 13
, the rolled-up electrode unit
4
comprises a positive electrode
41
and a negative electrode
43
which are each in the form of a strip and which are rolled up into a spiral form with a striplike separator
42
interposed between the electrodes. The positive electrode
41
comprises a striplike current collector foil
45
in the form of aluminum foil and coated over opposite surfaces thereof with a positive electrode active substance
44
comprising a lithium containing composite oxide. The negative electrode
43
comprises a striplike current collector foil
47
in the form of copper foil and coated over opposite surfaces thereof with a negative electrode active substance
46
containing a carbon material. The separator
42
is impregnated with a nonaqueous electrolyte.
The positive electrode
41
and the negative electrode
43
are each superposed on the respective separators
42
, as displaced from the separator widthwise thereof, and the assembly is rolled up into a spiral form, whereby the edge
48
of the current collector foil
45
of the positive electrode
41
is positioned as projected outward beyond the edge of the separator
42
at one of the axially opposite ends of the electrode unit
4
, and the edge
48
of the current collector foil
47
of the negative electrode
43
is positioned as projected outward beyond the edge of the separator
42
at the other end of the unit
4
. A current collecting plate
32
in the form of a disk is joined to each of the opposite ends of the electrode unit
4
by resistance welding and connected by a lead member
33
to the base end of the electrode terminal assembly
9
shown in FIG.
12
.
The electrode terminal assembly
9
comprises an electrode terminal
91
extending through a hole in the lid
12
of the can
1
and mounted on the lid
12
. The electrode terminal
91
has a flange
92
at its base end. An insulating packing
93
is fitted in the hole of the lid
12
for electrically insulating the electrode terminal
91
from the lid
12
and providing a seal therebetween. The electrode terminal
91
has a washer
94
fitted therearound from outside the lid
12
, and a first nut
95
and a second nut
96
screwed thereon. The first nut
95
is tightened up to clamp the insulating packing
93
between the flange
92
of the terminal
91
and the washer
94
and thereby seal off the hole more effectively. The outer end of the lead member
33
is fixedly joined to the flange
92
of the terminal
91
by spot welding or ultrasonic welding.
The lithium secondary cell having the current collecting structure shown in
FIG. 12
nevertheless has the problem that the edges
48
,
48
of the current collector foils
45
,
47
forming the positive electrode
41
and the negative electrode
43
of the rolled-up electrode unit
4
have a small area, which results in a small area of contact between each edge of the current collector foil and the corresponding current collecting plate
32
, consequently increasing the internal resistance of the cell. Further when the outermost peripheral portion of the current collecting plate
32
is joined to the electrode edge positioned radially most outwardly of the electrode unit
4
by laser welding, the laser beam is likely to leak out from the collecting plate
32
to irradiate the electrode or separator, causing damage to the electrode or separator.
A cylindrical secondary cell of improved power characteristics has been proposed which, as seen in
FIG. 17
, comprises a positive electrode
81
having an uncoated portion which extends upward beyond a portion thereof coated with an active substance
84
and varies in width longitudinally of the electrode, and a negative electrode
82
having an uncoated portion which extends downward beyond a portion thereof coated with an active substance
85
and varies in width longitudinally of the electrode. The positive and negative electrodes
81
,
82
are rolled up into a spiral form with a separator
83
interposed between the electrodes to obtain a rolled-up electrode unit
8
having conical projections
86
as seen in FIG.
18
. The electrode unit
8
is encased in a cell can
1
. Each of the electrode projections
86
is connected to an electrode terminal
90
by a current collecting lead
80
(JP-A No. 329398/1998).
Although improved to some extent in power characteristics, the secondary cell described requires the step of obliquely cutting an edge of each of the positive and negative electrodes
81
,
82
as shown in FIG.
17
. This not only makes the fabrication process complex but also presents difficulty in giving an accurately finished conical surface to the projection
86
of the rolled-up electrode unit
8
as shown in
FIG. 18
by rolling up the assembly of the two electrodes, consequently entailing the problem of an impaired yield and variations in the properties of cells. Especially in the case of lithium secondary cells for use as power sources in electric motor vehicles, there is a need to reduce the internal resistance to the greatest possible extent so as to obtain a high capacity and a high power. Furthermore, a manufacturing cost reduction requires a current collecting structure of high productivity.
Accordingly, a nonaqueous electrolyte secondary cell having low resistance and excellent in productivity is proposed which has a current collecting plate
7
of the shape shown in
FIG. 27
(JP-B No. 4102/1990). The collecting plate
7
has a central hole
74
and a lead portion
75
extending from the outer periphery thereof. The collecting plate
7
further has a plurality of ridges
72
V-shaped in cross section and extending radially from its center. As shown in
FIG. 28
, these ridges
72
are pressed against and weld to edge portions
48
of electrode of a rolled-up electrode unit
4
.
With this cell, the ridges
72
of the collecting plate
7
bite in the edge portions
48
of electrode of the electrode unit
4
. The collecting plate is therefore in contact with the edge
48
of the electrode over a greater area than the conventional collecting plate which is in the form of a flat plate. This results in an increase in the quantity of current collected to afford an increased cell power.
However, since the ridges of the collecting plate have a V-shaped cross section with an acute angle, the area of contact of the ridges with the edge of the current collector foil is not sufficiently great. Accordingly, the collecting plate not only has great contact resistance at the weld but is also poor in the state of contact at the portions other than the weld. Thus, the structure described has the problem of low current collecting performance. Moreover, the junction between the V-shaped ridge and the edge of the
Nakanishi Naoya
Nakano Noboru
Nohma Toshiyuki
Satoh Kouichi
Yonezu Ikuo
Gulakowski Randy
Kubovcik & Kubovcik
Sanyo Electric Co,. Ltd.
Wills Monique
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