Chemistry: electrical current producing apparatus – product – and – Plural concentric or single coiled electrode
Reexamination Certificate
2000-08-10
2004-02-17
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Plural concentric or single coiled electrode
C429S186000, C429S208000, C429S133000, C429S146000
Reexamination Certificate
active
06692863
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to nonaqueous electrolyte secondary cells, such as cylindrical lithium ion secondary cells, which comprise an electrode unit encased in a battery can and serving as an electricity generating element and which are adapted to deliver the electricity generated by the electrode unit to the outside via a positive terminal portion and a negative terminal portion like. The invention relates also to processes for fabricating such cells.
BACKGROUND OF THE INVENTION
Nonaqueous electrolyte secondary cells of the type mentioned comprise a rolled-up electrode unit formed by laying a positive electrode and a negative electrode, each in the form of a strip, over each other in layers with a separator interposed therebetween and rolling up the resulting assembly into a spiral form. The rolled-up electrode unit is encased in a battery can.
The electric power generated by the rolled-up electrode unit is delivered to the outside through an arrangement including a plurality of conductive current collector tabs having their base ends attached to each of the positive electrode and the negative electrode of the electrode unit. The positive current collector tabs extending from the positive electrode have outer ends connected to a positive terminal portion, and the negative current collector tabs extending from the negative electrode have outer ends connected to a negative terminal portion. This arrangement is widely used.
However, the current collecting arrangement comprising a plurality of collector tabs has the problem of failing to achieve a sufficient current collecting effect when used in nonaqueous electrolyte secondary cells of large size having a high current value since the cell has increased electrode areas although producing a satisfactory current collecting effect in nonaqueous electrolyte secondary cells of small size which are relatively low in current value.
Further the connection of the current collector tabs to each electrode terminal portion requires a complex structure and complicated procedure, hence the problem of low work efficiency or productivity.
Accordingly, a cylindrical nonaqueous electrolyte secondary cell has been proposed which has a current collecting structure comprising a negative electrode current collector plate
36
and a positive electrode current collector plate
30
as shown in FIG.
7
. This cell has a battery can
1
formed by a cylinder
15
and lids
16
,
16
secured to opposite open ends of the cylinder. A rolled-up electrode unit
2
is enclosed in the battery can
1
. The negative electrode collector plate
36
and the positive electrode collector plate
30
are arranged at respective ends of the electrode unit
2
and joined to the unit
2
by laser welding. The collector plates
36
,
30
are connected by lead portions
37
,
34
respectively to a negative terminal assembly
4
and a positive terminal assembly
40
mounted on lids
16
,
16
.
The rolled-up electrode unit
2
comprises a positive electrode
23
, separator
22
and negative electrode
21
each in the form of a strip. The positive electrode
23
is formed by coating a current collector of aluminum foil with a positive electrode active material. The negative electrode
21
is formed by coating a current collector of copper foil with a negative electrode active material.
The positive electrode
23
and the negative electrode
21
are each superposed on the separator
22
, as displaced from the separator widthwise thereof and rolled up into a spiral form, whereby the edge of the positive electrode
23
is positioned as projected outward beyond the edge of the separator
22
at one of opposite ends of the electrode unit
2
in the direction of its winding axis, and the edge of the negative electrode
21
is positioned as projected outward beyond the edge of the separator
22
at the other end of the unit
2
. The positive electrode current collector plate
30
is made of aluminum, and the negative current collector plate
36
is made of copper.
With the current collecting structure wherein the collector plates
36
,
30
are joined to the respective ends of the electrode unit
2
as described above, the collector plates can be welded to the unit
2
contactlessly without applying pressure to the plates for welding. This achieves an improved work efficiency or productivity.
The process for fabricating the nonaqueous electrolyte secondary cell shown in
FIG. 7
, however, has the problem that when the negative electrode collector plate
36
is disposed at and welded to the edge of the negative electrode
21
of the unit
2
, sufficient energy can not be given to the portion to be welded since the copper forming the collector plate
36
has high reflectivity for the laser beam used for welding, forming a faulty weld and increasing the electric resistance between the unit
2
and the negative electrode collector plate
36
to result in an impaired current collecting efficiency. If the collector plate
36
is made from nickel, the weldability of the plate
36
to the electrode unit
2
can be improved, whereas the collector plate
36
of nickel has greater electric resistance than the plate
36
of copper and therefore exhibits a lower current collecting efficiency.
FIGS. 20 and 23
show another conventional nonaqueous electrolyte secondary cell, which comprises a cylindrical battery can
1
including a cylinder
15
and lids
16
,
16
welded to respective opposite ends of the cylinder, and a rolled-up electrode unit
5
enclosed in the can
1
. A pair of positive and negative terminal assemblies
110
,
110
are mounted on the respective lids
16
,
16
and each connected to the electrode unit
5
by a plurality of electrode tabs
6
for delivering the electric power generated by the unit
5
to the outside through the terminal assemblies
110
,
110
. Each lid
6
is provided with a gas vent valve
13
which is openable with pressure.
As shown in
FIG. 22
, the rolled-up electrode unit
5
comprises a positive electrode
51
and a negative electrode
52
each in the form of a strip and rolled up into a spiral form with a striplike separator
52
interposed between the electrodes. The positive electrode
51
is prepared by coating opposite surfaces of a striplike current collector
55
of aluminum foil with a positive electrode active material
54
comprising a lithium containing composite oxides. The negative electrode
53
is prepared by coating opposite surfaces of a striplike current collector
57
of copper foil with a negative electrode active material
56
containing a carbon material. The separator
52
is impregnated with a nonaqueous electrolyte.
The positive electrode
51
has an uncoated portion having no active material
54
applied thereto, and base ends of the electrode tabs
6
are joined to the uncoated portion. Similarly, the negative electrode
53
has an uncoated portion having no active material
56
applied thereto, and base ends of the electrode tabs
6
are joined to the uncoated portion.
With reference to
FIG. 23
, the electrode tabs
6
of the same polarity have outer ends
61
connected to one electrode terminal assembly
110
. For the sake of convenience,
FIG. 23
shows only some of the electrode tabs as connected at their outer ends to the terminal assembly
110
, with the connection of the other tab outer ends to the assembly
110
omitted from the illustration.
The electrode terminal assembly
110
comprises an electrode terminal
111
extending through and attached to the lid
16
of the battery can
1
. The electrode terminal
111
has a base end formed with a flange
112
. The hole in the lid
16
for the terminal
111
to extend therethrough has an insulating packing
113
fitted therein to provide electrical insulation and a seal between the lid
16
and fastening members. The terminal
111
has a washer
114
fitted therearound from outside the lid
16
, and a first nut
115
and a second nut
116
which are screwed thereon. The insulating packing
113
is clamped between the flange
112
of the terminal
Nakanishi Naoya
Nohma Toshiyuki
Satoh Kouichi
Yonezu Ikuo
Alejandro Raymond
Kalafut Stephen
Kubovcik & Kubovcik
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