Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-06-07
2001-03-06
Maples, John S. (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S211000
Reexamination Certificate
active
06197074
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a lithium battery in which a current collector and an electrode external terminal are connected electrically by an electrode tab, and specifically relates to a lithium battery having a reduced electric resistance between the electrode tab and the current collector.
BACKGROUND OF THE INVENTION
Development of a secondary battery having high energy density and free from environmental pollution has lately been required.
A conventional manufacturing method of a lithium secondary battery is explained below in conjunction with
FIGS. 8
to
10
. Since the steps to manufacture a negative electrode and a positive electrode are the same, only the steps to manufacture the positive electrode are explained below.
In
FIG. 10
, a positive electrode (
40
) and a negative electrode (
50
) are wound as spiral coils with a separator (
60
) interposed therebetween, and are housed in a battery can (
61
). The positive electrode (
40
) is connected to a positive electrode external terminal (
42
) through a positive electrode tab (
41
). The negative electrode (
50
) is also connected to a negative electrode external terminal (
52
) through a negative electrode tab (
51
). An insulating packing (
65
) comprising a pair of insulators (
63
) and (
64
) is inserted at connected areas of a sealing board (
62
) and the positive electrode external terminal (
42
) and a sealing board (
62
) and the negative electrode external terminal (
52
). The insulating packing (
65
) is fastened by a pair of nuts (
66
) from both sides, i.e. upper and bottom, and is fixed to make the lithium secondary battery airtight.
FIG. 8
illustrates a positive electrode tab (
41
) joined to a positive electrode (
40
) in a conventional lithium secondary battery. The positive electrode (
40
) includes a current collector (
48
) having coated portions on both surfaces of active material layers (
47
) comprising an active material, an electrically conductive filler, and the like, and uncoated portions (
49
) provided at regular intervals. A positive electrode tab (
41
) is joined to an uncoated position on the surface of the current collector (
48
) at an end portion of the positive electrode tab (
41
).
A method of joining positive electrode tab (
41
) to positive electrode (
40
) is concretely explained below in conjunction with FIG.
9
. The uncoated portion (
49
) and the positive electrode tab (
41
) are placed together as shown in FIG.
9
(
a
), and are joined to each other by spot-welding. At this stage, the current collector (
48
) and the positive electrode tab (
41
) are joined only at portions where electricity passed during spot-welding, and remaining portions are not joined as shown in FIG.
9
(
b
). Pressure is applied to the current collector (
48
) and the positive electrode tab (
41
) at the joint area vertically by a pressing machine to increase the contact area and to reduce contact resistance between the current collector and the positive electrode tab.
A conventional current collector and electrode tab are formed by rolling, and the surface of the electrode tab is a so-called rolled finished surface (
44
). Portions of the electrode tab which are not joined by spot-welding become separated, or detached, after the pressing process by so-called elastic reset as shown in FIG.
9
(
c
). This causes a reduction in the contact area, increases internal resistance of the battery which is caused by contact resistance, and reduces output at high current discharge and reduces discharge capacity of the battery.
It has been disclosed that a contact area of a electrode active material and a current collector can be increased to reduce contact resistance and to improve output property (Japanese Patent Laid-open Hei 8-195202). However, contact resistance between an electrode tab and a current collector has not been reduced.
OBJECT OF THE INVENTION
An object of the present invention is to increase contact area between a electrode tab and a current collector and to reduce contact resistance between them, and to provide a lithium battery having improved discharge capacity at high electric current discharge and improved power.
SUMMARY OF THE INVENTION
A lithium battery of the present invention is characterized in that it comprises electrodes formed of an active material layer, the active material being capable of occluding and discharging lithium electrochemically, provided on the surface of a current collector, electrode external terminals for providing electricity to the outside of the battery, and an electrode tab joined at an end thereof to a surface of said current collector and being connected at another end thereof to said electrode external terminal, wherein said electrode tab has a roughened surface at the end joined to said current collector, and said roughened surface is welded to the surface of said current collector.
Peaks on the roughened surface of the electrode tab push in the surface of the current collector. Contact area of the electrode tab and the current collector increases and contact resistance is reduced. Therefore, a lithium battery having such an electrode tab has a smaller internal resistance as compared to a conventional battery, has improved discharge capacity at high electric current discharge and an improved output property.
The roughened surface of the electrode tab can be produced by chemical etching, abrasion by an abrasive, abrasion by ultrasonic waves or by blasting with an abrasive. Chemical etching useful for this invention is for example, acid treatment. As an abrasive, sandpaper, an abrasive material, can be illustrated. Abrasion by blasting is preferred because of simplicity and control of surface roughness.
The electrode tab and the current collector can be welded by spot-welding, ultrasonic welding, high frequency welding and the like.
A method of manufacturing a lithium battery which has electrodes formed of an active material layer provided on the surface of a current collector, the active material being capable of occluding and discharging lithium electrochemically, electrode external terminals to provide electricity to the outside of the battery, and electrode tabs joined at an end thereof to the surface of said current collector and being connected at the other end thereof to an electrode external terminal, comprises
a step to roughen the surface of said electrode tab;
a step to place said electrode tab in contact with said current collector with the roughened surface of said electrode tab facing the surface of said current collector, and to weld the electrode tab and current collector together; and
a step to apply pressure to said electrode tab and said current collector in the direction of contact, and to pressure weld.
A method of manufacturing a lithium battery of the invention is explained below in conjunction with FIG.
2
. The explanation below is directed to a positive electrode (
10
) and a positive electrode tab (
11
). However, negative electrode (
20
) and negative electrode tab (
21
) can also be prepared in the same manner.
The following is an illustration of forming a roughened surface by blasting and of joining the blast finished electrode tab and current collector.
In a step of blasting, an abrasive is blasted against the surface of the positive electrode tab (
11
) to roughen the surface and to form a blast finished surface (
13
). In a following step of connecting, the positive electrode tab (
11
) having peaks and valleys formed on the surface, i.e., roughened, and a positive electrode (
10
) are stacked together so that the blast finishing surface (
13
) faces the surface of an uncoated portion (
19
) of a current collector (
18
) as shown in FIG.
2
(
a
). The positive electrode tab (
11
) is joined to the current collector (
18
) by spot-welding. Further, the positive electrode (
11
) and the current collector are pressed together as shown in FIG.
2
(
c
). After the pressure is released, the positive electrode tab (
11
) tries to separate from the current collector by elastic reset. However, peaks of th
Chikano Yoshito
Nishio Koji
Nogami Mitsuzou
Ookita Kazunari
Satou Kouichi
Kubovcik & Kubovcik
Maples John S.
Sanyo Electric Co,. Ltd.
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