Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-11-30
2002-04-30
Chaney, Carol (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S162000, C429S094000
Reexamination Certificate
active
06379403
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to coating techniques of an electrode sheet of a non-aqueous cell, capable of improving productivity, providing a high discharge potential, and stabilizing a cell life time.
b) Description of the Related Art
In the course of developments on electronic apparatuses using secondary cells as their power sources, demands for a high capacity of secondary cells are rapidly expanding. To meet the requirement of high capacity, lithium secondary cells are being developed in place of nickel cadmium cells and nickel hydrogen cells. As compared to conventional secondary cells, although lithium secondary cells have already a higher capacity, a much higher capacity is still desired. In addition to developments on electrode materials, increasing the amount of electrode materials filled in a cell can has been studied in order to realize high capacity cells. Approaches to increasing the amount of electrode materials include an increased amount of electrode material capable of being coated and a reduced void factor of electrode material through pressing a coated electrode sheet.
FIG. 3
is a cross sectional view of a conventional electrode sheet taken along its longitudinal direction. Generally, an electrode sheet has depolarizing mix layers
52
a
and
52
b
formed on both sides of a current collector
51
by coating liquid containing electrode material (hereinafter called depolarizing mix coating liquid). The total thickness of the depolarizing mix layers
52
a
and
52
b
is greater than that of the current collector
51
, and the void factor of the depolarizing mix layers
52
a
and
52
b
after pressing is controlled in a range of 10% to 30%.
Conventional electrode sheets are, however, associated with some problems during manufacture, such as breaking and cutting off electrode sheets at a pressing process. At this pressing process, while an electrode sheet is transported by press rollers in the direction indicated by an arrow
53
, a portion of the current collector
51
not coated with electrode depolarizing mix is pressed and then a portion of the current collector
51
covered with the depolarizing mix layers
52
a
and
52
b
is pressed. The thickness of the electrode sheet to be pressed changes from that of only the current collector
51
to that of all the current collector
51
and depolarizing mix layers
52
a
and
62
b
. This thickness change is acute and severe to such an extend that the current collector
51
is broken at a thickness change portion
54
.
With such a steep thickness change, it is difficult to form a uniform circle at the winding start portion (portion of the current collector
51
not covered with depolarizing mix layers) of the electrode sheet and a separator wound together at a cell assembly process. Therefore, the final coiled assembly of an electrode sheet and a separator becomes likely to have a deformed cross section.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an electrode sheet capable of reducing manufacture troubles such as breakage of the electrode sheet during an electrode manufacture process.
It is a second object of the present invention to provide an electrode sheet capable of providing an improved circularity of a coiled assembly of an electrode sheet and a separator.
It is a third object of the present invention to provide a high capacity secondary cell using the electrode sheet as above.
According to one aspect of the present invention, there is provided an electrode sheet having a current collector coated with electrode depolarizing mix on both upper and lower surfaces of the current collector, wherein: the electrode sheet has a portion of the current collector not coated with the electrode depolarizing mix; and the electrode depolarizing mix coated ends on both the upper and lower surfaces of the current collector are shifted by 0.3 mm or longer and 30 mm or shorter in a longitudinal direction of the electrode sheet.
By shifting the electrode depolarizing mix coated ends on both the front and back surfaces by 0.3 mm or longer and 30 mm or shorter, electrode sheets can be manufactured at high productivity.
REFERENCES:
patent: 4333994 (1982-06-01), Urry
patent: 4783384 (1988-11-01), Van Beek et al.
patent: 5106707 (1992-04-01), Catotti et al.
patent: 5508122 (1996-04-01), Narukawa et al.
patent: 5554460 (1996-09-01), Wu et al.
patent: 5989743 (1999-11-01), Yamashita
patent: 6051333 (2000-04-01), Nagai et al.
patent: 6193765 (2001-02-01), Nakanishi et al.
patent: WO 96/10273 (1996-04-01), None
Fukumura Kenichi
Tanaka Mitsutoshi
Tomiyama Hideki
Chaney Carol
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
Tsang-Foster Susy
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