Solid electrolyte battery having reduced sized electrodes

Details Solid electrolyte battery having reduced sized electrodes Solid electrolyte battery having reduced sized electrodes

2000-02-16

2002-04-23

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S094000, C429S127000, C429S128000, C429S162000, C429S300000

Reexamination Certificate

active

06376128

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a solid electrolyte battery in which a positive electrode and a negative electrode are layered together with the interposition of a solid electrolyte.
2. Description of the Prior Art
Recently, portable electronic equipments, such as camera built-in tape recorder, portable telephone or a notebook type personal computer, have made their debut, and attempts are being made to reduce their size or weight. The batteries, as portable power sources for these electronic equipments, are also required to be small in size and weight. As batteries capable of meeting this demand, lithium ion batteries have been developed and put to commercial use. In these lithium ion batteries, a porous high molecular separator, having an electrolytic solution immersed therein, is used as an ion conductor arranged between the positive and negative electrodes. The entire battery is packaged in a massive metal vessel in order to prevent leakage of the electrolytic solution.
On the other hand, with a solid electrolyte battery, having a solid electrolyte as an ion conductor between the positive and negative electrodes, and in which there is no fear of liquid leakage, reduction in size and weight of the battery may be expected to be realized by package simplification. In particular, a high molecular solid electrolyte, in which is solid-dissolved a lithium salt, or a gel-like solid electrolyte, containing an electrolytic solution in a matrix polymer, is attracting attention.
This solid electrolyte battery may be manufactured in a manner now explained.
FIG. 1
shows a layered electrode assembly
5
comprised of positive electrodes
2
and negative electrodes
3
layered together with the interposition of solid electrolyte layers.
As for the positive electrode
2
, a positive electrode mixture, containing an active material for the positive electrode, an electrifying agent and a binder, is coated evenly on both surfaces of a positive electrode current collector
2
a
and dried in situ to form active material layers
2
b
for the positive electrode. After drying, the resulting dried product is pressed by a roll press to produce a positive electrode sheet.
As for the negative electrode
3
, a negative electrode mixture, containing an active material for the negative electrode and a binder, is coated evenly on both surfaces of a negative electrode current collector
3
a
and dried in situ to form active material layers
3
b
for the positive electrode. After drying, the resulting dried product is pressed by a roll press to produce a negative electrode sheet.
As for the solid electrolyte layers
12
, a sol-like electrolytic solution, containing a non-aqueous solvent, an electrolyte salt and a matrix polymer, is evenly coated on both surfaces of the positive electrode sheet and the negative electrode sheet and dried in situ to remove the solvent. This forms the gel-like solid electrolyte layers
12
on the active material layers
2
b
for the positive electrode and on the active material layers
3
b
for the positive electrode.
The positive electrode sheet, now carrying the solid electrolyte layers
12
, is sliced into e.g. rectangular strips. The portions of the solid electrolyte layers
12
and the active material layers
2
b
for the positive electrode which prove lead welding portions are then scraped off. In these portions, leads are welded to form the positive electrode
2
carrying the solid electrolyte layers
12
.
The negative electrode sheet, now carrying the solid electrolyte layers
12
, is sliced into e.g. rectangular strips. The portions of the solid electrolyte layers
12
and the active material layers
3
b
for the negative electrode which prove lead welding portions are then scraped off. In these portions, leads are welded to form the negative electrode
3
carrying the solid electrolyte layers
12
.
Finally, the positive electrode
2
and the negative electrode
3
, now carrying the solid electrolyte layers
12
, are layered together to form the layered electrode assembly
5
shown in FIG.
1
. This layered electrode assembly
5
is clinched by an external film and the outer rim portion of the external film is thermally fused under reduced pressure and sealed to encapsulate an electrode coil in the external film to complete the solid electrolyte battery.
In the above-described solid electrolyte battery, it is effective to reduce the thickness of the solid electrolyte layers
12
to improve the energy density. However, if the thickness of the solid electrolyte layers
12
is reduced, the solid electrolyte layers
12
are susceptible to breakage under an impact from outside, thus possibly leading to internal shorting. Thus, the thickness of the solid electrolyte layers
12
cannot be reduced to frustrate efforts in improving the energy density.
One of the reasons the internal shorting increases with the tendency towards a thinner thickness of the solid electrolyte layers
12
may be such that, with the conventional solid electrolyte battery, the ends of the positive electrode
2
and the negative electrode
3
are exposed at the ends of the layered electrode assembly
5
, so that, when the layered electrode assembly
5
is to be hermetically sealed in the external film, an external pressure is applied to the layered electrode assembly
5
, with the result that the end of the negative electrode
3
is bent at the end of the layered electrode assembly
5
to cause shorting thereof with the positive electrode
2
. The thinner the thickness of the solid electrolyte layers
12
, the smaller becomes the separation between the positive electrode
2
and the negative electrode
3
and hence the larger becomes the possibility of shorting.
Another problem caused by the thinner thickness of the solid electrolyte layers
12
is powder debris from the electrode surface. When layering the electrodes together, powders of the active material of the electrodes or of the metal collector descend to be clinched between the electrodes. If the solid electrolyte layers
12
are of reduced thickness, minute holes are produced in the solid electrolyte layers
12
to cause internal shorting. This powder debris occurs most outstandingly on the positive electrode
2
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a solid electrolyte battery of high energy density in which internal shorting is prevented from occurring.
The present invention provides a solid electrolyte battery including a positive electrode, a negative electrode arranged facing said positive electrode and a solid electrolyte layer formed at least on at least one of the major surfaces of the positive and negative electrodes. The positive and negative electrodes are layered with the major surfaces thereof carrying the solid electrolyte layers facing each other. One of the positive and negative electrodes is smaller than the other of the positive and negative electrodes. The solid electrolyte layer formed on the smaller electrode is larger than the smaller electrode.
In the solid electrolyte battery according to the present invention, the solid electrolyte layers formed on the smaller one of the positive and negative electrodes is larger than the smaller electrode, the end of the smaller electrode is covered by the solid electrolyte layers to prevent the positive and negative electrodes from being contacted with each other at the electrode ends and consequent shorting.
Thus, with the present invention, internal shorting can be prevented from occurring despite reduced thickness of the solid electrolyte layers, thus realizing a superior solid electrolyte battery having a high energy density.


REFERENCES:
patent: 5770331 (1998-06-01), Olsen et al.
patent: 6190426 (2001-02-01), Thibault et al.

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