Matsushita Electric Industrial Co., Ltd.

Kazuo Omine

Toshio Yoshida

The present invention provides a flat cell that employs strip-shaped electrode plates on which an active material layer has been formed by coating paste or by electrolytic deposition on both sides or one side of a core material consisting of a metal foil. By constructing an electrode group having an oval cross section by spirally winding in a manner folding, a strip-shaped positive plate having a striped recessed portion of a predetermined width of which the center is positioned on the line of folding formed on the active material layer at least the inner side of at least the inner-most folded portion close to a core portion, and a strip-shaped negative plate with a separator interposed, reduction in the battery capacity due to breakage of the electrode plates and/or peeling off and dropping of the active material layers and failure due to internal short circuit as has previously been caused when assembling an electrode group having an oval cross section can be completely eliminated, thus drastically improving the reliability of flat cells, especially flat type lithium-ion secondary batteries.

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Osaka, Japan

Kazuo Omine