Sanyo Electric Co., Ltd.

Shigeki Fujii

Hironori Marubayashi

Takuma Morishita

Yoshihiro Tobita

Yosihiro Tobita

A cell according to the present invention comprises a positive electrode, a negative electrode, an electrolyte solution, and an outer casing, wherein the outer casing comprises a valve platehaving a thickness, an annular-shaped break grooveformed on the valve plate, and one or more of break aiding groovesin the inner area of the break groove, and wherein the break aiding groove comprises such configurations that remaining thickness of the valve plate at the break aiding groove is thicker than remaining thickness of the valve plate at the break groove, and at least one end of the break aiding groove is connected with the break groove. In a cell provided with a valve plate which is a safety valvecomprising the break groove and the break aiding groove, the safety valve operates smoothly and releases a gas inside the cell quickly, and resistance to dropping impact is improved.

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Hyogo, Japan

Shigeki Fujii