| 摘要 |
PROBLEM TO BE SOLVED: To provide a secondary battery for appropriately discharging a gas and capable of using a plurality of cells by suppressing the expansion of an installation space and securing an excellent heat radiating effect. SOLUTION: A wound electrode body 3 of an Li ion secondary battery 1 is pressed and made flat so as to have an almost elliptic cross-section. Since joining degree of each member (a positive electrode sheet, a negative electrode sheet and a separator) at long diameter side portions 22 of the wound electrode 3 is loosened according to the pressed degree of short diameter side parts 21, gaps 23 are formed at the side parts 22. The gas generated inside the electrode 3 due to overcharge or the like is guided outside the electrode 3 and the gas is not retained in the electrode 3. Since the gas generated in a battery case 2 appropriately acts on an safety valve, and the valve is opened when the gas pressure (the inner pressure of the battery case 2) reaches a prescribed pressure, the generated gas is well discharged outside the battery case 2 and the safety can be improved. COPYRIGHT: (C)2005,JPO&NCIPI
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