| 摘要 |
A lithium ion secondary cell has an electrode group comprising (1) a winding core, (2) a positive electrode composed of a positive electrode core member and a positive electrode active material layer supported on the positive electrode core member, (3) a negative electrode composed of a negative electrode core member and a negative electrode active material layer supported on the negative electrode core member, and (4) a porous film formed at least on one of the positive and negative electrodes. The porous film is composed of a filler and a binder, and the positive and negative electrodes are wound on the winding core. At a portion near the winding-start end of the positive and/or negative electrode, a region where an active material layer is supported only on one side of the core member is provided. Further, at a portion nearer the winding-start end than the above region, a region where no active material layer is supported on both sides of the core member is provided. Since the electrode group has such a structure, the damage to the porous film can be reduced, and its safety can be improved. |
