Conventional structures of energy storage devices including batteries such as lithium-ion batteries include wound electrode assemblies formed by winding a positive electrode, a negative electrode, and a separator which are alternately layered. In energy storage devices having such wound electrode assemblies, the separator is fixed at a winding end point on the outermost layer of the wound electrode assembly. The separator is fixed, for example, by thermal bonding or with tape. Here, thermal bonding is preferred as a fixing method in terms of durability within the internal environment of the battery and impact on battery performance.
For example, in Patent Literature 1 (PTL 1) (Japanese Unexamined Patent Application Publication No. 11-250873), a separator which protrudes out beyond an end surface of the wound electrode assembly that is perpendicular to the winding axis is fixed by being bonded with a seal of the battery case made from a laminate sheet.