Patent ID: 8309249

Claim:
A lithium-ion secondary battery comprising: a battery element comprising a separator, and an electrode-stacked body having a first electrode and a second electrode disposed respectively on both surfaces of the separator in a stacking direction; and an exterior package covering the battery element, the exterior package comprising a first package member located at one side of the battery element in the stacking direction, and a second package member located at an other side of the battery element in the stacking direction, wherein the first and second package members each comprises a central portion and an outer peripheral portion disposed around the central portion and are joined to each other at the outer peripheral portions thereof, wherein a linear expansion coefficient α1 of the first package member is greater than a linear expansion coefficient α2 of the second package member, wherein an average thickness d1 and a Young's modulus s1 of the first package member, and an average thickness d2 and a Young's modulus s2 of the second package member satisfy a relation of d1×s1<d2×s2, and wherein the second package member comprises an extra margin that is a region of the central portion of the second package member and is bent in an inward direction or an outward direction of the secondary battery so that the extra margin extends to allow the first package member to expand freely.