Patent ID: 8802255

Claim:
A secondary battery, comprising: an electrode assembly; a can to contain the electrode assembly; a cap assembly including a cap plate attached to an open upper side of the can; a depression, arranged on either the cap plate or the can, the depression having a thickness less than a thickness of other portions of the cap plate or the can where the depression is arranged; and the depression further comprising: a flat section positioned within the center of the depression, the flat section being entirely flat and lying in a geometric plane of the cap plate; a rupture section entirely contained within the flat section having a thickness less than a thickness of other portions of the depression; and wrinkles entirely surrounding the flat section and arranged between and coupled to the flat section and a periphery of the depression, said flat section being of greater width than said wrinkles and said wrinkle having a height greater than a height of the flat section, wherein the rupture section has a “>--<” shape along an inner side of the wrinkles; and wherein the cap plate or the can has an upper and a lower side, the lower side being closer to an inner portion of the battery, wherein the depression is formed at the lower side; and wherein the wrinkles have a convex shape only, protruding outward from the cap plate or the can where the depression is arranged.