Patent ID: 8323825

Claim:
A secondary battery comprising: an electrode assembly comprising a positive electrode plate, a negative electrode plate, and a separator interposed between the positive and negative electrode plates; a can to house the electrode assembly; and a cap assembly comprising a vent plate, to seal an opening of the can, wherein the vent plate comprises a concave deforming portion and a protrusion formed in the center of the deforming portion, wherein the protrusion has first and second surfaces opposing each other, wherein the first surface extends away from the electrode assembly, and wherein the second surface is concave along an axis defined by a ray originating at the electrode assembly; wherein the cap assembly further comprises a current interrupt device disposed on the vent plate; a positive temperature coefficient thermistor disposed on the current interrupt device; and a cap-up disposed on the positive temperature coefficient thermistor; wherein the current interrupt device is activated by the operation of the vent plate.