Patent ID: 7981541

Claim:
A nonaqueous electrolyte secondary battery comprising: an external can opened at one end thereof; an electrode assembly contained in the external can, and comprising a negative electrode, a separator and a positive electrode; a nonaqueous electrolyte contained in the external can; and a sealing lid group tightly sealed at the opening of the external can by way of an insulating member, wherein the sealing lid group comprises a PTC element having a structure in which a resin sheet containing conductive carbon is interposed between a pair of electrodes composed of a metal thin film, a notch is formed at least in one of the pair of electrodes in the PTC element, and the notch has a minimum depth of at least 4% of a thickness of the at least one of the pair of electrodes and a maximum depth that extends through the at least one of the pair of electrodes into the resin sheet a depth of not more than 20% of the thickness of the resin sheet.