Patent ID: 7771863

Claim:
A cylindrical secondary battery that is provided with a mechanism for cutting off a current due to inversion of a diaphragm caused by internal pressure rising, the diaphragm being formed with a rupturing valve, wherein the rupturing valve is formed with a groove with a V-shaped section on a surface of the diaphragm opposite to a surface thereof on which an internal pressure acts and a groove with a U-shaped section is formed on the surface on which the internal pressure acts so as to correspond to a position where the groove with a V-shaped section is formed, wherein the groove with a V-shaped section is formed by combining a ring-like curved groove and a straight groove whose one end crosses the curved groove, the other end of the straight groove being positioned on the side of an outer periphery of the diaphragm, and the other end of the straight groove is smaller in depth than the one end thereof.