Cylindrical secondary battery

摘要

A cylindrical secondary battery where safety can be secured even when an external pressure accompanying rapid deformation of the battery acts on the battery is provided in a battery having a large capacity. A lithium ion secondary battery has a capacity of 14Ah, where an upper lid is fixed to a battery can which receives an electrode winding group therein. The upper lid includes a diaphragm (2) formed with a rupturing valve and an upper lid cap whose peripheral edge portion is fixed to a peripheral edge portion of the diaphragm (2). The rupturing valve includes a rupturing groove (8) with a V-shaped section formed on a surface of the diaphragm (2) positioned on the side of the upper lid cap and a rupturing groove (18) with a U-shaped section formed on a surface of the diaphragm (2) positioned on the side of the electrode winding group so as to correspond to the position of the rupturing groove (8). The diaphragm (2) is inverted due to internal pressure rising in the battery so that a current is cut off. When an external force accompanying rapid deformation of the battery acts on the battery, force acting on the diaphragm (2) tends to concentrate on the rupturing groove (18).