A sealing gasket for a cylindrical alkaline battery,
- the alkaline battery including
- an annular positive electrode mixture,
- a cylindrical separator closed at a bottom, the separator disposed inside the positive electrode mixture,
- a negative electrode gel disposed inside the separator,
- a cylindrical battery can closed at a bottom and open at a top, the battery can having a cylinder axis in a vertical direction,
- a negative electrode terminal plate to be fitted in an opening end portion of the battery can, and
- a rod-shaped negative electrode current collector,
- the positive electrode mixture, the separator, and the negative electrode gel being housed in the cylindrical battery can as a power generation element,
- the sealing gasket configured to be incorporated in the alkaline battery to insulate the opening end portion of the battery can and the negative electrode terminal plate from each other,
- the sealing gasket comprising:
- assuming that an upper side and a lower side of the sealing gasket correspond to an upper side and a lower side of the battery can, respectively:
- a resin boss part formed in a hollow cylindrical shape in the vertical direction such that the negative electrode current collector can stand;
- a disc-shaped partition part coupled to an outer periphery of the boss part;
- an outer periphery part standing upward from an outer rim of the partition part;
- and
- a thin-walled portion formed in the partition part in a groove shape to be concentric with the boss part,
- the thin-walled portion being formed in a region opposed to the negative electrode gel in the partition part in a state where the sealing gasket is incorporated in the alkaline battery, the thin-walled portion being thinner than another region in the partition part,
- the thin-walled portion having a thickness such that the thin-walled portion fractures when a pressure inside the battery can reaches a predetermined pressure in the state where the sealing gasket is incorporated in the alkaline battery,
- the region opposed to the negative electrode gel in the partition part including an annular breakage region having a thickness of 0.3 mm or smaller,
- the breakage region having a projected area, when seen from the vertical direction, equal to or greater than 25% of a projected area of entirety of the region opposed to the negative electrode gel.