Sealing gasket for cylindrical alkaline battery and cylindrical alkaline battery

A cylindrical alkaline battery comprising:

• 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;
• a negative electrode terminal plate fitted in an opening end portion of the battery can;
• and
• a rod-shaped negative electrode current collector,
• the positive electrode mixture, the separator, the negative electrode gel being housed in the cylindrical battery can as a power generation element,
• the negative electrode terminal plate being fitted in the opening end portion of the battery can, with a sealing gasket interposed therebetween to insulate the opening end portion of the battery can and the negative electrode terminal plate from each other,
• wherein the sealing gasket includes:
• an upper side and a lower side corresponding 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 upright by being press-fitted into the boss part;
• a disc-shaped partition part coupled to an outer periphery of the boss part;
• an outer periphery part projecting upward from an outer rim of the partition part;
• and
• an annular thin-walled portion formed in the partition part, the annular thin-walled portion having a groove shape and encircling the boss part so as 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, the thin-walled portion being a portion of reduced thickness thinner than another region in the partition part,
• the region opposed to the negative electrode gel in the partition part including an annular breakage region formed around the outer periphery of the boss part, with the thin-walled portion formed around the outer periphery of the breakage region,
• the breakage region having a thickness greater than a thickness of the thin-walled portion and occupying at least 25% of a projected area of entirety of the region opposed to the negative electrode gel when viewed from the vertical direction, wherein the thin-walled portion has a thickness such that the thin-walled portion fractures when a pressure inside the battery can reaches a predetermined pressure, such that substantially the entire breakage region ruptures thereby preventing the negative electrode gel from contacting the positive electrode mixture,
• the entirety of the region opposed to the negative electrode gel excluding the thin-walled portion has a constant thickness,
• the breakage region has a thickness of 0.3 mm or less but greater than 0.2 mm and the thin-walled portion has a thickness of 0.15-0.2 mm, and
• the region opposed to the negative electrode gel is bent at an angle to the separator.