Patent ID: 8679672

Claim:
A flat battery shaped in a coin extending in a radial direction, comprising: an exterior can having a cylinder with a bottom, the cylinder having a sidewall, and an opening edge provided on one end of the cylinder, the bottom provided on the other end of the cylinder; a seal can having a space formed therein, the seal can comprising: a flat portion having a peripheral edge; a first cylinder portion downward extended from the peripheral edge; a stepped portion below the first cylinder portion; a second cylinder portion below the stepped portion, the second cylinder portion extending straight downward, the second cylinder portion having a radius larger than that of the first cylinder portion; an opening edge portion located at a lower edge of the second cylinder portion extending straight downward; and the space formed between the flat portion and the bottom, wherein the second cylinder portion of the seal can is fitted within the sidewall of the exterior can such that the opening edge of the sidewall of the exterior can is engaged with the stepped portion of the seal can, a gasket molded between the second cylinder portion and the sidewall, the gasket extending inside the seal can around the opening edge portion extended to the flat portion, wherein the gasket has an inner surface exposing to the space, wherein the inner surface has a first angle and a second angle below the first angle, wherein the first angle is convex to the space, and the second angle is concave to the space, wherein both of the first angle and the second angle are located between a first portion and a second portion, the first portion corresponding to a part of the inner surface at the same level in the radial direction of the stepped portion, the second portion corresponding to a part of the inner surface at the same level in the radial direction of the opening edge portion, wherein the thickness of the gasket between the opening edge portion and the second portion is smaller than the thickness of the gasket in the radial direction between the second cylinder portion and the second portion.