Provided is a flat battery with a molded gasket extending from the opening edge of the seal can to the flat portion, where the gasket may be prevented from exfoliating from the inner surface of the seal can. A flat battery ( 1 ) includes: a negative electrode can ( 10 ) (exterior can) shaped as a cylinder with a bottom; a positive electrode can ( 20 ) (seal can) having a peripheral wall ( 22 ) (cylinder portion) and a flat portion ( 21 ), the positive electrode can being disposed as an inverted dish with respect to the negative electrode can ( 10 ); and a gasket ( 30 ) molded at least on an inner surface of the positive electrode can ( 20 ), extending from the opening edge of the peripheral wall ( 22 ) to the flat portion ( 21 ). The opening edge of the sidewall of the negative electrode can ( 10 ) is fitted onto the stepped portion ( 22 c ) of the positive electrode can ( 20 ), and a portion of the gasket ( 30 ) that is located inside the opening edge portion of the peripheral wall ( 22 ) of the positive electrode can ( 20 ) with respect to the positive electrode can has a thickness smaller than that of a portion of the gasket that is located inside the stepped portion ( 22 c ) of the positive electrode can ( 20 ) with respect to the positive electrode can.
1. 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.
2. The flat battery according to claim 1 , wherein:
in the radial direction inside the seal can, the gasket is tapered such that a surface thereof approaches the second cylinder portion as it goes toward the opening edge portion.
3. The flat battery according to claim 1 , wherein:
the seal can has a round portion on the peripheral edge of the flat portion for connecting the flat portion with the first cylinder portion in a curved surface, and
wherein inside the seal can, the gasket contacts the flat portion and the round portion.
4. The flat battery according to claim 3 , wherein:
the portion of the gasket located close to the flat portion of the seal can has a thickness that allows it to extend from the round portion to the flat portion of the seal can.
5. The flat battery according to claim 1 , wherein:
an electrode assembly formed by stacking a positive electrode and a negative electrode, each shaped as a plate, in an alternating manner in a thickness direction is disposed in the space formed between the exterior can and the seal can.
6. The flat battery according to claim 1 , wherein:
the gasket is formed outside the second cylinder portion of the seal can so as to be sandwiched by the sidewall of the exterior can and the second cylinder portion of the seal can when the exterior can and the seal can are combined with each other, and
a portion of the gasket that is located outside the second cylinder portion and close to the opening edge portion has a thickness smaller than that of a portion thereof that is located outside the second cylinder portion and close to the stepped portion before the exterior can is fitted onto the seal can.
7. The flat battery according to claim 6 , wherein:
the gasket is molded outside the second cylinder portion of the seal can, extending from the opening edge portion of the cylinder portion to the stepped portion.
8. The flat battery according to claim 1 , wherein:
the gasket inside the seal can has an uneven portion located between the stepped portion and the opening edge portion of the cylinder portion,
wherein in the radial direction inside the seal can, the portion of the gasket that is located inside the opening edge portion of the cylinder portion has a smaller thickness than that of the portion of the gasket that is located inside second cylinder portion just below the stepped portion.
9. The flat battery according to claim 1 , wherein the first angle and the second angle constitute an uneven portion.