Rechargeable battery and method for molding insulator

1. A rechargeable battery comprising:

a battery case that includes an open end and accommodates a power generating element;

a cover that closes the open end of the battery case, wherein the cover includes an upper surface, a lower surface, a through hole that extends between the upper surface and the lower surface, and an inner wall that defines the through hole;

a gasket that includes a tubular contact portion arranged on the inner wall of the cover, a through hole defined by the tubular contact portion, and a planar portion that is continuous with the tubular contact portion and arranged on the lower surface of the cover;

an insulator arranged on the upper surface of the cover, wherein the insulator includes an upper surface, a lower surface, and a through hole that extends between the upper surface and the lower surface and is in communication with the through hole of the gasket;

an external terminal arranged on the upper surface of the insulator, wherein the external terminal includes an upper surface, a lower surface, a through hole that extends between the upper surface and the lower surface and is in communication with the through hole of the insulator, and an inner wall that defines the through hole of the external terminal;

a power collection terminal that extends through the through hole of the gasket, the through hole of the insulator, and the through hole of the external terminal to supply power from the power generating element to the external terminal; and

an annular sealing member held between the lower surface of the cover and the planar portion of the gasket at an outer side of the tubular contact portion of the gasket, wherein

the insulator is a resin-molded component,

the inner wall of the insulator includes a lower open end, an upper open end, and a central portion located between the lower open end and the upper open end,

at least one of the lower open end and the upper open end of the inner wall of the insulator has a larger diameter than the central portion of the inner wall of the insulator, and

the diameter of the at least one of the lower open end and the upper open end is larger than a diameter of the through hole of the gasket and smaller than an inner diameter of the sealing member.

2. The rechargeable battery according to claim 1 , wherein the diameter of the at least one of the lower open end and the upper open end is smaller than or equal to an outer diameter of the tubular contact portion of the gasket.

3. The rechargeable battery according to claim 1 , wherein a step is formed between the central portion and the at least one of the lower open end and the upper open end.

4. The rechargeable battery according to claim 1 , wherein the inner wall of the insulator includes a tapered surface that narrows from the at least one of the lower open end and the upper open end toward a center of the through hole of the insulator.

5. The rechargeable battery according to claim 1 , wherein the lower open end of the inner wall of the insulator has a larger diameter than the central portion of the inner wall of the insulator.

6. The rechargeable battery according to claim 1 , wherein the resin is one of nylon (PA) and polyphenylene sulfide (PPS).

7. The rechargeable battery according to claim 1 , wherein

the inner wall of the cover includes a lower open end, and

the cover includes the sealing member at the lower open end of the inner wall.