Battery

1. A battery including:

a battery case having:

a case body member including an opening and an opening end portion defining this opening; and

a case lid member having a through hole formed through the case lid member and a peripheral edge portion joined to the opening end portion of the case body member to seal the opening;

a rivet engaged in the through hole, the rivet including:

a shaft portion inserted in the through hole; and

an outer flange continuous to the shaft portion on outside of the battery case, the outer flange being larger in diameter than the shaft portion; and

a gasket made in an annular form and of thermoplastic resin or rubber elastic material,

the gasket being interposed between and in close contact with a circumferential outer surface of an outer surface of the case lid member facing to the outside of the battery case, the circumferential outer surface being located around a peripheral edge of the through hole, and the outer flange of the rivet, to hermetically seal the through hole, the circumferential outer surface having a larger diameter than an outer diameter of the gasket,

wherein the case lid member is configured such that

the entire circumferential outer surface being in contact with the gasket is a uniform flat surface perpendicular to an axis line of the through hole and protrudes more outward than the peripheral edge portion in an axial outward direction facing outside along the axis line of the through hole, and the circumferential outer surface is positioned more outward in the axial outward direction facing outside along the axis line of the through hole than the peripheral edge portion and the opening end portion while the peripheral edge portion of the case lid member is joined to the opening end portion of the case body member, and

the case lid member comprises a stepped wall portion extending along the axis line between the peripheral edge portion and the circumferential outer surface so as to form a space between interior surfaces of the stepped wall portion, and

wherein a flange internal surface of the outer flange of the rivet facing the circumferential outer surface includes a contact portion contacting with the gasket, and

at least the contact portion of the flange internal surface is a flat surface perpendicular to the axis line.

2. The battery according to claim 1 , wherein

assuming that a first position is a position at which an outer-surface-side edge which is an edge contacting with the circumferential outer surface of an outer peripheral surface of the gasket interposed between the circumferential outer surface and the outer flange is visually identifiable when the battery case is observed from a radial outside of the axis line more than the battery case toward a radial inside of the axis line, and

assuming that a second position is a position at which an outer-flange-side edge which is an edge contacting with the outer flange of the outer peripheral surface of the gasket interposed between the circumferential outer surface and the outer flange is visually identifiable when the battery case is observed from a position on the radial outside of the axis line more than the battery case and at the same angle position in a circumferential direction of the axis line as the first position and more outward in the axial outward direction than the first position toward the radial inside of the axis line,

the case body member and the case lid member of the battery case and the outer flange of the rivet are configured such that the first position and the second position are present.

3. The battery according to claim 2 , wherein the outer flange of the rivet is configured to include a portion on a radial outside more than the outer-flange-side edge of the gasket so that the portion is positioned more outward in the axial outward direction than the outer-flange-side edge over an entire circumference.

4. The battery according to claim 1 , wherein the outer flange of the rivet is configured to include a portion on a radial outside more than the outer-flange-side edge of the gasket so that the portion is positioned more outward in the axial outward direction than the outer-flange-side edge over an entire circumference.

5. The battery according to claim 1 , wherein the battery case is configured such that the case lid member is inserted in the opening of the case body member.