A negative electrode terminal includes a flange, and a connection portion disposed on a first surface of the flange. The connection portion is inserted into a terminal attachment hole. The negative electrode terminal includes a first area made of aluminium or an aluminium alloy, and a second area made of copper or a copper alloy. In the flange, the second area is disposed adjacent to the first surface, and the first area is disposed adjacent to the second surface. A boundary between the first area and the second area is disposed between the first surface and the second surface. A thinnest portion of the first area of the flange in the thickness direction of the flange has a thickness of larger than or equal to 0.3 mm. An external electroconductive member made of aluminium or an aluminium alloy is welded to the flange to form a welded portion.