RECTANGULAR SECONDARY BATTERY

A prismatic secondary battery (C1) according to the present invention is provided in order to prevent the mixing of metallic foreign matters into the battery due to spatter caused in a process of welding a battery case (1) and a cover (6) together. The prismatic secondary battery (C1) according to the present invention achieving the above object comprises a battery case (1) in a prismatic shape and a battery cover (6) which seals up an opening part (1a) of the battery case (1). The battery cover (6) has a convex part (51) which projects toward the inside of the battery case (1), faces an inner surface of a side wall part (21) of the battery case (1), and extends continuously along the entire periphery of the side wall part (21). Cover thickness (Tu) of a contact part (52) of the battery cover (6) which is in contact with the upper end of the side wall part (21) of the battery case (1) at a position outside the convex part (51) is greater than 1/2 of cover thickness (Tt) of a blockage part (54) blocking up the opening part (1a) at a position inside the convex part (51) and is less than the cover thickness Tt of the blockage part (54).