The invention provides a secondary battery with high reliability. The secondary battery includes an electrode assembly including a positive electrode plate and a negative electrode plate, a rectangular exterior body having an opening and containing the electrode assembly, a sealing plate 2 that seals the opening in the rectangular exterior body, and a negative electrode terminal 9 electrically connected to the negative electrode plate and attached to the sealing plate 2. In the method for producing the secondary battery, a first negative-electrode current collector (8a) and a second negative-electrode current collector (8b) are welded to each other by irradiation of an energy ray. At least one of the first and second negative-electrode current collectors (8a, 8b) is provided with a rough surface portion. The first and second negative-electrode current collectors (8a, 8b) are welded together by irradiating the rough surface portion with an energy ray.