To provide a joining method capable of lessening poor welding and attaining stable welding results even though a collector becomes thinner in welding between a metal foil to be turned into a collector and a metal plate to be turned into a collector plate.

(1) A laminated structure 110 for making ends 111a of respective metal foils 111 locate outside rather than any of ends 112a of all insulating films 112 by alternately laminating the metal foils 111 and the insulating films 112 is produced so as to make the end 111a of the metal foil 111 locate outside rather than the end 112a of the insulating film 112. (2) A metal plate 120 is moved in the vertical direction until the metal plate 120 comes in contact with an end of the laminated structure 110, and the metal plate 120 is pushed to the laminated structure 110 while shifting the metal plate 120 in a laminating direction as the metal plate 120 comes in contact with an end of the laminated structure 110. (3) The ends 111a of the metal foils 111 and the metal plate 120 are welded while the ends 111a of the metal foils 111 are aligned and bent in the laminating direction.

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