To enhance adhesion between an electrode terminal and an armoring body and improve sealing performance and liquid-leakage resistance significantly by roughening the electrode terminal surface of a battery composed by laminating an outer insulation layer, an intermediate metal foil and the like, and using an armoring body of which thermoplastic resin layer to be bonded to the electrode terminal is surface treated.

The surface of an electrode terminal is roughened by chemical treatment by means of etching with acid, alkali or the like or mechanical processing by grinding the surface on a whetstone. At least a part of the surface of a thermoplastic resin to be abutted on the electrode terminal is processed by means of discharge, flame, ozone, ionizing active ray, or plasma treatment. The roughened electrode terminal is bonded to a battery cell composed of a positive electrode, a negative electrode and a separator, then the battery cell is covered with an armoring body formed from a layered product material having at least a metal layer, a thermoplastic resin and an insulating resin as constituents. and thereafter, a battery is finally formed by thermally welding and sealing it with the electrode terminal left outside. If corona discharge surface treatment is used, vapor phase treatment can be performed and thereby, productivity is improved.