To provide a collector for a secondary battery difficult to cut even if excessive charging is applied to the secondary battery.
This collector for a secondary battery is formed out of metal foil. Disengagement energy of the metal foil is 1.0×104-1.0×107 J/m3. The release energy of the metal foil is obtained by converting a work volume required in a time span from a starting point of breaking to a cutting point when the metal foil is subjected to a tensile test to a value per unit volume. In order to obtain such metal foil having this disengagement energy, when the average thickness of the metal foil in its width direction is set for (t0), it is preferably formed so as to have a thickness of 1.03 (t0) at an at least one location in the width direction. In the collector of such metal foil, partial breaking is caused by excessive charging, however, in many cases, it does not get to the cutting point. Accordingly, when it is discharged after excessively charged, it is not easily disconnected and stable discharge becomes possible.
TAKAGI JUNICHI
EGUCHI TATSUO
NIPPON FOIL MFG