PURPOSE: To make it possible to hold down increase in internal impedance during storage and to take out a large amount of current by adding expansive graphite to positive electrode active substance.

CONSTITUTION: Using a light metal such as lithium, sodium, etc., for a negative electrode active substance 3, and using an oxide of metal or fluoride of carbon for a positive electrode active substance 5, an organic solvent is used as an electrolyte with expansive graphite added to the positive electrode active substance 5. Since impurities contained in the electrolyte as represented by peroxide is adsorbed or partially decomposed with the expansive graphite and therefore the surface of the negative electrode active substance 3 is kept in an active condition, increase in short-circuit current and increase in internal resistance can be held down. This make it possible to take out a large amount of current and at the same time increase in internal impedance due to storage at high temperatures can be reduced.