PURPOSE: To maintain stable properties for a long duration by setting an electrode using a highly corrosion-resistant carbon carrier in a single cell at high average temperature and an electrode using a low corrosion-resistant carbon barrier in a single cell at low average temperature.

CONSTITUTION: A highly corrosion-resistant carbon A having narrow crystal lattice distance is used for a single cell 5 located in the center part in layered direction where the average temperature becomes the highest as high as 190-205°C at the operation time and a carbon C having relatively low corrosion resistance and wide crystal lattice distance is used for a single cell 5 located near cooling plates 6 and a carbon B having the middle values is used for a single cell 5 located between them. In this way, the operation temperature is made different in three layeres and the corrosion resistance of the carbon carriers are made different, so that unevenness of deterioration speeds among single cells according to the layered position or the location in the cells by the operation temperature is suppressed and independently of the locations almost the same deterioration speeds are obtained as the battery output is changed as time being.