in a secondary cell which generates a direct current when the positive electrode complex and the negative electrode complex thereof conduct a reversible redox reaction in the presence of an electrolyte , the positive electrode complex and the negative electrode complex are in a combination selected from the group consisting of lead / chromium complex , chromium complex / aluminum complex , and manganese complex / zinc complex . the secondary cell has relatively high capacitance and can be manufactured at low cost . moreover , it provides more stable chemical reactions and can therefore be stably charged / discharged with large current and without risk of explosion .