Usable examples of the active material include oxides, sulfides, and polymers. Examples of the oxides and sulfides include manganese dioxide capable of absorbing lithium (MnO₂), iron oxide, copper oxide, nickel oxide, a lithium manganese composite oxide (e.g., Li_xMn₂O₄ or Li_xMnO₂), a lithium nickel composite oxide (e.g., Li_xNiO₂), a lithium cobalt composite oxide (e.g., Li_xCoO₂), a lithium nickel cobalt composite oxide (e.g., LiNi_1-yCo_yO₂), a lithium manganese cobalt composite oxide (e.g., Li_xMn_yCo_1-yO₂), a lithium-manganese-nickel composite oxide having a spinel structure (e.g., LixMn_2-yNi_yO₄), a lithium phosphorus oxide having an olivine structure (e.g., Li_xFePO₄, Li_xFe_1-yMn_yPO₄, Li_xCoPO₄), iron sulfate [Fe₂(SO₄)₃], a vanadium oxide (e.g., V₂O₅), and a lithium nickel cobalt manganese composite oxide. In the above formula, x is more than 0 and 1 or less and y is more than 0 and 1 or less.

As the polymer, for example, conductive polymer materials such as polyaniline and polypyrrole, or disulfide-based polymer materials can be used. Sulfur (S) and carbon fluoride can also be used as the active material.