Examples of a more preferred active material include a lithium manganese composite oxide (e.g., Li_xMn₂O₄), 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-nickel composite oxide having a spinel structure (e.g., Li_xMn_2-yNi_yO₄), a lithium manganese cobalt composite oxide (e.g., Li_xMn_yCo_1-yO₂), lithium iron phosphate (e.g., Li_xFePO₄), 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. These active materials enable a high positive electrode potential to be obtained.

When a nonaqueous electrolyte containing room temperature molten salt is used, it is preferable to use lithium iron phosphate, li_xVPO₄F, a lithium manganese composite oxide, a lithium nickel composite oxide, and a lithium nickel cobalt composite oxide from the viewpoint of cycle life. This is because the reactivity of the positive electrode active material with room temperature molten salt is decreased.

The kind of the active material may be one kind or two kinds or more.