Sulfur-based positive electrode active material, a positive electrode and a lithium ion secondary battery

PROBLEM TO BE SOLVED: To provide: a novel sulfur-based positive electrode active material by which a lithium ion secondary battery can be largely enhanced in cycle characteristic; a positive electrode including the positive electrode active material; and a lithium ion secondary battery including the positive electrode.SOLUTION: A sulfur-based positive electrode active material comprises: a carbon skeleton originating a polymer including a monomeric unit having a heteroatom-containing part; and sulfur taken into the carbon skeleton as the carbon skeleton is formed from the polymer by a thermal treatment. The heteroatom-containing part is a part having a group selected from: a univalent functional group including at least one heteroatom selected from O, S, P and N; a heterocyclic group including at least one heteroatom selected from O, S, P and N; and a group expressed by -S- (where a is an integer of 2-4).SELECTED DRAWING: None