The present invention relates to a lithium-ion battery. The lithium-ion battery comprises a positive electrode containing, as a principal component, a lithium oxide having a layered rock-salt structure and represented by chemical formula: LixM1yM2zO2-d. In this chemical formula, 1.16≦x≦1.32, 0.33≦y≦0.63, 0.06≦z≦0.50, M1 represents a metal ion selected from Mn, Ti and Zr, or a mixture thereof, and M2 represents a metal ion selected from Fe, Co, Ni and Mn, or a mixture thereof. The lithium-ion battery also comprises a negative electrode containing, as a principal component, a material capable of intercalating/deintercalating lithium ions, wherein peroxide ion(s) (O22−) are contained in the positive electrode.