Patent ID: 7462421

Claim:
A lithium ion secondary battery comprising: a positive electrode including a positive electrode active material comprising a lithium-containing composite oxide, a conductive material and a binder; a negative electrode; and a non-aqueous electrolyte, wherein said lithium-containing composite oxide has a structure of lithium cobaltate where Co atoms are partially substituted by Na and/or K atoms and is represented by the chemical formula: Li a (Co 1-x-y Mg x Al y ) b M z O c where M is at least one element selected from the group consisting of Na and K, and the values a, b, c, x, y and z respectively satisfy 0≦a≦1.05, 0.005≦x≦0.15, 0.0001≦y≦0.01, 0.0002≦z≦0.008, 0.85≦b≦1.1 and 1.8≦c≦2.1.