Patent ID: 8197968

Claim:
A cathode active material containing: a lithium cobalt composite oxide containing lithium, cobalt, a first element, and a second element; a first sub-component element; and a second sub-component element, wherein said first element is at least one kind selected from the group consisting of aluminum, chromium, vanadium, manganese, and iron, said second element is at least one kind selected from the group consisting of magnesium and calcium, said first sub-component element is at least one kind selected from the group consisting of titanium, zirconium, and hafnium, said second sub-component element is at least one kind selected from the group consisting of silicon, germanium, and tin, when a composition of cobalt is expressed as a, a composition of the first element as b, and a composition of the second element as c, mole ratios of cobalt, the first element, and the second element in said lithium cobalt composite oxide lie within ranges of 0.9≦a≦1, 0.001≦b≦0.05, and 0.001≦c≦0.05, respectively, a content of said first sub-component element lies within a range from 0.01 mol % or more to 10 mol % or less as a ratio of said first sub-component element to cobalt in said lithium cobalt composite oxide, and a content of said second sub-component element lies within a range from 0.01 mol % or more to 10 mol % or less as a ratio of said second sub-component element to cobalt in said lithium cobalt composite oxide, wherein at least some of said first sub-component element exists in a crystal grain boundary of the lithium cobalt composite oxide as a first compound selected from the group consisting of: a compound containing oxygen, and a compound containing oxygen and lithium; and at least some of said second sub-component element exists in a crystal grain boundary of the lithium cobalt composite oxide as a second compound selected from the group consisting of: a compound containing oxygen, and a compound containing oxygen and lithium.