To provide a novel cathode active material for a lithium ion battery.

The cathode active material comprises a mixture that includes : (a) a lithium nickelate represented by an empirical formula of Lix4A*x5Ni(1-y4-z4)Coy4Qz4Oa, (wherein 0.1≤x4<1.3, 0≤x5≤0.2, 0≤y4≤0.2, 0≤z4 and about 0.2 or less, A* is either Ba, Mg or Ca, Q is either Al, Mn or B, and 1.5<a<2.1); and (b) one of (i) one of a lithium cobaltate including Li and Co modifiers, (wherein an Li modifier is one kind out of Mg and Na, a Co modifier is one kind out of Mg, Na, Al, Mn, B, Ti, and Ni) and a spinel of manganate salt and an olivine compound; and (ii) a lithium nickelate represented by an empirical formula of Lix3Ni1-z3M'z3O2, (wherein 0.05<x3<1.2, 0<z3<0.5, and M' is one or more than one elements out of Co, Mn, Al, B, Ti, Mg, Ca and Sr.).