Patent ID: 8852806

Claim:
A cathode active material for secondary batteries for reducing deintercalation of oxygen from a crystal structure at a high voltage of 4.3V to 4.6V through incorporation of excessive lithium in a cation layer composed of Ni and in a cation layer composed of Mn, the cathode active material being represented by Formula 1: (1− x )Li(Li a M′ b M 1−a−b )O 2 *x Li 2 M″O 3 (1) wherein 0<x<0.3; 0<a<0.2; 0≦b≦0.2; M is at least one element selected from Ni and Mn; M′ is a transition metal excluding Ni and Mn; and M″ is at least one element selected from Mn, Sn and Ti, wherein the compound of Formula 1 is a composite or solid solution with a layered structure.