POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY

Provided is a lithium transition metal oxide having an ±-NaFeO 2 layered crystal structure, as a cathode active material for lithium secondary battery, wherein the transition metal includes a blend of Ni and Mn, an average oxidation number of the transition metals except lithium is +3 or higher, and the lithium transition metal oxide satisfies Equations 1 and 2 below: 1.0 < m Ni / m Mn m �¢ Ni 2 + / Mn 4 + < 1 wherein m(Ni)/m(Mn) represents a molar ratio of nickel to manganese and m (Ni 2+ )/m(Mn 4+ ) represents a molar ratio of Ni 2+ to Mn 4+ . The cathode active material of the present invention has a uniform and stable layered structure through control of oxidation number of transition metals to a level higher than +3, in contrast to conventional cathode active materials, thus advantageously exerting improved overall electrochemical properties including electric capacity, in particular, superior high-rate charge/discharge characteristics.