Material for lithium secondary battery of high performance

Provided is a lithium mixed transition metal oxide having a composition represented by Formula I of Li x MyO 2 (m, x and y are as defined in the specification), wherein lithium ions intercalate into and deintercalate from mixed transition metal oxide layers ("MO layers") and some of the MO layer-derived Ni ions are inserted into intercalation/deintercalation layers of lithium ions ("reversible lithium layers") thereby resulting in the interconnection between the MO layers. The lithium mixed transition metal oxide of the present invention has a stable layered structure and therefore exhibits improved stability of the crystal structure upon charge/discharge. In addition, a battery comprising such a cathode active material can exhibit a high capacity and a high cycle stability. Further, such a lithium mixed transition metal oxide is substantially free of water-soluble bases, and thereby can provide excellent storage stability, decreased gas evolution and consequently superior high-temperature stability with the feasibility of low-cost mass production.