Patent ID: 8795897

Claim:
A cathode active material comprising a lithium mixed transition metal oxide having a composition represented by Formula I: Li x M y O 2 (I) wherein: M=M′ 1−k A k , wherein M′ is Ni 1−a−b (Ni 1/2 Mn 1/2 ) a Co b , 0.65≦a+b≦0.85 and 0.1≦b≦0.4; A is a dopant; 0≦k<0.05; and x+y=2 and 0.95≦x≦1.05, wherein the lithium mixed transition metal oxide has a Li 2 CO 3 content of less than 0.07% by weight of the cathode active material as determined by pH titration, and is prepared by a solid-state reaction of Li 2 CO 3 and a mixed transition metal precursor under an oxygen-deficient atmosphere, wherein the solid-state reaction includes a sintering process at 600° C. to 1100° C. for 3 to 20 hours, and wherein an amount of air exceeding 2 m 3 /kg of Li x M y O 2 during the sintering process is supplied to a reaction vessel equipped with a heat exchanger for pre-warming of the air.