Method of preparing material for lithium secondary battery of high performance

A method for preparing a lithium mixed transition metal oxide for a cathode active material, comprising subjecting a mixture of Li2CO3 and a mixed transition metal precursor to a solid-state reaction under an oxygen-deficient atmosphere having an oxygen concentration of 10 to 50% by volume;

• and forming a powdered lithium mixed transition metal oxide having a composition represented by Formula I:
• LixMyO2 (I)
• wherein:
• M=M′1−kAk, wherein M′ is Ni1−a−b(Ni1/2Mn1/2)aCob, 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 Li2Co3 content of less than 0.07% by weight of the cathode active material, the lithium mixed transition metal oxide being substantially free of water soluble bases such that less than 20 ml of 0.1M HCl is necessary to titrate 200 ml of a solution containing substantially all of the soluble bases present in 10 g of the lithium mixed transition metal oxide to a pH less than 5, the solution being prepared by repeated soaking and decanting of the lithium mixed transition metal oxide, and the solid-state reaction is a single heat treatment of the mixture.