Patent ID: 8765305

Claim:
A method for preparing a composite cathode active material for a lithium secondary battery, the method comprising: producing a first lithium metal composite oxide by (a) precipitating a first metal composite hydroxide from a first mixture of a first metal precursor, a first aqueous ammonia solution and a first basic solution, and (b) mixing and reacting the first metal composite hydroxide with a first lithium precursor to form the first lithium metal composite oxide; producing a second lithium metal composite oxide by (a) precipitating a second metal composite hydroxide from a second mixture of a second metal precursor, a second aqueous ammonia solution and a second basic solution, and (b) mixing and reacting the second metal composite hydroxide with a second lithium precursor to form the second lithium metal composite oxide; and mixing the first and second lithium metal composite oxides in a ratio of 20:80 parts by weight, respectively, to form a composite cathode active material for a lithium secondary battery; wherein the first lithium metal composite oxide has a mean particle diameter that is greater than 60% but less than 90% of a mean particle diameter of the second lithium metal composite oxide; the first and second lithium metal composite oxides comprise a primary particle having a particle diameter distribution between about 0.1 μm and about 0.2 μm, and a secondary particle having a mean particle diameter distribution between about 10 μm and about 20 μm when the primary particles are aggregated to form the secondary particles; and the first lithium metal composite oxide has a formula LiNi 1−x′−y CO x′ M′ y O 2 P z ; the second lithium metal composite oxide has a formula selected from the group consisting of Li 1+δ [Ni x Mn x−y/2 Co 1−2x−z M y N z ]O 2−a P a and Li 1+δ [Ni x Mn x+y Co 1−2(x+y) M y ]O 2−a P a ; M is selected from the group consisting of Mg, Zn, Ca, Sr, Cu and Zr; M′ is selected from the group consisting of Al, Mg, Zr and Ti; N is selected from the group consisting of Fe, Al, Ga, In, Cr, Ge and Sn; P is selected from the group consisting of F and S; δ has a value such that -1/10≦δ≦1/10; x has a value such that 0.2≦x≦0.4; x′ has a value such that 0.1≦x′≦0.3; y has a value such that 0≦y≦1/10; z has a value such that 0≦z≦1/10; and a has a value such that 0≦a≦0.3.