Positive Electrode Active Material For Lithium Secondary Battery, Method Of Preparing The Same, And Positive Electrode For Lithium Secondary Battery And Lithium Secondary Battery Which Include The Positive Electrode Active Material

A method of preparing a positive electrode active material, the method comprising:

• preparing a first transition metal-containing solution including a nickel raw material and a second transition metal-containing solution having a transition metal concentration different from that of the first transition metal-containing solution and including the nickel raw material, a cobalt raw material, and a manganese raw material;
• preparing a positive electrode active material precursor by mixing the first transition metal-containing solution and the second transition metal-containing solution while gradually changing a mixing ratio of the first transition metal-containing solution to the second transition metal-containing solution;
• and
• mixing the positive electrode active material precursor with a lithium-containing raw material to form a mixture and sintering the mixture to synthesize the positive electrode active material,
• wherein the preparing of the positive electrode active material precursor is controlled such that a pH is gradually decreased as a nickel content in the mixed solution is reduced.