Method of Preparing Positive Electrode Active Material Precursor, Positive Electrode Active Material Precursor, and Method of Preparing Positive Electrode Active Material Using the Positive Electrode Active Material Precursor

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

• (S1) performing a co-precipitation reaction on a transition metal solution containing nickel (Ni) and manganese (Mn) in the presence of a basic solution and an ammonium cationic complexing agent in a nitrogen atmosphere;
• and
• (S2) after the performing of the co-precipitation reaction, adding an ammonium cationic complexing agent and aging while maintaining the nitrogen atmosphere,
• wherein the ammonium cationic complexing agent during step (S2) is added such that a weight ratio of the ammonium cationic complexing agent during step (S1) to the ammonium cationic complexing agent during step (S2) is in a range of 1:0.5 to 1:3.5.