Positive Electrode Active Material, Method of Preparing the Positive Electrode Active Material, and Positive Electrode and Lithium Secondary Battery Which Include the Positive Electrode Active Material

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

• preparing a transition metal hydroxide which contains nickel in an amount of 60 mol % or more based on a total number of moles of transition metals and does not contain cobalt;
• mixing the transition metal hydroxide and a lithium raw material and sintering the mixture;
• and
• mixing a cobalt raw material in an amount such that an amount of the cobalt in a finally prepared positive electrode active material is in a range of greater than 0 ppm to 6,000 ppm or less in the mixing of the transition metal hydroxide and the lithium raw material and the sintering of the mixture, or after the sintering.

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

• preparing a transition metal aqueous solution containing a nickel raw material and a cobalt raw material;
• preparing a transition metal hydroxide by a co-precipitation reaction of the transition metal aqueous solution;
• and
• mixing the transition metal hydroxide and a lithium raw material and sintering the mixture,
• wherein the nickel raw material is included in an amount such that an atomic ratio of nickel is 60 mol % or more based on a total number of moles of transition metals in the transition metal aqueous solution, and
• the cobalt raw material is mixed in an amount such that an amount of cobalt in a finally prepared positive electrode active material is in a range of greater than 0 ppm to 6,000 ppm or less.