Method of Preparing Positive Electrode Active Material for Lithium Secondary Battery and Positive Electrode Active Material Prepared by the Same

A method of preparing a positive electrode active material includes preparing a lithium transition metal oxide containing nickel in an amount of 60 mol % or more based on a total number of moles of metals excluding lithium, impregnating the lithium transition metal oxide with 300 ppm to 1,000 ppm of moisture based on 100 parts by weight of the lithium transition metal oxide, and performing a heat treatment on the lithium transition metal oxide impregnated with the moisture, wherein a lithium by-product present on a surface of the lithium transition metal oxide and the moisture react to form a passivation layer on the surface of the lithium transition metal oxide. A positive electrode active material prepared by the above-described preparation method, and a positive electrode and a lithium secondary battery which include the positive electrode active material are also provided.