Positive Electrode Active Material for Secondary Battery, Method of Preparing the Same, and Lithium Secondary Battery Including the Positive Electrode Active Material

A method of preparing a positive electrode active material for a secondary battery includes preparing a precursor of a composite transition metal oxide compound represented by Formula 1, and mixing the precursor, a lithium source, and a doping element source and sintering the mixture to form a doped lithium composite transition metal oxide, wherein the doping element source is a hydroxide-based compound. NiCoM(OH) [Formula wherein, Mis at least one element selected from the group consisting of manganese (Mn) and aluminum (Al), and 0