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

A positive electrode active material for a secondary battery which includes a lithium composite transition metal oxide including nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium composite transition metal oxide has a layered crystal structure of space group R3m, includes the nickel (Ni) in an amount of 60 mol % or less based on a total amount of transition metals, includes the cobalt (Co) in an amount greater than an amount of the manganese (Mn), and is composed of single particles.