Positive Electrode Active Material For Lithium Secondary Battery, Method of Preparing the same, and Positive Electrode for Lithium Secondary Battery and Lithium Secondary Battery which include the positive Electrode Active Material

The present invention relates to a positive electrode active material, which includes a lithium transition metal oxide having an average composition represented by Formula 1 in which a cobalt content in the lithium transition metal oxide is less than a manganese content, wherein at least one of nickel, cobalt, and manganese in the lithium transition metal oxide has a concentration gradient that gradually changes from a center of a particle to a surface thereof, the positive electrode active material is in the form of a secondary particle formed by agglomeration of primary particles, and a ratio in which angles between c-axis directions, which are measured at at least 8 points on a surface of the positive electrode active material by TEM analysis, and a growth direction of the particle at the measuring point satisfy 85° to 95° is 60% or more, a method of preparing the positive electrode active material, and a positive electrode for a lithium secondary battery and a lithium secondary battery which include the positive electrode active material: LiNiCoMnMO [Formula 1]