Positive Electrode Active Material, and Positive Electrode and Lithium Secondary Battery Including the Same

A positive electrode active material includes: (1) a lithium nickel-based transition metal oxide with a large particle diameter; and (2) a lithium nickel-based transition metal oxide with a small particle diameter. The lithium nickel-based transition metal oxide with a large particle diameter is in the form of a secondary particle that is an aggregate of primary particles. The lithium nickel-based transition metal oxide with a small particle diameter is in the form of a single particle formed of one nodule and/or a quasi-single particle that is a composite of 30 or less nodules. The lithium nickel-based transition metal oxide with a large particle diameter has a Dof 5 μm to 30 μm, and a Y value defined by the factors of the particle size distribution characteristics is 2.2 or less. The positive electrode active material is applied to a positive electrode to provide a lithium secondary battery.