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

The present disclosure relates to a positive electrode active material including: a lithium nickel-based transition metal oxide with a large particle diameter and 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 a secondary particle. The lithium nickel-based transition metal oxide with a small particle diameter is 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, a Z value defined by factors of roundness distribution characteristics of 1.0 to 9.0, and a negative skewness factor (NSF) of 0.1 to 0.9. Use of the positive electrode active material in a lithium secondary battery results in improved lifespan and/or output characteristics of the battery.