Positive electrode active material, positive electrode and lithium battery including positive electrode active material

A positive electrode active material includes first and second lithium nickel complex oxides wherein said first lithium nickel complex oxide has a particle volume distribution of 3.0 µm ≤ D25 ≤ 10.0 µm, 5.0 µm ≤ D50 ≤ 20.0 µm, and 10.0 µm ≤ D75 ≤ 25.0 µm, and said second lithium nickel complex oxide has a particle volume distribution of 0.01 µm ≤ D25 ≤ 5.0 µm, 1.0 µm ≤ D50 ≤ 10.0 µm, and 5.0 µm ≤ D75 ≤ 15.0 µm. A positive electrode and lithium battery include the positive active material. The positive active material, and the lithium battery including the positive active material have increased filling density, are thermally stable, and have improved capacity.