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

A positive electrode active material of the present disclosure includes lithium nickel-based oxide particles in which a molar ratio of nickel among total transition metals ranges from about 50 mol % to 70 mol %, and a coating layer formed on a surface of the lithium nickel-based oxide particles and including cobalt. The lithium nickel-based oxide particles are in a single particle form having one nodule, or a quasi-single-particle form that is a composite of 30 or fewer nodules, and the full width at half maximum (FWHM) of the (104) peak measured by X-ray diffraction (XRD) analysis of the positive-electrode active material ranges from 0.078 to 0.082.