The present disclosure suppresses, by uniformly coating lithium transition metal composite oxide particles with LiwNbxOy (1≤w≤8, 1≤x≤13, 1≤y≤20), a direct contact between a positive electrode active material and a liquid electrolyte and thereby suppresses a side reaction between the positive electrode active material and the liquid electrolyte, and improves stability at high temperatures and high voltages, and in particular, is effective in enhancing battery performance by forming Li2O—Nb2O5 through reacting the coating layer with Li present on the surfaces of the lithium transition metal composite oxide particles.