POSITIVE ELECTRODE ACTIVE MATERIAL FOR SECONDARY BATTERY, AND SECONDARY BATTERY

The positive electrode active material for a secondary battery includes a lithium-transition metal composite oxide. The lithium-transition metal composite oxide is represented by the general formula Li[LiMnCoMe]O (in the formula, Me is at least one selected from Ni, Fe, Ti, Bi, and Nb, 0.5 < α < 1, 0.05 < x < 0.25, 0.4 < y < 0.7, 0 < z < 0.25) and has a crystal structure of O2 structure. The particle size distribution of the lithium-transition metal composite oxide has a first peak on the small particle size side and a second peak on the large particle size side.