Patent attributes
Active material particles of a lithium ion secondary battery includes at least a first lithium-nickel composite oxide: LixNi1-y-zCoyMezO2 (where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca) forming a core portion thereof. The surface layer portion of the active material particles includes nickel oxide having the NaCl-type crystal structure or a second lithium-nickel composite oxide, and further includes element M not forming the crystal structure of the first lithium-nickel composite oxide. Element M is at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn.