The positive electrode active material for a lithium ion secondary battery, its production method and a lithium ion secondary battery

An object of the present invention is to provide a lithium ion secondary battery having both the cycle characteristics and high energy density and high rate characteristics when using a layered compound at a high potential. A core portion made of lithium-metal composite oxide, made of different lithium-metal composite oxide in composition and said core portion, the positive electrode for a lithium ion secondary battery comprising particles and a surface layer portion provided on a surface of the core portion and an active material, and the core portion and the surface layer portion provided with both layered structure, the surface layer portion, Ni, wherein Mn and Li, and wherein the Ni / Mn molar ratio of the surface is less than 1 the positive electrode active material for lithium ion secondary battery to be.