▎ 摘　　要

NOVELTY - A positive electrode active material comprises a core portion having an average particle diameter of 3-30 mu m, an inner layer having a thickness of 2-80 nm, covering the core portion, and an outer layer having a thickness of 600-5000 nm, covering the inner layer. The core portion comprises secondary particles (P1) of a lithium complex oxide (I) or (II). The inner layer comprises a water-insoluble carbon powder chosen from graphite, graphene, carbon black, and carbon nanofibers. The outer layer comprises particles (P2) of lithium-based polyanion (III) or (IV), comprising carbon supported on the surface. The mass ratio of particles (P2) and particles (P1) is 5:95-55:45. USE - Positive electrode active material is used for multilayer-type lithium-ion secondary battery used as vehicle-mounted battery. ADVANTAGE - The positive electrode active material provides excellent battery characteristics and safety to the lithium-ion secondary battery, and can effectively suppress peeling of the lithium-based polyanion particles from the lithium composite oxide secondary particles, because it has a multilayer structure in which the lithium composite oxide secondary particles and lithium-based polyanion particles are strongly combined. The lithium-ion secondary battery has effective reduction in amount of metal elution and excellent capacity retention rate even when exposed to a high-temperature environment. DETAILED DESCRIPTION - A positive electrode active material comprises a core portion having an average particle diameter of 3-30 mu m, an inner layer having a thickness of 2-80 nm, covering the core portion, and an outer layer having a thickness of 600-5000 nm, covering the inner layer. The core portion comprises secondary particles (P1) of a lithium complex oxide of formula: LiNiaCobMncM1xO2 (I) or LiNidCoeAlfM2yO2 (II). The inner layer comprises a water-insoluble carbon powder chosen from graphite, graphene, carbon black, and carbon nanofibers. The outer layer comprises particles (P2) of lithium-based polyanion of formula: LigMnhFeiM3zPO4 (III) or Mnh'Fei'M3z'PO4 (IV), comprising carbon supported on the surface. The mass ratio of particles (P2) and particles (P1) is 5:95-55:45. M1 = Mg, Ti, Nb, Fe, Cr, Si, Al, Ga, V, Zn, Cu, Sr, Mo, Zr, Sn, Ta, W, La, Ce, Pb, Bi, and/or Ge; a = 0.3-1 (excluding 1); b,c = 0-0.7 (excluding 0); x = 0-0.3; 3a+3b+3c+(valence of M1)x x = 3; M2 = M1 excluding Al; d = 0.4-1 (excluding 1); e = 0-0.6 (excluding 0); f = 0-0.3 (excluding 0); y = 0-0.3; 3d+3e+3f+(valence of M2)x y = 3; M3 = Co, Ni, Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd; g,h,i,h',i', = 0-1.2 (excluding 0), where h+i and h'+i' are not 0; z,z' = 0-0.3;and g+(valence of Mn)x h+(valence of Fe)x i+(valence of M3)x z, (valence of Mn)x h'+(valence of Fe)x i'+(valence of M3)x z' = 3. An INDEPENDENT CLAIM is included for manufacture of the positive electrode active material, which involves obtaining a hydrothermal reaction product using a lithium compound and a metal compound containing an iron compound or a manganese compound, and a phosphoric acid compound, or a hydrothermal reaction product using the metal compound and phosphoric acid compound, mixing with a carbon source and spray-drying to obtain a granulated component made of particles (P2), adding the water-insoluble carbon powder to particles (P1) while mixing with an application of compressive force and shear force, and adding the granulated component.