▎ 摘　　要

NOVELTY - Lithium-ion secondary battery has positive electrode comprising a positive electrode active material. The positive electrode active material comprises a first region, a second region, a third region, and a fourth region. The first region (101) comprises a composite oxide containing lithium and a first transition metal. The second region (102) comprises lithium, aluminum, oxygen, and a second transition metal. The third region (103) comprises magnesium and oxygen. The fourth region (104) is a covering film which suppresses excessive reaction with electrolytic solution. The first region and the second region each comprises a layered rock-salt crystal structure. The third region comprises a rock-salt crystal structure. The first transition metal is cobalt, manganese, and nickel. The positive electrode active material comprises a region where a portion of the third region overlaps with a portion of the second region. USE - Lithium-ion secondary battery for use in portable information terminals such as mobile phone, smartphone, laptop computer, portable music player, and digital camera ADVANTAGE - The lithium-ion secondary battery has high output and high capacity, excellent charge and discharge characteristic, highly safe or highly reliable secondary battery, improves cycle performance, safe operation under a variety of environment, and longer-term reliability. DETAILED DESCRIPTION - Lithium-ion secondary battery has positive electrode comprising a positive electrode active material. The positive electrode active material comprises a first region, a second region, a third region, and a fourth region. The first region (101) comprises a composite oxide containing lithium and a first transition metal. The second region (102) comprises lithium, aluminum, oxygen, and a second transition metal. The third region (103) comprises magnesium and oxygen. The fourth region (104) is a covering film which suppresses excessive reaction with electrolytic solution. The first region and the second region each comprises a layered rock-salt crystal structure. The third region comprises a rock-salt crystal structure. The first transition metal is cobalt, manganese, and nickel. The positive electrode active material comprises a region where a portion of the third region overlaps with a portion of the second region. The fourth region is in contact with at least a portion of the third region, the fourth region being on a surface side. The crystal orientation of the layered rock-salt crystal structure in the second region is substantially aligned with a crystal orientation of the rock-salt crystal structure in the third region. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the lithium-ion secondary battery. First region (101) Second region (102) Third region (103) Fourth region (104)