| abstract |
(57) [Problem] To provide a lithium transition metal composite oxide for a positive electrode active material, which can constitute a lithium secondary battery having a small increase in internal resistance even when stored for a long time in a high charge state. SOLUTION: A primary particle of a lithium transition metal composite oxide is aggregated to form a secondary particle, the average particle diameter of the primary particle is 1 μm or more and 3 μm or less, and a composition formula Li Ni x Co y Al z O 2 (x + y + z = 1, 0.1 ≦ z ≦ Represented by 0.2), the main crystal structure is a layered rock salt structure of a hexagonal system, Li belonging to the space group P4 2 1 2 in that part It has a subphase having an AlO 2 structure. |