Method for producing positive electrode active material for lithium ion secondary batteries

A method for producing positive electrode active material for lithium ion secondary batteries, the method comprising:

• a mixing step of weighting and mixing a lithium carbonate and a compound containing respective metallic elements other than Li in Formula (1), LiαNixCoyM11-x-y-zM2zO2+β, so as to have a metallic constituent ratio of a composition formula in accordance with the Formula (1) to obtain a mixture,
• where values in the Formula (1) meet:
• 0.97≤α≤1.08, −0.1≤β0.1, 0.7<x≤0.9, 0.03≤y≤0.3, 0≤z≤0.1, and 0<1-x-y-z, M1 is at least one kind of an element selected from the group consisting of Mn and Al, and M2 is at least one kind of an element selected from the group consisting of Mg, Ti, Zr, Mo, and Nb;
• and
• a firing step of firing the mixture to obtain a lithium composite compound expressed by the Formula (1),
• wherein the firing step includes:
• a first precursor forming step of performing a heat treatment on the mixture at a heat treatment temperature of 200° C. or more and 400° C. or less for 0.5 hours or more and 5 hours or less to obtain a first precursor;
• a second precursor forming step of performing a heat treatment on the first precursor under an oxidizing atmosphere at a heat treatment temperature of 450° C. or more and 800° C. or less for 0.5 hours or more and 50 hours or less, the second precursor forming step reacting 92 mass % or more of the lithium carbonate to obtain a second precursor;
• and
• a finishing heat treatment step of performing a heat treatment on the second precursor under an oxidizing atmosphere at a heat treatment temperature of 755° C. or more and 900° C. or less for 0.5 hours or more and 50 hours or less to obtain the lithium composite compound.