Nickel manganese cobalt composite hydroxide, method for producing nickel manganese cobalt composite hydroxide, lithium nickel manganese cobalt composite oxide, and lithium ion secondary battery

A method for producing a nickel manganese cobalt composite hydroxide, which is a precursor of a positive electrode active material, and which is composed of secondary particles to which primary particles containing a nickel, a manganese, and a cobalt are aggregated, or composed of the primary particles and the secondary particles, comprising:

• a crystallization process for obtaining a transition metal composite hydroxide by crystallizing in a reaction solution obtained by adding a raw material solution containing a nickel, a manganese, and a cobalt, a solution containing an ammonium ion supplier, and an alkaline solution;
• and
• a washing process for washing the transition metal composite hydroxide obtained in the crystallization process by a washing liquid,
• wherein the alkaline solution in the crystallization process is a mixed solution of an alkali metal hydroxide and a carbonate,
• a ratio [CO32−]/[OH−] of the carbonate with respect to the alkali metal hydroxide in the mixed solution is 0.002 to 0.050,
• a crystallization is performed by switching an atmosphere in two stages of an oxidizing atmosphere and a non-oxidizing atmosphere in the crystallization process, and
• the washing liquid in the washing process is an ammonium hydrogen carbonate solution with a concentration of 0.05 mol/L or more.