Method for producing positive electrode active material

A method for producing a positive electrode active material, the method comprising the steps of:

• (1) mixing an activation agent containing at least one type of compound selected from the group consisting of a potassium compound and a sodium compound with an electrode material mixture which contains a positive electrode active material, a binder, and an electrolyte and from which at least a part of the electrolyte has been removed by contact with an electrolyte cleaning solvent, to obtain a mixture;
• (2) heating the obtained mixture to a retention temperature equal to or higher than a melting start temperature of the activation agent to activate the positive electrode active material contained in the obtained mixture;
• and
• (3) bringing the mixture after heating into contact with a water-containing liquid to obtain a slurry containing a solid component and a liquid component, and then separating the slurry into a solid component and a liquid component, in which a total content of potassium and sodium in the liquid component after separation is 0.090 to 2.0 mass % and a total content of potassium and sodium in the solid component after separation is 1.2 mass % or less.