Positive electrode active material for non-Aqueous electrolyte secondary battery, non-Aqueous electrolyte secondary battery, and method for producing positive electrode active material for non-aqueous electrolyte secondary battery

A method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery, the method including:

• a step of oxidizing and roasting a hydroxide containing at least Ni obtained by a crystallization method to provide a composite oxide;
• a step of mixing the composite oxide with a lithium compound and firing the mixed particles to provide a lithium transition metal composite oxide;
• and
• a step of washing the lithium transition metal composite oxide with water, thereafter mixing the composite oxide with at least one selected from magnesium sulfate, zirconium sulfate, and cobalt sulfate, and heat-treating the mixture under a vacuum condition at a temperature of 150 to 280° C.,
• the lithium transition metal composite oxide containing 80 mol % or more of Ni with respect to the total number of moles of metal elements excluding Li and containing at least one metal element selected from Co, Mn, Al, W, Mg, Mo, Nb, Ti, Si, and Zr,
• wherein when 250 mg of the positive electrode active material is added to 10 mL of a 17.5% by mass hydrochloric acid aqueous solution, heated and dissolved at 90° C. for 2 hours and then diluted to 50 mL, an amount of S dissolved in the diluted filtrate of the suspension is 0.002 mmol or more as determined by inductively coupled plasma mass spectrometry.