Abstract: Provided are a lithium-manganese-nickel composite oxide carrying an organic phosphate with a high capacity and a high cycle characteristic when used as a positive electrode active material of a secondary battery, a method for producing the same, and also a nonaqueous electrolyte secondary battery using the lithium-manganese-nickel composite oxide as a positive electrode active material. The positive electrode active material for a nonaqueous electrolyte secondary battery, wherein an organic phosphite compound or an organic phosphate compound having an organic functional group composed of an alkyl group, an aryl group, and the like adheres to a part or the entire of a particle surface of the lithium-manganese-nickel composite oxide represented by general formula: LitMn2-x-yNixMyO4 (wherein 0.96<t?1.25, 0.40?x?0.60, 0?y?0.20, and M represents at least one element selected from Mg, Al, Si, Ti, Cr, Fe, Co, Cu and Zn).

Abstract: Provided are a lithium-manganese-nickel composite oxide carrying an organic phosphate with a high capacity and a high cycle characteristic when used as a positive electrode active material of a secondary battery, a method for producing the same, and also a nonaqueous electrolyte secondary battery using the lithium-manganese-nickel composite oxide as a positive electrode active material. The positive electrode active material for a nonaqueous electrolyte secondary battery, wherein an organic phosphite compound or an organic phosphate compound having an organic functional group composed of an alkyl group, an aryl group, and the like adheres to a part or the entire of a particle surface of the lithium-manganese-nickel composite oxide represented by general formula: LitMn2-x-yNixMyO4 (wherein 0.96<t?1.25, 0.40?x=0.60, 0?y?0.20, and M represents at least one element selected from Mg, Al, Si, Ti, Cr, Fe, Co, Cu and Zn).