POSITIVE ELECTRODE ACTIVE MATERIAL AND PREPARATION METHOD THEREOF

A positive electrode active material and a preparation method thereof. The positive electrode active material includes a secondary particle composed of primary particles; and the primary particle includes LiFeMnA(PO), where −0.1≤a≤0.4, 0.5≤x≤0.7, 0≤y≤0.01, A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, or Y, and the positive electrode active material has a crystallinity of not less than 98%. The positive electrode active material has high crystallinity, and the ionic conductivity and electronic conductivity thereof are high. Applying the positive electrode active material to a lithium-ion battery can significantly improve the rate performance of the battery.