Preparation method for positive electrode active material, and positive electrode active material

For overcoming the problems of irregular shape, uneven element distribution and partial agglomeration of metal elements of a positive electrode active material prepared by a method in the prior art, the invention provides a preparation method for the positive electrode active material, comprising the steps of S1, mixing a reaction seed crystal with a complexing agent solution, wherein the reaction seed crystal is hydroxide of one or more of nickel, cobalt, manganese or aluminum; and the D50 of the reaction seed crystal is less than or equal to 2-6 [mu]m; S2, under a condition of stirring and ultrasonic processing, adding a metal salt solution and a precipitator solution, regulating PH to 9-13; and then washing and drying to obtain a precursor, wherein the metal salt solution is a solution containing nickel salt, cobalt salt, manganese salt and aluminum salt; and S3, mixing the precursor with a lithium source, performing heat preservation at a temperature of 500-950 DEG C for 2-24h, and cooling. Meanwhile, the invention also discloses the positive electrode active material prepared by the method. The positive electrode active material provided by the invention is regular in shape, high in degree of sphericity, uniform in element distribution and free of partial agglomeration of metal elements; and in addition, the positive electrode active material is high in cycling performance, thermal stability and security.