Positive electrode active material and preparation method therefor, positive electrode, and lithium ion secondary battery

A positive electrode active material, comprising a lithium nickel manganese oxide modified material and a coating layer on the surface of the lithium nickel manganese oxide modified material;

• the coating layer is composed of an inorganic compound, with the inorganic compound being any one or more selected from oxides, fluorides, phosphides, and borides;
• the lithium nickel manganese oxide modified material is a primary particle with a core-shell-like structure comprising a spinel phase and a rocksalt-like structure phase, with the spinel phase being an inner core, and the rocksalt-like structure phase being distributed on the surface of the spinel phase to form an outer shell;
• the spinel phase is a spinel-structured lithium nickel manganese oxide;
• the rocksalt-like structure phase is formed by inducing the spinel-structured lithium nickel manganese oxide and the rocksalt-like structure phase contains at least one of Mg, Zn, Ni, Mn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Sr, Al, Nb, B, Si, F and S as a site occupying element, with the site occupying element occupying the 16c or 8a site of the spinel structure;
• and
• the rocksalt-like structure phase is further doped with a phosphorus element, with the phosphorus element being distributed in a gradient concentration from the outer surface to the interior of the rocksalt-like structure phase, forming a phosphorus gradient doping layer.