Lithium supplement material and preparation method thereof, positive electrode material and secondary battery

The invention discloses a lithium supplementing material and a preparation method thereof, a positive electrode material and a secondary battery, the lithium supplementing material comprises an inner core and a coating layer, the inner core comprises a lithium-rich material, the lithium-rich material is of a high decomposition voltage type, the lithium decomposition potential of the lithium-rich material is greater than or equal to 4.2 V, the coating layer coats the outer surface of the inner core, and the coating layer comprises in-situ generated boron acylate. The structure of the lithium supplementing material can effectively reduce the particle size of the whole material, so that the lithium decomposition potential is reduced; the coating layer and the inner core form an integrated structure, the stability of the lithium supplementing material can be guaranteed, the boron acylate further modifies the lithium-rich material, the electrochemical activity of the lithium-rich material in the inner core can be