Lithium manganate positive electrode material and preparation method thereof

The chemical formula of the lithium manganate positive electrode material is LiaAlbMn2-b-cBcO4-dFd, a is more than or equal to 0.96 and less than or equal to 1.15, b is more than 0 and less than or equal to 0.3, c is more than 0 and less than or equal to 0.03, and d is more than 0 and less than or equal to 0.03; the secondary particles are spherical, fluorine permeates into the spherical lithium manganate positive electrode material, and the fluorine content is distributed in a gradually decreasing gradient mode from the surfaces of the spherical lithium manganate positive electrode material particles to the centers of the spherical lithium manganate positive electrode material particles. The preparation method comprises the following steps: mixing a lithium source, a manganese source and a boron source, and performing primary sintering to obtain a lithium manganate positive electrode material precursor; and mixing with an aluminum source and a fluorine source, and carrying out secondary sintering to obtain t