Lithium manganese iron phosphate composite material as well as preparation method and application thereof

The invention relates to the field of lithium ion battery positive electrode materials, in particular to a lithium manganese iron phosphate composite material and a preparation method and application thereof. The method comprises the following steps: carrying out first washing on precipitation slurry; aging the primary washing filter cake; carrying out second washing on the reaction system after aging is finished; mixing the first clear liquid with an iron source; mixing the first mixed system with ammonia water, and carrying out a first reaction; mixing the reaction system after the first reaction and the second clear liquid, and then carrying out a second reaction; performing third washing on the precursor suspension to obtain a lithium manganese iron phosphate precursor; mixing a lithium source, a carbon source, the lithium manganese iron phosphate precursor and the primary washing filter cake, and then carrying out hydrothermal reaction; and carrying out fourth washing, drying and sintering on the reactio