Lithium manganese iron phosphate base material, positive electrode material, preparation methods of lithium manganese iron phosphate base material and positive electrode material and lithium battery

The invention discloses a lithium manganese iron phosphate base material, a positive electrode material, a preparation method of the positive electrode material and a lithium battery, and belongs to the technical field of lithium ion batteries. The preparation method of the lithium manganese iron phosphate base material comprises the following steps: dissolving soluble ferrous salt, soluble manganese salt, phosphoric acid and lithium hydroxide in deionized water for reaction to obtain a material A; filtering the material A, taking a filter cake, and drying to obtain a material B; and carrying out heat treatment on the material B in an inert gas atmosphere to obtain the lithium manganese iron phosphate base material, the surface of a carbon-free nanometer lithium manganese iron phosphate base material is coated with metal oxide or metal salt and carbon, so that a coating layer generated on the surface of the composite lithium manganese iron phosphate material prevents a lithium battery from reacting with an el