Ferromanganese phosphate, preparation method thereof, positive electrode material and secondary battery

The invention provides a preparation method of ferromanganese phosphate, a manganese source, an iron source containing iron phosphate and/or iron phosphate dihydrate, a phosphorus source and the like are used as raw materials to prepare a seed crystal induction liquid, the seed crystal induction liquid is heated, NH4Fe (HPO4) 2 is generated in a system, the new biological phase can reduce the (Mn + Fe)/P ratio of a product in the system in the subsequent recrystallization process of the ferromanganese phosphate, and the yield of the ferromanganese phosphate is improved. And after the ammonium ferromanganese phosphate slurry is added for aging recrystallization treatment, ferromanganese phosphate with a proper (Mn + Fe)/P ratio can be obtained through post-treatment. According to the preparation method disclosed by the invention, the generation amount of a new phase can be regulated and controlled by controlling the use amounts of the iron phosphate and the iron phosphate dihydrate in the raw materials, so tha