Preparation method of high-purity battery-grade anhydrous iron phosphate

The invention discloses a preparation method of high-purity battery-grade anhydrous iron phosphate; the method includes the following steps: firstly, preparing a phosphoric acid solution, dissolving ferrous salt slowly in an acid solution, then adding an oxidant, carrying out oxidation, and finally, slowly adding a sodium phosphate solution, or firstly adding the sodium phosphate solution, then slowly adding the oxidant, carrying out oxidation, then heating, and carrying out a reaction to obtain a precipitate, namely iron phosphate dihydrate; and cleaning the iron phosphate dihydrate, filtering, dehydrating, and thus obtaining anhydrous ferric phosphate. The washing discharge solution is a sodium sulfate (mirabilite) solution, and is recycled and crystallized to form an additional solid product.