Cathode properties of amorphous and crystalline FePO₄

FePO₄ is an attractive rare-metal-free cathode active material. Simple and inexpensive new synthesis routes obtained from solution were investigated. P₂O₅ and Fe metal powders, both of which react in water at room temperature, were selected as inexpensive starting materials. Amorphous powders obtained through ball milling were annealed at various temperatures (100-650 °C) in air. IR spectra showed that PO ₄ tetrahedra units existed even in the amorphous matrix. XRD peaks of the trigonal FePO₄ phase appeared above 500 °C. Reversible Fe³⁺/Fe²⁺ redox reactions in the amorphous and crystalline FePO₄ were confirmed by ⁵⁷Fe Mössbauer spectroscopy. The heating temperature dependence of the cathode properties is reported.