FePO₄ as a positive electrode material for lithium secondary batteries

Amorphous hydrated iron (III) phosphate was prepared by spontaneous precipitation from aqueous solution of FeCl₃ and Na₃PO₄ under control pH. The material was characterized by chemical analysis, thermal analysis, X-ray diffraction and scanning electron microscopy. The as prepared amorphous FePO₄·1.3H₂O which delivered an initial capacity of up to 130 mA·h·g^-1 at a current density of 0.2 mA·cm^-2 with good rechargeability, appears to be a promising candidate to positive electrode materials for lithium batteries. However, the crystalline hexagonal FePO₄ which was obtained by heating the amorphous hydrate at 700°C exhibits a lower capacity. Ball-milling could improve the electrochemical performance of the products due to more active materials content. The loss of capacity for materials formed at high temperature could be related to the formation of inactive phases of Fe₃PO at 500°C and Fe₃P_2.93O_19.17 at 700°C.