Reactivity,stability and electrochemical behavior of lithium iron phosphates

LiFePO₄ is a potential cathode candidate for the next generation of secondary lithium batteries. Its reactivity and thermodynamic stability have been determined. At low potentials it can be reduced to lithium phosphate and iron. The fully charged state, orthorhombic FePO₄, is metastable relative to the trigonal all tetrahedral form; however, the massive structural rearrangement necessary makes the structural change kinetically unfavorable at room temperature. LiFePO₄ has been prepared by a variety of routes. When synthesized at elevated temperatures in the presence of a carbon gel, only LiFePO₄ was detected by X-ray diffraction even when the starting material was LiFePO₄(OH). At a C/2 discharge/charge rate, LiFePO₄ retained about 80% of the theoretical capacity cycling at room temperature. The hydrothermal form shows some iron disorder, which impacts its electrochemical and chemical reactions.