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 get, 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. (C) 2002 Elsevier Science B.V. All rights reserved.