Thermal stability of LiFePO4-based cathodes

The capacity and cyclability of solid-state synthesized LiFePO4-based laminate cells of type <Li \ liq. el. \ LiFePO4> have been studied at 23, 40, and 60 degrees C. Larger capacities were obtained for cells cycled at the elevated temperatures. No evidence was found of potentially troublesome reactions between the different components of the cells under charged and discharged conditions up to 85 degrees C. Remanant X-ray diffraction peaks were observed from the delithiated FePO4/heterosite phase for cells cycled at ambient temperature. Mossbauer spectroscopy showed different residual amounts of Fe3+ at the different temperatures: 22, 7, and 8% at 23, 40, and 60 degrees C, respectively The amount of residual Fe3+ was thus largest for cells cycled at room temperature, suggesting that slow kinetics hinder effective lithium insertion. (C) 1999 The Electrochemical Society. S1099-0062(99)09-027-6. All rights reserved.