Lithium extraction/insertion in LiFePO4:: an X-ray diffraction and Mossbauer spectroscopy study

The extraction and insertion of lithium in solid-state synthesized LiFePO4 has been followed by in situ X-ray diffraction and Mossbauer spectroscopy in 'coffee-bag' cells of type [Li-metal \ liq. el. \ LiFePO4] during the first cycle. Two-phase Rietveld refinement of the X-ray diffractograms gives the triphylite (LiFePO4) to heterosite (FePO4) phase-ratios as charging and discharging of the cell proceeds. The Fe3+/Fe2+ ratios at each step, as measured by Mossbauer spectroscopy and X-ray diffraction, were in good general agreement with the amount of lithium calculated from the charge passed through the cell; there was, however, a slight tendency for the Mossbauer technique to record a higher concentration of the oxidized phase. The possible existence of a thin interface region at the phase boundary is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.