A LixMnPO4 (x=1.0-0.15) composite cathode was investigated by Fourier-transform infrared spectroscopy at different states of charge. Significant spectral changes of the PO43- vibrations, which are correlated with the Jahn-Teller distortion of Mn3+ in MnPO4 and the 3rd ionization potential of Mn, were observed upon electrochemical delithiation of LiMnPO4. The presence of two sets of peaks observed in the series of delithiated LixMnPO4 spectra is consistent with a two-phase process for delithiation. These results provide insight into the structural changes that occur during lithium extraction and insertion in LiMnPO4. (C) 2011 Elsevier Ltd. All rights reserved.