Local structure and redox energies of lithium phosphates with olivine- and Nasicon-like structures

An experimental relationship between local structure and electrochemical properties is established for lithium metal phosphates LiMePO4 (Me = Fe, Co, Mn), LiFeP2O7 and Li3Fe2(PO4)3 which crystallise with either the olivine-like or the Nasicon-like structure. Structural features of several lithium metal phosphates are investigated by a local probe such as the FTIR spectroscopy in order to explain the influence of either PO43− or P2O74− covalent bonds on redox energies. The local cationic arrangement is also discussed with the aid of a molecular vibration model to figure out the strong covalent bonds within a PO43− complex for glassy Nasicon compounds.