Published online by Cambridge University Press: 10 February 2011
Transition metal oxides are high-capacity lithium storage materials of interest as possible anode materials in the next generation of Li ion batteries. By using X-ray absorption spectroscopy we have obtained an understanding of the process of Li uptake and removal within Na0.25MoO3. Our results show the Li2O matrix on reduction is not inert; Mo-O bonds are reversibly consumed on discharge and are regenerated on charge, with the Li2O matrix acting as the oxygen reservoir. The migration of oxygen atoms from the matrix to the active centers occurs at a voltage below that expected for the Li2O free energy of formation. Polarization on charge is not due only to oxygen migration but also to metal rearrangement within the electrode material. The reversibility of the Mo-O bond formation on repeated cycles is a function of the depth of discharge, with 200 mV being the lower limit.