Structural Evolution of Li2Fe1-yMnySiO4 (y=0, 0.2, 0.5, 1) Cathode Materials for Li-Ion Batteries upon Electrochemical Cycling

Nanocrystalline Li2Fe1-yMnySiO4 (y = 0, 0.2, 0.5, 1) powders with in situ carbon coating have been prepared by a sol-gel route and their structural evolution during the first electrochemical charge-discharge cycles has been investigated in detail by X-ray diffraction in combination with Li-7 MAS NMR, Fe-57 Mossbauer spectroscopy and in situ X-ray absorption spectroscopy. These results provide detailed information about the amorphization, phase transitions and the partially reversible change in the local environment of Li nuclei upon cycling. The redox processes of the metal cations responsible for the cycling performance of the first few cycles and for the cyclability are also derived from the combined structural characterizations.