Lithiation-driven structural transition of VO2F into disordered rock-salt LixVO2F

Abstract

We synthesize a new vanadium oxyfluoride VO2F (rhombohedral, R[3 with combining macron]c) through a simple one-step ball-milling route and demonstrate its promising lithium storage properties with a high theoretical capacity of 526 mA h g−1. Similar to V2O5, VO2F transfers into an active disordered rock-salt (Fm[3 with combining macron]m) phase after initial cycling against the lithium anode, as confirmed by diffraction and spectroscopic experiments. The newly formed nanosized LixVO2F remains its crystal structure over further cycling between 4.1 and 1.3 V. A high capacity of 350 mA h g−1 at 2.5 V was observed at 25 °C and 50 mA g−1. Furthermore, superior performance was observed for VO2F in comparison with a commercial crystalline V2O5, in terms of discharge voltage, voltage hysteresis and reversible capacity.