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

Abstract

We synthesize a new vanadium oxyfluoride VO₂F (rhombohedral, Rc) 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 (Fmm) phase after initial cycling against the lithium anode, as confirmed by diffraction and spectroscopic experiments. The newly formed nanosized Li_xVO₂F 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.