Understanding of the nanosize effect on the structure and electrochemistry of V2O5 obtained via fluorine chemistry

Abstract

We demonstrate the benefit of an original vanadium pentoxide (V2O5) nanostructuration on the electrochemical performances. A new synthesis way consists in a facile fluorination reaction in aqueous HF solution followed by a moderate heat treatment at 230°C. Highly porous calisson-like particles with low crystallite sizes of 13-30nm are obtained. Outstanding rate capability and cycling stability are observed. This material can deliver reversible capacities of 260mAhg-1 at C/10 and 150mAhg-1 at 2C rate, as well as a stable capacity of 200mAhg-1 at 1C rate after 50 cycles. A systematic structural study at long range order by XRD and at the chemical bond scale by Raman microspectrometry reveals the crucial impact of nanosized particles on the Li ion insertion-extraction. The structural answer of nano-V2O5 is found to produce a solid solution behavior over the largest Li composition range never reached for a Li intercalation compound (0≤x≤1.8). This result completely upsets the expected phase diagram for micro-LixV2O5 dominated by three wide biphasic regions. Such a finding explains the original sloped discharge-charge curves observed for nano-V2O5. Also we provide evidence for the better kinetics of Li insertion reaction induced by the nanosize effect of the material