Amorphous vanadium oxide films synthesised by ALCVD for lithium rechargeable batteries

This study addresses the lithium insertion performances of amorphous vanadium oxide films, synthesized by atomic layer chemical vapour deposition (ALCVD). AFM and SEM investigations showed that the as-deposited films are amorphous, compact and homogeneous. As revealed by XPS and Raman spectroscopy, the ALCVD oxide films after deposition are mainly composed of V2O5, with V4+ surface content (about 10%). The insertion of Li+ into the lattice was investigated in 1 M LiClO4-PC. The results show that the electrochemical performances obtained with amorphous vanadium oxide films, with an optimal thickness of 200 nm (455 mAh g−1, i.e. composition of Li2.9V2O5), were superior to crystalline V2O5 films. The amorphous films exhibit higher capacity and better cycle ability even for deep lithium insertion ratio compared to crystalline V2O5 films. The chemical diffusion coefficients, deduced from numerical simulation of chronopotentiograms, were comprised between 3 × 10−12 and 10−13 cm2 s−1 for a lithium insertion ratio comprised between 0 and 2.9. AFM and Raman spectroscopy performed before and after lithiation showed that neither the morphology nor the local order of the amorphous films were significantly affected by the insertion/extraction of lithium. Raman measurements also revealed that a very small amount of lithium are locally trapped in the oxide lattice.