Atomic-scale investigation of the reversible α- to ω-phase lithium ion charge – discharge characteristics of electrodeposited vanadium pentoxide nanobelts

Abstract

Using an electrochemical potential pulse methodology in a mixed solvent system, electrochemical deposition of amorphous vanadium pentoxide (V₂O₅) nanobelts is possible. Crystallisation of the material is achieved using in air annealing with the temperature of crystallisation identified using in situ heating transmission electron microscopy (TEM). The resulting α-phase V₂O₅ nanobelts have typical thicknesses of 10–20 nm, widths and lengths in the range 5–37 nm (mean 9 nm) and 15–221 nm (mean 134 nm), respectively. One-cycle reversibility studies for lithium intercalation (discharge) and de-intercalation (charge) reveal a maximum specific capacity associated with three lithium ions incorporated per unit cell, indicative of ω-Li₃V₂O₅ formation. Aberration corrected scanning TEM confirm the formation of ω-Li₃V₂O₅ across the entirety of a nanobelt during discharge and also the reversible formation of the α-V₂O₅ phase upon full charge. Preliminary second cycle studies reveal reformation of the ω-Li₃V₂O₅, accompanied with a morphological change in the nanobelt dimensions. Achieving α-V₂O₅ to ω-Li₃V₂O₅ to α-V₂O₅ reversibility is extremely challenging given the large structural rearrangements required. This phenomenon has only been seen before in a very limited number of studies, mostly employing nanosized V₂O₅ materials and never before with electrodeposited material.