High capacity and enhanced structural reversibility of β-LixV2O5nanorods as the lithium battery cathode

Abstract

Li_xV₂O₅ (x ∼ 0.42) nanorods, an overdoped β-phase vanadium oxide bronze with a rigid three-dimensional framework, have been fabricated for the first time via a simple two-step synthetic method. It is found that the δ-type structure of the as-prepared hydrated nanobelts through the hydrothermal route is converted into the tunnel β geometry upon annealing-induced dehydration. After annealing at 600 °C, the β-Li_xV₂O₅ nanorods exhibit the desired electrochemical properties: an initial gravimetric discharge capacity of 388.4 mA h g⁻¹ (corresponding to an uptake of ca. 2.68 lithium per cell unit) and a specific energy density of 1039.6 W h kg⁻¹ are achieved within a 2.0 V cut-off voltage at C/20, which decreased to 295.3 mA h g⁻¹ (ca. 2.04 Li/V₂O₅) and 789.0 W h kg⁻¹ after 50 cycles, respectively. The irreversible formation of ω-Li_xV₂O₅ for layered V₂O₅ cathodes upon deep lithiation is not presented during cell operation, and such improved structural reversibility is attributed to the highly retrievable host framework of the β-Li bronze, as well as further strain relaxation facilitated by the one-dimensional nanostructures. Based on the distinctive crystallographic structure and superior electrochemical properties, this β-lithium vanadium bronze has shown promising potential as a cathode material for secondary lithium-based batteries.