Unidirectional growth of single crystalline β-Na_0.33V₂O₅ and α-V₂O₅ nanowires driven by controlling the pH of aqueous solution and their electrochemical performances for Na-ion batteries

We describe a novel synthetic route of highly single crystalline sodium vanadate (β-Na_0.33V₂O₅) and vanadium pentoxide (α-V₂O₅) nanowires via a simple thermal annealing process followed by the formation of amorphous nanoparticles of V(OH)₃ and Na-containing V(OH)₃ precursors prepared by controlling the pH of precursor solutions. The distinct crystal growth process suggests that the intercalation of Na ions is governed by the pH of the aqueous solution. In addition, the binding nature to the amorphous V(OH)₃ nanoparticle precursors could be a key factor in determining the unidirectional growth of highly single crystalline β-Na_0.33V₂O₅ and α-V₂O₅ nanowires. The obtained single crystalline β-Na_0.33V₂O₅ nanowire shows promising electrode performance for sodium-ion batteries (SIB) with greater discharge capacity and better rate characteristics compared with those of the α-V₂O₅ nanowire. The superior electrode functionality of β-Na_0.33V₂O₅ over α-V₂O₅ is attributable to its better charge transfer kinetics and its higher structural and morphological stability.