Nanostructured sodium vanadate hydrate as a versatile sodium ion cathode material for use in organic media and for aqueous desalination

Abstract

Sodium vanadate hydrate (NaV₃O₈·xH₂O, NVOH) exhibits a wider interlayer spacing than its anhydrous form (NaV₃O₈, NVO), allowing a greater volume for sodium intercalation and, consequently, a higher specific capacity in sodium-ion batteries (SIBs). However, the presence of H₂O hinders the long-term cycling stability of the material in an organic medium, whereas its application in aqueous media has received significant attention. In this work, the hydrothermal synthesis of NVO is optimised to maximise both sodium and crystalline water content, thereby enhancing battery performance in both organic cells and aqueous desalination cells. When tested within organic half-cells, the optimised structure provided an exceptional specific capacity of 280 mA h g⁻¹ at 10 mA g⁻¹ and demonstrated cycling stability (150 cycles, > 100 mA h g⁻¹, 100 mA g⁻¹). The performance of this material was confirmed in a full sodium ion battery (SIB) with a C@V₂O₃ counter electrode, yielding 70 mA h g⁻¹ at 100 mA g⁻¹. This optimised structure was then measured in a new platform designed to provide low-cost high-throughput three-electrode electrochemical testing. Using NaCl(aq) as the electrolyte verified promise of NVOH for desalination batteries as a sodium extraction anode, showing a high estimated desalination capacity of 173 mg_NaCl g⁻¹.