Enhancing lithium/sodium-ion storage behaviors in a V₂O₅ nanosheet by freeze-drying

A porous V₂O₅ nanosheet is synthesized via freeze-drying followed by a heat-treatment process. Observably, transmission electron microscopy and atomic force microscopy analysis indicate that a porous and thin layer microstructure is achieved with V₂O₅. Electrochemical measurement demonstrates that the as-obtained V₂O₅ exhibits evident advantage toward the sodium/lithium ion storage. When evaluated as a cathode for sodium ion batteries, the V₂O₅ nanosheet delivers an initial discharge capacity of 199.8 mA h g⁻¹. Even after 200 cycles at 50 mA g⁻¹, the V₂O₅ nanosheet can retain a capacity of 123.9 mA h g⁻¹, which is 2.3 times higher than that of bulk V₂O₅. Cyclic voltammetry and electrochemical impedance spectroscopy analysis further confirm that this rationally-designed porous nanosheet can increase the electroactive sites for the redox reaction and shorten the pathway of charge transfer, consequently leading to an enhanced capacitive sodium ion storage behavior.