Boosting the cycling stability of hydrated vanadium pentoxide by Y3+ pillaring for sodium-ion batteries

Hydrated V2O5 has attracted considerable attention for sodium ion batteries (SIBs) due to its high theoretical capacity. However, the poor cycling performance caused by structural instability during sodiaton/desodiation greatly hampers its application. Herein, Y3+ pre-intercalated hydrated V2O5 samples (YxV2O5, x = 0.0, 0.02 and 0.06) are synthesized by a facile sol-gel and freeze-drying routes followed by heat treatment in air at 200 °C. It is found that the morphology, oxidation state of vanadium, and sodium storage performance of hydrated V2O5 could be largely modulated by Y3+ pre-intercalation. As cathode material for SIBs, the Y0·02V2O5 sample exhibits much enhanced cycling stability, higher Na+ diffusion coefficient, lower electrochemical reaction resistance, and improved rate capability compared to the pure V2O5 counterpart. First-principle calculations reveals that the pre-intercalated Y3+ forms [YO6] pillar with two oxygen atoms from the VO5 pyramids and four oxygen atoms from the intercalated water molecules, which firmly binds the V2O5 double layers together. Ex-situ XRD, SEM, and TEM analysis demonstrate that Y3+ pre-intercalation effectively strengthens the structural integrity, stabilizes the layered structure, and suppress the irreversible phase transition of hydrated V2O5 during repeated discharge/charge cycling, and therefore leading to enhanced cycling stability and improved rate capability.