Reticular V₂O₅·0.6H₂O Xerogel as Cathode for Rechargeable Potassium Ion Batteries

Potassium ion batteries (KIBs), because of their low price, may exhibit advantages over lithium ion batteries as potential candidates for large-scale energy storage systems. However, owing to the large ionic radii of K-ions, it is challenging to find a suitable intercalation host for KIBs and thus the rechargeable KIB electrode materials are still largely unexplored. In this work, a reticular V₂O₅·0.6H₂O xerogel was synthesized via a hydrothermal process as a cathode material for rechargeable KIBs. Compared with the orthorhombic crystalline V₂O₅, the hydrated vanadium pentoxide (V₂O₅·0.6H₂O) exhibits the ability of accommodating larger alkali metal ions of K⁺ because of the enlarged layer space by hosting structural H₂O molecules in the interlayer. By intercalation of H₂O into the V₂O₅ layers, its potassium electrochemical activity is significantly improved. It exhibits an initial discharge capacity of ∼224.4 mA h g^-1 and a discharge capacity of ∼103.5 mA h g^-1 even after 500 discharge/charge cycles at a current density of 50 mA g^-1, which is much higher than that of the V₂O₅ electrode without structural water. Meanwhile, X-ray diffraction and X-ray photoelectron spectroscopy combined with energy dispersive spectroscopy techniques are carried out to investigate the potassiation/depotassiation process of the V₂O₅·0.6H₂O electrodes, which confirmed the potassium intercalation storage mechanisms of this hydrated material. The results demonstrate that the interlayer-spacing-enlarged V₂O₅·0.6H₂O is a promising cathode candidate for KIBs.