Reticular VO·0.6HO 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 VO·0.6HO xerogel was synthesized via a hydrothermal process as a cathode material for rechargeable KIBs. Compared with the orthorhombic crystalline VO, the hydrated vanadium pentoxide (VO·0.6HO) exhibits the ability of accommodating larger alkali metal ions of K because of the enlarged layer space by hosting structural HO molecules in the interlayer. By intercalation of HO into the VO layers, its potassium electrochemical activity is significantly improved. It exhibits an initial discharge capacity of ∼224.4 mA h g and a discharge capacity of ∼103.5 mA h g even after 500 discharge/charge cycles at a current density of 50 mA g, which is much higher than that of the VO 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 VO·0.6HO electrodes, which confirmed the potassium intercalation storage mechanisms of this hydrated material. The results demonstrate that the interlayer-spacing-enlarged VO·0.6HO is a promising cathode candidate for KIBs.