Chemically Preintercalated Bilayered K_xV₂O₅·nH₂O Nanobelts as a High-Performing Cathode Material for K-Ion Batteries

Tailoring the structure of the electrode material through chemical insertion of charge-carrying ions emerged as an efficient approach leading to enhanced performance of energy storage devices. Here, we for the first time report the effect of chemically preintercalated K+ ions on electrochemical charge storage properties of bilayered vanadium oxide (δ-V2O5) as a cathode in nonaqueous K-ion batteries, a low-cost alternative to Li-ion batteries, which is attractive for large-scale energy storage. δ-K0.42V2O5·0.25H2O with expanded interlayer spacing of 9.65 Å exhibited record high initial discharge capacity of 268 mAh·g–1 at a current rate of C/50 and 226 mAh·g–1 at a current rate of C/15. K-preintercalated bilayered vanadium oxide showed capacity retention of 74% after 50 cycles at a constant current of C/15 and 58% capacity retention when the current rate was increased from C/15 to 1C. Analysis of the mechanism of charge storage revealed that diffusion-controlled intercalation dominates over nonfaradaic capacitive contribution. High electrochemical performance of δ-K0.42V2O5·0.25H2O is attributed to the facilitated diffusion of electrochemically cycled K+ ions through well-defined intercalation sites, formed by chemically preintercalated K+ ions.