Ammonium Vanadate\nNanobelts Combined with Reduced\nGraphene Oxide as Cathode Materials for K‑Ion Batteries

In this work, an (NH<sub>4</sub>)<sub>0.5</sub>V<sub>2</sub>O<sub>5</sub> nanobelt (NVO) was prepared by a facile hydrothermal\nreaction\nusing NH<sub>4</sub>VO<sub>3</sub> as the precursor and oxalic acid\n(C<sub>2</sub>H<sub>2</sub>O<sub>4</sub>) as the reducing agent. The\ncrystal structure and quantity of NH<sub>4</sub><sup>+</sup> intercalated\nfor NVO can be adjusted via postheat treatment, resulting in variable\nK<sup>+</sup> storage property when utilized as a cathode for K-ion\nbatteries (KIBs). Therein, NVO-150 °C obtained exhibits an optimal\nK<sup>+</sup> storage capacity (86.8 mA h/g at the first discharge\nand 74.0 mA h/g at the 50th cycle under 50 mA/g between 1.5 and 3.8\nV vs K/K<sup>+</sup>) and rate capability (58.4 mA h/g under 500 mA/g),\nwhich can be ascribed to the appropriate structural fine-tuning toward\nNVO, increasing its active sites for K<sup>+</sup> storage. Furthermore,\nNVO was uniformly combined with rGO by a one-pot hydrothermal process\nthrough the bridging effect of cetyltrimethylammonium bromide. The\nacquired NVO-rGO also delivers a significantly improved K<sup>+</sup> storage performance (89.7 mA h/g at the initial discharge and 71.9\nmA h/g after 50 cycles; 56.5 mA h/g under 500 mA/g) compared to NVO,\nwhich benefits from the good conductivity and separation function\nof rGO, promoting the fast transport of electrons and K<sup>+</sup>. Both the postheat treatment and introduction of rGO are feasible\nto enhance K<sup>+</sup> storage in NVO. This study proposed effective\nmodification strategies to optimize K<sup>+</sup> storage in a potential\nNVO cathode for KIB application.