Ammonium Vanadate Nanobelts Combined with Reduced Graphene Oxide as Cathode Materials for K-Ion Batteries

In this work, an (NH4)0.5V2O5 nanobelt (NVO) was prepared by a facile hydrothermal reaction using NH4VO3 as the precursor and oxalic acid (C2H2O4) as the reducing agent. The crystal structure and quantity of NH4+ intercalated for NVO can be adjusted via postheat treatment, resulting in variable K+ storage property when utilized as a cathode for K-ion batteries (KIBs). Therein, NVO-150 °C obtained exhibits an optimal K+ storage capacity (86.8 mA h/g at the first discharge and 74.0 mA h/g at the 50th cycle under 50 mA/g between 1.5 and 3.8 V vs K/K+) and rate capability (58.4 mA h/g under 500 mA/g), which can be ascribed to the appropriate structural fine-tuning toward NVO, increasing its active sites for K+ storage. Furthermore, NVO was uniformly combined with rGO by a one-pot hydrothermal process through the bridging effect of cetyltrimethylammonium bromide. The acquired NVO-rGO also delivers a significantly improved K+ storage performance (89.7 mA h/g at the initial discharge and 71.9 mA h/g after 50 cycles; 56.5 mA h/g under 500 mA/g) compared to NVO, which benefits from the good conductivity and separation function of rGO, promoting the fast transport of electrons and K+. Both the postheat treatment and introduction of rGO are feasible to enhance K+ storage in NVO. This study proposed effective modification strategies to optimize K+ storage in a potential NVO cathode for KIB application.