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.