Graphene-like VO2 vertically growing on carbon cloth enables fast and high-capacity ammonium ion storage

Among these aqueous (non-)metal ion battery systems, ammonium ions are drawing increasing attention due to its unique advantages including small molar mass, abundant reserves and nontoxicity. However, suitable NH4+ hosting materials with rational structure design are still in high demand to build high performance ammonium ion batteries (AIB). Herein, a graphene-like vanadium dioxide (VO2) vertically growing on carbon cloth (CC) is reported as self-supporting electrode for AIB. The three-dimensional conductive carbon fiber substrate and the warped graphene-like VO2 lead to enhanced NH4+ transport and shortened diffusion length. As a result, the as-prepared VO2@CC displays an initial specific capacity up to 250.1 mAh g−1 at the current density of 1 A g−1. After 1000 cycles, it still maintains a capacity of 60.4 m Ah g−1. A series of ex-situ characterizations provides firm evidence that the insertion and extraction of NH4+ in VO2 are realized through the formation and breakage of hydrogen bonds. When combined with activated carbon (AC) to form a hybrid battery VO2@CC//AC, an initial discharge capacity of 74.98 mAh g−1 with the capacity retention of 43.64 % after 200 cycles is achieved, while the efficiency is maintained at about 92 %, surpassing other reported vanadium-based materials.