Amorphous Carbon Against Reduced Graphene Oxide in Li- and Na-Ion Electrochemical Storage Devices: The Case of Nb2O5

Two-dimensional (2D) reduced graphene oxide (rGO) is often combined with metal oxides for energy-storage applications, owing to its unique properties. Here, we show that amorphous carbon sources, such as organic molecules, can be more efficient in controlling the size of small metal oxide particles and in achieving uniform carbon-oxide contacts, which benefits the energy-storage performance. A composite made of Nb₂O₅ and amorphous carbon (using 1,3,5-triphenylbenzene as carbon source) outperforms the Nb₂O₅-rGO counterpart as high rate anode electrode material in Li-ion and Na-ion half-cells and hybrid supercapacitors, delivering specific capacities of 134 mAh g^-1 at 25C against 98 mAh g^-1 for the rGO-based composite (in Li electrolyte) and 125 mAh g^-1 at 20C against 98 mAh g^-1 (in Na electrolyte). These findings suggest that amorphous carbon sources and the development of amorphous carbon-based composites for Li-ion and Na-ion energy-storage devices are worthy of more attention and research efforts than those currently given compared to 2D rGO-based composites.