Facile preparation of Nb2O5 microspheres and their excellent electrochemical performance in aqueous zinc-ion hybrid supercapacitors

The aqueous solution-based zinc-ion hybrid supercapacitors (ZHSCs) have attracted immense attention as they are characterized by high power and energy densities. Electrode materials with high performance should be developed for ZHSCs to resolve power imbalances between capacitor- and battery-type electrode materials. To address this issue, Nb2O5 microspheres (with the structure like sweet dumplings with exposed stuffing) were produced following a hydrothermal process which was followed by a high-temperature calcination process. The specific capacity of the as-synthesized Nb2O5 microspheres was up to 324 F.g(-1) when the current density was 0.1 A.g(-1), and the long-term capacity retention was 85% at the end of 5000 cycles. The results revealed that the nanospheres could be used as battery-type electrode materials for the fabrication of ZHSCs. Nb2O5//AC ZHSCs were fabricated with Nb2O5 microspheres as the negative electrode materials, and activated carbon (AC) was used as the positive electrode material. As a result, a specific capacity of 108 F.g(-1) was achieved when the current density was 0.1 A.g(-1). The power density was high (8020 W.kg(-1)) at 28 Wh.kg(-1), and the energy density was high (60 Wh.kg(-1)) at 100 W.kg(-1). The structurally novel Nb2O5 microspheres can be potentially used for the development of the next-generation ZHSCs that exhibit excellent performance.