Electrospun Na3V2(PO4)3/carbon composite nanofibers as binder-free cathodes for advanced sodium-ion hybrid capacitors

Sodium-ion hybrid capacitors (SIHCs) are promising technology for energy storage because they combine the merits of high-energy batteries and high-power capacitors as well as naturally abundant sodium resource. However, conventional SIHCs consume a mass of electrolyte during the charge process, thus generating some side reactions at high potentials. In this work, we report a novel rocking-chair SIHC using Na3V2(PO4)3/carbon composite nanofibers (denoted as “[email protected]”) as binder-free cathodes and SiO2-templated hollow carbon nanofibers (HCNF) as the capacitive anode. Resulting from the unique carbon-encapsulation configuration, the [email protected] cathode demonstrates excellent rate capability (105.8 mAh/g at 0.5C; 66.9 mAh/g at 100C) and long-term cycling stability (98% capacity retention after 2000 cycles) in sodium half-cells. The as-fabricated HCNF||[email protected] SIHC device delivers a high energy density of 216.4 Wh/kg at a power density of 381.8 W/kg. Even at an increased power density of 15272.7 W/kg, the energy density is still as high as 123.0 Wh/kg (based on the total mass of active materials in both electrodes). These results provide a new route to design various flexible self-supporting composite fiber electrodes through a simple electrospinning encapsulation strategy, which finally pushes the development of next-generation hybrid energy storage devices.