Decoration of carbon nanofibers with NiCo2S4 nanoparticles for flexible asymmetric supercapacitors

Highlights: • NiCo₂S₄ grown on carbon nanofibers to form hybrid carbon nanofibers are obtained. • Hybrid carbon nanofibers exhibited excellent specific capacity and cycle stability. • Flexible supercapacitor devices were assembled using hybrid carbon nanofibers. Flexible supercapacitors with both high energy and high power densities are critical for flexible electronics. In this paper, hybrid flexible carbon nanofibers decorated with NiCo₂S₄ nanoparticles are successfully prepared by combination of electrospinning, carbonization and hydrothermal treatments. The obtained hybrid carbon nanofibers display remarkable specific capacitance (527.8 F g⁻¹ at the current density of 0.2 A g⁻¹ and 622.5 F g⁻¹ at 2 mV s⁻¹), good rate capability (310.5 F g⁻¹ at 4.0 A g⁻¹) and excellent cycle stability (retaining 90.0% after 3000 cycles). The flexible asymmetric supercapacitors based on carbon nanofibers decorated with NiCo₂S₄ and porous carbon nanofibers coated with activated charcoal are fabricated. The combined unique properties of each of these components enable highly flexible and mechanically strong films that can serve as electrodes directly without using any current collectors or binders. The fabricated device shows an energy density of 32.1 Wh kg⁻¹ at power density of 67.6 W kg⁻¹ and cycle stability retaining 88.5% after 1500 cycles at 1.0 A g⁻¹. Therefore, the novel flexible asymmetric device with perfect flexibility and stability can be applied as one of the most promising power supplies.