Ultraflexible Reedlike Carbon Nanofiber Membranes Decorated with Ni–Co–S Nanosheets and Fe₂O₃–C Core–Shell Nanoneedle Arrays as Electrodes of Flexible Quasi-Solid-State Asymmetric Supercapacitors

Flexible and lightweight supercapacitors with satisfactory energy density and long-term stability are urgently required to provide power for flexible, foldable, and wearable electronic devices. Herein, reedlike carbon nanofibers (RCNFs) with hierarchical macropores in the core and micropores and honeycomb mesopores in the shell are designed by electrospinning, carbonization, and etching, leading to high electronic conductivity and satisfactory mechanical flexibility and foldability. Subsequently, flowerlike Ni–Co–S nanoarrays are grown in situ on RCNFs by electrodeposition, and fern leaf-like Fe₂O₃–C core–shell nanoneedles, in which porous Fe₂O₃ are coated with ultrathin carbon layers, are decorated on RCNFs via hydrothermal synthesis, polydopamine modification, and thermal annealing. Because of unique core–shell structures and synergistic effects of these active components, the RCNF@Ni–Co–S cathode and the RCNF@Fe₂O₃–C anode exhibit high specific capacitances of 1728 and 221.5 F g^–1 at 1 A g^–1, respectively. With a poly­(vinyl alcohol) (PVA)/potassium hydroxide (KOH) solid gel as both an electrolyte and a separator, the assembled flexible quasi-solid-state asymmetric supercapacitor achieves a high energy density of 44.9 W h kg^–1 at 1549.7 W kg^–1, and the capacitance remains at 94% after bending the asymmetric supercapacitor to 180°. The flexible electrodes with excellent electrochemical performances are highly promising for high-performance wearable energy storage devices.