Integration of flexibility, cyclability and high-capacity into one electrode for sodium-ion hybrid capacitors with low self-discharge rate

Metal-ion hybrid capacitors are regarded as promising power sources for portable electronics because of numerous opportunities in designing the anode/cathode couple to realize high performance and device flexibility. Here we demonstrate our rational design of a porous-fiber network based electrode for quasi-solid-state flexible Na-ion hybrid capacitors. A SiO₂-etching approach is deployed to synthesize the freestanding porous carbon nanofiber (PCNF) membrane that is both mechanically robust and light (~1 mg cm⁻²). The PCNF serves as a 3D scaffold for the uniform growth of MoS₂@poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell nanosheets. The resultant PCNF@MoS₂@PEDOT double core/shell nanofiber electrode not only maintains the intrinsic high-capacity of MoS₂ for Na-ion storage, but also renders long-term cyclability and high rate performance. The constructed quasi-solid-state Na-ion hybrid capacitors can tolerate arbitrary bending and folding, and has a much lower self-discharge rate (15 mV h^-1) compared to symmetric capacitors.