Hollow Nitrogen-Doped Carbon Nanofibers for Flexible Zinc-Ion Capacitors

Hollow spindle-like porous nitrogen-doped carbon nanofibers (HS-PNCNFs) were synthesized and chosen as cathode materials for flexible zinc-ion capacitors (FZICs). The synthesis was achieved through a combination of electrospinning and heat treatment techniques, incorporating poly(tetrafluoroethylene) nanoparticles (PTFE NPs) as sacrificial templates. This approach led to the creation of an open hollow spindle-like structure within the fibers, significantly including enhancing their high specific surface area (SSA) and defect level. When utilized as the cathode material in aqueous zinc-ion capacitors (AZICs), the HS-PNCNFs exhibited impressive performance, specific capacity of 105 mAh g–1 at 0.2 A g–1, excellent rate performance retaining 60% of capacity at 10 A g–1, and remarkable cycling stability maintaining 89.4% of capacity after 25,000 cycles. Additionally, in FZICs, the HS-PNCNF cathode exhibited satisfactory specific capacity and energy density, maintaining excellent stability even after 150 folding/unfolding cycles. This work not only demonstrates a controllable fabrication method for hierarchical porous carbon nanofibers with rich defects but also highlights their vast potential in flexible energy storage devices. The successful application of HS-PNCNFs in AZICs and FZICs suggests their broad applicability in various energy storage applications demanding high performance and flexibility.