Hollow Nitrogen-Doped\nCarbon Nanofibers for Flexible\nZinc-Ion Capacitors

Hollow\nspindle-like porous nitrogen-doped carbon nanofibers (HS-PNCNFs)\nwere synthesized and chosen as cathode materials for flexible zinc-ion\ncapacitors (FZICs). The synthesis was achieved through a combination\nof electrospinning and heat treatment techniques, incorporating poly(tetrafluoroethylene)\nnanoparticles (PTFE NPs) as sacrificial templates. This approach led\nto the creation of an open hollow spindle-like structure within the\nfibers, significantly including enhancing their high specific surface\narea (SSA) and defect level. When utilized as the cathode material\nin aqueous zinc-ion capacitors (AZICs), the HS-PNCNFs exhibited impressive\nperformance, specific capacity of 105 mAh g<sup>–1</sup> at\n0.2 A g<sup>–1</sup>, excellent rate performance retaining\n60% of capacity at 10 A g<sup>–1</sup>, and remarkable cycling\nstability maintaining 89.4% of capacity after 25,000 cycles. Additionally,\nin FZICs, the HS-PNCNF cathode exhibited satisfactory specific capacity\nand energy density, maintaining excellent stability even after 150\nfolding/unfolding cycles. This work not only demonstrates a controllable\nfabrication method for hierarchical porous carbon nanofibers with\nrich defects but also highlights their vast potential in flexible\nenergy storage devices. The successful application of HS-PNCNFs in\nAZICs and FZICs suggests their broad applicability in various energy\nstorage applications demanding high performance and flexibility.