B, F Co-doping flexible carbon nanofibers as a fast and stable anode for potassium-ion hybrid capacitor

Potassium ion hybrid capacitors (PIHCs) have attracted widespread attention as combining the advantages of potassium ion batteries (PIBs) with supercapacitors. However, the sluggish kinetics caused by the large radius of K⁺ hinder the practical application of PIHCs. Herein, we synthesized a boron and fluorine co-doping interlaced network porous carbon nanofibers (BF-PCNFs), which was used as the freestanding anode of PIHCs the freestanding anode of PIHCs to alleviate large volume expansion and increase conductivity. Benefiting from the B, F co-doping and porous interlace nanostructure of BF-PCNFs, the anode shows 185 mA h g⁻¹ under a load of 12.6 mg cm⁻², a reversible capacity of 176 mA h g⁻¹ at 1000 mA g⁻¹ after 6000 cycles, and the capacity retention from 100 mA g⁻¹ to 5000 mA g⁻¹ is 62%. Furthermore, the PIHCs based on BF-PCNFs as anode and activated carbon as cathode exhibit an energy density of 87 Wh kg⁻¹ and a power density of 393 W kg⁻¹. The capacity retention is as high as 78% over 4000 cycles. Considering the exceptional rate performance, long cyclability and high-mass-loading, our work may supply a new strategy for designing novel energy storage devices with outstanding performance.