Pearl-Necklace Structured Se-Doped Hollow Carbon Nanofibers for High-Capacity and Ultrastable Potassium Ion Storage

Carbon-based materials are promising anodes for potassium-ion batteries due to their natural abundance and structural stability. However, their practical application remains hindered by limited capacity and poor rate performance. Here, we report the design of selenium-doped hollow carbon nanofibers (SeHCF-x) with a unique pearl necklace-like morphology, synthesized via electrospinning in combination with a SiO₂ templating strategy. The hollow architecture ensures intimate electrolyte/electrode contact, reduces K⁺ diffusion distances, and accommodates volume fluctuations during cycling. Selenium doping introduces abundant defects and active sites, lowers the K⁺ diffusion energy barrier, and enhances electronic conductivity. As a result, the optimized SeHCF electrode delivers a high reversible capacity of 470 mAh g^-1 at 0.05 A g^-1 and maintains 167 mAh g^-1 at 5 A g^-1 after 6000 cycles. Ex-situ analyses reveal a reversible Se/K₂Se conversion mechanism that underpins its potassium storage capability. Density functional theory calculations show that selenium doping has a significant contribution to K adsorption and electronic conductivity. When assembled into a potassium-ion hybrid capacitor, the SeHCF anode achieves an energy density of 145 Wh kg^-1 and retains 85 % of its capacity after 10000 cycles. This work offers key insights into selenium-doped carbon frameworks and highlights a viable pathway for designing high-performance hollow-structured electrodes in next-generation energy storage systems.