Phosphorus/nitrogen co‐doped hollow carbon fibers enabling high‐rate potassium storage

Abstract Potassium‐ion hybrid capacitors (PIHCs) reconcile the advantages of batteries and supercapacitors, exhibiting both good energy density and high‐power density. However, the low‐rate performance and poor cycle stability of battery‐type anodes hinder their practical application. Herein, phosphorus/nitrogen co‐doped hollow carbon fibers (P‐HCNFs) are prepared by a facile template method. The stable grape‐like structure with continuous and interconnected cavity structure is an ideal scaffold for shortening the ion transport and relieving volume expansion, while the introduction of P atoms and intrinsic N atoms can create abundant extrinsic/intrinsic defects and additional active sites, reducing the K + diffusion barrier and improving the capacitive‐controlled capacity. The P‐HCNFs delivers a high specific capacity of 310 mAh·g −1 at 0.1 A·g −1 with remarkable ultra‐high‐rate performance (140 mAh·g −1 at 50 A·g −1 ) and retains an impressive capacity retention of 87% after 10,000 cycles at 10 A·g −1 . As expected, the as‐assembled PIHCs present a high energy density (115.8 Wh·kg −1 at 378.0 W·kg −1 ) and excellent capacity retention of 91% after 20,000 cycles. This work not only shows great potential for utilizing heteroatom‐doping and structural design strategies to boost potassium storage, but also paves the way for advancing the practicality of high‐energy PIHCs devices.