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

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. Graphical abstract