Phosphorus and Oxygen Dual-Doped Porous Carbon Spheres with Enhanced Reaction Kinetics as Anode Materials for High-Performance Potassium-Ion Hybrid Capacitors

Hard carbons with low cost and high specific capacity hold great potential as anode materials for potassium-based energy storage. However, their sluggish reaction kinetics and inevitable volume expansion degrade their electrochemical performance. Through rational nanostructure design and a heteroatom doping strategy, herein, the synthesis of phosphorus/oxygen dual-doped porous carbon spheres is reported, which possess expanded interlayer distances, abundant redox active sites, and oxygen-rich defects. The as-developed battery-type anode material shows high discharge capacity (401 mAh g(-1) at 0.1 A g(-1)), outstanding rate capability, and ultralong cycling stability (89.8% after 10 000 cycles). In situ Raman spectroscopy and density functional theory calculations further confirm that the formation of P-C and P-O/P-OH bonds not only improves structural stability, but also contributes to a rapid surface-controlled potassium adsorption process. As a proof of concept, a potassium-ion hybrid capacitor is assembled by a dual-doped porous carbon sphere anode and an activated carbon cathode. It shows superior electrochemical performance, which opens a new avenue to innovative potassium-based energy storage technology.