Hollow carbon bowls with cobalt single-atom sites enable fast and reversible potassium storage

Abstract

Hard carbon has shown promise as the most viable anode material for potassium-ion batteries (PIBs) due to the tunable interlayer spacing and inherent voids. However, it always suffers from sluggish K⁺ diffusion and limited active sites. Herein, we report a cobalt/nitrogen co-doped hollow bowl-like hard carbon (Co/N-HCB) anode, which is synthesized through a self-polymerization and carbonization strategy. The hollow bowl-like carbon architecture ensures a high surface area, structural robustness, and expanded interlayer spacing, while the construction of atomically dispersed Co–N₄ configurations modulates electronic conductivity and maximizes the edge-nitrogen content. This synergistic structural and chemical modulation significantly improves potassium storage kinetics and surface capacitive behaviors. The resulting Co/N-HCB anode delivers exceptional reversible capacity and cycling stability. Furthermore, the assembled asymmetric hybrid capacitor based on Co/N-HCB achieves a high energy density of 327.6 W h kg⁻¹ at 802.3 W kg⁻¹. This work demonstrates a rational design strategy combining heteroatom doping and structural engineering to develop carbonaceous anodes for high-performance PIBs.