Kinetics compensation mechanism in nitrogen-sulfur co-doping carbon nano-onions for dual-carbon potassium-ion hybrid capacitors

Dual-carbon potassium-ion hybrid capacitors (PIHCs) offer the potential to deliver cost-effectiveness, extended cycle durability, high energy and power densities. Nevertheless, their widespread implementations are significantly restricted by the sluggish kinetics of conventional carbon-based anodes. Herein, nitrogen-sulfur co-doped carbon nano-onions (NS-CNOs) are introduced as advanced anode materials for dual-carbon PIHCs. The unique architecture of NS-CNOs characterized by concentric graphitic layers with moderate specific surface area and suitable interlayer spacing, not only effectively mitigates the stress variations induced by repeated K⁺ insertion/extraction but also enhances K⁺ storage capability. The synergies of N, S co-doping expand the interlayer spacing of graphene, introduce abundant potassiophilic sites/defects, and establish efficient ion/electron transport pathways. Through a combination of in/ex-situ experimental characterizations and theoretical simulations, it is demonstrated that K⁺ ions are preferentially adsorbed at the N-sites during potassiation process, and S atoms provide additional defects for K⁺ extraction. These advantages contribute to excellent rate performance (100 mAh g⁻¹ at 20 A g⁻¹) and good cycling stability for NS-CNOs. When integrated into dual-carbon PIHCs, the device enables high energy and power densities (174.4 Wh kg⁻¹ and 14.0 kW kg⁻¹) while maintaining long-term cycling stability (86.7 % capacity retention after 10,000 cycles). This work explores a potential design strategy of anode materials for high-performance dual-carbon PIHCs.