Regulating the oxygen-atom configuration of carbon anode enabling extremely fast-charging potassium-ion hybrid capacitors

Metal-ion hybrid capacitors, such as potassium-ion hybrid capacitors (PIHCs), are regarded as promising fast-charging energy storage devices. However, the kinetics mismatch between the battery anode and the capacitive cathode restricts their fast-charging performance. Precisely constructing carbon anodes with enhanced kinetics is an innovative approach to address this challenge. Herein, using epigallocatechin gallate with high oxygen content as the precursor, oxygen-enriched carbon materials (OEC) with tunable C=O content are successfully synthesized. Effortlessly, the C=O content of OEC is regulated by adjusting the pyrolysis temperature. Serving as an anode for PIHCs, OEC-600 with the highest C=O content exhibits an attractive fast-charging specific capacity of 135.2 mAh∙g⁻¹ at 20 A∙g⁻¹, along with a superior fast-charging cycling stability. Combining theoretical calculations, comprehensive kinetics analysis and in-situ Raman, the positive effects of C=O on the potassium storage capability and reversibility of OEC-600 are revealed. Consequently, PIHCs assembled based on an OEC-600 anode deliver impressive energy/power density of 145.1 Wh∙kg⁻¹/45.9 kW∙kg⁻¹ and superior fast-charging cycling stability with 87.5% of capacity retention over 20,000 cycles at 5 A∙g⁻¹. This work is anticipated to provide an optional design concept toward the carbon anode for fast-charging PIHCs.