Sulfur Functionalization-Modulated Kinetics-Enhanced Multicavity Carbon Spheres for Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors (PIHCs) are appealing candidates to alleviate the supply anxiety of lithium-ion batteries. However, their widespread adoption is hindered by sluggish kinetics and an inferior specific capacity at the anode side. To circumvent these issues, herein, a sulfur functionalization strategy is proposed to construct sulfur-functionalized multicavity carbon spheres (S x -MCS) anode with enhanced potassium storage kinetics and high capacitive reaction content. By precisely regulating the sulfur dosage, the content and configuration of sulfur species in S x -MCS are tailored, and even the intrinsic properties of the S x -MCS can be manipulated. Acting as an anode for PIHCs, S3-MCS with a sulfur content of 8.9 at.% demonstrates ultrahigh specific capacity, attractive fast-charging performance, and outstanding cycling stability. Combining kinetics analysis and ex situ XPS, the dual roles of sulfur-containing groups are elucidated: accelerating charge transfer kinetics and contributing additional capacity through reversible capacitive reactions in the high-voltage region. Consequently, the as-constructed PIHCs based on the S3-MCS anode deliver impressive energy/power density of 121.5 Wh kg –1 /24 kW kg –1, along with excellent cycling stability (100.7% capacity retention over 10000 cycles at 2 A g –1 ). This work provides a potentially universal strategy to synchronously boost the potassium storage kinetics and capacitive reaction contribution of carbon-based anodes.