Facile preparation of heteroatom S doped dumbbell-like hard carbon for boosting potassium-ion storage capability

Potassium-ion storage devices have gained increasing interest in applications such as large-scale energy storage and smart grids due to the advantages of high abundance, low cost, high working voltage, and fast charge transport in electrolytes. However, obtaining high-performance anodes with excellent rate performance and cycling stability remains a challenge due to the much larger size of K+ ions. In this contribution, heteroatom S doped dumbbell-like hard carbon (SDHC) are synthesized using sucrose as the carbon source. SDHC-700, which is carbonized at 700 °C, exhibits the highest sulfur doping degree (9.3 at.%), remarkable reversible capacity (416 mAh g-1 at 0.05 A g-1), and superb rate performance (174 mAh g-1 at 5.0 A g-1). Ex situ X-ray photoelectron spectroscopy (XPS) tests reveal that covalent C-S bonds can undergo a reversible reaction with K to form K2Sx. In situ electrochemical impedance spectroscopy (EIS) results suggest that the diffusion of long-chain potassium polysulfides may be the main reason for the degradation of SDHC during long-term cycling. Moreover, using SDHC-700 as the anode and commercial activated carbon as the cathode, a dual-carbon potassium-ion hybrid capacitor has been successfully constructed, which can deliver a high energy/power density of 96.5 Wh kg-1/160.3 W kg-1. This study provides a straightforward and practical approach for developing sulfur-doped hard carbons as high-performance anode materials for alkali metal ion storage.