Covalently Confined Sulfur Composite with Carbonized Bacterial Cellulose as an Efficient Cathode Matrix for High-Performance Potassium–Sulfur Batteries

Although the development of potassium–sulfur batteries (KSBs) is in the nascent stage, KSBs draw keen interest as they offer a few unique advantages over Li– and Na–sulfur battery systems, including lower cost and highest ionic mobility of K+ ions. However, shuttling of intermediate polysulfides and the insulating nature of sulfur result in poor utilization of the active material and significant capacity loss during cycling. In this study, we overcome these critical issues of KSBs by developing an active cathode material as a covalently confined sulfur composite with carbon derived from a sustainable precursor (bacterial cellulose) (hereinafter referred to as CCS@CBC). The synthesis temperature of CCS@CBC is varied from 150 to 450 °C to achieve the optimal covalent fixing of sulfur in the carbon matrix verified by X-ray diffraction and infrared spectroscopy. The increase in the synthesis temperature of CCS@CBC ensures proper covalent confinement of sulfur with the carbon matrix that facilitates the relieving of the shuttle effect as revealed in the electrochemical performance of as-prepared KSBs. The CCS@CBC prepared at 450 °C delivers an impressive initial capacity of 615 mAh g–1 and retains 383 mAh g–1 after 250 cycles at a current density of 200 mA g–1. Furthermore, the rate-capability and the self-discharge tests reveal the superior performance of CCS@CBC at 450 °C compared to lower synthesis temperature. A higher sulfur loading (2.5 mg cm–2) electrode is also tested to evaluate the commercial aspect. The first-principles calculations are also performed to investigate the interaction of the host material with polysulfides to better understand the experimental findings. The outcome of this study can be helpful in the future development of high-performance KSBs.