Anthraquinone-Based Charge Redox Mediator in Sulfolane-Based Electrolyte for Lithium–Sulfur Batteries

Lithium–sulfur battery has attracted attention as a next-generation secondary battery because of its high energy density (2500 Wh kg–1), low cost, and low environmental impact. However, it has some disadvantages such as poor electronic conductivity of Li2S, which leads to high overvoltage, and polysulfide dissolution, which causes capacity decay and charge–discharge inefficiency. The overvoltage during charge was overcome by utilizing charge redox mediators (C-RM). Meanwhile, sulfolane (SL)-based electrolytes have been reported to reduce polysulfides elution. This paper first reports a selection of suitable C-RMs and modifications of functional groups to obtain suitable redox potentials in SL electrolyte. The findings of this study are particularly useful for systems with high overvoltage, such as those using Li2S cathode, and systems with low polysulfide solubility, since these systems are significantly affected by RM.