Nonpolar Solvent‐based Electrolytes with a Quasi‐Solid‐State Redox Reaction for Lithium‐Sulfur Batteries

Li−S batteries are one of the most promising next‐generation batteries because of their high theoretical energy density and abundance of active material sulfur reducing the cost. However, conventional ether‐based electrolytes suffer from active material loss due to side reactions between dissolved polysulfides and Li metal anode, and consequential shuttle phenomenon. Herein, a promising concept of nonpolar solvent‐based electrolytes consisting of nonpolar solvent of 1,4‐difluorobenzene, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and chelating agent for Li + cations, such as 15‐crown‐5 or 1,3‐dioxolane, is introduced to suppress the dissolution of polar polysulfides. Nonpolar electrolytes show a distinctive reaction mechanism that involved a quasi‐solid‐state redox reaction, compared to conventional ether‐based electrolytes. The discharge and charge process of nonpolar electrolytes include phase transitions with sparingly soluble and insoluble polysulfides. As a result, nonpolar solvent‐based electrolytes show excellent electrochemical performance, such as stable capacity retention and Coulombic efficiency of 93.1 % after 100 cycles at 30 °C.