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 degrees C.