Lithium‐Sulfur Batteries with Triethylsulfonium Bis(trifluoromethane sulfonyl)imide Ionic Liquid During First Charge‐Discharge Cycling: EIS & DFT Study

Abstract With high theoretical capacity and energy density, lithium‐sulfur batteries (Li−S) have the potential to meet future energy demands including electric vehicles. Various strategies have been developed to address the challenges of Li−S batteries such as polysulfide shuttling, capacity fading, and lithium dendrite formation. By using suitable electrolyte additives, it is possible to enhance the interfacial properties of Li−S batteries and mitigate polysulfide shuttling. In the present work, an aprotic ionic liquid Triethylsulfonium bis(trifluoromethane sulfonyl)imide ([S 222 ][TFSI]) has been used as an electrolyte additive, and the physico‐electrochemical and interfacial properties are investigated. The Li||Li cell with hybrid electrolyte shows stable interfacial resistance and the EIS study during the first discharge and charge of Li−S cell demonstrates stable charge transfer and bulk resistances which indicate the enhanced interfacial properties and the inhibition of polysulfide shuttling. The first‐principles calculations were conducted to investigate the nature of the interaction between the lithium polysulfides (LiPSs) and the [S 222 ][TFSI] molecule. Long chain LiPSs (Li 2 S x , 4< x <8) interact with [S 222 ][TFSI] molecule via Li‐bond and hyperconjugation effect. [S 222 ][TFSI] shows the ability to dissolve Li 2 S and Li 2 S 2 precipitation at the cathode surface which can result in increased utilization of active sulfur and reduced capacity fading.