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

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 ([S222][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 [S222][TFSI] molecule. Long chain LiPSs (Li2Sx, 4<8) interact with [S222][TFSI] molecule via Li-bond and hyperconjugation effect. [S222][TFSI] shows the ability to dissolve Li2S and Li2S2 precipitation at the cathode surface which can result in increased utilization of active sulfur and reduced capacity fading. Triethylsulfonium bis(trifluoromethane sulfonyl)imide ([S222][TFSI]) ionic liquid as an electrolyte additive demonstrated stable charge transfer and bulk resistances. It also enhanced interfacial properties and controlled polysulfide shuttling. The DFT calculations show that the lithium polysulfides interact with [S222][TFSI] molecule via Li-bond and hyperconjugation effect. [S222][TFSI] shows the ability to dissolve Li2S and Li2S2 precipitation at the cathode.image

Automated summary

By using suitable electrolyte additives, the interfacial properties of lithium-sulfur batteries can be enhanced and the polysulfide shuttling can be mitigated. This study investigates the use of an aprotic ionic liquid Triethylsulfonium bis(trifluoromethane sulfonyl)imide ([S222][TFSI]) as an electrolyte additive and demonstrates its stable charge transfer and bulk resistances, as well as its ability to enhance interfacial properties and control polysulfide shuttling.