<i>Operando</i> Raman Spectroscopic Analysis for Electrolyte/Electrode Interface Reaction in Lithium–Sulfur Batteries with Sparingly Solvating Electrolyte

Understanding electrolyte/electrode interface reactions during battery operation is essential for the development and optimization of next-generation secondary batteries. There have been many reports on the discharge reaction mechanism in lithium sulfur batteries, which are next-generation secondary batteries. However, most of these reports are related to the sulfur reduction reaction, which is strongly affected by the electrolyte system. Here, we investigated not only the active material sulfur but also the electrolyte near the interface during discharging using operando Raman spectroscopic methods to reveal the discharge behavior in a Lithium sulfur battery with sulfolane (SL)-based concentrated electrolyte and lithium-glyme solvate ionic liquid (Li-G SIL). We have succeeded in experimentally demonstrating that the concentration polarization of Li+ occurs significantly in the Li-G SIL system with a low Li+ transference number. This is consistent with the fact that the intermediate products differ: the intermediates produced in the SL-based electrolyte system contain Li+, whereas in the G4-based electrolyte system, the chemical species containing Li+ is hardly confirmed. We believe that the difference in the Li+ concentration at the interface affects the overvoltage of the battery.