Stabilizing Effect of Polysulfides on Lithium Metal Anodes in Sparingly Solvating Solvents

Electrolytes with sparingly polysulfide solubility such as 1.5 M LiTFSI in tetramethylene sulfone (TMS) and 1,1,2,2-tetrafluoroethyl- 2,2,3,3-tetrafluoropropyl ether (TTE) are beneficial for the cycle stability of Li-S pouch cells. In this work, this specific electrolyte system and the role of dissolved polysulfides (PS) in symmetrical Li/Li cells is investigated. By studying varying TMS/TTE volume ratios and polysulfide addition aided by both ex situ and operando spectroscopic as well as microscopic techniques, the positive impact of PS on the lithium plating/ stripping behavior is evaluated. The composition of the solid-electrolyte interphase (SEI) as well as the microscopic morphology differs for electrolytes with PS from those without PS addition. These findings are crucial for the development of electrolytes for cycle-stable Li-S prototype cells.