Lithium-Sulfur-Batteries under Lean Electrolyte Conditions: Improving Rate Capability by the Choice of the Lithium Salt in Dimethoxyethane-Hydrofluoroether-Based Electrolyte

Lithium-sulfur batteries (LSBs) are discussed as the most promising post-lithium-ion battery technology due to the high theoretical energy density and the cost-efficient, environmental-friendly active material sulfur. Unfortunately, LSBs still suffer from several limitations such as cycle life and rate capability. To overcome these issues, the development of adapted electrolytes is one promising path. Consequently, in this study, we focus on the influence of the lithium salt on the performance of LSBs. In a fixed solvent system without employing LiNO₃, five different lithium salts are compared. The electrolyte properties as well as the influence of polysulfides are determined and discussed in relation with the battery performance. Interestingly, although the different salts lead to different electrolyte properties, only a minor influence of the salt is observed at low C-rates. By performing a rate capability test, however, a strong influence of the lithium salt is detected at high C-rates, with LiFSI outperforming the other salts. This correlates well with ionic conductivity and a suppressed influence of polysulfides in case of LiFSI. To verify the results, multi-layered pouch cells were tested under lean electrolyte conditions. The study emphasizes the significance of the lithium salt and provides guidance for electrolyte design under lean electrolyte conditions.