Prevention of Electrolyte Degradation in Lithium–Oxygen Batteries Using Highly Concentrated Electrolytes

Lithium–oxygen battery performance is limited by the instability of the electrolytes. Herein, it is shown that highly concentrated DMSO and DMF electrolytes improved resistance to degradation compared to lower electrolyte concentrations. Gravimetric capacities of DMSO-based electrolytes decreased modestly with increasing molar ratio up to 0.4, demonstrating the ability of highly concentrated electrolytes to perform relatively well at the higher concentrations needed to help reduce electrolyte degradation. These cells maintain their cycling lifetimes up to a molar ratio of 0.3 before a dramatic decrease is seen. Previously, DMF had been disregarded as a viable electrolyte in Li–O2 batteries due to very low gravimetric capacities at low concentrations and a very short cycle life. Here, it is demonstrated for the first time that performance in DMF greatly improves with increasing the Li salt-to-solvent molar ratio, with the capacity peaking at 0.4 for LiTFSI–DMF electrolytes matching the best performance in DMSO at low concentrations. Furthermore, increasing the LiTFSI–DMF concentration greatly improves cycling lifetimes, with cycling lifetimes almost tripling when the LiTFSI–DMF molar ratio increases from 0.1 to 0.25, ~60% larger than that achieved with DMSO. These results suggest that other electrolyte solvents previously thought unusable should be reconsidered for use in Li–O2 batteries at high concentrations.