Computational Study of Triethylsulfonium-Based Ionic Liquids in lithium-battery electrolyte systems

We hereby report an in-silico investigation of a few lithium-triethylsulfonium electrolytes and correlate our results to the recently published electrochemical study. All chosen organic and inorganic anions were recently used in the supercapacitor and lithium-battery electrolyte systems: bis(trifluoromethylsulfonyl)imide, perchlorate, hexafluorophosphate, trifluoromethanesulfonate. By analyzing potential energy surfaces, ion-ionic coordination, electron density distributions, and structure properties, we identified that the best-performing electrolyte system is lithium bis(trifluoromethylsulfonyl)imide dissolved in triethylsulfonium bis(trifluoromethylsulfonyl)imide. In the mentioned system, we found the weakest cation-anion binding that resulted in the fastest ionic transport. The lithium-ion plays a paramount role in the coordination of all investigated anions, whereas the impact of the triethylsulfonium cation is relatively insignificant. The lithium-induced structural changes in the local order of the electrolyte are reflected by the computed vibrational spectra. In the lithium-free systems, the anions strongly bind the triethylsulfonium cation via its electron-deficient α-methyl groups. Some of these electrostatically-driven interactions may be classified as medium-strength hydrogen bonds. The computed cohesion energies explain the conductivity and viscosity trends obtained for similar electrolyte compositions in the recent experiments. The reported results will be interesting for researchers who develop Li-based energy storage devices that use room-temperature ionic liquids as non-volatile and electrochemically stable media.

Keywords:

lithium-ion , ionic liquids , sulfonium , supercapacitor , Li-battery