Cage Dynamics-Mediated High Ionic Transport in Li-O2 Batteries with a Hybrid Aprotic Electrolyte: LiTFSI, Sulfolane, and N,N-Dimethylacetamide

Abstract

Mixed electrolytes perform better than single solvent electrolytes in aprotic lithium-O2 batteries in terms of stability and transportation. According to an experimental study, a mixed electrolyte consisting of dimethylacetamide (DMA)/sulfolane (TMS) with lithium bisfluorosulfonimide (LiTFSI) showed high ionic conductivity, oxygen solubility, remarkable stability, and better cycle life than only DMA-based or TMS-based electrolytes. In this work, we used classical molecular dynamics simulations to explore the structure and ionic dynamics of the DMA/TMS hybrid electrolytes at two compositions. We calculated radial, combined, and spatial distribution functions for the structural examination. These properties depict a minimal change in the electrolyte structure by increasing the DMA content in the electrolyte from 20 to 50% by volume. We used the diffusive regimes from mean square displacements for diffusion coefficient calculations. Ionic conductivities calculated using the Green-Kubo equation have an acceptable agreement with the experimental values, whereas the Nernst-Einstein relation is found insufficient to explain the ionic transport. The relatively lower value of the ion-cage lifetime of electrolyte components with 50% DMA shows their faster dynamics. Moreover, we present the new physical insight by focusing on ion-pair and ion-cage formation and their correlation with ionic conductivity. The atomic-level understanding through this work may assist in designing electrolytes for aprotic Li-O2 cells.