The Solvation Structure of Lithium Ions in an Ether Based Electrolyte Solution from First-Principles Molecular Dynamics.

Abstract

The solvation and desolvation of the Li ion play a crucial role in the electrolytes of Li based secondary batteries, and their understanding at the microscopic level is of great importance. Oligoether (glyme) based electrolytes have attracted much attention as electrolytes used in Li based secondary batteries, such as Li-ion, Li-S, and Li-O2 batteries. However, the solvation structure of the Li ion in glyme based electrolytes has not been fully clarified yet. We present a computational study on the solvation structure of lithium ions in the mixture of triglyme and lithium bis(trifluoromethylsulfonyl)-amide (LiTFSA) by means of molecular orbital and molecular dynamics calculations based on density functional theory. We found that, in the electrolyte solution composed of the equimolar mixture of triglyme and LiTFSA, lithium ions are solvated mainly by crown-ether-like curled triglyme molecules and in direct contact with an TFSA anion. We also found the aggregate formed with Li ion and TFSA anions and/or triglyme molecule(s) is equally stable, which has not been reported in the previous classical molecular dynamics simulations, suggesting that in reality a small fraction of Li ions form aggregates and they might have a significant impact on the Li ion transport. Our results demonstrate the importance of performing electronic structure based molecular dynamics of electrolyte solution to clarify the detailed solvation structure of the Li ion.