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-O 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.

Nonpolar Alkanes Modify Lithium‐Ion Solvation for Improved Lithium Deposition and Stripping

“…presence around the lithium ion. 42 However, hexane and cyclohexane are not present within the first two solvation shells around lithium, but TTE is (dashed line in 5g). A snapshot of the first solvation shell at a distance (r = 0.33 nm) further confirms this and the inset in Figure 5g shows that TTE is present within the first solvation shell whereas the insets in Figures 5e-f do not show hexane or cyclohexane present.…”

Ionic transport in highly concentrated lithium bis(fluorosulfonyl)amide electrolytes with keto ester solvents: structural implications for ion hopping conduction in liquid electrolytes

“…[7][8][9][10][11][12] Although the basic assumptions underlying models of the ion transport processes in liquid electrolytes rely predominantly on simple physical diffusion of ions according to the Stokes-Einstein relationship, recent molecular dynamics simulation studies predicted that Li ion hopping or exchange mechanisms through frequent exchange of solvents and anions with labile Li ion coordination can contribute to the ionic conduction of highly concentrated electrolytes. [13][14][15] Despite low ionic conductivity and high viscosity, stable cycling of Li and Na ion batteries with high current density was reported for ionic liquid (IL)-based concentrated electrolytes. The improved rate capability was considered to be influenced by the increased mass transfer via ion hopping or exchange mechanisms through large ionic aggregates (Li m + X n À ) present in the IL-based concentrated electrolytes.…”

Ab initio simulations of liquid electrolytes for energy conversion and storage

“…In additional to extensive experimental studies, FPMD simulations have started to be utilized to investigate properties of this new class of electrolytes. [170,[173][174][175] For instance, Yamada et al [173] employed FPMD simulations to unravel the unique electronic structures of the superconcentrated acetonitrile solution, which can be directly related to the enhanced reductive stability of the solution in lithium-ion batteries. However, the fundamental understanding of these complex electrolytes is generally still in its infancy, which continues to stimulate further theoretical studies in the near future.…”