The mechanism of Li+ transport in ether-based electrolyte

Abstract

Molecular dynamics (MD) simulations are performed on the ether-based electrolyte, composed of 1 M lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) dissolved in the ether-based electrolyte of 1,3-dioxolane (DOL)/ 1,2-dimethoxyethane (DME) (v:v=1:1), at temperatures of 298.15 K, 273.15 K, 253.15 K, 233.15 K, and 213.15 K, respectively. The simulation demonstrates that the solvated Li⁺ is much more strongly binding with DME than with DOL or TFSI^-, various coordination structures of Li⁺, including solvent separated Li⁺’s (SSLis), contact ion pairs (CIPs), and aggregates (AGGs), co-exist in the electrolyte. The migration of Li⁺ is driven by vehicular mechanism, in the sense that the strongly coordinating DME acts as vehicle of Li⁺, which migrates with DME while exchanging the weakly coordinating DOL or TFSI^-. At low temperature, the populations of CIPs and AGGs are much reduced, and the dominant solvation structure is the SSLi consisting of Li⁺ coordinated by three DMEs. In such case, Li⁺ is trapped in the cage solely consisting of the strongly coordinating DME with low ionic conductivity, featured by decrease of the partial transference number of the self-contribution of Li⁺ with decreasing temperature.