Computational Investigation of Mixed Anion Effect on Lithium Coordination and Transport in Salt Concentrated Ionic Liquid Electrolytes.

The use of high concentrations of alkali metal ion salts in ionic liquids (ILs) has been demonstrated to significantly improve electrolyte performance, increase alkali metal ion transference numbers, and promote the formation of favorable SEI structures enabling long-term stable cycling. One challenge in using this material is the overall low ionic conductivity, which is a common effect of increased salt concentration. This simulation work first investigated the strategy of using mixed anions to tune the ionic conductivity in a concentrated IL (or "ionic liquid-in-salt") system having 50 mol % lithium salt. The effects of binding strength, size, and mobility of selected anions on coordination and dynamics of lithium ions were discussed. The results confirm its feasibility and provide general guidance for the selection of anions to improve the ionic conductivity of salt-concentrated electrolyte systems based on ionic liquids and other solvent systems.