Understanding Ion Transport in Alkyl Dicarbonates: An Experimental and Computational Study

In an effort to improve safety and cycling stability of liquid electrolytes, the use of dicarbonates has been explored. In this study, four dicarbonate structures with varying end groups and spacers are investigated. The effect of these structural differences on the physical and ion transport properties is elucidated, showing that the end group has a significant influence on ion transport. The solvation structure and ion transport in the dicarbonates are compared to those of the linear carbonates dimethyl carbonate (DMC) and diethyl carbonate (DEC). Although the carbonate coordination numbers (CN) are similar in the different systems, the CN from the anion is higher in dicarbonate electrolytes. At low salt concentrations, rapid solvent exchange is observed in the DMC- and DEC-containing systems, transitioning to a more correlated ion transport at high salt concentration. In contrast, the exchange of solvents around lithium ions (Li⁺) is limited in the dicarbonate systems regardless of the salt concentration, with only one carbonate group from each molecule participating in the coordination. In addition, according to the molecular dynamics simulations, Li⁺ mainly moves together with coordinating dicarbonate molecules and anion(s).