Deciphering Ionic Conductivity Differences in Linear Carbonate Electrolytes: Conformational Shrinkage and Solvation Structure in Dimethyl vs Diethyl Carbonate
Year: 2026
Type: preprint
Abstract: Dimethyl carbonate (DMC)-based electrolytes consistently show higher ionic conductivity than diethyl carbonate (DEC)-based ones despite their comparable viscosities and dielectric constants. Here, classical MD simulations with LiPF 6 as the salt are used to elucidate the molecular origins of this difference. LiPF 6 -DMC electrolytes contain a larger population of solvent-separated ion pairs (SSIPs), whereas LiPF 6 -DEC electrolytes exhibit a higher population of ion aggregates (AGGs). Among various species, SSIPs make the dominant contribution to ionic conductivity, accounting for the higher conductivity of DMC-based electrolytes. Both solvents exist predominantly in two conformations, cis-cis (CC) and cis-trans (CT), defined by the torsional angle about the C-O bond; the former is largely non-polar, while the latter has a substantial dipole moment of nearly 4 D. In both electrolytes, the CT fraction increases with salt concentration, consistent with the stronger ion-dipole interactions of the CT conformer with ions and the fractions are comparable for DMC and DEC. Nevertheless, DMC retains a larger fraction of lithium ions as SSIPs. Although CT-DMC and CT-DEC have nearly identical polarities, more CT-DMC molecules coordinate Li + than CT-DEC molecules do. This difference arises from their distinct conformational sizes: CT-DMC has a volume approximately 8% smaller than that of CC-DMC, whereas the corresponding decrease for DEC is only about 2%. The smaller relative size of CT-DMC permits more of it to coordinate Li + to yield effective electrostatic shielding. This, in turn, leads to a larger SSIP population and higher ionic conductivity of LiPF 6 -DMC relative to LiPF 6 -DEC.
Source: ChemRxiv
Authors: Mansi Jain, Sundaram Balasubramanian
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214611367