Solvation of the Fluorine Containing Anions and Their Lithium Salts in Propylene Carbonate and Dimethoxyethane

TL;DR

This study uses PM7-MD simulations to investigate the solvation behavior of fluorine-containing anions in PC-DME electrolyte mixtures, revealing weak anion solvation and the formation of neutral ion pairs in concentrated solutions.

Contribution

It provides new insights into anion solvation and pairing in electrolyte solutions relevant for lithium-ion batteries, using electronic-structure level simulations.

Findings

Anions are weakly solvated in PC-DME mixtures.

Both BF4 and PF6 tend to form neutral ion pairs in concentrated solutions.

The absence of suitable coordination sites explains weak anion solvation.

Abstract

Electrolyte solutions based on the propylene carbonate (PC)-dimethoxyethane (DME) mixtures are of significant importance and urgency due to emergence of lithium-ion batteries. Solvation and coordination of the lithium cation in these systems have been recently attended in detail. However, analogous information concerning anions (tetrafluoroborate, hexafluorophosphate) is still missed. This work reports PM7-MD simulations (electronic-structure level of description) to include finite-temperature effects on the anion solvation regularities in the PC-DME mixture. The reported result evidences that the anions appear weakly solvated. This observation is linked to the absence of suitable coordination sites in the solvent molecules. In the concentrated electrolyte solutions, both BF4 and PF6 prefer to exist as neutral ion pairs (LiBF4, LiPF6).