Structure and dynamics of highly concentrated LiTFSI/acetonitrile electrolytes

Filippa Lundin, Luis Aguilera, Henriette Wase Hansen, Sebastian Lages, Ana Labrador, Kristine Niss, Bernhard Frick, Aleksandar Matic*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

Abstract

High salt concentration has been shown to induce increased electrochemical stability in organic solvent-based electrolytes. Accompanying the change in bulk properties is a structural ordering on mesoscopic length scales and changes in the ion transport mechanism have also been suggested. Here we investigate the local structure and dynamics in highly concentrated acetonitrile electrolytes as a function of salt concentration. Already at low concentrations ordering on microscopic length scales in the electrolytes is revealed by small angle X-ray scattering, as a result of correlations of Li+ coordinating clusters. For higher salt concentrations a charge alternation-like ordering is found as anions start to take part in the solvation. Results from quasi-elastic neutron spectroscopy reveal a jump diffusion dynamical process with jump lengths virtually independent of both temperature and Li-salt concentration. The jump can be envisaged as dissociation of a solvent molecule or anion from a particular Li+ solvation structure. The residence time, 50-800 ps, between the jumps is found to be highly temperature and Li-salt concentration dependent, with shorter residence times for higher temperature and lower concentrations. The increased residence time at high Li-salt concentration can be attributed to changes in the interaction of the solvation shell as a larger fraction of TFSI anions take part in the solvation, forming more stable solvation shells.

Original languageEnglish
JournalPhysical Chemistry Chemical Physics
Volume23
Issue number25
Pages (from-to)13819-13826
Number of pages8
ISSN1463-9076
DOIs
Publication statusPublished - 7 Jul 2021

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