Structure and Dynamics of Polysulfide Clusters in a Nonaqueous Solvent Mixture of 1,3-Dioxolane and 1,2-Dimethoxyethane

Structure and Dynamics of Polysulfide Clusters in a Nonaqueous Solvent Mixture of 1,3-Dioxolane and 1,2-Dimethoxyethane

TitleStructure and Dynamics of Polysulfide Clusters in a Nonaqueous Solvent Mixture of 1,3-Dioxolane and 1,2-Dimethoxyethane
Publication TypeJournal Article
Year of Publication2019
AuthorsAmity Andersen, Nav Nidhi Rajput, Kee Sung Han, Huilin Pan, Niranjan Govind, Kristin A Persson, Karl T Mueller, Vijayakumar Murugesan
JournalChemistry of Materials
Volume31
Issue7
Pagination2308 - 2319
Date Published02/2019
ISSN0897-4756
Abstract

Molecular clustering and associated dynamic processes of lithium polysulfide species were unraveled using classical molecular dynamics and ab initio metadynamics calculations. The spectroscopic signatures of polysulfide clusters were analyzed using a multimodal analysis including experimental and computational nuclear magnetic resonance (NMR) and X-ray absorption spectroscopies. Lithium polysulfide solutes (Li2S4, Li2S6, and Li2S8) and their mixtures in a 1,3-dioxolane and 1,2-dimethoxyethane (DOL/DME) solvent undergo aggregation driven by intramolecular lithium–sulfur (Li–S) interactions, leading to distributions of cluster sizes, which could critically influence the functioning of lithium–sulfur batteries. Representative polysulfide clusters with systematic increases in molecular size were extracted from the classical molecular dynamics trajectories for subsequent structural and spectroscopic property calculations using density functional theory analysis. Structural analysis of these clusters reveals progressively decreasing solvent involvement in Li+coordination varying from Li2S4 to Li2S8, with more pronounced variation and changes in DME compared with those in DOL. These observations are reflected in the analysis of the experimental and theoretical 7Li and 17O NMR chemical shifts and pulsed field gradient-NMR diffusion measurements. A comparison of experimental and theoretical S K-edge X-ray absorption near edge spectra shows that relatively large lithium sulfide chain clusters are likely to occur in the DOL/DME-solvated lithium sulfide systems. Ab initio metadynamics simulations and NMR analysis indicate that Li+ solvated by only the solvent can occur through Li+ dissociation from sulfide chains. However, the occurrence of “sulfide-free” Li+ is a minor mechanism compared with the dynamic aggregation and shuttling processes of polysulfide solvates in DOL/DME-based electrolytes of Li–S batteries. Overall, atomistic insights gained about clustering and lithium exchange dynamics will be critical for the predictive understanding of the polysulfide shuttling and nucleation process that dictates the Li–S battery performance.

DOI10.1021/acs.chemmater.8b03944
Short TitleChem. Mater.
Refereed DesignationRefereed