(696h) Molecular Structure and Dynamics of Lithium Polysulfide Clusters in Organic Solvent Mixture

Authors: 
Murugesan, V., Pacific Northwest National Laboratory
Andersen, A., Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory
Han, K. S., Oak Ridge National Laboratory
Rajput, N. N., Tufts University
Mueller, K., Pacific Northewest National Laboratory
Govind, N., Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory
Lithium –Sulfur (Li-S) battery is plagued by dissolution and shuttling of polysulfide species during electrochemical processes, causing materials degradation and irreversible capacity loss. Our recent works on polysulfide disproportionation reactions leading to sulfide radicals (mainly S3-* ) have been observed in both experiment and theory. However, considering relatively low energy barrier (<0.5eV) of disproportionation reactions, these radicals can recombine with other polysulfide species and possibly exhibit in a dynamic equilibrium within electrolyte solution. This recombination processes can lead to polysulfide clustering and directly influence the shuttling between electrodes, interfacial reactivity at Li-anode and re-nucleation dynamics at sulfur cathode. We studied the lithium polysulfide clustering and associated dynamic processes using classical molecular dynamics and ab initio metadynamics calculations. Lithium polysulfide solutes (Li2S4, Li2S6, and Li2S8) and their mixtures in 1,3-dioxolane and 1,2-dimethoxyethane (DOL/DME) solvent exhibit distributions of polysulfide clusters. Representative polysulfide clusters with systematic increases in molecular size were extracted from the classical MD trajectories and their NMR and XAS spectroscopic signatures were analyzed at DFT level theory and compared with experimental measurements. This presentation will discuss both polysulfide clustering process and lithium exchange dynamics that can help us gain predictive understanding of lithium-sulfur electrochemical process.