Solvent-Dictated Lithium Sulfur Redox Reactions: An Operando UV–vis Spectroscopic Study

• Published in: The journal of physical chemistry letters 2016-04, Vol.7 (8), p.1518-1525
• Main Authors: Zou, Qingli, Lu, Yi-Chun
• Format: Article
• Language: English
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.6b00228

Fundamental understanding of solvent’s influence on Li–S redox reactions is required for rational design of electrolyte for Li–S batteries. Here we employ operando UV–vis spectroscopy to reveal that Li–S redox reactions in high-donor-number solvents, for example, dimethyl sulfoxide (DMSO), undergo multiple electrochemical and chemical reactions involving S8 2–, S6 2–, S4 2–, and S3 •–, where S3 •– is the most stable and dominant reaction intermediate. In low-donor-number solvents, for example, 1,3-dioxolane:1,2-dimethoxyethane, the dominant reaction intermediate, is found to be S4 2–. The stability of these main polysulfide intermediates determines the reaction rates of the disproportionation/dissociation/recombination of polysulfides and thereby affects the reaction rates of the Li–S batteries. As an example, we show that dimethylformamide, a high-donor-number solvent, which exhibits stronger stabilization of S3 •– compared with DMSO, significantly reduces Li–S cell polarization compared with DMSO. Our study reveals solvent-dependent Li–S reaction pathways and highlights the role of polysulfide stability in the efficiency of Li–S batteries.