Unraveling the Correlation between Solvent Properties and Sulfur Redox Behavior in Lithium-Sulfur Batteries

Abstract

Systematic understanding of how solvent property influences Li-S redox chemistry is required to develop an effective electrolyte for Li-S batteries. In this study, we investigate the correlation between solvent property and Li-S redox chemistry in nine non-aqueous electrolyte solvents that cover a wide range of three main solvent physiochemical properties, namely dielectric constant (ε), Gutmann donor number (DN), and acceptor number (AN). We exploit various analytical techniques including cyclic voltammetry, rotating ring disk electrode technique, UV-Vis spectroscopy and galvanostatic measurement in a two-compartment cell. We show that the potential of S 8-reduction increases with increasing AN and that the polysulfide-reduction/oxidation is strongly influenced by the DN. The common discrepancy in the literature on the role of dielectric constant and donor number is addressed by examining the redox reactions, polysulfide stability, and the effect of salt concentration in acetonitrile-a solvent with high dielectric constant and low DN. We show that the DN is the primary descriptor for polysulfide redox reactions, as it controls the effective charge density of the solvated cation (Li +), which affects the stability of polysulfides with different charge density via Pearson's Hard Soft Acid Base theory.

Electrocatalytic H2 Evolution by the Co‐Mabiq Complex Requires Tempering of the Redox‐Active Ligand

“…A platinum wire, separated via a glass fitting was used as the counter electrode. Ag/AgNO 3 (0.1 M AgNO 3 and 0.1 M LiBF 4 in MeCN) was used as the reference electrode, separated via a Vycor 3535 frit (Advanced Glass & Ceramics, Holden, MA) …”

Editors' Choice—Understanding Chemical Stability Issues between Different Solid Electrolytes in All-Solid-State Batteries

“…In order to confirm the development of polysulfides during aging of LSPS with PEO as suggested by XPS analysis (Figure 5a), UV-Vis spectroscopy based studies showed that the detected S n 2− species thereby depends on the properties of the solvent. [54][55][56] In solvents with anion. To determine whether polysulfides were produced during the aging of the PEO 15 LiTFSI | LSPS interface at 60°C over 7 days, the aged PEO 15 LiTFSI membranes were rinsed in DMA and diglyme, respectively.…”

Understanding the Reaction Steps Involving Polysulfides in 1 M LiTFSI in TEGDME : DOL Using Cyclic Voltammetry Experiments and Modelling

“…The polysulfides are produced via the dissolution of S 8(s) and the subsequent reduction of dissolved sulfur (S 8 ) in the electrolyte. The presence of different polysulfide intermediates and their reaction steps change with the solvents used in the electrolyte [3–5] . Therefore identifying all the possible polysulfides in the electrolyte and their reaction steps can assist in improving the assessment of performance limitations.…”

“…Cyclic voltammograms (CVs) of dissolved sulfur (S 8 ) in nonaqueous organic electrolytes, have long been known to possess two distinctive reduction peaks and sometimes with a small intermediate peak termed prewave in between them which is observed in some electrolytes [9,12,13,15,16] . However, CV of S 8 in 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dioxane:dimethoxyethane (Diox:DME) consists only one reduction peak [5] . While, the number of oxidation peaks vary from one to three based on the solvents used in the electrolyte solutions [5] …”

“…However, CV of S 8 in 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dioxane:dimethoxyethane (Diox:DME) consists only one reduction peak [5] . While, the number of oxidation peaks vary from one to three based on the solvents used in the electrolyte solutions [5] …”