The Quest for Polysulfides in Lithium–Sulfur Battery Electrolytes: An Operando Confocal Raman Spectroscopy Study

Abstract

Confocal Raman spectra of a lithium-sulfur battery electrolyte are recorded operando in a depth-of-discharge resolved manner for an electrochemical cell with a realistic electrolyte/sulfur loading ratio. The evolution of various possible polysulfides is unambiguously identified by combining Raman spectroscopy data with DFT simulations.

Quantitative Galvanostatic Intermittent Titration Technique for the Analysis of a Model System with Applications in Lithium−Sulfur Batteries

“…Impedance spectroscopy has also been used to evaluate the individual contributions from electrolyte resistance, charge transfer, ion diffusion and electrode surface layers, which in turn has been used to refine mechanistic models of Li−S cells,, as well as to investigate capacity fading . Other experimental techniques used to elucidate redox and diffusion properties in Li−S cells include XAS, in‐operando optical imaging of the temporal and spatial distribution of polysulfides, UV‐Vis spectroscopy, NMR, EPR/ESR,, XRD, Raman, HPLC, and gas evolution, among other electrochemical studies . The mechanism and kinetics of Li 2 S precipitation has been studied using chronoamperometry .…”

Applications of Conventional Vibrational Spectroscopic Methods for Batteries Beyond Li‐Ion

“…Artificial DFT‐calculated Raman spectra of different PS species, obtained by using B3LYP/6‐311+G* and the polarizable continuum model with diethylether (ε 15) as the solvent. Reproduced with permission . Copyright 2015, Wiley‐VCH.…”

“…[132] As a complementary technique, Raman spectroscopy has also been employed to investigate PSs at different state of charge in Li-S cells. [131] Using density functional theory (DFT) calculations and molecular dynamics simulations, the Raman features of PS ions were predicted, [133][134][135] and some simulated spectra are shown in Figure 15. [135] Typically, all of the polysulfide anions and radicals Small Methods 2018, 2, 1700332 display Raman shifts in the region of low wave numbers, i.e., <550 cm −1 .…”

“…[131] Using density functional theory (DFT) calculations and molecular dynamics simulations, the Raman features of PS ions were predicted, [133][134][135] and some simulated spectra are shown in Figure 15. [135] Typically, all of the polysulfide anions and radicals Small Methods 2018, 2, 1700332 display Raman shifts in the region of low wave numbers, i.e., <550 cm −1 . The number of peaks and vibrational modes are higher for longer PS chains; however, the trend in the wavelength of these peaks is unclear, rendering any individual assignment difficult due to the overlapping of many peaks for different PSs.…”

“…The number of peaks and vibrational modes are higher for longer PS chains; however, the trend in the wavelength of these peaks is unclear, rendering any individual assignment difficult due to the overlapping of many peaks for different PSs. With in situ and ex situ Raman experiments, [133,[135][136][137][138][139] the bands of S 8 (150, 220, and 470 cm −1 ), long-chain PS anions, such as S 8 2− and S 6 2− (≈360 and 425 cm −1 , respectively), S 4 2− (202 cm −1 ), and S 3 •− radical (≈530 cm −1 ) can be detected; however, the peaks attributed to shorter PSs, including S 3 2− and S 2 2− , are not well resolved, although the theoretical calculations by Partovi-Azar et al suggested unambiguously the presence of the Li 2 S 2 structure in the discharged product of Li-S cells. [134] Furthermore, at the end of discharge, bands for S 6 2− , S 4 2− , and S 3 •− can still be observed, which indicates an incomplete reduction.…”