Quantitative Chromatographic Determination of Dissolved Elemental Sulfur in the Non-Aqueous Electrolyte for Lithium-Sulfur Batteries

Abstract

A fast and reliable analytical method is reported for the quantitative determination of dissolved elemental sulfur in non-aqueous electrolytes for Li-S batteries. By using high performance liquid chromatography with a UV detector, the solubility of S in 12 different pure solvents and in 22 different electrolytes was determined. It was found that the solubility of elemental sulfur is dependent on the Lewis basicity, the polarity of solvents and the salt concentration in the electrolytes. In addition, the S content in the electrolyte recovered from a discharged Li-S battery was successfully determined by the proposed HPLC/UV method. Thus, the feasibility of the method to the online analysis for a Li-S battery is demonstrated. Interestingly, the S was found super-saturated in the electrolyte recovered from a discharged Li-S cell.

Progress in Mechanistic Understanding and Characterization Techniques of Li‐S Batteries

“…[ 29,51 ] In addition, lithium polysulfi des can be readily formed in many solvents by adding elemental sulfur and Li 2 S together. [ 26,[52][53][54][55] Different polysulfi de anions in solution usually co-exist with dynamic equilibrium, because the Gibbs free energy (Δ G o ) of each polysulfi de anion is very close, as shown in Table 1 .…”

“…In fact, even sulfur can be weakly dissolved in an aprotic electrolyte. [ 29,59,[64][65][66] This feature facilitates the sulfur reduction process to some degree. It is worth mentioning that sulfur reduction kinetics is easier than Li 2 S oxidation because the solubility of sulfur is higher than that of Li 2 S in most organic solvents, despite the conductivity of S being even lower than that of Li 2 S. However, the sulfur species dissolution had a negative impact on Li-S battery performance.…”

“…Contrary to the limitations in differentiating the various lithium polysulfi des in the solid state, the speciation of polysulfi de anions and radicals in non-aqueous solution has been realized by using several advanced characterization techniques, including NMR, [ 20,112,114 ] Raman spectroscopy, [ 19,105,115 ] XAS, [ 116,117 ] UV-vis, [ 29,59,118 ] Adv. Energy Mater.…”

“…Energy Mater. 2015, 5, 1500408 www.MaterialsViews.com www.advenergymat.de wileyonlinelibrary.com liquid chromatography/mass spectrometry (LC/MS) [ 29,59,114,119,120 ] and electron paramagnetic resonance/electron spin resonance (EPR or ESR). [ 27,59 ] The peak attributions were mainly performed by either comparing them with lithium polysulfi de reference solutions prepared with different ratios of sulfur and Li 2 S [ 27,59,112,118 ] or by simulations, [ 20,30,116,121 ] or both.…”

“…The most recent cutting-edge analytical technologies enable the direct observation of polysulfi de radicals in the electrolyte, though an in situ electron paramagnetic resonance (EPR) technique; [ 27 ] visualization of the sulfur particle changes and polysulfi de dissolution during charge and discharge; [ 28 ] and the quantitative chromatographic determination of dissolved elemental sulfur in organic solvents. [ 29 ] To complement the characterization efforts, modeling and calculations are important with respect to peak identifi cation in experimental spectroscopy and kinetics and dynamics studies. [30][31][32] This review mainly focuses on the fundamental Li-S electrochemistry and the advanced characterization techniques, which help gain insight into the Li-S battery mechanism and direct future cell design.…”