In-Situ Raman Investigation of Polysulfide Formation in Li-S Cells

Abstract

To obtain information about the Li-S reaction mechanism through spectroscopy, a Raman literature study, polysulfide vibrational mode calculations and experimental in-situ measurements were performed. A special test cell was constructed to examine in-situ Raman spectra in the spectral range from 100 cm−1 to 600 cm−1 during charge and discharge in the voltage range of 1.5 V to 3.0 V. In order to assign the in-situ Raman data and to support the interpretation of the observed changes in the overall Raman-spectrum, several reference measurements on well-defined substances were conducted. The reference measurements included pure solvents, electrolytes and polysulfide solutions prepared from stoichiometric mixtures of S8 and Li2S powders. The assignment of the observed Raman-spectra was further based on a comparison with purely theoretical data for the vibrational modes of the polysulfide di-anions Sn2− and radical mono-anions Sn− calculated at the B3PW91/6–311G(2df,p) level of density functional theory (DFT). The DFT data for the vibrational spectra, corrected for solvent effects in the framework of the polarizable continuum model (PCM), allowed an identification of several characteristic features in the in-situ Raman spectra.

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

“…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.…”

“…[ 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. [ 19 ] Simulations can avoid ambiguities present in experiments, such as the potential coexistence of multiple polysulfi de species in ratios that are likely a complex function of experimental conditions and electrochemical state.…”

“…Also, recent in-situ experiments confi rmed Li 2 S deposition during discharge and sulfur re-precipitation during charge on the cathode. [19][20][21][22][23] Furthermore, recent characterization results changed the speculation on the main reason for the poor cycle life, which is now believed to be electrolyte depletion along with Li 2 S layer formation [ 8,16,24,25 ] rather than the polysulfi de dissolution that was widely believed previously. [ 17,26 ] These new understandings in Li-S electrochemistry were based on the application of advanced characterization techniques, especially in-operando techniques, such as X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), ultraviolet-visible (UV-vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-performance liquid chromatography (HPLC).…”

A simple, experiment-based model of the initial self-discharge of lithium-sulphur batteries

“…However, in the pathway of sulphur reduction, lithium polysulphides of variable chain length, Li 2 S n , are formed [13][14][15][16][17][18][19][20][21]:…”

Efficient Electrolytes for Lithium–Sulfur Batteries

“…In the recent years, many review articles are available in the literature describing the working principles, advantages, and limitations of lithium/sulfur batteries (Ji and Nazar, 2010;Barghamadi et al, 2013;Bresser et al, 2013;Manthiram et al, 2013;Nazar and Evers, 2013). Also, numerous articles appear on the fundamental chemistry Zhang, 2013a), performance of modified cathode materials (Ji et al, 2009;Liang et al, 2009;Yang et al, 2011;Fu et al, 2012), their fading mechanism (Diao et al, 2013), AFM, and Raman characterizations (Aurbach et al, 2009;Elazari et al, 2010;Yeon et al, 2012;Hagen et al, 2013) in situ XRD (Canas et al, 2013a) and impedance analysis (Yuan et al, 2009;Canas et al, 2013b). The preparation and characterization of cathode and anode materials for Li-S batteries are beyond the scope of this article.…”