Lithium sulfur battery reaction intermediates (Li2Sx, where 'x' ranges from 2 to 8) formed during charge and discharge of Li-S batteries are known to diffuse out of the cathode during cycling, thereby lowering battery capacity and lifetime. While many approaches have been taken to prevent the issue of polysulfide dissolution, many questions remain regarding the reaction mechanisms through which polysulfides are formed. Studies of the redox pathways have been challenged by the fact that Li2Sx species are difficult to differentiate experimentally. Lithium polysulfides cannot be isolated and instead only exist in solution, wherein they may undergo disproportionation reactions (e.g. 2Li2S6 goes to Li2S4 + Li2S8). This makes it difficult to obtain spectral standards for single polysulfide species that could be used to elucidate Li-S battery reaction pathways. To address these challenges, X-ray absorption spectra (XAS) of lithium polysulfide species dissolved in a model solvent (tetraethylene glycol dimethyl ether) (TEGDME) were obtained from first-principles calculations. Calculated spectra are used in tandem with experimentally obtained spectra of polysulfide species dissolved in poly(ethylene oxide) (PEO) and a block copolymer of polystyrene-poly(ethylene oxide) (SEO). The coupling of these two techniques has enabled us to obtain spectral standards for single polysulfide species and provides a rigorous approach to the analysis of experimental spectral data. Recent work has focused on explaining the molecular origin of sulfur K-edge spectral features, and how these spectral features are affected by the physical and chemical nature of polysulfide species. Here, we present the effect that varying experimental parameters may have on obtained polysulfide sulfur K-edge XAS. By exploring these effects, we provide a basis of understanding for future spectroelectrochemical studies of Li-S battery reaction mechanisms.

X-ray absorption spectroscopy of lithium sulfur battery reaction intermediates

249th National Meeting (2015)

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