Solid Electrolyte Interphase (SEI) layer is generally formed due to the inorganic and organic electrolyte decomposition products on electrodes. Ideally, this protective layer prevents further decomposition of electrolyte by blocking the electron transport while Li ions can be transported through the layer for the Li batteries to function. Several factors can influence the chemical and structural properties of SEI layer during charging and discharging cycles resulting in capacity fading. In particular, parasitic reactions of electrolyte and polysulfides with Li-anode lead to the formation of complex SEI layers, which is the major reason behind severe capacity fading in the lithium sulfur (Li-S) batteries. Recently, we have developed a chemically specific capability which combines the in-situ x-ray photoelectron spectroscopy (XPS) and chemical imaging analysis with ab initio molecular dynamics (AIMD) computational modeling to gain fundamental understanding regarding the evolution of SEI layer in these battery materials. This study uniquely revealed that the SEI layer evolution has three major stages: (i) the formation of a primary composite mixture phase involving stable lithium compounds (including Li2S, LiF, and Li2O); (ii) the formation of a secondary matrix type phase due to cross interaction between reaction products and electrolyte components and (iii) an observation of a highly dynamic mono-anionic polysulfide (i.e. LiS5) fouling process. In this presentation, these results will be highlighted along with the pros and cons of this unique capability.

Chemical imaging of redox active molecules in SEI layer of Li-S batteries using in-situ x-ray photoelectron spectroscopy

254th National Meeting (2017)

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