Deciphering the Reaction Mechanism of Lithium-Sulfur Batteries by In Situ/Operando Synchrotron-Based Characterization Techniques

Lithium-sulfur (Li-S) batteries have received extensive attention as one of the most promising next-generation energy storage systems, mainly because of their high theoretical energy density and low cost. However, the practical application of Li-S batteries has been hindered by technical obstacles arising from the polysulfide shuttle effect and poor electronic conductivity of sulfur and discharge products. Therefore, it is of profound significance for understanding the underlying reaction mechanism of Li-S batteries to circumvent these problems and improve the overall battery performance. Advanced characterization techniques, especially synchrotron-based X-ray techniques, have been widely applied to the mechanistic understanding of Li-S batteries. Specifically, in situ/operando synchrotron-based techniques allows chemical and structural evolution to be directly observed under real operation conditions. Here, recent progress in the understanding of the operating principles of Li-S batteries based on in situ/operando synchrotron-based techniques, including X-ray absorption spectroscopy, X-ray diffraction, and X-ray microscopy, is reviewed. The aim of this progress report is to provide a comprehensive treatise on in situ/operando synchrotron-based techniques for mechanism understanding of Li-S batteries, and thereby provide guidance for optimizing their overall electrochemical performances.