Investigation of the Reaction Mechanism of All-Solid-State Lithium-Sulfur Batteries by Operando in Situ Raman Spectroscopy

In recent years, all-solid-state lithium-sulfur batteries (ASSLSBs) with sulfide-based solid electrolytes have become a leading energy storage system due to their high ionic conductivity, ultra-high energy density, high safety, and low cost. There have been many challenges with the practical applications of Li-S batteries, however, as a result of the sluggish redox kinetics of lithium polysulfide (LPS) and its shuttling effects. Single-atom catalysts (SACs) with atomically dispersed metal-based sites have proven to be promising electrocatalysts in Li-S batteries. To construct the ASSLSBs, we design and develop MoS 2 /SnS 2 and Fe SACs with MoS 2 /SnS 2 cathodes, Li 5.4 PS 4.4 Cl 1.6 sulfide-based solid electrolytes, and Li-In anode. In the current study, in situ Raman spectroscopy is used to determine the LPS species in the sulfur cathode with SACs and without SACs during the ASSLSBs cycling. The aim is to understand the charge-discharge mechanism and the influence of SACs on the dissolution of sulfur and poly-sulfides. As compared to the MoS 2 /SnS 2 cathode, the Fe@MoS 2 /SnS 2 cathode exhibit the highest catalytic LPS conversion. In addition, the Fe@MoS 2 /SnS 2 cathode delivers a high discharge capacity and long-cycling performance with high coulombic efficiency in ASSLSBs. In operando in situ Raman studies, SACs provide important new insights into the charge-discharge reaction mechanism for the next generation of ASSLSBs.