Ex-Situ Raman Microscopic Investigation of the High-Order Polysulfide Restriction of Encapsulated Sulfur Nanowires

Lithium-sulfur (Li−S) batteries are attracting significant research attention because of their high theoretical energy density (2500 Wh kg⁻¹) and excellent economic feasibility. However, commercialization has proven difficult owing to their low electronic conductivity and the dissolution of lithium polysulfide (Li₂S_x; x=1–8). In particular, lithium polysulfide dissolution is known to be caused by high-order polysulfide generated at the start of the discharge process. Thus, the control of this factor is important because it determines the electrochemical performance of the cell. In this study, three types of sulfur nanocomposites in the orthorhombic, amorphous, and monoclinic phases, were designed and successfully manufactured. The mechanism of polysulfide generation was confirmed to differ according to the location of sulfur on the carbon matrix (inner pores and surfaces) and allotropic form of sulfur (S₄–S₈) via electrochemical tests. Furthermore, the electrochemical reaction mechanism was identified by tracing the lithium polysulfide species according to the reaction region using ex-situ Raman spectroscopy. In this research, suppression of the high-order polysulfide generation reaction by controlling the monoclinic sulfur was represented by a single plateau galvanostatic curve, suggesting a clear strategy for maximizing cycle stability in next-generation Li−S batteries.