Reaction behavior of sulfur cathode composites in all-solid-state Li-S batteries

Abstract

This study investigates the reaction behavior of cathode composites in all-solid-state lithium–sulfur batteries as a function of sulfur content. Cathode composites with sulfur contents of 30, 50, and 70 wt% are denoted as S30, S50, and S70, respectively. In all-solid-state systems, sulfur conversion reactions proceed along constrained solid-state pathways, and increasing sulfur content leads not only to a reduced reaction extent but also to changes in the spatial pathways of the conversion reaction. Full cell and dQ/dV analyses show that higher sulfur content lowers the onset voltage of the conversion reaction and increases polarization, causing the reaction to become confined to localized regions. Structural analyses reveal that S30 maintains relatively stable and reversible conversion behavior, whereas S50 exhibits limited reaction activity. In contrast, S70 shows pronounced structural instability accompanied by non-uniform conversion reactions in bulk and surface regions. Overall, the performance limitation of high-sulfur electrodes originates from spatial disconnection of conversion reaction pathways and associated structural instability, rather than from reduced sulfur utilization alone. These results provide insights into high-sulfur cathode design in all-solid-state lithium– sulfur batteries and may also serve as a reference for studies on solid–solid interfacial reactions.