Understanding carbon-based electrode architectures for all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur (Li-S) batteries offer improved safety, energy density, and cost efficiency. However, the electronically and ionically insulating nature of S necessitates substantial incorporation of conductive carbon and solid electrolyte. To enhance S utilization, it is essential to understand how effective phase boundaries govern the electrochemical behavior of S composite electrodes. In this study, the relationship between carbon surface area and its spatial distribution within the S composite electrode is systematically examined. S electrodes incorporating Ketjen black exhibit largely improved utilization of Li₆PS₅Cl and S, along with enhanced electron and ion transport at higher active-material ratios compared with those using acetylene black and Super P. Galvanostatic intermittent titration technique and electrochemical impedance spectroscopy analyses further confirm that S redox kinetics are facilitated in composite electrodes containing Ketjen black. As a result, optimized electrodes with 40 wt.% S demonstrate improved rate performance even at low stack pressure (700 mAh·g_S⁻¹ at 1 C under both 75 and 10 MPa) and stable cycling (1000 cycles at 1 C under 75 MPa and 350 cycles at 0.2 C under 10 MPa). This study highlights the critical role of carbon architecture in forming effective interphases that enable high S utilization and improved cycling and rate performances in all-solid-state Li-S batteries.