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 SuperP. 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 1C under both 75 MPa and 10 MPa) and stable cycling (1000 cycles at 1C under 75 MPa and 350 cycles at 0.2C 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.