Sulfur/carbon cathode composite with LiI additives for enhanced electrochemical performance in all-solid-state lithium-sulfur batteries

The high theoretical energy density and superior safety of all-solid-state lithium-sulfur batteries (ASSLSBs) make them a promising candidate for large-scale energy storage applications. The sulfur active material used in the positive electrode exhibits a higher power density compared to the lithium sulfide active material employed in the electrode. However, the limited utilization of sulfur in the positive electrode is due to its low ionic and electronic conductivity. Herein, sulfur is confined within porous carbon (S/C) by vapor deposition to ensure electronic conductivity. Subsequently, LiX additives (where X = F, Cl, Br, and I) are introduced into the S/C composite to enhance ionic conductivity. In situ electrochemical impedance spectroscopy (EIS) with distribution of relaxation times (DRT) analysis and electrochemical evaluations demonstrated that the introduction of LiI additives significantly enhances ion transfer on the S/C composite, thereby improving its reaction electrochemical reaction activity during cycling. The electrochemical performance of ASSLSBs with LiX additives on S/C composite generally exhibits a decreasing trend in the order of LiI > LiBr > LiCl > LiF. The S/C composite with LiI additives (S/C@LiI) cathode employed in ASSLSBs demonstrated an impressive high discharge capacity of 2016.9 mAh g(-1) after 275 cycles with a capacity retention of 100% and a reversible discharge capacity of 627.1 mAh g(-1) at 1C for up to 450 cycles.