Fluorine-Doped High-Performance Li₆PS₅Cl Electrolyte by Lithium Fluoride Nanoparticles for All-Solid-State Lithium-Metal Batteries

All-solid-state lithium-metal batteries (ASSLMBs) are widely considered as the ultimately advanced lithium batteries owing to their improved energy density and enhanced safety features. Among various solid electrolytes, sulfide solid electrolyte (SSE) Li₆PS₅Cl has garnered significant attention. However, its application is limited by its poor cyclability and low critical current density (CCD). In this study, we introduce a novel approach to enhance the performance of Li₆PS₅Cl by doping it with fluorine, using lithium fluoride nanoparticles (LiFs) as the doping precursor. The F-doped electrolyte Li₆PS₅Cl-0.2LiF(nano) shows a doubled CCD, from 0.5 to 1.0 mA/cm² without compromising the ionic conductivity; in fact, conductivity is enhanced from 2.82 to 3.30 mS/cm, contrary to the typical performance decline seen in conventionally doped Li₆PS₅Cl electrolytes. In symmetric Li|SSE|Li cells, the lifetime of Li₆PS₅Cl-0.2LiF(nano) is 4 times longer than that of Li₆PS₅Cl, achieving 1500 h vs. 371 h under a charging/discharging current density of 0.2 mA/cm². In Li|SSE|LiNbO₃@NCM721 full cells, which are tested under a cycling rate of 0.1 C at 30 °C, the lifetime of Li₆PS₅Cl-0.2LiF(nano) is four times that of Li₆PS₅Cl, reaching 100 cycles vs. 26 cycles. Therefore, the doping of nano-LiF offers a promising approach to developing high-performance Li₆PS₅Cl for ASSLMBs.