Surface Coating Enabling Sulfide Solid Electrolytes with Excellent Air Stability and Lithium Compatibility

Abstract

All-solid-state lithium metal batteries (ASSLMBs) featuring sulfide solid electrolytes (SEs) are recognized as the most promising next-generation energy storage technology because of their exceptional safety and much-improved energy density. However, lithium dendrite growth in sulfide SEs and their poor air stability have posed significant obstacles to the advancement of sulfide-based ASSLMBs. Here, a thin layer (approximately 5 nm) of g-C3N4 is coated on the surface of a sulfide SE (Li6PS5Cl), which not only lowers the electronic conductivity of Li6PS5Cl but also achieves remarkable interface stability by facilitating the in situ formation of ion-conductive Li3N at the Li/Li6PS5Cl interface. Additionally, the g-C3N4 coating on the surface can substantially reduce the formation of H2S when Li6PS5Cl is exposed to humid air. As a result, Li–Li symmetrical cells using g-C3N4-coated Li6PS5Cl stably cycle for 1000 h with a current density of 0.2 mA cm−2. ASSLMBs paired with LiNbO3-coated LiNi0.6Mn0.2Co0.2O2 exhibit a capacity of 132.8 mAh g−1 at 0.1 C and a high-capacity retention of 99.1% after 200 cycles. Furthermore, g-C3N4-coated Li6PS5Cl effectively mitigates the self-discharge behavior observed in ASSLMBs. This surface-coating approach for sulfide solid electrolytes opens the door to the practical implementation of sulfide-based ASSLMBs.