Enhancing Moisture Stability of Sulfide Solid-State Electrolytes by Reversible Amphipathic Molecular Coating

The all-solid-state battery (ASSB) is a promising next-generation energy storage technology for both consumer electronics and electric vehicles because of its high energy density and improved safety. Sulfide solid-state electrolytes (SSEs) have merits of low density, high ionic conductivity, and favorable mechanical properties compared to oxide ceramic and polymer materials. However, mass production and processing of sulfide SSEs remain a grand challenge because of their poor moisture stability. Here, we report a reversible surface coating strategy for enhancing the moisture stability of sulfide SSEs using amphipathic organic molecules. An ultrathin layer of 1-bromopentane is coated on the sulfide SSE surface (e.g., Li₇P₂S₈Br_0.5I_0.5) via Van der Waals force. 1-Bromopentane has more negative adsorption energy with SSEs than H₂O based on first-principles calculations, thereby enhancing the moisture stability of SSEs because the hydrophobic long-chain alkyl tail of 1-bromopentane repels water molecules. Moreover, this amphipathic molecular layer has a negligible effect on ionic conductivity and can be removed reversibly by heating at low temperatures (e.g., 160 °C). This finding opens a new pathway for the surface engineering of moisture-sensitive SSEs and other energy materials, thereby speeding up their deployment in ASSBs.