Water‐Stable Sulfide Solid Electrolyte Membranes Directly Applicable in All‐Solid‐State Batteries Enabled by Superhydrophobic Li+‐Conducting Protection Layer

Abstract Sulfide solid electrolytes (SEs) represent one most promising technical routes to realize all‐solid‐state batteries (ASSBs) due to their high ionic conductivity and low mechanical stiffness. However, the poor air/moisture/water stability of sulfide SEs leads to completely destroyed structure/composition, reduced Li + conductivity, and toxic H 2 S release, limiting their practical application in ASSBs. To solve this problem, a universal method applicable to all types of sulfide SEs is developed to realize water‐stable sulfide SE membranes, by spray coating a Li + ‐conductive superhydrophobic protection layer with Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 (LATP) nanoparticles and fluorinated polysiloxane (F‐POS) via hydrolysis and condensation of tetraethyl orthosilicate and 1 H ,1 H ,2 H ,2 H ‐perfluorodecyltriethoxysilane molecules. The F‐POS@LATP coating layer exhibits excellent superhydrophobicity (water static contact angles > 160°) to resist extreme exposure (direct water jetting), because of its micro‐/nanoscale roughness and low surface energy. Moreover, ASSBs using the extreme‐condition‐exposed modified Li 6 PS 5 Cl membrane exhibit a reversible capacity of 147.3 mAh g ‐1 , comparable with the ASSBs using pristine sulfide membranes. The superhydrophobic Li + ‐conducting layer is demonstrated to be an effective protection method for sulfide membranes so that they remain stable and functionable in extreme water exposure conditions, providing a new approach to protect all types of sulfide SEs and other air/moisture/water‐sensitive materials without sacrificing electrochemical performance.