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 H₂S 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_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) nanoparticles and fluorinated polysiloxane (F-POS) via hydrolysis and condensation of tetraethyl orthosilicate and 1H,1H,2H,2H-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 Li₆PS₅Cl 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.