Suppressing Atmospheric Degradation of Sulfide-Based\nSolid Electrolytes via Ultrathin Metal Oxide Layers

Sulfide-based solid-state electrolytes\n(SSEs) are promising materials\nwith superior Li-ion conductivity; however, their poor atmospheric\nstability limits commercial manufacturing at scale. Here, we investigate\nthe impact of ultrathin metal oxide layers deposited via atomic layer\ndeposition (ALD) on the stability of Li<sub>6</sub>PS<sub>5</sub>Cl\n(LPSCl). Al<sub>2</sub>O<sub>3</sub> layers grown directly on LPSCl\nparticles significantly stabilize the surface chemistry and Li-ion\ntransport properties relative to uncoated material upon exposure to\nboth an ambient atmosphere (22% relative humidity, RH) and humidified\nO<sub>2</sub> (100% RH). Detailed investigations indicate that coatings\nimpede the surface and bulk degradation kinetics of exposed materials,\neven for coatings as thin as ∼1 Å. This suggests that\nstabilization is due to more than just a physical barrier. Shifts\nin valence band edge positions of coated LPSCl indicate that ALD coatings\nalter the surface electronic structure and resulting oxidation tendency\nof underlying LPSCl, suggesting new avenues to improving the environmental\nstability of sulfide SSEs.