Stabilization of the Li3PS4/Li interface by a 4 nm Al2O3 coating studied by in situ HAXPES

Li-metal based All-Solid-State Batteries (ASSBs) offer a safer and higher-energy alternative to conventional lithium-ion batteries, but their performances are hindered by interfacial instability between the solid-state electrolyte (SSE) and lithium metal electrode. To stabilize the interface, a nanometer-thick Al 2 O 3 film made by Atomic Layer Deposition (ALD) technique is evaluated as a surface protective layer at the SSE/Li metal interface. We unveil the interfacial stability between β-Li 3 PS 4 (LPS) SSE and deposited lithium metal using in situ hard X-ray photoemission spectroscopy (HAXPES) approach. Our results on LPS/Al 2 O 3 /Li metal system reveal that 4 nm-thick Al 2 O 3 coating enhances interfacial stability by mitigating undesirable side reactions. Although some LPS reduction to Li 2 S still occurs, it is significantly less pronounced as compared to the pristine LPS/Li metal interface. Additionally, metallic lithium deposition is detected on the surface, with no observable reduction of phosphorus element. These findings underscore the capability of ultrathin oxide coatings made by ALD to significantly stabilize Li/SSE interface thus contributing to the development of more reliable and safety Li-metal based ASSBs.