Enhancing All-Solid-State Batteries Performance Through Thickness Control and Surface Passivation of Thermally...

Thin lithium metal anodes are key to realizing high-energy-density and enhanced safety in all-solid-state batteries (ASSBs). However, extruded lithium foils below 50 µm suffer from poor structural integrity, rough surfaces, and resistive, native passivation layers, which limit cycling stability. In this study, thermally evaporated, high-purity lithium with smooth grain-boundary surface morphology significantly improves interfacial contact and electrochemical performance. Replacing extruded lithium with a 50 µm evaporated lithium anode increases the critical current density (CCD) from 1.6 to 2.1 mA cm^-2 and enables 161 cycles at 1.5 mA cm^-2 and 1.6 mAh cm^-2. A thickness-dependence study reveals that maintaining a sufficient lithium reservoir is crucial to mitigate void formation and compensate for solid electrolyte interphase (SEI) growth. To overcome limitations at reduced thickness, an ultra-thin 65 nm LiF passivation layer was applied to 25 µm evaporated lithium. The LiF coating suppresses chemical degradation during storage, stabilizes lithium/LPSCl interface, limits SEI growth, and mitigates dendrite, increasing the CCD to 2.6 mA cm^-2. In full cells, LiF-coated 25 µm lithium delivers over 500 and 300 cycles at current densities of 1.5 and 3 mA cm^-2 respectively. These results establish LiF-passivated thermally evaporated lithium as a high-performance anode design for next-generation ASSBs.