Enhancing All-Solid-State Batteries Performance through Thickness Control and Surface Passivation of Thermally Evaporated Lithium Metal Anodes

Thin lithium metal anodes are key to realizing high-energy-density and enhanced safety in all-solid-state batteries (ASSBs). However, extruded lithium foils thinner than 50 µm suffer from poor structural integrity, rough surfaces, and resistive native passivation layers which severely limit cycling stability. Here, we demonstrate that thermally evaporated, highly pure lithium with smooth, grain-boundaries surfaces morphology significantly improves interfacial contact and electrochemical performance. For a fixed lithium thickness, 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 in Li|Li symmetric cells using Li6PS5Cl (LPSCl) as solid electrolyte separator. In LiNi0.8Co0.1Mn0.1O2 (NCM811)|LPSCl|Li full cells, this configuration enables 161 stable cycles at 1.5 mA cm-2 and 1.6 mAh cm-2. A systematic thickness dependence study reveals that reducing the evaporated lithium metal to 25 µm severely limits full-cell performance (~20 cycles), underscoring the need for a sufficient electrochemically active lithium reservoir to mitigate void formation and to compensate for the solid electrolyte interphase (SEI) growth. To address this limitation, an ultra-thin 65 nm LiF passivation layer was applied to 25 µm evaporated lithium. The LiF coating suppresses chemical degradation during storage, stabilizes the lithium/LPSCl interface, limits SEI growth, and mitigates dendrite formation, thereby 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 density of 1.5 mA cm-2 and 3 mA cm-2 respectively. These results establish LiF-passivated thermally evaporated lithium as a high-performance anode design for next-generation ASSBs.