Highly Stable Lithium Metal Anode Enabled by Chemical Vapor Functionalization Using Trimethylaluminum Atomic Layer Deposition Precursor

The development of high energy density batteries is essential for addressing global environmental challenges and enabling innovative technologies. In this regard, Li metal anodes offer significant promise for next generation batteries, such as all-solid-state, Li-metal, and Li-sulfur systems, due to their high theoretical capacity (3860 mAh g^-1) and low reduction potential (–3.04 V vs. the standard hydrogen electrode). However, their practical use is limited by an unstable solid electrolyte interface (SEI), which deteriorates during repeated deposition and stripping, causing dendrite growth, volume expansion, and increased impedance. Stabilizing this interface is crucial to prevent uneven lithium deposition, localized overpotentials, and high current density regions, which compromise cycle performance.
Moreover, to exceed the energy density of state-of-the-art Li-ion batteries, Li metal anodes must have a thickness of approximately 40 μm or less. These thin foils are produced via rolling, where Li ingots are flattened with lubricants to control tension and uniformity. Despite inert conditions, SEI components such as Li₂CO₃, Li₂O, and LiOH form on the surface, creating mechanically unstable, low-conductivity layers that disrupt uniform ion transport.
Herein, we demonstrate the chemical vapor functionalization mechanism of trimethylaluminum (TMA) as an atomic layer deposition (ALD) precursor on a Li metal anode. This simple and effective approach removes irregular native SEI layers on pristine Li metal anode and establishes uniform nucleation sites. Through in-situ experimental studies, including quartz crystal microbalance and quadrupole mass spectrometry, as well as computational analyses, we elucidated the reaction mechanism between Li metal and TMA. Furthermore, uniform submicron-sized nuclei composed of Li-Al alloy and graphite layers were formed after chemical vapor functionalization. The synthesized 20 μm Li metal anode exhibited highly stable cycling performance in both Li-metal-ion cells with liquid electrolytes and all-solid-state cells with sulfide solid state electrolytes. These findings provide valuable insights into the design of uniform and stable SEI layers and the understanding of complex ALD mechanisms in battery materials with non-uniform surface functional groups.