Moisture‐Tolerant, Lithiophilic Artificial Solid Electrolyte Interphase Enables Ambient‐Processable Lithium Metal Anodes

Lithium (Li) metal offers exceptional energy density as an anode material, but its uncontrolled electrodeposition and unstable interphase formation during cycling remain critical barriers to practical implementation. In addition, its extreme reactivity toward ambient moisture necessitates highly energy‐intensive dry room facilities, substantially increasing the cost and energy footprint of battery manufacturing. Here, we introduce a molecularly engineered artificial solid electrolyte interphase (SEI) that combines moisture tolerance and lithiophilicity to enable ambient‐processable Li metal anodes. A polyethyleneimine (PEI) partially substituted with fluoroalkyl moieties is designed as the protective layer, in which the nitrogen‐rich backbone guides uniform Li⁺ flux, while the fluorinated side chains impart hydrophobicity to block ambient moisture and simultaneously induce the in situ formation of LiF‐rich SEI species. A comprehensive set of analyses during humidity exposure qualitatively elucidates the protective function of the artificial SEI and quantitatively tracks corrosion products in ambient environments. Various electrochemical and depth‐resolved post‐mortem analyses demonstrate that the fluorinated PEI‐based artificial SEI effectively protects Li metal under ambient conditions while enabling fast interfacial kinetics and stable long‐term cycling. This work provides a viable pathway toward energy‐efficient Li metal battery manufacturing and offers new molecular‐level insights into the design of protective artificial interphases.