Thin-Film Engineering of Artificial Interphases for Lithium Batteries

Interfacial instability has become a bottleneck for lithium batteries targeting higher energy density, longer cycle life, and safety. Native solid electrolyte interphases (SEIs) and cathode electrolyte interphases (CEIs), formed through spontaneous electrolyte decomposition, are heterogeneous, dynamically evolving, and difficult to regulate, especially at high-voltage cathodes and reactive anodes. Thin-film-engineered artificial SEI/CEI offers a strategy by enabling control over interfacial composition, thickness, architecture, and function. These interphases can regulate Li⁺ transport, suppress electronic leakage, enhance chemical/electrochemical stability, and improve chemomechanical compatibility. However, rational design remains challenging because deposition methods differ in material compatibility, process capability, conformality, scalability, cost, and application windows. This review establishes a process-structure-function-application framework for thin-film artificial interphases, beyond material-by-material summaries or method-specific coating discussions. We compare native and artificial SEI/CEI and summarize design principles, including ion-selective transport, electronic insulation, chemical/electrochemical stability, chemomechanical robustness, and process compatibility. We then discuss physical vapor deposition, chemical vapor deposition, atomic layer deposition, and molecular layer deposition, highlighting capabilities, limitations, trade-offs, and selection logic. Advances in thin-film artificial interphases for liquid-state and solid-state lithium batteries are reviewed, emphasizing transport evidence, failure modes, electrolyte-family-specific requirements, and device integration. Perspectives are provided on scalable manufacturing, buried-interface characterization, and design.