Molecular Engineering Approaches to Fabricate Artificial Solid-Electrolyte Interphases on Anodes for Li-Ion Batteries: A Critical Review

An intrinsic challenge of Li-ion batteries is the instability of electrolytes against anode materials. For anodes with a favorably low operating potential, a solid-electrolyte interphase (SEI) formed during initial cycles provides stability, traded off for capacity consumption. The SEI is mainly determined by the anode material, electrolyte composition, and formation conditions. Its properties are typically adjusted by changing the liquid electrolyte's composition. Artificial SEIs (Art-SEIs) offer much more freedom to address and tune specific properties, such as chemical composition, impedance, thickness, and elasticity. Art-SEIs for intercalation, alloying, conversion and Li metal anodes have to fulfil varying requirements. In all cases, sufficient transport properties for Li-ions and (electro-)chemical stability must be guaranteed. Several approaches for Art-SEIs preparation have been reported: from simple casting and coating techniques to elaborated Phys-Chem modifications and deposition processes. This review critically reports on the promising approaches for Art-SEIs formation on different type of anode materials, focusing on methodological aspects. The specific requirements for each approach and material class, as well as the most effective strategies for Art-SEI coating, are discussed and a roadmap for further developments towards next-generation stable anodes are provided.