Revealing Rate‐Determining Factors of Interfacial Lithium‐Ion Transport for Efficient Membrane Lithium Separation

Abstract Extracting lithium from seawater, which contains 70% of global lithium reserves, is highly critical for the sustainable development of lithium‐ion batteries. However, low concentration of lithium‐ion (Li + ) and abundant interfering cations in seawater requires highly selective and efficient Li + transport at the solid‐liquid interface. In this study, key factors influencing interfacial Li + transport across the surface of a perovskite solid‐state electrolyte are investigated, including surface hydrophilicity, Li + concentration, and interfering ions. The solvation structure of lithium ions at the interface and near‐surface regions is examined using depth‐profiling Raman spectroscopy for the first time. It is revealed that a surface with lower hydrophilicity reduces the hydration degree of Li + at the surface, resulting in lower desolvation energy, which in turn promotes Li⁺ conduction at the solid‐liquid interface. Similarly, increasing Li + concentration or the presence of other cations with high hydration capability will also promote the de‐solvation of Li + . By unveiling the rate‐limiting factors of Li⁺ transport at liquid‐solid interfaces, this study offers valuable insights for designing practical lithium extraction membranes.