Ligand-engineered layered solid–liquid interfaces enable fast and selective ion transport

Ion transport behaviors are central to ion separation, micro-/nano-fluidics, and interfacial catalysis, yet achieving high ion transport rate and selectivity remains challenging in nonaqueous systems. Here, we propose a unique solid–liquid cooperative interface built from a layered cyano-bridged metal framework (CMF) and nonaqueous solvents to simultaneously increase cation (Li⁺) conductivity (9.5 mS·cm⁻¹) and transport selectivity (~0.9). Mechanistic analysis based on theoretical calculations, supported by electrochemical measurements, shows that the nonaqueous solvents can work as functional interfacial ligands at the surface of layered CMFs, including outer-layer solvent ligands (OSLs) and interlayer solvent ligands (ISLs), which can restructure the interfacial Li⁺ migration environment and salt speciation. It is found that OSLs with higher polarity symmetry would interact more strongly with the unsaturated metal sites on the CMF's surface, thereby promoting coordination competition at the interface, accelerating solvation-renewal dynamics, and increasing the Li⁺ transport rate. ISLs with higher polarity symmetry could stabilize a low-curvature surface of CMF, strengthen anion anchoring at the unsaturated metal sites, increase selectivity for Li⁺ transport, and further improve overall Li⁺ transport rate. Therefore, we provide a potential strategy to construct a unique solid-liquid interface using CMF solids and rationally designed interfacial solvent ligands to promote the ion transport behaviors.