Enabling an ultraefficient lithium-selective construction through electric field–assisted ion control

Membranes with precise ion transport behaviors are regarded as an alternative for lithium (Li) extraction from water streams. Current membranes demonstrate limited viability due to the lack of efficient Li⁺-selective architectures. We propose an electric field-assisted ion control hypothesis in reinforcing ultraefficient Li⁺-selective membranes, in which an ionized zeolitic imidazolate framework layer (Q-PEI@ZIF) is constructed via polyethylenimine (PEI) in situ confinement conversion and subsequent quaternization of 2,3-epoxypropyl trimethyl ammonium chloride. In electrodialysis at 5 milliampere per square centimeter, the resulting membrane Q(5%)-PEI(1.0)@ZIF#CEM shows that the ion permeation rates follow the order of K⁺ ~ Li⁺ > Na⁺ > Ca²⁺ ~ Mg²⁺, corresponding to 0.31, 0.30, 0.25, 0, and 0 mole per square meter per hour in 120 minutes, respectively. With a 25-millimolar Li⁺/Mg²⁺ mixed solution, it exhibits an unprecedented Li⁺/Mg²⁺ permselectivity of 20,000 and 99.99% purity of Li⁺ product in 120 minutes. This study expands the hypothesis of electric field-assisted ion control in enabling an ultraefficient Li⁺-selective construction.