Designing Gemini‐Electrolytes for Scalable Mg2+/Li+ Separation Membranes and Modules

High performance polyamide nanofiltration membranes play important roles in Mg2+/Li+ separation and Li+ extraction, but they are prepared via multiple time‐/labor demanding steps. Both the scalability of these membranes and the engineering of membrane modules remain an elusive challenge. Here the design of a Gemini‐electrolyte monomer (GEM) featuring bidentate amine groups, quaternary ammonia, and endocyclic contorted conformation is reported. The monomer's low interfacial diffusivity is balanced by high condensational reactivity during its interfacial polymerization with trimesoyl chloride (TMC), leading to the straightforward formation of defect‐free, ≈14 nm thick membranes. The membrane shows the highest permeance (≈19.2 L m−2 h−1 bar−1) among Mg2+/Li+ nanofiltration membranes prepared via straightforward interfacial polymerization without post‐modification, combined with good Mg2+/Li+ selectivity (≈15.4) and stability. The validity of GEM design is verified by control monomers. Large‐area (1 × 2 m2) GEM‐TMC membranes and spiral‐wound modules (effective area: 0.5 m2) are prepared, both of which show reproducible and high performance. A Gemini‐like electrolyte monomer is designed to tackle the challenge in preparing high‐performance, large‐area Mg2+/Li+ separation membranes (≈2 m2) and spiral‐wound modules, both of which show high permeance. High‐purity lithium carbonates are efficiently extracted from simulated brine with 40 Mg2+/Li+ ratio.