Advanced Lithium Extraction Membranes Derived from Tagged‐Modification of Polyamide Networks

Abstract Efficient Mg 2+ /Li + separation is crucial to combating the lithium shortage worldwide, yet current nanofiltration membranes suffer from low efficacy and/or poor scalability, because desirable properties of membranes are entangled and there is a trade‐off. This work reports a “tagged‐modification” approach to tackle the challenge. A mixture of 3‐bromo‐trimethylpropan‐1‐aminium bromide (E 1 ) and 3‐aminopropyltrimethylazanium (E 2 ) was designed to modify polyethylenimine – trimesoyl chloride (PEI‐TMC) membranes. E 1 and E 2 reacted with the PEI and TMC, respectively, and thus, the membrane properties (hydrophilicity, pore sizes, charge) were untangled and intensified simultaneously. The permeance (34.3 L m −2 h −1 bar −1 ) and Mg 2+ /Li + selectivity (23.2) of the modified membranes are about 4 times and 2 times higher than the pristine membrane, and they remain stable in a 30‐days test. The permeance is the highest among all analogous nanofiltration membranes. The tagged‐modification method enables the preparation of large‐area membranes and modules that produce high‐purity lithium carbonate (Li 2 CO 3 ) from simulated brine.