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

Efficient Mg2+/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 (E1) and 3‐aminopropyltrimethylazanium (E2) was designed to modify polyethylenimine – trimesoyl chloride (PEI‐TMC) membranes. E1 and E2 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 Mg2+/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 (Li2CO3) from simulated brine. A tagged‐modification approach has been developed to selectively modify the top and bottom parts of a polyamide membrane, thereby resulting in the highest current Mg2+/Li+ separation performance that is stable over a 30‐day test. A large‐area (0.24 m2) membrane was prepared and made into spiral‐wound modules, which show high efficacy in extracting lithium from simulated brines.