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 (Li₂ CO₃ ) from simulated brine.