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

Abstract

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 trade‐off. This work reported a “tagged‐modification” chemistry to tackle the challenge. A mixture of 3‐bromo‐trimethylpropan‐1‐aminium bromide (E1) and 3‐aminopropyl‐trimethylazanium (E2) was designed to modify polyethylenimine – trimesoyl chloride (PEI‐TMC) membranes. E1 and E2 reacted with the PEI and TMC, respectively, and thus, membrane properties (hydrophilicity, pore sizes, charge) were untangled and intensified simultaneously. Permeance (34.3 L m‐2 h‐1 bar‐1) and Mg2+/Li+ selectivity (23.2) of modified membranes are ~4 times and ~2 times higher than the pristine membrane, and 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.