Positively Charged Polyamide Membranes with Expanded Ion Passage Channels Enabling Exceptional Lithium Extraction from Battery Leachate
Polyamide (PA) membranes are promising for lithium extraction from spent lithium-ion battery (LIB) leachate but face a trade-off between selectivity and permeability. Here, we demonstrate that nascent PA membranes post-grafted with triaminoguanidinium (TAG) monomers (PA-TAG membranes) gain expanded ion passage channels (0.8–7.1 Å) and enhanced positive charge, achieving high-performance lithium separation. The PA-TAG membrane exhibits a pure water permeance (PWP) of 15.5 L m−2 h−1 bar−1, superior divalent ion rejection (~98%), and an excellent separation factor (~30), significantly outperforming pristine PA membranes. In a simulated acidic battery leachate, the PA-TAG membrane achieved a relative volumetric lithium recovery rate of 48.2% after a two-stage nanofiltration process, with the Li+/M2+ mass ratio of the second permeate reaching 53.35, 445 times that of the feed (0.12). The membrane maintained stable performance over 45 hours of nanofiltration and resisted acidic conditions (pH=2) for at least 20 days. These results highlight the potential of PA-TAG membranes for efficient lithium extraction from acidic battery leachate, addressing the critical need for sustainable recycling of spent LIBs.