Key Takeaways & Executive Findings
- •• • The PA-TAG membrane achieves a pure water permeance of 15.5 L m−2 h−1 bar−1 and a separation factor of ~30, breaking the selectivity-permeability trade-off in lithium extraction. • • Divalent ion rejection exceeds 98%, enabling a Li+/M2+ mass ratio increase from 0.12 in the feed to 53.35 after two-stage nanofiltration, a 445-fold enrichment. • • The relative volumetric lithium recovery rate reaches 48.2% after two-stage nanofiltration, with LiCl purity of 99.3%, demonstrating industrial viability. • • The membrane exhibits robust chemical stability in acidic conditions (pH=2) for at least 20 days, ensuring durability in real battery leachate environments.
Abstract
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.
1. Introduction
The escalating demand for lithium-ion batteries (LIBs) in electric vehicles and portable electronics has intensified the need for efficient recycling of spent batteries. By 2030, the volume of spent LIBs is projected to exceed 2 million tons, representing a market opportunity surpassing $5.56 billion. However, current hydrometallurgical recycling processes, particularly acid leaching, produce complex multi-metal leachates containing Li+, Ni2+, Co2+, and Mn2+. Traditional separation methods such as precipitation and solvent extraction are energy-intensive and often fail to achieve the precise selectivity required for high-purity lithium recovery. Nanofiltration (NF) membranes offer a promising alternative due to their ability to separate monovalent and divalent ions, but conventional polyamide (PA) membranes suffer from a trade-off between permeability and selectivity, limiting their practical application.
This study addresses this bottleneck by post-grafting triaminoguanidinium (TAG) monomers onto nascent PA membranes, creating PA-TAG membranes with expanded ion passage channels (0.8–7.1 Å) and enhanced positive surface charge. This design promotes rapid transport of Li+ ions while effectively rejecting divalent cations, achieving a separation factor of ~30 and a pure water permeance of 15.5 L m−2 h−1 bar−1. The membrane's performance in simulated acidic battery leachate demonstrates a 445-fold increase in Li+/M2+ mass ratio after two-stage NF, with a lithium recovery rate of 48.2% and LiCl purity of 99.3%. These results provide a scalable, energy-efficient solution for lithium extraction from spent LIBs, addressing both environmental and economic challenges in the recycling industry.
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Zebin Zhu, Yijun Qian, Weihao Yu, Tong Wu, Tao Qian, Chenglin Yan, Jianmei Lu (2026). Positively Charged Polyamide Membranes with Expanded Ion Passage Channels Enabling Exceptional Lithium Extraction from Battery Leachate. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3559-5
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Frequently Asked Questions
What is the mechanism behind the enhanced lithium selectivity of PA-TAG membranes?
The TAG monomer introduces triamine groups that increase the positive charge density on the membrane surface. This enhances Donnan exclusion of divalent cations (Ni2+, Co2+, Mn2+) while facilitating the passage of monovalent Li+ ions. Additionally, the grafting expands the effective pore size to 0.8–7.1 Å, allowing faster water and Li+ transport without compromising rejection of larger hydrated divalent ions.
How does the PA-TAG membrane perform under acidic conditions typical of battery leachate?
The membrane was immersed in HCl solution at pH=2 for at least 20 days and maintained its structural integrity and separation performance. This acid resistance is critical for practical application, as battery leachate is often acidic (e.g., H2SO4 or HCl-based). The stability is attributed to the chemical robustness of the polyamide matrix and the covalent attachment of TAG monomers.
What is the economic viability of the two-stage nanofiltration process using PA-TAG membranes?
The two-stage process achieves a lithium recovery rate of 48.2% with LiCl purity of 99.3%, which is competitive with conventional methods. The high permeance (15.5 L m−2 h−1 bar−1) reduces energy consumption and processing time. Compared to the PA-DAG membrane (recovery rate of 20.5%), PA-TAG offers significantly higher efficiency, making it economically attractive for industrial scale-up.
Can the PA-TAG membrane be scaled up for industrial applications?
The membrane fabrication involves post-grafting of TAG onto nascent PA membranes, which is compatible with existing roll-to-roll manufacturing processes. The performance metrics (PWP, selectivity, stability) suggest that scale-up is feasible. However, long-term fouling behavior and performance under real leachate conditions (with organic impurities) need further validation in pilot-scale studies.
What are the limitations of the PA-TAG membrane in terms of selectivity and permeability?
While the PA-TAG membrane shows a separation factor of ~30, which is high, it is not infinite. For extremely high purity requirements, additional polishing steps may be needed. The permeance of 15.5 L m−2 h−1 bar−1 is good but could be improved further. The trade-off between selectivity and permeability is not completely eliminated but significantly optimized compared to pristine PA membranes.
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