Interfacial Slip‐Induced Mitigation of Concentration Polarization and Fouling in Liquid‐Like Nanofiltration Membranes for High‐Efficiency Lithium Recovery

ABSTRACT Nanofiltration (NF) membranes are highly promising for selective lithium recovery from brines, yet their efficiency is significantly hindered by concentration polarization (CP) and membrane fouling. In this study, polyethyleneimine (PEI)‐based NF membranes functionalized with “liquid‐like” surfaces were developed via the covalent grafting of highly flexible molecular chains. These surfaces are demonstrated to induce an interfacial slip effect with a significantly increased slip length, which enhances cross‐flow velocity and effectively mitigates CP resistance. Meanwhile, the dynamic behavior of the flexible chains inhibits contaminant deposition, endowing the membranes with superior antifouling properties. Coupled with the enhanced chlorine resistance of the liquid‐like surfaces, stable separation performance was maintained throughout a 12‐day continuous operation test. The hydrophilic NH 2 ‐PEG‐functionalized membrane delivers a higher permeance of 21.7 L·m −2 ·h −1 ·bar −1 , along with an exceptional Mg/Li selectivity ( S Mg/Li = 67.8). The hydrophobic NH 2 ‐PDMS‐functionalized membrane achieves an even higher S Mg/Li of 88.5 while maintaining a permeance of 10.9 L·m −2 ·h −1 ·bar −1 . Both membranes maintain excellent Mg 2+ rejection, particularly under high‐salinity conditions. This work provides a versatile strategy for designing high‐performance membranes for sustainable lithium resource recovery.