Advanced membrane materials for lithium extraction: Design strategies and separation mechanisms

Amid the accelerating global electrification, the growing demand for lithium resources has highlighted the urgent need for efficient, low-energy, and environmentally friendly separation technologies. Compared with conventional evaporation–crystallization and chemical precipitation processes, membrane-based lithium extraction offers a continuous alternative, enabled by tunable separation interfaces and potentially reduced energy input. Accordingly, this review systematically summarizes recent advances in lithium-selective membranes for complex brines, organized into five material classes: (i) polyamide-based nanofiltration membranes, (ii) two-dimensional material membranes, (iii) crown ether-functionalized polymer membranes, (iv) porous framework membranes (metal-organic frameworks and covalent organic frameworks), and (v) inorganic solid-state electrolyte membranes. Among these, inorganic solid-state electrolyte membranes, endowed with ultrahigh ion selectivity and excellent stability, can adapt to complex salt-lake brines of varying concentrations and are deemed highly promising. Focusing on the structural characteristics of these membranes, ion-selective regulation strategies, and transmembrane transport behaviors, this review outlines the key features governing lithium-selective separation across different material systems. Furthermore, critical challenges associated with membrane-based lithium extraction in realistic salt-lake brines, such as interference from coexisting ions, membrane fouling, material stability, and engineering implementation, are discussed. Finally, perspectives on future directions in membrane material development, mechanistic studies, and large-scale applications are provided.