Interfacial dual regulation of charge density and structural accessibility for efficient electrodialytic lithium extraction.

Synergistically regulating interfacial charge chemistry and transport microenvironment remains a fundamental challenge for achieving precise mono-/divalent cation separation in electrodialysis membranes. Herein, we report a stepwise interfacial engineering strategy that integrates Schiff-base assembly and Aza-Michael quaternization to construct a quaternary ammonium-enriched selective layer with dual regulation over electrostatic exclusion and structural accessibility. Experiments and electrochemical analyses reveal that quaternization not only amplifies the positive interfacial charge density, thereby strengthening Donnan exclusion against divalent cations, but also loosens the selective network through intralayer electrostatic repulsion, creating more accessible conduction pathways for monovalent ions. This dual-regulation effect enables simultaneous suppression of Mg2+ migration and facilitation of Li+ transport. As a result, the optimized membrane achieves a Li+ flux of 0.98 mol·m-2·h-1 with a Li+/Mg2+ perm-selectivity of 28.2. In a two-stage electrodialysis process using concentrated salt-lake brine, the Mg2+/Li+ ratio decreases from 40.00 to 0.026, corresponding to an overall 1500-fold reduction, and enables the recovery of Li2CO3 with a purity of 99.3%. This work provides a general framework for designing high-performance ion-selective membranes for energy-efficient lithium extraction from Mg-rich brines.