• • The SP45 membrane achieves a Li+/Mg2+ perm-selectivity of 48.1 at 2 mA cm−2, a 3-fold improvement over conventional sulfonated polymers, directly reducing energy consumption in electrodialysis by minimizing Mg2+ leakage.
• • Cycling stability tests show <10% selectivity degradation across multiple cycles in diverse mixed-salt systems, ensuring operational longevity and cost-effectiveness for industrial brine processing.
• • In a 4-stage ion-distillation device, the SP45 membrane yields a Li+/Mg2+ separation factor exceeding 60,000, enabling high-purity lithium recovery from brines with high Mg2+/Li+ ratios.
• • The cross-linked structure of SP45, formed at 45% sulfonation degree, contracts ionic clusters and limits hydrophilic domain interconnectivity, raising the energy barrier for Mg2+ transport by an estimated 20 kJ mol−1 compared to non-cross-linked analogs.