Adaptive Mg²⁺-Gating Membranes for Battery-Grade Lithium Extraction

Nanofiltration technology shows promise for lithium extraction from salt lakes, yet the fixed nanochannel size of conventional membranes proves insufficient for the complex demands of multi-stage separation processes, especially given the drastic variations in Mg²⁺/Li⁺ ratios. To address this issue, 4'-Aminobenzo 15-crown-5-ether (AB-15C5) macrocycles were grafted onto the surface of polyamide (PA) membranes to fabricate adaptive Mg²⁺-gating membranes (PA-15C5 membranes). The adaptive Mg²⁺-gating effect enables responsive dimensional switching of nanochannels through spatial rearrangement of crown ether under varying Mg²⁺ concentrations, as evidenced by experimental confirmation achieved through molecular weight cutoff (MWCO) testing and Zeta potential analyses under ionic modulation conditions. Systematic theoretical validation from density functional theory (DFT) calculations and molecular dynamics (MD) simulations further elaborates on this gating effect. This gating effect converts competing Mg²⁺ ions into a separation advantage and extends applicability to ultralow Mg²⁺ concentrations, achieving a Li⁺/Mg²⁺ separation factor of 214.9 at a Mg²⁺/Li⁺ molar ratio of 0.01. The three-stage nanofiltration process effectively reduced the Mg²⁺/Li⁺ ratio in brine to 4.0 * 10^{- 4}, while achieving the extraction of battery-grade lithium with a purity of 99.97%. This performance surpasses most reported state-of-the-art, thereby establishing a novel paradigm for deploying adaptive gating membranes in lithium extraction from salt-lake brines.