Hierarchical electroactive ion permselective membrane with electrochemical switched ion pump effect for continuous lithium-ion recovery

Abstract

Highly selective extraction of lithium ions (Li+) from salt-lake brines is crucial to mitigate lithium supply shortages. In this work, a novel electrochemically switched lithium ion permselective membrane (ESLPM) was rationally designed through an ingenious tactic with an electroactive layer of lithium manganate (LiMn2O4) as the active radical and a dense and positively charged polyamide (PA) on each side of polyethersulfone (PES) substrate for the rapid and selective separation of Li+ from salt-lake brines with high Mg/Li ratios. Here, the reversible uptake/release and enhancement electro-sorption selectivity of Li+ are controlled by changing the electrochemical potential of the membrane with an ion-pump effect coupling with the electric field to achieve the continuous recovery of Li+. As a result, the flux of Li+ in the optimum hierarchical ESLPM-240 of the electrochemically switched ion permselective (ESIP) membrane separation system reached 0.032 mol m−2 h−1 for the separation of Li+ from the salt lake brine with a high Mg/Li ratio (Mg2+/Li+ = 20), which is 25% higher than in electrodialysis (ED) system. Meanwhile, by constructing a hierarchical structure, the separation factor of Li+/Mg2+ was increased to 7.8 under the ESIP system, which is about 3.5 times higher that of PA layer, and about 2.2 times higher than that of the electroactive layer. In addition, theoretical calculation confirmed that electroactive LiMn2O4 and positively charged PA layers are more favorable for Li+ transport when compared to Mg2+. Besides, the ESLPM-240 exhibited excellent long-term stability, indicating that the proposed strategy is promising for large-scale industrial applications in the Li+ extraction from salt lakes.