High Crystallinity Acid-Resistant COF Membranes toward Efficient Lithium Recovery from Spent Lithium-Ion Batteries

Lithium recovery with high efficiency from acidic leachates of spent lithium-ion batteries (LIBs) is critically important for sustainable resource utilization. Electrodialysis (ED) offers a promising, environmentally friendly method for lithium separation and concentration, but the low selectivity of conventional ion-exchange membranes in acidic environments still limits its application. We propose a dual-regulation strategy for pore size and molecular interactions to dynamically control the monomer diffusion and reaction process, aiming to prepare acid-resistant β-ketoenamine-linked covalent organic framework (COF) membranes with enhanced crystallinity. Carboxylated poly(ether ether ketone) (CPEEK) was synthesized to enhance the uniform distribution of −COOH groups in the substrate membrane at the molecular level, while the porogen content was regulated to control both the pore size and the distribution of functional groups. The porous substrate with uniformly distributed carboxyl functional groups and tunable pore sizes serves as a temporary reservoir for monomers during the unidirectional diffusion process in COF membrane fabrication, enabling dynamic control over the slow and uniform diffusion of the monomers. The optimized M 10 –COF membrane exhibited an excellent Li + flux of 2.18 × 10 –8 mol·cm –2 ·s –1 in simulated acidic leachate system, with Li + /Ni 2+, Li + /Co 2+, and Li + /Mn 2+ selectivities reaching 17.91, 14.76, and 11.83, respectively.