# Synergistic Interfacial Design of Cation Exchange Membranes via Sequential Electro-Assembly for High-Efficiency Lithium Separation

## TL;DR

A new in-situ method for making ion-exchange membranes improves lithium separation efficiency from complex salt solutions.

## Contribution

A novel electro-assembly strategy for fabricating selective membrane layers directly in electrodialysis stacks.

## Key findings

- The method achieves a Li+/Mg2+ selectivity of 107.9.
- The membrane retains a selectivity of 47 after 10 cycles in real salt lake brine.
- The fabricated membrane shows enhanced ion transport and stability.

## Abstract

The industrial application of modified ion-exchange membranes is limited by complex, discontinuous ex-situ processes. This study introduces an in-situ electro-assembly strategy that enables the direct fabrication of a selective layer within an electrodialysis stack without disassembly. By utilizing a programmed current reversal to orchestrate the sequential deposition of polyethyleneimine (PEI), glutaraldehyde cross-linking, and polystyrene sulfonate (PSS) adsorption, we achieve meticulous interfacial engineering on a commercial cation exchange membrane. Comprehensive characterization confirms the successful construction of a hydrophilic, charge-tuned multilayer, which enhances ion transport kinetics and raises the limiting current density. This method culminates in a membrane with an exceptional Li+/Mg2+ selectivity of 107.9 and robust stability, retaining a significant selectivity of 47 over 10 cycles in real salt lake brine. This synergistic integration of operational simplicity, interfacial precision, and superior performance establishes a transformative and scalable platform for manufacturing high-performance membranes for selective ion separation from complex brine sources.