Rational Design of Lithium Sulphonamide Polymeric Cation Exchange Membranes for LiOH Production by Electro‐Electrodialysis

Electrodialytic conversion of lithium salts obtained from either hard-rock minerals or brines into high-value battery-grade lithium hydroxide is gaining traction as an alternative green technology. Current cation exchange membranes employed in Li-salt electrodialysis possess low selectivity towards Li and are dominated by polyfluoroalkyl polymer-based membranes which pose significant environmental challenges. Hence, there is a need for the development of inexpensive membranes for Li-salt electrodialysis applications with a lower content of environmentally hazardous fluorinated compounds. In this work, novel self-standing Li-selective and low fluorine content membranes have been developed based on inexpensive methacrylic monomers including a lithium sulfonyl-1-(trifluoromethylsulfonyl)imide monomer. The membranes were prepared via a fast UV-curing photopolymerisation process. Rational design of the membranes with different co-monomer compositions and crosslinking degrees enabled the tailoring of the membrane properties including water uptake, mechanical strength and electrochemical performance. The membranes showed a high Li-ion conductivity of up to 6.2 mS cm-1 and comparable electrodialytic performance to that of the NafionTM 117 membrane as benchmark, i.e., relatively low energy consumption of 13.9 kWh kg-1LiOH and high molar flux of up to 3.9 mmol h-1, with superior Li+/Na+ separation of 0.98.