Production of lithium hydroxide by electrodialysis with bipolar membranes

In conventional lithium extraction processes, highly purified lithium sulfate is generated as an intermediate, which is transformed into lithium hydroxide for lithium-ion battery applications. This study illustrates the technical feasibility of converting the pre-purified lithium sulfate (Li2SO4) into lithium hydroxide (LiOH) and sulfuric acid (H2SO4) using an electrodialysis with bipolar membrane (EDBM) process. A feed solution of 1.5 mol/L Li2SO4 is converted into 2.2 mol/L LiOH and 1.3 mol/L H2SO4 with a specific energy consumption of less than 10 kWh/kg LiOH produced. Due to the increased acid and base volume caused by electroosmosis, both acid and base concentrations are lower than that estimated based on stoichiometry. Increasing the initial LiOH solution concentration decreases the sulfate transfer from the acid and feed solutions to the base solution. Maintaining a low concentration of H2SO4 in the acid compartment (0.05 mol/L) significantly reduces the migration flux of sulfate ions through the bipolar membrane, leading to a LiOH purity of ~99.75%. This also lowers the energy consumption to ~7 kWh/kg, with a reduced average sulfate leakage flux into the base solution (~0.008 mol/m2hr). Battery grade LiOH could be obtained after a small further reduction of the sulfate content. This work demonstrates that EDBM can potentially replace the current chemical precipitation technique to produce LiOH from Li2SO4, by eliminating the use of a large quantity of alkali and the associated precipitation and solid–liquid separation steps.