An Ecofriendly and Cost-Effective Method for Producing LiOH from Li₂SO₄ Using Indigenously Engineered Bipolar...

Lithium hydroxide, which is utilized in lithium-ion battery applications, is produced as an intermediary from lithium sulfate (Li₂SO₄) in the conventional lithium extraction process. This work represents a more convenient way for the production of LiOH from lithium sulfate using the bipolar membrane electrodialysis (BMED) process at various applied potentials. Here, we have prepared the bipolar membrane (BPM) using the solution casting technique, having an interfacial layer (IL) of sulfonated molybdenum sulfide (S-MoS₂) to boost the water splitting rate. Sulfonated poly(ether sulfone) and quaternized poly(phenylene oxide) were used as the cation exchange layer (CEL) and the anion exchange layer (AEL) in the bipolar membrane (BPM), respectively. Various characterization techniques, such as NMR, FE-SEM, UTM, and XRD, were carried out for the membranes and the S-MoS₂ catalyst. The current-voltage curves (CVCs) for the prepared BPMs were recorded in 0.1 M LiCl to evaluate the various operational parameters for the BMED process. The feed solution of 0.4 M Li₂SO₄ produced 0.62 M of LiOH. To produce high-purity LiOH, dilute H₂SO₄ was circulated in the acid compartment (Acid mode), which reduced the migration of sulfate ions from the acid to the base compartment. This reduced the average sulfate flux from 0.034 × 10^-4 mol m^-2 s^-1 to 0.021 × 10^-4 mol m^-2 s^-1 for the dissociation of 0.2 M Li₂SO₄ at 6 V/pair. All Acid-mode experiments showed more than 90% lithium recovery and higher product purity with an energy consumption of 1.77 kWh kg^-1. After further reducing the sulfate content, battery-grade LiOH could be obtained. This work illustrates that the BMED process can effectively produce LiOH from Li₂SO₄ and replace the conventional solvent extraction and chemical precipitation process by excluding the large amounts of bases, related precipitation, and solid-liquid separation steps.