Sustainable Production of Lithium Acetate by Bipolar Membrane Electrodialysis Metathesis

As one of the most important cathode materials for lithium-ion batteries, LiFePO4 has been receiving extensive attention from industry and academia. In this study, we propose a novel process for the sustainable production of high-purity lithium acetate (LiAc), which would be a very good precursor to the LiFePO4/C composite. First, the LiAc product solution is prepared by a new two-compartment electrodialysis metathesis of lithium sulfate (Li2SO4) and acetic acid (HAc). Despite both being anions, the initial permselectivity PAcSO4 is as high as 15.4, and the final PAcSO4 can still be maintained at 4.14 with the conventional anion exchange membrane. Compared with the conventional four-compartment configuration, this effective and simplified design requires fewer membranes and lower energy consumption. Evaporation is subsequently employed for further purification. The impurity of solid Li2SO4·H2O, which can be directly reused, first forms unexpectedly due to the salting-out effect. After that, LiAc·2H2O crystals with extraordinary dimensions (∼10 mm) are obtained when the solution is cooled down to room temperature, in which the SO42– impurity is as low as 0.075% wt. This atomically economic mass flow achieved here maximizes all the materials (such as lithium, sulfate, and acetate) and completely eliminates waste discharge. Furthermore, the optimal process cost is only 0.319 $/kg as LiAc·2H2O solid (selling price 30–40 $/kg). Therefore, this is a high-yield, cost-effective, and green synthetic route for pure LiAc, and it is also a good application of bipolar membrane electrodialysis (BPED) in the upgrading to cleaner production processes.