Sustainable Production of Lithium Acetate by Bipolar Membrane Electrodialysis Metathesis

As one of the most important cathode materials for lithium-ion batteries, LiFePO 4 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 LiFePO 4 /C composite. First, the LiAc product solution is prepared by a new two-compartment electrodialysis metathesis of lithium sulfate (Li 2 SO 4 ) and acetic acid (HAc). Despite both being anions, the initial permselectivity P Ac SO 4 is as high as 15.4, and the final P Ac SO 4 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 Li 2 SO 4 ·H 2 O, which can be directly reused, first forms unexpectedly due to the salting-out effect. After that, LiAc·2H 2 O crystals with extraordinary dimensions (∼10 mm) are obtained when the solution is cooled down to room temperature, in which the SO 4 2– 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·2H 2 O 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.