Bipolar membranes electrodialysis of lithium sulfate solutions from hydrometallurgical recycling of spent lithium-ion batteries

Abstract

This study investigates the use of bipolar membrane electrodialysis (BMED) for recovering LiOH and H2SO4 from lithium sulfate (Li2SO4) solutions, aiming to establish a closed-loop hydrometallurgical recycling process for spent lithium-ion batteries. A 2.2 mol/L LiOH and 1.3 mol/L H2SO4 were recovered from a 1.1 mol/L Li2SO4 solution. Experiments were conducted under constant current conditions, and the effects of current density, number of cell pairs, and flow rates on performance were analyzed. Key findings include that BMED is an environmentally-friendly and energy-saving method for recovering Li+ as LiOH. The voltage loss across the bipolar membrane (1 V) is a major component of the total voltage drop (1.27 V) in the cell. Increasing the number of cell pairs enhances production efficiency and reduces energy consumption per cell pair, with theoretical energy costs for LiOH production in a 100-pair stack reduced to 1.57 kWh/kg. Durability tests and SEM analysis showed structural changes and highlighted the importance of maintaining high cleanliness in pre-treated solutions to extend membrane lifespan. This study provides insights into optimal BMED operation and design, demonstrating its potential for industrial-scale applications. Adjusting the Li+ recovery rate to around 80 % and using multiple cycles can further reduce energy consumption and improve the purity of recovered solutions.