toward green recycling of spent Li-ion batteries

The global transition to electric vehicles and renewable energy systems has heightened the demand for lithium-ion batteries (LIBs), creating an urgent need for sustainable battery recycling methods to recover critical raw materials, including lithium. Lithium-selective cation-exchange polymeric membranes are one of the emerging options to achieve such lithium recycling. To make this change even greener, instead of using traditional fossil-origin polymers to produce membranes, this research employed bacterial cellulose acetate (BCA), a bio-derived and eco-friendly polymer. By adding 5 wt% N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13–TFSI), an ionic liquid (IL) which is a plasticizer and lithium-ion conductor, and 20 wt% hydrogen manganese oxide (HMO), which is a lithium-selective inorganic filler, four BCA-based membranes (BCA, BCA-IL, BCA-HMO and BCA-IL-HMO) were prepared. The membranes were extensively characterized for their morphology, thermal stability, chemical, and mechanical properties. Subsequently, they were tested in diffusion cells (without applying any external driving force) for ionic conductivity, lithium selectivity, and lithium flux using binary salt mixtures and synthetic LIB leachate. The BCA-IL membrane outperformed other BCA-based membranes in terms of separation factors, achieving values of 10.50 (Li+/Mn2+), 11.75 (Li+/Ni2+), and 10.95 (Li+/Co2+) with a lithium flux of 0.12 mol m−2 h−1 when processing synthetic LIB leachate. Under the same conditions, the BCA-HMO membranes exhibited a higher lithium flux (0.51 mol m−2 h−1) but with lower separation factor values of 3.39 (Li+/Mn2+), 3.62 (Li+/Ni2+), and 3.36 (Li+/Co2+). The use of plant-derived cellulose acetate (CA) as an alternative to BCA was also assessed; however, despite promising ideal lithium selectivity values (for example, 112 for Li+/Ni2+ in the case of CA-HMO membrane), their conductivity was up to two orders of magnitude lower than that of BCA-based membranes. All these findings highlight the promising potential of BCA-based membranes for lithium recovery from lithium-ion battery leachates.