Surface charge and pore size regulation for nanofiltration membrane enables enhanced Co/Li separation performance

With the rapid retirement of lithium-ion batteries (LIBs), efficiently and environmentally friendly recovering Co 2+ and Li + from LIBs acidic leachates is crucial for meeting the demand for strategic metals. Nanofiltration (NF) membranes, featuring the potential of selective separation of ions, has shown remarkable promise in LIBs acidic leachate recycling. In this work, PDA@PEI surface deposition was employed to endow commercial NF membranes with surface charge and pore size regulation. The modified membrane exhibited a Co 2+ /Li + separation factor (SF) of 70.8 in LIBs acidic leachates—far exceeding the intrinsic performance of conventional negatively charged NF membranes (SF = 11.5). DSPM-DE modeling demonstrated that membrane modification intensifies Donnan exclusion by enriching surface positive charge, while simultaneous pore-size reduction reinforces steric screening, synergistically enhancing Co 2+ /Li + selectivity. Notably, the modified membrane achieved permeate quality comparable to that of a conventional two-stage NF process under single-stage operation and reduced energy consumption by 13% at a low operating pressure of 10 bar. Collectively, these findings demonstrate the feasibility of efficient Co 2+ /Li + separation from spent LIBs leachates and highlight its potential to enhance both the resource-recovery efficiency and environmental sustainability of lithium-ion battery recycling.