Zwitterionic Molecule Intercalation in Nanoporous Multilayer Graphene Oxide Membrane for Metal Ion Recovery from Spent Li-Ion Batteries

The increasing demand for lithium-ion batteries has intensified the need for efficient recovery of lithium and transition metals from spent battery materials. Membrane-based ion separation provides a low-energy alternative or can be combined with conventional hydrometallurgical purification routes. In this study, graphene oxide (GO) membranes were engineered through the intercalation of a zwitterionic molecule, 3-(1-vinyl-3-imidazolio)propanesulfonate (VIPS), followed by hot-press treatment to produce structurally stabilized VIPS-intercalated GO membranes. Structural and spectroscopic analyses reveal that VIPS molecules expand the interlayer spacing of GO and introduce positively charged groups, which suppress the permeation of divalent cations. Hot-pressing further generates nanopores and reinforces the layered structure, enabling improved Li ion transport. Concentration-driven permeation tests demonstrated that the GO membrane containing a 1:1 weight ratio of GO to VIPS achieved a lithium-ion permeation rate of 33.2 mmol m–2 h–1 with markedly enhanced selectivity over divalent ions, including a lithium/manganese selectivity of 18. Long-term forward osmosis operation conducted for 480 h exhibited stable Li-selective permeation behavior, yielding permeation rates of 33.0, 8.3, 4.0, and 3.8 mmol m–2 h–1 for Li+, Co2+, Ni2+, and Mn2+, respectively. Although extended operation caused slight swelling and partial loss of selectivity, a multistep forward osmosis enrichment process produced high-purity lithium solutions (>99%) and decreased the concentrations of Co2+, Ni2+, and Mn2+ to undetectable levels after three cycles. This study demonstrates that the combination of zwitterionic molecule intercalation and hot-press treatment produces structurally stable graphene oxide membranes capable of selective lithium transport and high-purity lithium enrichment, offering a practical and energy-efficient platform for lithium recovery from hydrometallurgical recycling streams.