Space-confined nafion nanochannels in PVDF membranes enable efficient Li+/Mg2+ separation

The rising demand for lithium in energy storage technologies has increased the need for efficient and sustainable extraction methods. Seawater and brines contain abundant lithium reserves, yet separating lithium from coexisting magnesium remains challenging due to their similar ionic properties. Membrane-based separation offers an energy-efficient and environmentally friendly approach for lithium recovery. In this study, a tetrapropylammonium (TPA)-modified Nafion/polyvinylidene fluoride (PVDF) nanochannel membrane was developed to achieve highly efficient Li + /Mg 2+ separation. The hydrophobic PVDF matrix restricts Nafion swelling, ensuring stable channel dimensions. TPA cations interact with Nafion's sulfonate groups to promote uniform dispersion and facilitate the formation of continuous ion-conducting nanochannels. The optimized TPA-Nafion/PVDF membrane exhibits a lithium flux of 26 mmol m −2 h −1 and a Li + /Mg 2+ selectivity of approximately 42, demonstrating outstanding performance compared to advanced membranes. Besides, it maintains stable performance during extended operation. This work provides a practical strategy for constructing high-performance polymer membranes with tunable ion transport channels from widely accessible materials, paving the way for energy-efficient and cost-effective lithium extraction. • Nafion/PVDF composite membranes with space-confined cation-selective nanochannels for efficient Li + /Mg 2+ separation. • Nafion is embedded within the hydrophobic PVDF matrix to form continuous and size-regulated ion transport pathways. • TPA-assisted dispersion ensures uniform Nafion distribution within confined domains. • Membrane delivers outstanding Li + /Mg 2+ selectivity–flux combinations with excellent long-term stability.