Solid-vapor interface confined repair for pH-resistant nanofiltration membranes with high performance in lithium-ion battery recycling

Nanofiltration (NF) application in recovering valuable metals from spent lithium-ion batteries (LIBs) is limited by the poor acid resistance and inadequate selectivity of conventional polyamide membranes. Triazine-based polyamine networks inherently possess superior pH stability and positive surface charges favorable for multivalent cation rejection, yet their synthesis is hampered by the low reactivity of cyanuric chloride (CC), resulting in loosely cross-linked active layers with suboptimal separation performance. Here, we introduce a solid-vapor interface confined repair (SVICR) strategy that transforms a preformed loose triazine-polyamine network into a dense, defect-free separation layer through spatially confined post-repair with diethylenetriamine vapor. This interface-limiting process efficiently consumes residual chlorine sites while minimizing thickness increase and hydraulic resistance. The resulting membranes exhibit exceptional mono−/multivalent ion selectivity in 2 M H₂SO₄, with separation factors of 53, 40, and 55 for Li + /Co 2+ , Li + /Ni 2+ , and Li + /Mn 2+ , respectively, alongside a water permeance of 4–8 L·m −2 ·h −1 ·bar −1 . Moreover, the membranes demonstrate outstanding long-term stability under extreme conditions, sustaining less than 2% performance decline after 21 days of exposure to 2 M H₂SO₄, 2 M HCl, or 1 M NaOH. The SVICR strategy establishes a processable and effective platform for fabricating pH-resistant NF membranes, advancing sustainable LIB recycling technologies.