Upcycling waste lithium-ion battery separators into nanofiltration membranes for seawater desalination and hydrogen production

The rapid expansion of electric vehicles is anticipated to generate millions of end-of-life lithium-ion batteries (LIBs), creating both resource and environmental challenges. Conventional recycling primarily targets metal recovery, leaving polymeric separators largely discarded. We present a sustainable upcycling approach that transforms waste LIB separators into high-performance nanofiltration (NF) membranes for desalination and hydrogen production. Guided by mechanistic modelling, the used polyethylene separators were engineered to achieve optimal pore dimensions (1.5-3 nm) and surface charge densities exceeding ±20 mV, yielding simultaneous high flux and ionic selectivity. The resulting membranes exhibited 93.2% salt rejection and 1.7 L bar-1 m-2 h-1 water permeability under low salinity and 99.6% rejection via two-stage seawater filtration. Electrolysis of filtered seawater generated 54.5 mL H2 in 10 h, representing a 127.1% increase relative to direct seawater electrolysis and reaching 83% of the H2 production achieved using freshwater, while suppressing electrode scaling and corrosion. This work establishes a circular-economy strategy that repurposes low-value LIB waste into functional membranes, enabling clean hydrogen production from seawater and providing a scalable pathway toward sustainable energy and environmental technologies.