Valorisation of spent battery separators into functional nanomaterials for heavy metal adsorption from contaminated water: A sustainable waste-to-resource approach

The rapid growth of electric vehicles, portable electronics, and renewable energy storage systems has led to a dramatic increase in the production and disposal of rechargeable batteries worldwide, generating a large volume of solid waste. While significant progress has been made in recovering valuable metals such as lithium, cobalt, and nickel from spent batteries, non-metallic components, particularly battery separators, are still largely neglected and commonly discarded through landfilling or incineration. Battery separators, which constitute approximately 3 – 10 wt% of lithium-ion batteries and are mainly composed of polyethylene (PE), polypropylene (PP), or composite polymeric materials, represent an abundant but underutilized waste resource. At the same time, heavy metal contamination in water caused by industrial effluents, mining activities, and electronic waste recycling poses a serious environmental threat due to toxicity, persistence, and bioaccumulation of metals such as Pb² ⁺ , Cd² ⁺ , Cr(VI), Hg² ⁺ , As3⁺ , and Ni² ⁺ . In this context, spent battery separators offer a promising carbon-rich precursor for the synthesis of functional nanomaterials through green and sustainable conversion approaches. This review summarizes recent advances in separator waste valorisation into nano materials, mechanism of adsorption, and heavy metal removal performance. Challenges, scalability issues, and future perspectives are also discussed, highlighting the potential of separator-derived nanomaterials as efficient, low-cost, and sustainable adsorbents for wastewater treatment applications.