Electrochemical Stability of Fibrous Separators from Recycled Polyethylene Terephthalate Cups in Lithium-Based Batteries

Abstract

This study demonstrates a sustainable approach for converting post-consumer polyethylene terephthalate (PET) drink cups into electrospun fibrous separators. The recycled PET membrane exhibits a uniform bead-free nanofibrous structure with high porosity and an interconnected network, enabling enhanced electrolyte uptake and ion transport. Compared with Celgard 2400, it shows superior thermal stability, retaining structural integrity up to 190 °C without shrinkage, as well as nearly four-fold higher ionic conductivity (3.15×10^-1 S·cm^-1) and lower bulk resistance. However, the electrochemical stability of the PET separator is strongly electrolyte-dependent: ether-based systems induce pronounced instability, while carbonate-based electrolytes provide relatively improved, yet still limited, stability. The PET separator operates stably with LiFePO₄ cathodes but shows limited compatibility with graphite and lithium-sulfur cells due to side reactions and interfacial instability. Overall, recycled PET is shown to be a promising eco-friendly separator material, although further optimization of interfacial chemistry and electrolyte compatibility is required for broader application.