PFAS-free quasi-solid polymer electrolytes with enhanced performance for sustainable lithium-ion batteries

Abstract

Quasi-solid polymer electrolytes (QSPEs) integrate electrolyte and separator functions, offering mechanical flexibility, favorable ionic conductivity, and enhanced safety compared with liquid electrolytes. Most prior studies rely on PVDF-based systems that use PFAS-containing polymers and toxic solvents, raising environmental concerns. Here, we report PFAS-free QSPEs prepared from poly(ether sulfone) (PES) and poly(ethylene oxide) (PEO) using the green solvent dimethyl sulfoxide (DMSO). PES provides excellent thermal stability, robust mechanical properties, and an amorphous framework that disrupts PEO crystallinity and induces a porous structure, enabling continuous ion-conduction pathways. The resulting PES/PEO QSPEs exhibit an electrochemical stability window up to ∼4.23 V and an ionic conductivity of 6.05 × 10⁻⁴ S cm⁻¹, and stable Li stripping/plating behavior with low polarization. In Li|LiFePO₄ cells, they exhibit good capacity retention over multiple cycles, outperforming PES-only QSPEs and commercial separator Celgard 2325. Compared with PVDF-based systems, PES/PEO QSPEs deliver comparable electrochemical performance with superior thermal tolerance and the added benefit of being PFAS-free, providing a sustainable pathway toward safe and durable next-generation lithium-ion batteries.