Synthesis of Polyimide-PEO Copolymers: Toward thermally stable solid polymer electrolytes for Lithium-Metal batteries

The rapid pace of technological advancement in field of electric vehicles and need in sustainable energy sources calls for new, high-performance energy storage technologies. Lithium metal batteries (LMBs) based on solid polymer electrolyte represent a promising battery technology to increase energy density of conventional batteries while enhancing safety, eliminating dendrite formation, and providing mechanical flexibility. In this study, we developed novel polyimide-poly(ethylene oxide) (PI-PEO) copolymers and employed them as solid polymer electrolytes for LMBs. Copolymers with 5, 15, and 30 mol% of PEO-containing diamine were synthesized by reacting with aromatic dianhydride and diamine, using a facile and eco-friendly method in a benzoic acid melt. Chemical structures were confirmed using NMR and IR spectroscopy. Glass transition temperatures varied from 24 °C to 195 °C, increasing with a decrease in the PEO/PI moiety ratio. All copolymers demonstrated good thermal stability up to T5% > 345 °C with a two-step degradation and favorable mechanical properties below the glass transition temperature, as observed by DMA measurements. Solid polymer electrolytes with 70 wt% of LiTFSI exhibited an ionic conductivity of 1.4 × 10−4 S cm−1 at 70 °C, with a transference number of 0.7. The polymer electrolyte exhibited non-flammable properties and the potential for utilization in lithium metal batteries, indicating the promising application of these new polymers for high-safety battery systems.