Wide-Bandgap Polyimide by Molecular Engineering for High-Temperature Capacitive Energy Storage

Dielectric capacitors are critical components in advanced energy systems. However, their energy storage capability at elevated temperatures remains limited. Here, the effects of functional groups on bandgap and trap distributions are systematically investigated. Four polyimide (PI) films are synthesized using monomers containing sulfonyl, trifluoromethyl, and ether linkages. The optimized PI with high trifluoromethyl content exhibits a twisted molecular configuration that disrupts chain planarity, widens the bandgap, and introduces dense trap sites to suppress charge transport. As a result, it achieves a high breakdown strength of 595 MV/m and a discharged energy density of 4.1 J/cm³ with an efficiency exceeding 90% at 200 °C, outperforming most reported dielectric polymers. This work provides a scalable molecular design strategy for high-temperature polymer dielectrics.