Polyimide composites crosslinked by aromatic molecules for high-temperature capacitive energy storage

High-temperature polymer-based dielectric capacitors are crucial for application in electronic power systems. However, the storage performance of conventional dielectrics polymer dramatically deteriorates due to the thermal breakdown under concurrent high temperatures and electric fields, and there are hardly reports on the causes of thermal breakdown from the aspects of the high-temperature conduction loss and Joule heat dissipation. Herein, a combined strategy of crosslinking and compositing for polyimide-based composites is proposed, which minimizes the thermal breakdown by significantly inhibiting the high-temperature conduction loss and enhancing the thermal conductivity. Furthermore, the rationale of the strategy was theoretically and experimentally verified from multiple perspectives. The charge-trapping effect is directly observed by Kelvin probe force microscopy probed (KPFM) with nano-level resolution and quantitatively by thermally stimulated depolarization current measurements, indicating that the crosslinking network introduces local deep traps and effectively suppresses the charge transport. The thermal conductivity of the composites inhibits the high-temperature thermal breakdown, which is confirmed by phase-field simulations. Consequently, the optimized composites possess an ultra-high discharge energy density (U_d) of 5.45 J/cm³ and 3.54 J/cm³ with a charge–discharge efficiency (η) of 80 % at 150 and 200 °C, respectively, which outperforms the reported polyimide-based dielectric composites. This work provides a scalable direction for high-temperature polymer-based capacitors with excellent performance.