Tuning Nanofillers in In Situ Prepared Polyimide Nanocomposites for High‐Temperature Capacitive Energy Storage

Abstract Modern electronics and electrical systems demand efficient operation of dielectric polymer‐based capacitors at high electric fields and elevated temperatures. Here, polyimide (PI) dielectric composites prepared from in situ polymerization in the presence of inorganic nanofillers are reported. The systematic manipulation of the dielectric constant and bandgap of the inorganic fillers, including Al 2 O 3 , HfO 2 , TiO 2 , and boron nitride nanosheets, reveals the dominant role of the bandgap of the fillers in determining and improving the high‐temperature capacitive performance of the polymer composites, which is very different from the design principle of the dielectric polymer composites operating at ambient temperature. The Al 2 O 3 ‐ and HfO 2 ‐based PI composites with concomitantly large bandgap and moderate dielectric constants exhibit substantial improvement in the breakdown strength, discharged energy density, and charge–discharge efficiency when compared to the state‐of‐the‐art dielectric polymers. The work provides a design paradigm for high‐performance dielectric polymer nanocomposites for electrical energy storage at elevated temperatures.