Polymer nanocomposites with concurrently enhanced dielectric constant and breakdown strength at high temperature enabled by rationally designed core-shell structured nanofillers

Polymer dielectrics are required to maintain high energy density at elevated temperatures for advanced power and electronic systems. Herein, we report a novel solution-processed core-shell structured polyimide (PI) nanocomposite with moderate dielectric constant HfO2 core and wide-bandgap Al2O3 shell, effectively addressing the typical trade-off between dielectric constant and breakdown strength in dielectric nanocomposites predominant at elevated temperatures. The formation of improved dielectrically matching interfaces by the rationally designed dielectric constant gradient from core-shell-matrix remarkably mitigates the distortion of the electric field around the interfaces, resulting in a high breakdown strength. Wide band gap Al2O3 shell also introduces deeper traps to impede the conduction loss. The validity of Al2O3 shell has been proved via experiments and simulations. Accordingly, HfO2@Al2O3/PI nanocomposite exhibits an excellent charge-discharge efficiency of 91.7 % at 300 MV/m and a maximum discharged energy density of 2.94 J/cm3 at 150 °C, demonstrating its potential for high-temperature energy storage.