Enhancing high-temperature capacitor performance of polymer nanocomposites by adjusting the energy level structure in the micro-/meso-scopic interface region

The interface plays a major role in the conduction and breakdown behaviors of dielectric materials. Enhancing interface compatibility and Schottky barrier to reduce conduction loss and enhance breakdown strength of nanocomposites has been widely studied. Nevertheless, there are few reports on the effect of the energy level structure in filler/polymer and electrode/dielectric interface region on the breakdown strength and high-temperature energy storage performances. Herein, the polyimide (PI) films sandwiched by Al 2 O 3 layers and filled with SiO 2 shell-coated high- K BaTiO 3 nanofibers were prepared. Our results reveal that the wide bandgap oxide layer can regulate the energy level structure of the interface region, introduce deep traps in the nanocomposites and increase the Schottky barrier at the electrode/dielectric interface to impede charge injection and transport. Moreover, the nanocomposites combine the advantages of anisotropic dielectric properties from the Al 2 O 3 layer, SiO 2 shell, and BaTiO 3 core, enhancing dielectric constants of the nanocomposites. The optimal nanocomposites show greatly enhanced discharge energy density and breakdown strength at 150 °C, which are 370% and 38% higher than those of PI, respectively. This work provides more insight into the mechanism of electrical conduction and breakdown in polymer nanocomposites and offers an effective strategy for developing polymer nanocomposites with superior capacitive performance at elevated temperatures. A novel polymer nanocomposite sandwiched by wide bandgap oxide layer and filled with high- K BaTiO 3 nanofibers coated with a wide bandgap oxide shell is reported. The trap energy level and interface Schottky barrier were greatly improved by adjusting the band structure in the micro-/meso-scopic interface region of the nanocomposites, yielding concurrent enhancements in both dielectric constant and breakdown strength at elevated temperatures. • Preparing a novel high- K nanocomposites with multi-scale interfaces. • Overcoming the negative correlation between K and E b of nanocomposites. • Revealing the band structure effect of interface region on the dielectric properties. • The U e of the optimal nanocomposites is kept at 1.75 J cm −3 with η > 90% at 200 °C.