Physics

Nanotechnology

Nanocomposite

Composite number

Dielectric

Nanoparticle

Composite material

Materials science

Polyetherimide

Polymer nanocomposite

Quantum mechanics

Optoelectronics

Polymer

Electric field

Advanced Energy Materials

High‐energy‐density polymer dielectrics capable of high temperature operation are highly demanded in advanced electronics and power systems. Here, the polyetherimide (PEI) composites filled with the core–shell structured nanoparticles composed of ZrO 2 core and Al 2 O 3 shell are described. The establishment of a gradient of the dielectric constants from ZrO 2 core and Al 2 O 3 shell to PEI matrix gives rise to much less distortion of the electric field around the nanoparticles, and consequently, high breakdown strength at varied temperatures. The wide bandgap Al 2 O 3 shell creates deep traps in the composites and thus yields an order of magnitude lower leakage of current density of the composites with respect to those with pristine ZrO 2 at high temperatures. Accordingly, the composite delivers a discharged energy density of 5.19 J cm −3 and 150 ° C, which outperforms the current free‐standing high‐temperature dielectric polymer and polymer composite films measured at 10 Hz. Moreover, the core–shell structured composites endow great thermal stability, charge–discharge efficiency, and the improved energy density with increasing temperature from 25 to 150 ° C. The finite element simulations and numerical calculations are performed to reveal the mechanistic impacts of the core–shell structure on the electric field distribution and electrical conduction of the composites.

High‐Temperature High‐Energy‐Density Dielectric Polymer Nanocomposites Utilizing Inorganic Core–Shell Nanostructured Nanofillers