Enhancing High‐Temperature Energy Density through Al2O3 Nanoplates with Charge Barrier Effect in Polyetherimide‐Based Composites

Abstract Polymer‐based dielectric composites have a wide range of applications in modern electronics and power systems owing to their incomparable reliability, but remain a challenge to energy density at high temperatures. In this work, polyetherimide (PEI)‐based nanocomposites with a small amount of aluminium oxide (Al 2 O 3 ) nanoplates are prepared and obtain excellent energy density at elevated temperatures. The high‐temperature energy density of the nanocomposites is significantly improved and reaches to 5.2 J cm −3 at 550 kV mm −1 and 150 °C after adding 0.6 wt% Al 2 O 3 nanoplates. The enhanced energy density is attributed to the wide band gap and flaky morphology of Al 2 O 3 nanoplates that can induce charge barrier effect and thus reduce the leakage current density within the nanocomposites. Furthermore, finite element simulations further reveal the mechanism of Al 2 O 3 nanoplates acting as charge barrier to capture the charges transmitted from PEI matrix at the interface. This work offers a promising pathway to high‐energy density polymer dielectrics capable of operating under high temperatures.