Improved high-temperature energy storage performance of composite dielectrics via optimizing the interface of nano-alumina/polyimide

Polymer-based electrostatic capacitors have a broad application prospect in modern electric power systems due to their advantages of high breakdown strength ( E b ) and power density. However, at high-temperatures, both the increase in dielectric loss and the deterioration of insulation properties triggered by the Joule heat result in a sharp decrease in the energy storage property of polymer-based capacitors, which greatly restricts the development of advanced electronics. To address this challenge, this study proposes a molecular engineering strategy that constructs an inorganic-organic cross-linked system with strong interfacial bonding via covalent linkages between amino-functionalized alumina (Al 2 O 3 –NH 2 ) nanorods and the polyimide (PI) matrix. This design enables synergistic regulation of charge transport through cross-linked networks and interfacial traps, effectively suppressing conductive losses in the composite at elevated temperatures. Notably, at 150 °C with a charge-discharge efficiency ( η ) of 92 %, the 1.5 wt% Al 2 O 3 -NH 2 /PI composite achieved a high energy storage density ( U e ) of 4.74 J/cm 3 , which was 204 % higher than that of pure PI ( U e  ∼ 1.56 J/cm 3 ). Thus, this study provides a promising strategy for advancing high-temperature energy storage capacitors.