Significantly Enhancing the High‐temperature Breakdown and Capacitive Performances of Dielectric Polymers via Incorporating Alumina Nanotubes as Equivalent Crosslinking Points

Abstract Polymer‐based electrostatic capacitors are important energy storage components in power systems, yet they suffer from low breakdown strength due to the vigorous movement of molecular chains at elevated temperatures. Herein, hollow‐structured alumina nanotubes are prepared by an ion exchange method and introduced into polyetherimide films. In this design, the alumina nanotubes act as equivalent crosslinking points which can restrain the movement of polymer molecular chains that pass through the alumina nanotubes. Meanwhile, the wide bandgap alumina nanotubes can trap and scatter charges which further contribute to the enhancement of breakdown strength. Accordingly, when merely 0.3 wt.% alumina nanotubes are incorporated into the polyetherimide film, a significantly boosted breakdown strength of 679.54 MV m −1 , which is 143.80% of pure polyetherimide, is achieved at 200 °C. Consequently, an ultrahigh energy density of 6.54 J cm −3 (efficiency > 90%), which reaches 641.18% that of pristine polyetherimide (1.02 J cm −3 ), is obtained at 200 °C. This work provides an innovative strategy, i.e., constructing equivalent crosslinking points, to greatly enhance the high‐temperature breakdown and pulsed energy storage performances of polymer dielectrics.