Unifying and Suppressing Conduction Losses of Polymer Dielectrics for Superior High‐Temperature Capacitive Energy Storage

Abstract Superior high‐temperature capacitive performance of polymer dielectrics is critical for the modern film capacitor demanded in the harsh‐environment electronic and electrical systems. Unfortunately, the capacitive performance degrades rapidly at elevated temperatures owing to the exponential growth of conduction loss. The conduction loss is mainly composed of electrode and bulk‐limited conduction. Herein, the contribution of surface and bulk factors is unified to conduction loss, and the loss is thoroughly suppressed. The experimental results demonstrate that the polar oxygen‐containing groups on the surface of polymer dielectrics can act as the charge trap sites to immobilize the injected charges from electrode, which can in turn establish a built‐in field to weaken the external electric field and augment the injection barrier height. Wide bandgap aluminum oxide (Al 2 O 3 ) nanoparticle fillers can serve as deep traps to constrain the transport of injected or thermally activated charges in the bulk phase. From this, at 200 °C, the discharged energy density with a discharge–charge efficiency of 90% increases by 1058.06% from 0.31 J cm −3 for pristine polyetherimide to 3.59 J cm −3 for irradiated composite film. The principle of simultaneously inhibiting the electrode and bulk‐limited conduction losses could be easily extended to other polymer dielectrics for high‐temperature capacitive performance.