Surface ion-activated polymer composite dielectrics for superior high-temperature capacitive energy storage

Polymer dielectrics for high-temperature capacitive energy storage suffer from low discharge energy density and inferior efficiency owing to their exponential growth of conduction losses at elevated temperatures and electric fields. The electrode and bulk-limited conduction losses are two types of conduction mechanisms in polymer dielectrics. Unlike previous nanodielectric strategies that involve incorporating wide bandgap inorganic components inside the bulk phase or on the surface of polymer films, herein, we describe a surface ion-activated polymer composite dielectric composed of abundant surface polycarboxylate (RCOO-) ions to simultaneously inhibit the electrode and bulk-limited conduction losses. The strong electrostatic repulsion between the negatively charged dielectric surface and the metal electrode effectively alleviates the charge injection from the electrode and consequently leads to a reduction in the electrode-limited conduction loss. For the suppression of bulk-limited conduction loss, wide bandgap aluminium oxide nanoparticles in the bulk phase of dielectrics significantly increase the trap density and constrain the charge mobility, contributing to the suppression of conduction loss. Accordingly, the energy loss of polymer dielectrics at high temperatures and electric fields is thoroughly inhibited. Therefore, the discharge energy density with an efficiency of around 90% at 150 degrees C increases by 421.43% from 1.26 J cm-3 for the pure film to 6.57 J cm-3 for the ion-activated composites. More importantly, for the capacitive performance with an efficiency of ca. 90% at 200 degrees C, the activated composite sample exhibits a discharge density of 4.22 J cm-3, which increases by 1355.17% in comparison to 0.29 J cm-3 of the pristine film and outperforms those of most existing polymer dielectrics. The concept of employing ions to regulate the electrode/dielectric interfacial charge transport and the strategy of simultaneously inhibiting electrode and bulk-limited conduction losses in this contribution provide a novel perspective and approach for the improvement of the high-temperature capacitive performance of polymer dielectrics. The construction of a negatively charged layer on the surface of polymer composite dielectric can significantly suppress the conduction loss at high temperatures and electric fields, consequently contributing to the improvement in the capacitive energy storage performance.