Improvement of high-temperature energy storage performance in polymer dielectrics by nanofillers with defect spinel structure

The electrostatic energy storage performance of polymer dielectrics at high temperature and high electric field can be significantly improved by the incorporation of wide-bandgap, nano-sized particles. It is traditionally believed that the embedded nanoparticles can scatter the hot charges and lead to charge trapping in the interfacial region, which suppress the conduction loss and promote the energy storage performance. In this work, the nano-sized γ-Al 2 O 3 with cubic defect spinel structure and nano-sized α-Al 2 O 3 with a wider bandgap are introduced into a heat-resistant dielectric polymer, respectively, to form two different nanocomposites. The field-dependent energy storage performance, electrical conductivity , and breakdown strength of the polymer nanocomposites at high temperatures, as well as the thermally stimulated depolarization current , are investigated. The results indicate that the intrinsic deep traps introduced by γ-Al 2 O 3 with cubic defect spinel structure are a more critical factor in improving the energy storage performance of the polymer-based composites. We anticipate that our findings reported in this work may help to better guide the selection of nanofillers for high-temperature dielectric polymer nanocomposites. • In this work, pure-phase nanoscale α-Al 2 O 3 powders were prepared by high-energy ball milling process. • The origin of the improved high-temperature energy storage by using Al 2 O 3 nanofillers is not solely the large bandgap. • γ-Al 2 O 3 with defective spinel structures is more beneficial to suppress charge transport under extreme conditions.