聚合物纳米复合电介质电热耦合分子断裂击穿特性与机理研究

Film dielectric capacitors are high-power energy storage devices widely used in power systems, new energy vehicles, and electromagnetic energy equipment. However, with increasing operating temperatures, the breakdown strength of dielectrics considerably decreases, resulting in a considerable energy storage density decrease of the capacitor. To elucidate the quantitative relation between dielectric breakdown characteristics and temperature, polypropylene/alumina and polyetherimide/alumina nanocomposite dielectrics were prepared, and temperature dependence of their breakdown strength was investigated in this study. The results revealed that the breakdown strength of the dielectrics decreased with increasing temperature, and the relation between the two dielectrics was a convex function. However, all the traditional breakdown models obtained the relation between breakdown strength and temperature as a concave function, which contradicted the experimental results. Herein, an electrothermally coupled molecular fracture breakdown model with a maximum error of only 3.57% between the analytical value of the model and the experimental data was established. The breakdown mechanism of polymers was revealed from the fact that the directional movement of the molecules decreases the contact strength of the local molecular chains. The doping of nanofillers will bind the molecular chains in the composite dielectrics, improving the interaction between the molecular chains in the interface region, reducing weakly bound molecular chain segments, and improving the breakdown strength and temperature stability of the dielectric. This study provides theoretical model support for the development of high-temperature-resistant energy storage capacitors.