▎ 摘　　要

Dielectric capacitors have been the major enabler for a number of applications in advanced electronic and electrical power systems due to their capability of ultrafast charging-discharging and ultrahigh power density. High energy density dielectrics are highly desirable in order to reduce the size and cost of dielectric capacitors, which is critical for electrical pulse-power systems and power electronics in electric vehicles. Polymer nanocomposites are promising in raising the low energy density of neat polymer dielectrics of current use. In this study, a class of sandwich-structured nanocomposites are prepared by a facile hot-pressing method. Polyvinylidene fluoride nanomcomposite layers filled with graphene oxide nanosheets coated with TiO2 nanoparticles (G-layers) or Ba0.6Sr0.4TiO3 nanofibers (B-layers) are cast from solution and assembled into sandwich-structured nanocomposites with reversed topological strcuture (BGB a GBG). An ultrahigh energy density of 14.6 J/cm(3) is achieved in the BGB nanocomposites. Phase-field simulations reveal the significant implications of topological structure on the dielectric performance of the nanocomposites. By rational design of topological structure and the dielectric property of the individual layers, favorable distribution of local electrical field could be achieved among the constituent layers of the sandwich-structured nanocomposites, giving rise to the concomitant enhancement of electrical polarization and dielectric breakdown strength, and hence ultrahigh energy density. (C) 2015 Elsevier Ltd. All rights reserved.