Significantly Enhanced Breakdown Strength and Energy Density in Nanocomposites by Synergic Modulation of Structural Design and Low-Loading Nanofibers

Polymer-based dielectric nanocomposites have attracted great attention due to the advantages of high-power density and stability. However, due to the limited breakdown strength (Eb) of the dielectrics, the unsatisfactory energy density becomes the bottleneck that restricts their applications. Here, newly designed sandwich-structured nanocomposites are proposed, which includes the introduction of low-loading 0.4BiFeO3-0.6SrTiO3 (BFSTO) nanofibers into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix as the polarization layer (B-layer) to offer high permittivity and the selection of poly(methylmethacrylate) (PMMA)/P(VDF-HFP) all-organic blend film as the insulation layer (P-layer) to improve Eb of the nanocomposites. The optimized sandwich-structured PBP nanocomposite exhibits significant enhancement in Eb (668.6 MV/m), generating a discharged energy density of 17.2 J/cm3. The dielectric and Kelvin probe force microscope results corroborate that the outer P-layer has a low surface charge density, which can markedly impede the charge injection from the electrode/dielectric interface and thereby suppress the leakage current inside the nanocomposite. Furthermore, both the finite element simulations and capacitive series models demonstrate that the homogenized distribution of electric field in the PBP sandwich-structured nanocomposite favors the improvement of energy storage performance. This work not only provides insightful guidance into the in-depth understanding of the dielectric breakdown mechanism in sandwich-structured nanocomposites but also offers a novel paradigm for the development of polymer-based nanocomposites with high Eb and discharged energy density.