Polymeric dielectrics have garnered significant interest worldwide due to their excellent comprehensive performance. However, developing polymeric dielectric films with high permittivity (ε_r) and breakdown strength (E_b) and low dielectric loss (tanδ) presents a huge challenge. In this study, amorphous aluminum oxide (Al₂O₃, AO) transition interfaces with nanoscale thickness were constructed between titanium oxide (TiO₂, TO) nanosheets and polyvinylidene fluoride (PVDF) to manufacture composites (PVDF/TO@AO). TO@AO nanosheets showed favorable dispersion in the polymer-based composites. Improved permittivity, suppressed dielectric loss, and enhanced breakdown strength were achieved by introducing AO coating with intermediate permittivity onto TO nanosheets to build a transition interface. The transition interface efficiently depressed the mobility of the charge carrier and electric conduction of the PVDF/TO@AO composites. As a result, the PVDF-based composite with 1 wt% TO@AO showed superior comprehensive performance, including high ε_r of ~12.7, low tanδ of ~0.017, and exceptional E_b of ~357 kV/mm. This strategy supplies a novel paradigm for the application of fabricating dielectric films with excellent comprehensive performance.

With the rapid development of modern electrical and electronic applications, the demand for high-performance film capacitors is becoming increasingly urgent. The energy density of a capacitor is dependent on permittivity and breakdown strength. However, the development of polymer-based composites with both high permittivity (ε_r) and breakdown strength (E_b) remains a huge challenge. In this work, a strategy of doping synergistic dual-fillers with complementary functionalities into polymer is demonstrated, by which high ε_r and E_b are obtained simultaneously. Small-sized titania nanosheets (STNSs) with high ε_r and high-insulating boron nitride sheets coated with polydopamine on the surface (BN@PDA) were introduced into poly(vinylidene fluoride) (PVDF) to prepare a ternary composite. Remarkably, a PVDF-based composite with 1 wt% BN@PDA and 0.5 wt% STNSs (1 wt% PVDF/BN@PDA−STNSs) shows an excellent energy storage performance, including a high ε_r of ~13.9 at 1 Hz, a superior E_b of ~440 kV/mm, and a high discharged energy density U_e of ~12.1 J/cm³. Moreover, the simulation results confirm that BN@PDA sheets improve breakdown strength and STNSs boost polarization, which is consistent with the experimental results. This contribution provides a new design paradigm for energy storage dielectrics.