Sandwich-Structured Polymer Composites with Core–Shell Structure BaTiO₃@SiO₂@PDA Significantly Enhanced Breakdown Strength and Energy Density for a High-Power Capacitor

Polymer-based dielectric materials with high energy storage performance have become an important part of electric power and electronic systems. But due to the low intrinsic dielectric constant of polymers, it is usually needed to mingle high dielectric constant nanofillers to improve their dielectric properties. However, the addition of nanoparticles often results in higher dielectric loss and lower breakdown strength. Herein, using a simple method of surface modification of BaTiO3, silica and polydopamine are coated on the surface of BaTiO3, significantly improving the dielectric properties of the polymer. Meanwhile, the composite with a sandwich structure is prepared by using BaTiO3@SiO2@PDA/PVDF as the central layer and pure PVDF as the two outer layers, achieving an ultrahigh breakdown strength (633 MV/m). The sandwich-structured composite with 1 wt % BaTiO3@SiO2@PDA has the highest discharge energy density (15.4 J/cm3). The simulation results reveal that the sandwich structure not only acts as an interface carrier barrier but also optimizes the electric field concentration inside the composite, which reduces the probability of electric breakdown. This work can broaden the way for dielectric films to be used in the field of high energy density, and the modification strategy can also provide ideas for other fields.