BaTiO₃ Nanoparticles Coated with Polyurethane and SiO₂ for Enhanced Dielectric Properties

Core–shell structures are commonly employed in dielectric nanocomposites to improve the energy storage capacity of polymers. However, few studies have focused on organic–inorganic double-layered shell structures. Thus, there is an urgent need to elucidate the detailed effects of the flexible segment of polymer shells and inorganic shells on the dielectric properties. Herein, we synthesized a hierarchical core–double shell BT/PU/SiO 2 nanofiller with a thickness of 3–5 nm PU and 15 nm SiO 2 layers. This unique shell structure possesses a gradient permittivity that regularly decreases from the inside to the outside of shells. Detailed electrical characterizations reveal that the intermediate PU shell with shorter flexible segments can limit the carrier migration and thus decrease the dielectric loss. The interfacial polarization in double-layered BT/PU/SiO 2 is beneficial to improve the dielectric constant of the as-prepared nanocomposites. COMSOL Multiphysics simulation results also confirm that the delicate structure enables the internal electric field more homogeneous, which enhances the breakdown strength owing to its gradient dielectric constant. In addition, the dielectric loss of BT/PU/SiO 2 -PVDF is 0.032 when the filling is <4 wt %, which is only 45% compared with that of BT-PVDF. Meanwhile, the energy density of the nanocomposite reaches 7.41 J cm –3, which is 1.74 times higher than that of pure PVDF (2.7 J cm –3 ). Accordingly, our current work provides insight into the design of hierarchical core–double shell nanoparticles and their derived polymer nanocomposite capacitors for high-energy-density storage applications.