Ultrahigh enhancement rate of the energy density of flexible polymer nanocomposites using core-shell BaTiO₃@MgO structures as the filler

Dielectric energy storage capacitors are critical components widely used in electronic equipment and power systems due to their advantages of ultrahigh power density and high voltage. Herein, a novel core-shell BaTiO₃@MgO (BT@MO) nanostructure was fabricated, in which highly insulating MgO was directly coated on a continuous ferroelectric nanoparticle BaTiO₃shell through a chemical precipitation method to improve the breakdown strength and electric displacement under high electric field. A large electric displacement (D≈ 9.8 μC cm⁻²under 571.4 MV m⁻¹) was observed along with a high discharge energy density (Ud ≈ 19.0 J cm⁻³) for BT@MO/P(VDF-HFP) composites, which was 187% higher than that for a P(VDF-HFP) film when the filler content was 3 wt%. The enhancement rate ofU_din this study achieved the highest level among the reported results. It was revealed that the highly insulating MgO shell can enhance the breakdown strength by preventing charge injection from electrodes and impeding the development of electrical stress during the breakdown process, as confirmed by the leakage current measurements and the finite element simulations. The core-shell BT@MO structured filler provided an effective way to improve the energy storage properties of the polymer-based dielectrics.