Polarization Structural Design in Core–Shell Fillers: An Approach to Significantly Enhance the Energy Storage Properties of BST/PVDF Composite Films

Abstract

Flexible dielectric energy storage capacitors have important application potentials in pulsed power systems. However, low energy storage density has always been an obstacle to practical applications because it is difficult to increase the dielectric constant of flexible dielectrics while reducing dielectric loss. In this study, a strategy is proposed to solve this problem. As the filler of polyvinylidene fluoride (PVDF), a special inorganic core–shell structure is constructed. The core–shell filler structure includes a donor Y-doped BST core and acceptor Mn-doped BST shell, wrapping ZrO2 as the outermost layer (Y@M-BST@ZrO2). Through this design, the simultaneous optimization of dielectric constant and dielectric loss is finally realized in the BST/PVDF composites. When an electric field is applied, the separation of electrons and holes formed in the core–shell fillers Y@M-BST@ZrO2 enhances the composite polarization and dielectric constant of Y@M-BST@ZrO2/PVDF and meanwhile reduces its dielectric loss at 1 kHz; therefore, the composite energy storage properties are significantly improved in comparison with the sample BST@ZrO2/PVDF. In experiments, the Y@M3-BST@ZrO2/PVDF composite film has a dielectric constant of 20.9, a dielectric loss of 0.024, and an energy storage density of 7.555 J/cm3 at 600 kV/cm, which is 74.6% higher than that of BST/PVDF composite film. It reaches 2.1 times the energy storage density of pure PVDF film. This study shows that the formation of a polarization structure caused by a positioning doping in core–shell structural fillers may provide a path for functional dielectrics of high-energy-density capacitors.