Microstructure Design and Dielectric Properties of Sandwich Structured Poly (Vinylidene Fluoride) Based Dielectric Composite

In order to investigate the influences of the filling phases and the sandwich structure on the dielectric and energy storage properties of polyvinylidene fluoride(PVDF) dielectric composite, the single composites and the sandwich-structured composites with inorganic fillers of two-dimensional boron nitride sheets and barium titanate particles were prepared by solution casting and hot pressing process. The crystal structure and morphology of the composite films were analyzed by X ray diffraction and scanning electron microscopy. The dielectric properties and energy storage properties of the thin films were obtained by using a broadband dielectric spectrometer and a ferroelectric tester. The results show that the sandwich structure of the composite film has excellent properties, including that the relative dielectric constant of BN-PVDF/BaTiO₃-PVDF/BN-PVDF sandwich structure composite films is 13 at 10 Hz. The discharged energy density of this composite film is up to 6.2 J/cm³ at 350 MV/m, which is 1.6 times higher than that of BaTiO₃-PVDF composite films. Its breakdown strength is as high as 370 MV/m, which is 1.5 times greater than that of BaTiO₃-PVDF composite. In addition, its discharged efficiency keeps at 0.55. In conclusion, because the two-dimensional BN thin plate introduced in the upper and lower two layers of sandwich structure enhances the breakdown strength of thin films, the saturation polarization is delayed. The introduction of BaTiO₃ in the intermediate layer will enhance the polarization property. Therefore, the PVDF composite films with the excellent dielectric property and energy storage characteristic can be obtained.