Decorating Biaxially Oriented PVDF Nanocomposites with Ultralow Contents of Functionalized BNNSs for Excellent Energy Storage

Poly(vinylidene fluoride) (PVDF) polymers are considered as promising high energy density capacitor dielectrics because of their high dielectric constants and melt processability. However, their industrialization and practicalization suffer from low breakdown strengths and high leakage conduction losses. Hence, it is of great necessity to develop dielectrics with a high energy storage capability. Herein, we fabricated biaxially oriented nanocomposite PVDF films decorated with ultralow contents of surface-functionalized boron nitride nanosheets (BNNSs) by combining melt blending and biaxial orientation technology. The functionalized BNNSs exhibited an ideal horizontal distribution. Both experimental characterization and phase-field simulation validate that the horizontally distributed BNNSs effectively inhibit the propagation of the dielectric breakdown phase and reduce the leakage conduction loss of the composite films. The breakdown field strength of the nanocomposite film doped with only 0.1 wt % functionalized BNNSs reached up to 755.94 MV/m, which is 16.8% higher than that of the pristine biaxially oriented PVDF film. Meanwhile, a maximum discharge energy density of 15.66 J/cm3 was attained, which was 1.57 times that of the pristine counterpart (9.98 J/cm3). This study sheds light on the fundamental understanding of dielectric breakdown behavior of polymer nanocomposites and provides a promising strategy for the scaled-up fabrication of dielectric capacitors with high insulating and low loss properties.