The dielectric behavior and mechanisms of improved energy storage density of sandwich-structured different dimensions of Na0.5Bi0.5TiO3 /PVDF composites were studied. Compared with NBT-NPs/PVDF, optimized NBT-NFs/PVDF has a greater dielectric polarization strength, so the dielectric constant of NBT-NFs/PVDF is greater than that of composite materials filled with NBT-NPs with the same volume content. With the benefit from the addition of optimized high-aspect-ratio one-dimension NBT fiber as filler and the sandwich configuration for the composites, the experimental results prove that sandwich-structured NBT-NFs/PVDF can achieve a large energy storage density of 11.7 J/cm3 at a relatively lower electric field of 350 kV/mm for the composites with 1% volume fraction of NBT-NFs in the outer layers. The stronger polarization of composites filled by NBT-NFs is proved via electric modulus and the crystallinity of the composite films. Last but not least, the study found that composite materials also have excellent stable performance and good bending cycle stability. In summary, the composite materials obtained in this study can be used in electronic components for flexible energy storage in the future.

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In order to adapt to the development of electronic devices, it is necessary to improve the thermal conductivity and breakdown strength of composites. Boron nitride (BN) is an ideal candidate material with high breakdown strength and thermal conductivity. Therefore, the introduction of BN nanosheets into the polyvinylidene fluoride (PVDF) matrix can improve the thermal conductivity and breakdown strength of the composites at the same time. However, BN nanosheets can easily agglomerate in the matrix, which limits the improvement of the properties of the composites. To overcome this difficulty, appropriate water‐bath heating was used to improve the fluidity of PVDF. Therefore, the dispersion of the filler is improved. When the volume fraction of BN nanosheets is 3% and the preparation temperature is 45°C, the energy storage density of the composites reached 18.5 J/cm3 at 540 kV/mm. At this point, the thermal conductivity was 0.49 W/(m⋅K), 3.5 times that of the pure PVDF film.

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Organic film capacitors have incredibly high power density and have an irreplaceable position in pulsed power systems, high‐voltage power transmission networks and other fields. At present, the energy storage density and energy storage efficiency of organic film capacitors are relatively low, resulting in excessive equipment volume. The performance of organic film capacitors is determined by polymer materials, so it is crucial to develop a polymer composite with high energy storage density and high charge–discharge efficiency. Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (P(VDF−CTFE)) is incorporated into the polyvinylidene fluoride (PVDF) matrix by solution blending. The successful preparation of the all‐polymer composite material solves the problems of low breakdown electric field strength, low discharge energy density, and low charge–discharge efficiency of high‐dielectric ferroelectric materials. The discharge energy density of the PVDF/P(VDF−CTFE) (70/30) film is more than twice that of pure PVDF due to the increase of phases α and γ and the decrease of crystallinity. Under the breakdown electric field (380 kV mm−1), PVDF/P(VDF−CTFE) (70/30) film also has an ultrahigh energy storage efficiency of 64%. The relationship between the structure and properties of composite materials is investigated in this study, which has important implications for the development of capacitors with high energy storage density.