Effect of structural design of core-shell particles and core-shell-shell particles on PVDF dielectric energy storage composite films

The structure of added fillers can be used to regulate the balance between dielectric properties and energy storage efficiency in composite materials for dielectric energy storage. In this study, acid-treated carbon nanotubes (CNT-OH) were encapsulated with silicon dioxide (SiO2) and polydopamine (PDA) to create two types of core-shell particles with different structures. Composite films, namely CNT-OH@SiO2/PVDF and CNT-OH@SiO2@PDA/PVDF, were prepared using a solution casting method. The core-shell particles were characterized through TEM, SEM, and XPS, while the composite films microstructure was examined using XRD and SEM. By comparing the effects of different core-shell fillers and their amounts on the dielectric properties and energy storage efficiency, it was observed that the addition of CNT-OH@SiO2@PDA facilitated the transformation of the PVDF matrix crystalline phase from α and γ phases to the β phase. This resulted in an increased dielectric constant while maintaining a low dielectric loss in the composite film. Specifically, the PVDF composite films with 2.0 wt% of CNT-OH@SiO2 and 2.0 wt% CNT-OH@SiO2@PDA exhibited dielectric constants of 11.29 and 11.86 at 1000 Hz, with dielectric losses of 0.0129 and 0.0109, respectively. Furthermore, both composite films demonstrated enhanced energy storage density. At 0.5 wt% of CNT-OH@SiO2 and CNT-OH@SiO2@PDA, the breakdown field strengths were 156.76 kV/mm and 172.30 kV/mm, the energy storage densities were 1.77 J/cm3 and 2.17 J/cm3, and the charge-discharge efficiencies were 55.0% and 56.8%, respectively. The core-shell particle structure developed in this study offers a novel approach for designing dielectric energy storage composite materials.