Multiple Interfacial Modifications in Poly(vinylidene fluoride)/Barium Titanate Nanocomposites via Double-Shell Architecture for Significantly Enhanced Energy Storage Density

Capacitors with high energy density are pressingly demanded in pulsed power systems and recent achievements in polymer-based nanocomposites with increasingly high energy storage capacity demonstrate their great potential in this field. Poly(vinylidene fluoride) (PVDF)-based composites with barium titanate (BT) nanoparticles as fillers are one of the most studied material systems. Here, we demonstrated in BT/PVDF composite that balance between high breakdown strength, moderately high dielectric constant, and low dielectric loss could be controlled via rational interfacial modification between fillers and polymer matrix. Insulating shell layer constructed from coherent and dense amorphous Al₂O₃ (AO) and organic polydopamine (PDA) has been encapsulated outside BT nanoparticles to gradually mitigate the large disparity in dielectric constants between BT and PVDF. Good dispersion of nanoparticles in the PVDF matrix is another important merit resulting from interfacial modification. The effects of different shell layer on the crystallinity, microstructures, transmittance of light, and dielectric performances were studied comprehensively. A suppressed dielectric loss of 0.016 with a high discharged energy density of 20.6 J cm^-3 has been achieved at 659.1 MV m^-1 in BT@AO@PDA/PVDF nanocomposite with 1 vol % loading. Three-dimensional finite element analysis was employed to analyze the effects of shell layers on local electric field distribution. This study shows that a significant increase in energy storage capacity of the nanocomposites incorporating a very small fraction of fillers could be realized via successful interface construction which enables them to be good candidates for pulse power system.