Synergistic Effect of Al₂O₃@BaTiO₃–BNNSs Hybrid Fillers for Improved Energy Storage and Thermal Conductivity Properties of PVDF-Based Composites

Motivated by growing energy demands, dielectric materials with improved energy storage density and thermal conductivity are highly desirable. In this paper, hybrid fillers composed of BaTiO3 nanofibers, Al2O3 nanoparticles, and hexagonal boron nitride nanosheets (BNNSs) were utilized to prepare different poly(vinylidene fluoride) (PVDF)-based composite films. The effects of hybrid filler nanostructures on the comprehensive properties of composite films are investigated systematically. The designed Al2O3@BaTiO3 nanofibers (AO@BT NFs) and BNNSs are constructed for the synergistic enhancement of breakdown strength and thermal conductivity. Consequently, PVDF composite films with 1.5 vol % AO@BT NFs and 4.0 vol % BNNSs exhibit the highest energy storage density of 8.3 J/cm3 at 353.9 kV/mm, along with a thermal conductivity of 0.508 W/(m·K), which are 2.86 and 2.85 times those of the pristine PVDF, respectively. This work provides a convenient and effective strategy for flexible energy storage materials with designed hybrid fillers, which show potential applications in high-performance dielectric capacitors.