Construction of ternary core-shell Fe3O4@BaTiO3/PVDF nanocomposites with enhanced permittivity and breakdown strength for energy storage

Highlights: • Ferroelectric polymer-based composites possess high energy density materials. • Introducing conductive nanoparticles into polymer-based composites reduces breakdown strength. • Fe₃O₄@BaTiO₃ core-shell nanofillers enhance the permittivity of PVDF matrix with low loss. Introducing conductive nanoparticles into ferroelectric polymers gives rise to significant enhancement of permittivity (ε), making these composites practically promising for energy storage devices. However, the breakdown strength (E_B) of such composites is reduced with few exceptions, which limits high-performance applications. Here we study the energy storage behavior of well-designed Fe₃O₄@BaTiO₃ core-shell nanoparticle/poly(vinylidene fluoride) (PVDF) nanocomposites in which conductive Fe₃O₄ nanoparticles (NPs) are coated by ferroelectric BaTiO₃ (BT), together with the PVDF matrix, forming the ternary nanocomposite films with high energy storage performance. Notably, the permittivity is enhanced by increasing the volume fraction of the Fe₃O₄@BT NPs, reaching 38 with 2 vol% Fe₃O₄@BT NPs and remaining low dielectric loss (~0.066). In particular, the nanocomposites exhibit moderate breakdown strength (~430 kV/mm), which is attributed to the "voltage dispersion layer" (the BaTiO₃ shell) between the polymer matrix and Fe₃O₄ NPs. The finite element simulation substantiates the experimental results and further confirms the positive correlation of the breakdown strength and the permittivity of the "voltage dispersion layer". With the synergistic effect of both breakdown strength and electric displacement, a remarkable energy density (16 J/cc, at 430 kV/mm) is obtained.