Sandwich-Structured PVDF-Based Composite Incorporated with Hybrid Fe₃O₄@BN Nanosheets for Excellent Dielectric Properties and Energy Storage Performance

High-performance energy storage materials are of essential importance in advanced electronics and pulsed power systems, and the polymer dielectrics have been considered as a promising energy storage material, because of its higher dielectric strength and more excellent flexibility compared with that of inorganic ceramic dielectrics. However, the energy storage capability of pristine polymer has been limited by its low intrinsic dielectric permittivity and ordinary ferroelectric performance. Herein, this work demonstrates a favorable method to achieve a sandwich-structured poly(vinylidene fluoride) (PVDF)-based composite by the electrospinning, solution casting, thermal quenching, and hot-pressing process. This innovative method combines with the 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ nanofibers (BZT-BCT NFs), which possesses good ferroelectric hysteresis, and the hybrid particles of hexagonal boron nitride nanosheets (BNNSs) coated by ferroferric oxide (Fe₃O₄@BNNSs), which hold high breakdown strength (E_b). It is worth mentioning that the Fe₃O₄ particles disperse well on the surface of BNNSs to form the dipoles with the BNNSs at the interfacial region, resulting in an enhancement of the electric displacement and the dielectric permittivity of the composite. Furthermore, the influence of the volume fraction of filler particles on the electrical performance of composite was systematically investigated. Notably, the enhanced performance in terms of electric displacement (D), E_b, and discharged energy density (U_e) was achieved in the sandwiched BZT-BCT NFs-PVDF/Fe₃O₄@BNNSs-PVDF/BZT-BCT NFs-PVDF composite. The U_e of ∼8.9 J/cm³ was achieved at 350 kV/mm, which was 740% higher than the U_e of biaxially oriented polypropylene (BOPP, U_e ≈ 1.2 J/cm³ at 640 kV/mm). Of particular note is that the hybrids Fe₃O₄@BNNSs play a critical role to enhance the D and E_b and suppress the remnant displacement (D_r) of sandwiched composite. This contribution proposes an efficient and scalable method to prepare polymer-based dielectric composite for the demanded applications.