Excellent Energy Storage of Sandwich-Structured PVDF-Based Composite at Low Electric Field by Introduction of the Hybrid CoFe₂O₄@BZT-BCT Nanofibers

The high-performance energy-storage dielectric capacitors are increasingly necessary for the development of miniaturization, integration, and multifunctionality of electronic devices. Here, we describe a new strategy of a sandwich-structured polymer-based dielectric composite with inorganic fillers of semiconductor@perovskite hybrid fibers, and this novel dielectric composite possesses an excellent energy-storage performance at low electric field. It is of crucial importance to achieve hybrid nanofibers of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ nanofibers (BZT-BCT NFs) deposited by CoFe₂O₄ nanoparticles (CFO; hereafter, CFO@BZT-BCT NFs in short). Herein, the BZT-BCT NF ceramic has the typical perovskite structure and large dielectric constant, which is used as the ceramic-support for CFO. Meanwhile, the semiconductor of CFO works as the electron donor to offer a great interfacial polarization for the improvement of overall dielectric constant of the composite. Remarkably, the trilayer structure is composed of outer poly(vinylidene fluoride) (PVDF) layer to improve the breakdown strength and middle CFO@BZT-BCT NFs-PVDF nanocomposite to enhance the dielectric properties. The BZT-BCT NFs were prepared by electrospinning, and then the CFO@BZT-BCT NFs were gained by hydrothermal method. Furthermore, the BZT-BCT NFs and the CFO@BZT-BCT NFs were modified by polydopamine (PDA). Finally, the sandwich-structured composites were gotten by a typical process of solution-casting and hot-pressing. The influences of fillers' volume fraction and type on the performances of composites have been systematically investigated. The PVDF/CFO@BZT-BCT NFs-PVDF/PVDF composite (P/CFO@BZT-BCT NFs-P/P) exhibits an outstanding energy density performance under a low electric field. The trilayer structure composite with an optimized content of nanofibers possesses an excellent dielectric performance (dielectric constant ∼20.1 at 100 Hz) and great energy-storage performance (electric displacement ∼10.7 μC/cm², discharged energy density ∼11.3 J/cm³, and efficiency ∼55.5% at a low electric field of 350 kV/mm). This work paves the way for potential applications in integrated electronic devices.