Enhanced Energy Storage Performance of Poly(vinylidene fluoride-<i>co</i>-hexafluoropropylene)/Polypropylene Composite Films by Forming an Oriented Fiber-Embedded Structure

To meet the increasing demands of high energy storage and miniaturization of power electronic devices, maintaining high charge–discharge efficiency while improving energy density is crucial for dielectric polymer film applied in electrostatic capacitors. Here, the dielectric composite films, consisting of ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and linear polypropylene (PP), were fabricated by a continuous process of physical blending-melting extrusion-uniaxial stretching. The results showed that P(VDF-HFP) was successfully compounded into the PP matrix. The P(VDF-HFP) fiber-embedded structure of the composites enabled the film to utilize the polarization characteristics of the ferroelectric polymer, thereby enhancing the dielectric constant while maintaining the original high breakdown strength and charge–discharge efficiency. The results indicated that polar P(VDF-HFP) provided more shallow traps for the composites, which was beneficial for charge dissipation and promotes carrier migration. The 20 wt % P(VDF-HFP)/PP sample enhanced a discharge energy density of 5.63 J/cm3 and over 90% efficiency at a field of 650 MV/m. This study presents a composite film that has the advantages of simple processing technology, high charge–discharge efficiency, and high discharge energy density, offering a new strategy for industrial production of capacitor films with high energy storage density.