Enhanced Breakdown Strength of Ferroelectric Polymer Films for Capacitive Energy Storage by Incorporating Oriented Fluorographene

Abstract

Ever-increasing electrification scenarios call for high energy density (Ue) polymer nanodielectric films beyond the commercial benchmark biaxially oriented polypropylene. Ferroelectric polymers of intrinsic high dielectric constant εr, if integrated with improved breakdown strength (Eb) and dielectric loss from nanofillers, would be a promising paradigm for high-Ue polymer nanodielectrics. Yet, this expectation is still in its infancy because of the great challenge of increasing the Eb and needs introduction of new approaches. Here, fluorographene (FG), as a young halogen derivative of graphene, is employed as an emerging nanofiller to develop high-Eb polymer nanodielectrics. A dramatically enhanced Eb, which is 39.4% higher than that of a neat polymer film from casting, is achieved in a composite film along with a reduced dielectric loss by incorporating only 0.2 wt % FG with in-plane orientation from electrospinning. The origin of such a high Eb-reinforcing effect of FG is traced by both experimental characterizations and phase-field simulation. It is found that the in-plane oriented FG of appropriate loading level would induce both the favorable low crystallinity of the polymer matrix and the FG–polymer interface with deep traps and less defects. This, together with the high out-of-plane insulation of FG from a high fluorine/carbon ratio, regulates the charge behaviors and breakdown paths and thus significantly enhances the voltage endurance of composite films. The results demonstrate the remarkable Eb-reinforcing effect of emerging FG fillers in polymer nanodielectrics and offer a strategy toward high-Eb/high-Ue flexible dielectric capacitors.