Dielectric property, electric breakdown, and discharged energy density of a poly(vinylidene fluoride-co-chlorotrifluoroethylene) copolymer with low temperature processing

Different thermal processing methods were used to fabricate the crystalline properties of poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF-co-CTFE)] films. We observed that the crystallinity and crystal grain size of the various samples decreased with the quenching temperature. Compared to that of the annealed P(VDF-co-CTFE) sample, a higher dielectric constant of 13.9 at a frequency of 100 Hz was obtained in the film with liquid nitrogen quenching because the increasing small crystalline regions were susceptible to the excitation of external electric field. Meanwhile, the breakdown electric strength of the low-temperature-quenched film increased to 530 MV/m when the depth of shallow electronic energy level decreased, as depicted by Fröhlich collective electron approximated electric breakdown theory. Moreover, when we introduced the leakage current density curves, the effect of the space charges on the electric displacement was proven. As a result, the discharged energy density of the liquid-nitrogen-quenched P(VDF-co-CTFE) film was enhanced to 15.32 J/cm³ at an electric field of 530 MV/m; this provided an effective way in addition to chemical modification to achieve a high energy storage ability in this poly(vinylidene fluoride)-based fluoropolymer.