The Structure−Property Relationship of Poly(vinylidene difluoride)-Based Polymers with Energy Storage and Loss under Applied Electric Fields

Abstract

This paper systematically examines the family of poly(vinylidene difluoride) (PVDF)-based fluoropolymers, including homo-, co-, and terpolymers containing vinylidene fluoride (VDF), trifluorethylene (TrFE), and chlorotrifluoroethylene (CTFE) units, with the objective of tuning the polymer chain conformation and crystal structure in order to identify the most suitable polymer for energy storage (capacitor) applications. All polymers have high molecular weight, uniform composition distribution, semicrystallinity, and high purity. They were prepared by a borane/oxygen control radical initiator in a homogeneous solution at ambient temperature. The resulting polymers were solution-cased, then melt-conditioned into uniform (defect-free) thermoplastic thin films (thickness 10−20 μm). The combination of thermal, dielectric, and uni- and bipolar charge displacements reveals their polarization profiles, which are dependent on chain conformation, crystal phase, crystal size, Curie temperature, and ac and dc fields. Ferroelectric VDF/TrFE copolymers, having all-trans chain conformation and polar β-phase crystals, exhibiting huge remnant polarization, are not suitable for energy storage (capacitor) applications. Some poled PVDF homopolymer and VDF/CTFE copolymers with γ-phase crystals show potential for dc (not ac) powered applications. The most suitable polymer is the VDF/TrFE/CTFE terpolymer having a TTTG chain conformation, small polar γ-phase crystals, relaxed dielectric properties, and a Curie transition at near ambient temperature, providing both ac and dc powered capacitors with a balance of properties, high-energy density and low-energy loss.

Polypropylene/Polyaniline Nanofiber/Reduced Graphene Oxide Nanocomposite with Enhanced Electrical, Dielectric, and Ferroelectric Properties for a High Energy Density Capacitor

“…(1) The secondary doping of PANI induces the expanded coil conformation and higher linearity of the PANI chains. (2) The RGO sheets with high electron mobility further enhance the face-to-face interactions in the PANI structure, which subsequently result in the extended conjugation lengths of the PANI structure. 30 To further confirm the crystalline type of the PP nanocomposites filled with different fillers, the XRD spectra of the pristine PP, PP/PANI, PP/PANI/RGO, PP/d-PANI/RGO, and PP/r-PANI/RGO are shown in Figure 3b.…”

“…(1) RGO sheets may enhance face-to-face stacking interactions between PANI chains, which extend the π-conjugated structure of PANI. (2) Due to the elongated conjugation length, r-PANI/RGO cofiller may permit better transport of charge carriers compared to those of the PANI and r-PANI. (3) Consequently, the enhanced charge carrier transport of r-PANI/RGO cofiller facilitates the protonation of PANI from a reduced structure (benzenoid unit) to an oxidized structure (quinoid unit).…”

“…65,66 Despite the increase in dielectric loss of the nanocomposites, the PP/r-PANI/RGO with 10 vol % cofiller exhibited more than 10 times lower dielectric loss compared with that of the conventional PVDF (0.11). [1][2][3][4][5][6][7][8][9][10][11]16 Judging from these results, the dielectric properties of PP filled with r-PANI/RGO make them suitable for use as energy-harvesting devices. For further insights into the effect of each phase in the PP/r-PANI/RGO nanocomposites, ε′ and ε″ of the PP nanocomposites filled with different v r-PANI /v RGO ratios are represented in Figure S3.…”

“…Furthermore, the excessive filler loading causes more consumption of the electric energy in the formation of leakage currents during the polarization of the PP/ r-PANI/RGO nanocomposites, resulting in a decrease of the polarization degree. [1][2][3]5,6,[8][9][10][11][12][13][15][16][17][18][33][34][35][36][37]42,62,65,66 Thus, the energy density of PP/r-PANI/RGO with 10 vol % cofiller was larger than that of the nanocomposite with 12 vol % cofiller ( Figure S4b). Considering these results, the r-PANI/RGO cofiller with an optimal cofiller content can be an efficient means to improve the energy-harvesting properties of the PP nanocomposites.…”

Novel Ag–BaTiO3/PVDF three-component nanocomposites with high energy density and the influence of nano-Ag on the dielectric properties

“…PVDF was chosen as the polymer matrix for its high dielectric breakdown strength and high dielectric constant [13]. Since BaTiO 3 was a widely used inclusion for organic/polymer composite for its good dielectric property [14,15], in this study, BaTiO 3 nano-powders were used as the high dielectric constant fillers.…”