Composition-Driven Polarization Distribution in Poly(vinylidene fluoride)-Based Copolymer Blends for High Power Density Capacitors

Abstract

High power density capacitors have been highly demanded in modern electronics and pulsed power systems. Yet the long-standing challenge that restricts achieving high power in capacitors lies in the inverse relationship between the breakdown strength and permittivity of dielectric materials. Here, we introduce poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) into the host poly(vinylidene fluoride-co-hexafluoro­propylene) (PVDF-HFP) to produce PVDF-based copolymer blends, resulting in composition-driven 0–3 type microstructures, featuring nanospheres of P(VDF-TrFE) lamellar crystals dispersed homogeneously in a P(VDF-HFP) matrix together with crystalline phase evolution from the γ-phase to the α-phase. At the critical composition, the TrFE/HFP mole ratio is equal to 1, and the blend film achieves maximum energy storage performance with discharged energy density (U dis) ∼ 24.3 J/cm3 at 607 MV/m. Finite element analyses reveal the relationship between microstructures, compositions, and the distribution of local electric field and polarization, which provide an in-depth understanding of the microscopic mechanism of the enhancement in energy storage capability of the blend films. More importantly, in a practical charge/discharge circuit, the blend film could deliver an ultrahigh energy density of 20.4 J/cm3, i.e., 88.3% of the total stored energy to 20 kΩ load in 2.8 μs (τ0.9), resulting a high power density of 7.29 MW/cm3, outperforming the reported dielectric polymer-based composites and copolymer films in both energy and power densities. The study thus demonstrates a promising strategy to develop high-performance dielectrics for high power capacitors.

Polyphenylene Oxide Film Sandwiched between SiO2 Layers for High-Temperature Dielectric Energy Storage

“…Many studies have been performed to modify BOPP to achieve better energy-storage performance at high temperatures. ,, One of the most popular methods is depositing inorganic layers (such as Al 2 O 3 , SiO 2 , and AlN) to improve the high-temperature resistance of BOPP, mainly because these wide-bandgap materials can form a barrier at the interface to prevent charge injection. − For example, double sides of the BOPP film were coated by AlN layers to fabricate AlN/BOPP/AlN composite films, which can release a discharged energy density ( U e ) of 1.5 J/cm 3 with a high η of 90% at 125 °C . However, the discharged energy density still remains low because of the low dielectric constant of ∼2.2 for PP …”

Gradient core–shell structure enabling high energy storage performances in PVDF-based copolymers

“…Our previous study proposed an alternative approach via utilizing a core–shell structure design that is usually employed for inorganic fillers, where the core is composed of a polymer with large polarization, and the shell is composed of a polymer with small polarization, to adjust the topological structure and polarization distribution in poly(vinylidene fluoride) (PVDF)-based hybrid copolymers. 21–23 Despite a significantly improved E b of 660 kV mm −1 being realized, giving rise to a high U e of 21.2 J cm −3 , the efficiency is unsatisfactory, probably due to hysteresis and conduction losses caused by a locally concentrated component of large polarization in a high electric field. 23 Consequently, it is crucial to elaborately adjust the polarization distribution to simultaneously maintain high polarization and suppress losses.…”