High-Energy-Density Flexible Dielectric Film via One-Step Extrusion Processing

Flexible dielectric films based on fluoropolymers demonstrate a high breakdown strength and dielectric constant and are considered better potential candidates for high-energy-density capacitors than is commercial biaxially oriented polypropylene (BOPP). More importantly, the continuous production of fluoropolymer films is becoming increasingly common to meet the demands for state-of-the-art energy storage devices. Herein, poly(vinylidene fluoride-cohexafluoropropene) (P(VDF-HFP)) is extruded with poly-ω-aminoundecanoyl (PA11), then subjected to a calendering process with the blends in an elastomeric state to control crystallization, and styrene-maleic anhydride (SMA), which acts as a compatibilizer, is introduced to enhance interaction. The as-prepared P(VDF-HFP)/PA11-g-SMA has an energy density as high as 15.4 J/cm3 at 500 MV/m, which is 1200% higher than that of BOPP (1.2 J/cm3 at 640 MV/m). The high energy density mainly originates from a high breakdown strength and high dielectric constant. The hydrogen-bonding interaction between P(VDF-HFP) and PA11 can drive the alignment of segments in P(VDF-HFP); thus, high crystallinity and breakdown strength are achieved. The interaction also induces the phase transformation from α-phase to β-phase in P(VDF-HFP), which assists in maintaining the dielectric constant of the blend films as high as 15.3. Another key determinant of high energy density is the limited remnant polarization attributed to reduced crystal size, which results from the dilutive effect of PA11-g-SMA. Therefore, extrudable dielectric films will facilitate the continuous production of high-performance film capacitors in terms of energy density