Polymer-based film capacitors with ultra-fast discharge rate and high-power density play a key role in many fields, such as pulsed power technology, advanced electric and electronic systems. In this paper, the flexible all-organic composite films with thermoplastic polyurethanes (TPU) and poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) are prepared by a solution coating method, combined with a variety of characterization methods to systematically study the microscopic properties, dielectric properties, insulation properties, energy storage properties and mechanical properties of the composite films. The typical experimental procedure for the fabrication of all-organic composite films is as follows: First, the TPU and P(VDF-HFP) pellets were dried in the oven for 24 h. Then, 1 g P(VDF-HFP) and corresponding TPU (0, 1% (φ), 2% (φ), 3% (φ), 4% (φ), 5% (φ)) were added into 10 mL N,N-dimethylformamide (DMF) solution, and were stirred vigorously at room temperature for 24 h. The mixtures were moved into vacuum oven for 30 min to eliminate the air. The solutions were cast onto a clean glass, and finally were dried at 70 ℃ for 12 h to obtain the TPU/P(VDF-HFP) films. Systematic observation and tested results show that: adding an appropriate amount of thermoplastic polyurethane to P(VDF-HFP) can form a two-phase cross-linked structure with excellent dispersibility and compatibility, thereby further improving the electrical, energy storage, and mechanical properties of the composite films. In TPU/P(VDF-HFP) composite film with 2% (φ) TPU, the characteristic breakdown strength of the composite film is 450 MV/m, and the corresponding discharge energy density is 7.03 J/cm³, which are increased by 25.35% and 49% compared to the pristine film, respectively. Moreover, the mechanical properties of the composite films have been improved to a certain extent owing to the addition of TPU, and the Young's modulus, tensile strength and elongation at break of the TPU-2% (φ)/P(VDF-HFP) composite film reaches 591.22 MPa, 25.6 MPa, and 362%, respectively. Through the above characterization and analysis, it can be found that adding elastomer rubber to the ferroelectric polymers can form flexible dielectric materials with high breakdown strength, high energy density as well as high charge-discharge efficiency, which is expected to have better applications in large-scale industrial production for film capacitors.

Key words: dielectrics, P(VDF-HFP), all-organic composite, breakdown strength, energy density, film capacitor