Ultrahigh energy density of poly(vinylidene fluoride) from synergistically improved dielectric constant and withstand voltage by tuning the crystallization behavior

Capacitor dielectrics with high energy density are urgently needed in power electronics and pulsed power system applications. To date, the most explored ceramic/polymer nanocomposites still suffer from the common challenge of a contradictory relationship between permittivity and the electric breakdown strength due to the overloading of nanofillers. Orientated films are considered the most prospective and scalable manufacturing option to overcome the above problems. Herein, a series of stretched PVDF polymer films were fabricated, and they demonstrated a substantial and concurrent increase in both electric displacement and breakdown strength (e.g.16.10 μC cm⁻²at 798.8 kV mm⁻¹) by tuning its crystallization behavior in multiaspects. The phase transition and crystal orientation led to enhanced electric polarization, while the high strain-induced enhancement of Young's modulus and suppression of leakage current brought significant improvement in electric breakdown strength. Particularly, the effects of crystalline morphologies and orientations on the electric polarization behavior and stress distribution under high electric fields have been revealed by theoretical simulation, for the first time. As a consequence, the stretched PVDF films at a high strain of 500% (R= 5) almost presented the highest discharge energy density of 34.90 J cm⁻³among dielectric polymers, along with a high energy efficiency of 68.2%, based on the solid-state drawing process. This work provides a feasible and paradigmatic approach to developing high-performance dielectrics for electrostatic energy storage applications.