Achieving High Energy Density in PVDF-Based Polymer Blends: Suppression of Early Polarization Saturation and Enhancement of Breakdown Strength

Abstract

Polymers with high dielectric strength and favorable flexibility have been considered promising materials for dielectrics and energy storage applications, while the achievable energy density (U_e) of polymer is rather limited by the intrinsic low dielectric constant and ferroelectric hysteresis. Polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CFE)) with ultrahigh ε_r of >50 is considered promising in achieving high U_e of polymer dielectrics. However, P(VDF-TrFE-CFE) only exhibits moderate U_e due to the early saturation of electrical polarization at low electric field. In this contribution, we show that, by blending P(VDF-TrFE-CFE) with polyvinylidene fluoride (PVDF), the early saturation of P(VDF-TrFE-CFE) is substantially suppressed, giving rise to concomitant enhancement of dielectric permittivity and breakdown strength. An ultrahigh energy density of 19.6 J/cm³ is thus achieved at ～640 kV/mm, which is 1600% greater than U_e of the benchmark biaxially oriented polypropylene (BOPP, 1.2 J/cm³ at 640 kV/mm). Results of phase field simulations reveal that the interfaces between PVDF and P(VDF-TrFE-CFE) play a critical role by not only suppressing early saturation of electrical polarization in P(VDF-TrFE-CFE) but also inducing additional interfacial polarization. Binary phase diagram of P(VDF-TrFE-CFE)/PVDF blends is also systematically explored with their dielectric and energy storage behavior studied.