Improved dielectric properties and energy storage density of poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) composite films with aromatic polythiourea

Abstract

Energy storage materials are crucial for efficient utilization of electricity in modern electric power supply and renewable energy systems. Film capacitors are promising technologies for electrical energy storage for their high power densities and charge–discharge rate, yet they are limited by their relatively low energy densities. The addition of high-k inorganic particles can lead to high dielectric constant, but at the expense of low breakdown strength and low energy efficiency, which limits their practical applications at high electric fields. In this work, we report all-organic dielectric films based on poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) (PVDF–TrFE–CTFE) terpolymer and aromatic polythiourea (ArPTU) and having enhanced energy density, energy storage efficiency, and breakdown field. Aromatic polythiourea was prepared by a conventional polycondensation method. The ArPTU/PVDF–TrFE–CTFE composite films were fabricated by solution-blending followed by hot pressing. The composite films have lower dielectric loss and higher breakdown field than the PVDF–TrFE–CTFE matrix. More importantly, the blend films also show improved released energy density and reduced loss at high fields. For ArPTU/PVDF–TrFE–CTFE (15/85) composite film, the maximum released energy density is 19.2 J/cm3 at 700 MV/m with an efficiency of 85%. The improved energy density and reduced energy loss are related to the increase in electric resistivity and structural changes. The findings of this research could provide a simple and scalable approach to produce compact and flexible high energy density materials for energy storage devices.