Significantly enhanced breakdown field for core-shell structured poly(vinylidene fluoride-hexafluoropropylene)/TiO2 nanocomposites for ultra-high energy density capacitor applications

Abstract

Organic/inorganic nanocomposite materials have been extensively studied for high energy density capacitor applications due to their relatively large dielectric constant. However, most of these nanocomposite materials suffer from a very low breakdown field. In this investigation, poly(methyl methacrylate) (PMMA) grafted titanium dioxide (TiO2) (TiO2-g-PMMA) was synthesized through a seeded emulsion polymerization method. Then, the hybrid nanoparticles were incorporated into a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) film using solution casting to form a PVDF-HFP/TiO2-g-PMMA nanocomposite. After the characterization, it was revealed that the TiO2 nanoparticles were perfectly coated with the PMMA layer. Furthermore, the dielectric measurement results showed that the permittivity nanocomposite was enhanced by 13.9% as compared with the pristine PVDF-HFP film. The polarization loop data of the nanocomposite indicated that the highest breakdown field and energy density of the PVDF-HFP film with 1 vol. % TiO2-g-PMMA reached 560 MV/m and 14.2 J/cm3, respectively. The breakdown field of the nanocomposite with grafting is doubled as compared with the nanocomposite without grafting. Furthermore, as compared with the pristine PVDF-HFP at the same electric field, the energy density of the PVDF-HFP/TiO2-g-PMMA nanocomposite (1 vol. %) is increased by 14.4% (from 12.4 to 14.2 J/cm3). The nanocomposite film also showed an improved charge-discharge energy efficiency of 47% under 500 MV/m electric field, which was much higher than the pristine PVDF-based polymer. The PVDF-HFP/TiO2-g-PMMA nanocomposite shows a great promise for future high energy density capacitor applications.