Poly(Vinylidene Fluoride-co-Hexafluoropropylene) Matrix Nanocomposites Reinforced With Various Types of BaTiO3 Nanoparticles for Flexible Energy Storage Applications

Poly(vinylidene fluoride-co-hexafluoropropylene), (PVDF-HFP), matrix nanocomposites have been prepared by solution casting, reinforced with BaTiO3 nanoparticles (BT NPs) and surface modified BT NPs (BT-VTS NPs) with a silane coupling agent (VTS) by 0, 5, 15, and 25 wt.%. The effects of filler content and surface modification of nanofillers on the microstructure development, phase evolution, crystallization behavior, and dielectric properties of the nanocomposites are investigated. Furthermore, the energy storage performance of BT-VTS-reinforced nanocomposites is evaluated. The surface modification of BT NPs presents some advantages: it prevents aggregation, restricts interface polarization, and keeps dielectric loss of the nanocomposites low as the relative permittivities rise with filler content. 25% BT-VTS-reinforced nanocomposites with a beta-phase fraction of 45% and a crystallinity of 14% provide a higher relative permittivity (22. at 1 kHz) than that of the neat PVDF-HFP thin films (11). Moreover, they present a low loss tangent (0.043) as the neat thin films (0.042). 25% BT-VTS/PVDF-HFP nanocomposites demonstrate a discharged energy density of 4.8 J cm-3 at 220 MV m-1 with a charge-discharge efficiency of 26%. Consequently, the energy density of the neat PVDF-HFP thin films (3.4 J cm-3 at 238 MV m-1) is improved by 40% after the addition of 25% BT-VTS NPs.