Role of bandgap and permittivity of nanofiller in the energy storage performance of PEI-based nanocomposites

Since the promotion of the concept of nanodielectrics, the composite approach has long been considered as an effective way to improve the energy density of electrostatic capacitor films for energy storage applications. However, the selection criteria of nanofiller are blur in spite of multifarious attempts, such as Al2O3, HfO2, BaTiO3, TiO2, MnO2, MgO, etc. This paper is devoted to demonstrating the priority consideration of bandgap and permittivity in the filler selection of capacitive nanocomposite. The antagonistic effect between the bandgap and permittivity of fillers in the capacitive nanocomposite was revealed by the study of the physicochemical, dielectric, electric breakdown, and capacitive energy storage properties of polyetherimide (PEI) nanocomposites, i.e., PEI/ZrO2, PEI/SiO2, and PEI/TiO2 nanocomposites with systematically varied bandgap and permittivity. It is found that the ZrO2 nanofillers combine a wide bandgap and moderate permittivity; hence, the corresponding PEI/ZrO2 nanocomposite shows the highest discharged energy density over PEI/SiO2 and PEI/TiO2 nanocomposite. Specifically, the PEI/ZrO2 nanocomposite exhibits a maximum discharged energy density of 6.15 J/cm3 at an optimal filler content of 3 vol%, which is 57.7% higher than that of neat PEI.