Poly(ether imide) Nanocomposites with BaTiO3@TiO2@SiO2 or BaTiO3@SiO2@TiO2 Fillers Improve Energy Storage Capacity and Dielectric Thermal Stability

The core–shell structures have been widely accepted as an effective way to adjust the dielectric properties of polymer-based nanocomposites. However, there rarely exist systematic studies, considering the core–double-shell sequence comparison (gradient or antigradient permittivity) on comprehensive dielectric and thermal stability properties for linear PEI polymer-based nanocomposites. To fill this gap, we herein successfully fabricated a series of BaTiO3@TiO2@SiO2/PEI and BaTiO3@SiO2@TiO2/PEI nanocomposites, the energy storage density of which can reach 5 and 5.41 J/cm3 with 10 vol % of filler, respectively. The resulting energy storage capacities are 2.7 and 2.85 times that for pure PEI. The BaTiO3@TiO2@SiO2/PEI nanocomposites possess excellent breakdown strength (∼470 MV/m) and low dielectric loss (∼0.008) with a 5 vol % of filler. Both the core–double-shelled nanocomposites exhibit excellent dielectric stability over a wide temperature range from RT to 150 °C compared to BaTiO3/PEI and BaTiO3@SiO2/PEI. The electric field simulation and DFT calculation results are highly consistent with the analysis of experimental data. This innovative work lays a solid foundation for further investigation on core–double-shell-structured dielectrics.