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 BaTiO 3 @TiO 2 @SiO 2 /PEI and BaTiO 3 @SiO 2 @TiO 2 /PEI nanocomposites, the energy storage density of which can reach 5 and 5.41 J/cm 3 with 10 vol % of filler, respectively. The resulting energy storage capacities are 2.7 and 2.85 times that for pure PEI. The BaTiO 3 @TiO 2 @SiO 2 /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 BaTiO 3 /PEI and BaTiO 3 @SiO 2 /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.