Enhanced energy storage properties of thermostable sandwich-structured BaTiO3/polyimide nanocomposites with better controlled interfaces

The energy density of polymers for high temperature applications is still relatively low. Among them, polyimide (PI) is one of the most attractive matrixes because of its high thermal stability. Instead of the mono thermal imidization method to fabricate multilayer PI nanocomposites in the literature, a novel method was proposed herein to better control the multilayer morphology, which could help to further enhance the energy storage properties. The method's effect on the morphology especially on the interfaces between adjacent layers was studied, and then the mechanism of breakdown strength change was discussed by a proposed model based on bipolar charge transport. The sandwich-structured PI nanocomposites, composed of the middle polarization layer with high BaTiO3 (BT) content and the two outer insulation layers with low BT content, were fabricated. Enhanced breakdown field and discharged energy density of 550 kV/mm and 5.1 J/cm3 with the efficiency of about 70% were achieved, while keeping a high thermal stability (500 kV/mm and 3.9 J/cm3 at 100 °C). This work presents a promising polymer nanocomposite for energy storage capacitors especially in extreme temperature environments, and a new concept to fabricate multilayer dielectric composites.