Improved energy storage performance of polyimide nanocomposites by constructing the meso- and macroscopic interfaces

Polyimide (PI) is a promising material for the dielectric capacitor due to its excellent electrical insulation and mechanical properties and so on. However, the low dielectric constant limits the enhancement of energy storage density and its further practical application. Here, we construct the sandwich-structured PI/BaTiO₃ nanocomposites by in-situ synthesis and solution casting techniques. The energy density of the sandwich-structured nanocomposites reaches the maximum value of 7.44 J/cm³, contributed by the synergistically enhanced breakdown strength and dielectric constant (486.34 kV/mm and 7.24), while keeping a good charge-discharge efficiency. Combined with the three-dimensional simulation results, it can be seen that the organic/inorganic interfacial polarization in polarized layer and the interlayer polarization can significantly increase the dielectric constant. Meanwhile, the sandwich structure can redistribute the electric field and mitigate the electric field concentration in the polarized layer. The outer insulation layer can block the high current and heat breakdown paths caused in the middle layer. Consequently, the breakdown strength and dielectric constant are improved synergistically, leading to an enhancement in the energy density. The work provides a new paradigm to explore polyimide nanocomposites with enhanced energy density based on the combination of experiments and simulations.