Excellent high-temperature energy storage capacity for polyetherimide nanocomposites with hierarchically structured nanofillers

High-temperature electronic power systems need reliable dielectric energy storage materials, but conductive losses in extreme conditions impair their performance. Hierarchically-structured fillers are promising to not only integrate the benefits of diverse components but also effectively utilize interface engineering and electron scattering effects to optimize dielectric and breakdown properties, thereby modulating energy storage performance in polymer-based composites. In this work, we successfully fabricated hierarchical nanofillers comprising 2D boron nitride nanosheets (BNNS) and 0D ultrafine strontium titanate (ST) nanoparticles. The paraelectric ceramic ultrafine ST possesses a high dielectric constant and low residual polarization, which enhances the energy storage density of composite materials while ensuring high conversion efficiency. The PEI-based nanocomposites loaded with hierarchical BNNS@ST nanofillers attain remarkable discharged energy density (4.29 J cm−3) and charging and discharging efficiency (η > 80%) at 150 °C. This approach utilizing hierarchically-structured nanofillers offers a feasible strategy to explore high-energy–density polymer dielectrics applied in extreme environments.