Ultra‐High Capacitive Energy Storage Density at 150 °C Achieved in Polyetherimide Composite Films by Filler and Structure Design

Abstract Polymer dielectrics are crucial for electronic communications and industrial applications due to their high breakdown field strength (Eb), fast charge/discharge speed, and temperature stability. The upcoming electronic‐electrical systems pose a significant challenge, necessitating polymeric dielectrics to exhibit exceptional thermal stability and energy storage capabilities at high temperatures. Here, ultra‐high dielectric constant (ɛr) and charge/discharge efficiency (η) of 0.55Bi0.5(Na0.84K0.16)0.5TiO3‐0.45(Bi0.1Sr0.85)TiO3 (BNKT‐BST) ceramics are prepared by the solid‐phase reaction method and added to polyetherimide (PEI) to form BNKT‐BST/PEI nanocomposites with various structures. The findings indicate that the sandwich‐structured BNKT‐BST/PEI nanocomposite achieves the highest discharged energy density (Ud) of 7.7 J cm−3 with η of 80.2% when the Eb is 650 MV m−1 at 150 °C. This is primarily due to the incorporation of BNKT‐BST nanoparticles and the multilayer structure design, which significantly improves the composite's ɛr and Eb. Additionally, the sandwich‐structured composites show excellent cycling stability at 500 MV m−1 and 150 °C, with Ud of ≈ 4.7 J cm−3 and η greater than 90%. The research presents nanocomposites with high energy storage density and excellent stability, crucial for the practical application of polymer dielectrics in high‐temperature environments.