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 ( E b ), 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 ( ɛ r ) and charge/discharge efficiency ( η ) of 0.55Bi 0.5 (Na 0.84 K 0.16 ) 0.5 TiO 3 ‐0.45(Bi 0.1 Sr 0.85 )TiO 3 (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 ( U d ) of 7.7 J cm −3 with η of 80.2% when the E b 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 ɛ r and E b . Additionally, the sandwich‐structured composites show excellent cycling stability at 500 MV m −1 and 150 °C, with U d 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.