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_0.84K_0.16)_0.5TiO₃‐0.45(Bi_0.1Sr_0.85)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 (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.