High energy storage density in high-temperature capacitor films at low electric fields.

High-power applications, particularly in electromagnetic catapults, electric vehicles, and aerospace, necessitate the use of polymer dielectrics that demonstrate reliable performance in high-temperature environments. This study focuses on synthesizing three distinct morphologies of innovative wide-bandgap high-dielectric materials-hydroxyapatite (HAP). By conducting a combination of experiments and Multiphysics finite element simulations, a comprehensive comparison was made regarding the properties exhibited by three polyimide (PI) composites: PI/sea urchin-like HAP, PI/spherical HAP, and PI/rodlike HAP. The incorporation of high-surface-area spherical HAP or high aspect ratio rodlike HAP introduces intricate and convoluted growth paths for electric tree formation within the PI matrix, thereby augmenting the energy storage density (U_e) at elevated temperatures (U_{η > 90%} = 4.82 J/cm³, U_{η > 80%} = 6.11 J/cm³, U_{η > 70%} = 8.73 J/cm³, at 150 ℃). The incorporation of HAP increases the dielectric constant ε_r to a maximum value of 4.96 in pure PI matrices, enabling the resulting PI/HAP composites to achieve remarkable values for both U_e (4.82 J/cm³) and η (92.4 %) even under low electric field (E) conditions (350 MV/m). The PI/HAP composite film demonstrates high energy storage density under low E, offering an innovative solution for energy storage applications in film capacitors operating in high-temperature environments.