Structural tailoring enables ultrahigh energy density and charge–discharge efficiency of PAEK copolymer dielectrics at high temperatures

High-temperature film capacitors have great potential for high-power-density applications, in which polymer films are often utilized as energy-storage dielectrics. However, their application in film-capacitor dielectrics is hindered by their large leakage currents at high temperatures, which leads to low energy density (U_e) and low charge–discharge efficiency (η). Here, a structural-tailoring strategy is demonstrated to suppress the high-temperature leakage currents of polyaryletherketone (PAEK) copolymers. For this purpose, a novel functional monomer containing benzimidazole and pyridine groups (BBP) was synthesized and the corresponding cross-linked c-P(AEK-BBP) dielectric films were successfully to prepared. Thanks to the introduction of the BBP units and the cross-linked network, the leakage current of c-P(AEK–BBP) is suppressed by nearly two orders of magnitude at 150 °C. This dielectric film exhibits 7.3 J·cm⁻³ under 600 MV·m⁻¹ and 150 °C, which is superior to current state-of-the-art heat-resistant dielectric polymers.