Tailoring a dual crosslinking network in all-organic aramid composite film for superior high-temperature capacitive energy storage

Polymer-based film capacitors play an irreplaceable part in the energy storage domain of advanced electrical systems. However, in high-temperature applications, a substantial surge in leakage current is commonly observed, causing undesired energy loss. Here, we present all-organic composite films consisting of poly(m-phenylene isophthalamide) (PMIA) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). The strong Coulomb attraction between PMIA and PTCDA draws adjacent PMIA chains closer, which in turn enhances the formation of intrinsic hydrogen bonds. Therefore, a dual crosslinking network emerges, tailoring the long-range disordered PMIA chains into a short-range ordered state, which is also proved to maintain stable even under high-temperature conditions. Consequently, the thermal stability, storage modulus, and breakdown strength are enhanced, while the dielectric loss is effectively suppressed. Moreover, the high electron affinity of PTCDA inhibits intermolecular π-delocalized electron transport, entrapping carries by increasing deep trap density and depth. By suppressing high-temperature leakage current, the PMIA-PTCDA film (optimized at 0.3 wt%) achieves a discharge energy density (U_d) of 7.86 J cm^-3 at 150 °C and 3.37 J cm^-3 at 200 °C, with an efficiency (η) exceeding 90 %. A record maximum U_d of 11.79 J cm^-3 is attained at η > 80 % and 150 °C. Furthermore, the ultra-low cost of PTCDA offers possibilities for large-scale production and potential commercialization.