Ultra-high electron affinity and peripheral electronegativity co-constructing all-organic dielectrics with outstanding capacitive performance at high temperature

High temperature resistance is essential for electrostatic capacitors, for example, the operating temperature of the capacitors used in inverters for hybrid electric vehicles is around 140–150 °C. However, the reliability of current commercial dielectrics biaxial stretching polypropylene (BOPP) significantly degrades when the operating temperature exceeds 105 °C. In this work, an all-organic dielectric utilizing two mechanisms—high electron affinity and physical interaction—is designed to enhance the capacitive performance. Specifically, the molecular semiconductor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), with ultra-high electron affinity (5.24 eV) and peripheral electronegativity, is incorporated with polyetherimide (PEI). Deep electron traps are successfully constructed to capture free electrons due to the incorporation of high-electron-affinity F4-TCNQ. Moreover, it is difficult for the captured electrons to escape because of the Coulomb force between electrons in low unoccupied molecular orbital (LUMO) of F4-TCNQ and holes in highest occupied molecular orbital (HOMO) of PEI. From another point of view, physical interaction is formed between peripherally electronegative groups of F4-TCNQ and the positively charged phenyls of PEI, improving the packing density among polymer chains and the Young's modulus. Consequently, the electromechanical breakdown strength is enhanced. These two mechanisms play their part simultaneously, realizing significantly suppressed conductivity loss and increased breakdown electric field. Accompanied with improved dielectric constant, the discharged energy density of F4-TCNQ/PEI composites is significantly increased in a wide temperature range. Especially at 150 °C, the discharged energy density (Ue) of 0.6 wt% F4-TCNQ/PEI reaches 7.84 J/cm3 at 670 kV/mm, which is 123 % higher than that of PEI (3.52 J/cm3). The Ue is still as high as 5.12 J/cm3 even the discharged efficiency (η) is over 90 %. This work exhibits a promising prospect of all-organic dielectrics in capacitive application at high temperature.