Optimizing the Charge Transfer Complex Structure of Polyimides with Fluorinated Side Biphenyl for Superior High‐Temperature Capacitive Performance

Abstract With advancements in electrical insulation technology for higher temperatures, polymer dielectrics with high thermal stability are becoming increasingly significant. As one of the most thermally stable polymers, polyimide (PI) is regarded as a promising high‐temperature dielectric material. However, the intra/inter‐chain charge transfer complex (CTC) in PI significantly increases conduction current, resulting in a substantial decline in discharged energy density ( U _d ) and charge/discharge efficiency ( η ) under high temperatures. In this study, a series of PIs based on fluorinated side biphenyl diamines and 1,2,4,5‐cyclohexanetetracarboxylic dianhydride (CHDA) is designed. Compared with traditional PI, the introduced fluorinated side phenyl group acts as a strong carrier trap, efficiently suppressing the production of CTC. Furthermore, the rigid side group improves Young's modulus and heat resistance, while also reducing the electrostatic interaction, thereby endowing PI with high breakdown strength ( E _b ) and low polarization loss at elevated temperatures. Ultimately, the designed PI exhibits excellent U _d (6.16 J cm ⁻³ @ 150 °C and 4.88 J cm ⁻³ @ 200 °C, η = 90%). The molecular design strategy presented in this study offers a novel approach to high‐temperature polymer‐based dielectric materials and is expected to provide new avenues for the development of high‐energy‐density polymers for next‐generation film capacitors.