Polyimide Regulated by Molecular Engineering Exhibits Excellent High‐Temperature Energy Storage Performance

Under high temperature and high electric field, the excitation and migration of electrons in polymer dielectrics are significantly accelerated, resulting in a sharp increase in conduction loss and a deterioration of breakdown performance. To address these issues, this study designed the molecular structure of polyimide monomers to synthesize an intrinsically fluorine‐containing polyimide (MFPI), followed by the construction of a molecular cross‐linked network within the polymer matrix. The cross‐linked network reduces the free volume between molecular chains, increases the molecular packing density, and further enhances the insulation strength and thermal stability of the material. Experimental results show that the energy storage density of the MF‐2.0 composite dielectric reaches 5.06 J cm −3 at 150 °C and 620 kV mm −1 , which is 2.54 times that of pure PI and 1.34 times that of pure FPI. Moreover, no significant degradation in energy storage performance is observed after 10 4 cycles at 150 °C and 200 kV mm −1 . In addition, the thermal conductivity of the MF‐2.0 composite dielectric increases to 0.489 W m −1 K −1 , representing a 59.28% improvement compared with FPI. The resulting material achieves efficient thermal management while exhibiting excellent high‐temperature toughness, hydrophobicity, and bending fatigue resistance. Through molecular engineering design, this study realizes synergistic enhancement of multiple properties of polyimide, enabling it to meet the application requirements of high‐temperature energy storage devices under complex operating conditions.