Temperature‐Dependent Energy Storage Mechanism in Polyimide Films: Optimizing High‐Temperature Performance via Dihedral Angle Engineering

ABSTRACT Polyimide (PI) films exhibit degraded energy storage performance under extreme high‐temperature conditions, limiting their applications in advanced fields such as new energy vehicles and aerospace systems. Investigating temperature‐induced mechanisms affecting PI's energy storage properties and improving its high‐temperature energy storage density are critical. A fully organic modification strategy is proposed through molecular structural design by introducing isopropyl groups (–C(CH3)2) to regulate dihedral angles between benzene rings. This enhances spatial hindrance in molecular chains, suppresses charge migration, and improves breakdown field strength and energy storage density. Three PI films with distinct average dihedral angles (PMDA+ODA, ODPA+ODA, BPADA + ODA) are synthesized, and their dielectric properties, breakdown strength, and energy storage performance are analyzed under high temperatures. Results show that BPADA + ODA, with the largest dihedral angle, achieves 422 kV/mm breakdown field strength at 423 K (37.03% higher than traditional PI) and 2.79 J/cm3 discharge energy density (99.28% improvement). A DC breakdown model coupling charge transport with molecular chain dynamics clarifies the synergistic suppression mechanism of dihedral angle regulation on charge migration and chain mobility under high temperatures, while revealing temperature‐dependent energy storage behavior. This study provides theoretical insights and technical pathways for molecular design and performance optimization of high‐temperature dielectric materials.