Fatigue‐Resistant Mechanically Interlocked Co‐Crosslinked Polyimide Films for Reliable High‐Temperature Capacitive Energy Storage

ABSTRACT During long‐term operation, repeated thermal expansion and contraction inevitably generate cyclic thermal stresses that cause dielectric film buckling, cracking, and eventual device failure. As promising candidates for next‐generation dielectric films, polyimides (PIs) are therefore required to combine high energy‐storage performance with mechanical fatigue resistance under coupled thermal, electrical, and mechanical stresses. Here, we report a mechanically interlocked crosslinked topology designed to meet this requirement. A maleimide‐functionalized crown ether monomer (CM) forms mechanically interlocked junctions with PI chains, while co‐crosslinking with a bismaleimide monomer (SiMI) extends these junctions into a three‐dimensional network and creates nanoscale multiphase interfaces through SiMI self‐crosslinking. This topology improves high‐temperature energy‐storage performance and imparts strong mechanical integrity to the PI films, especially resistance to mechanical fatigue. Dielectric‐optimized PI‐CM0.75‐M7.5 achieves a breakdown strength of 600 MV/m at 200°C and maintains η ≥ 90% up to 450 MV/m. Mechanically optimized PI‐CM0.25‐M2.5 shows a Young's modulus of 2.9 GPa and a stable cyclic mechanical response, with only 5.8% stress decay after 50 tensile loading‐unloading cycles and a peak stress that approaches a plateau during cycling. This work provides a topology‐guided strategy for balancing thermal stability, high‐temperature dielectric energy storage, and cyclic mechanical reliability in polymer dielectrics.