Enhanced High‐Temperature Energy Storage Performance in Semi‐Ladder Alicyclic Polyimide Dielectrics

Abstract To keep pace with the rapid advancement of electronics and electrical engineering industry, it is imperative to develop novel polymer dielectrics with high discharge energy density ( U d ) in harsh environments. Although thermally stable aromatic polyimide capacitors possess desirable thermal properties, they suffer from considerable energy loss at elevated temperatures and electric fields because of high conductive loss caused by their strong charge transfer and narrow bandgaps. To break the contradictory relations between the high temperature resistance and conductive loss, a series of dielectric polyimide films featuring semitrapezoidal and alicyclic structures are designed and synthesized. On the one hand, rigid double‐chain ladder structures can endow excellent heat stability and heat dissipation of the polymers. On the other hand, non‐conjugated and nonplanar structures can increase bandgap width and decrease charge transfer. As a result, semi‐ladder alicyclic polyimide film with maximal molecular flatness parameter (CANAL‐PI‐2) achieves a largest U d of 5.48 J cm − 3 at 200 °C under 600 MV m −1 . Furthermore, CANAL‐PI‐2 maintains high dielectric stability even after 10 5 charge–discharge cycles at 200 °C, ensuring long‐term stable operation at high temperatures. This study provides a novel molecular engineering strategy for enhancing energy storage performance of polyimide dielectrics at elevated temperatures.