The scalable and high performance polyimide dielectrics containing alicyclic structures for high-temperature capacitive energy storage

Polyimide (PI) dielectrics have attracted much attention in the field of film capacitors because of outstanding high temperature resistance, well film-forming and mechanical properties. However, high conductive loss leads to low energy density and efficiency at elevated temperatures, which is caused by the conjugation effect of the benzene ring on the main chain of PI. In order to solve this problem, a semi-aromatic PI with alicyclic structure is designed and prepared. Compared with the all-aromatic PI (Kapton), the semi-aromatic PI exhibits much higher discharge energy density (Ud) and efficiency (η) at room temperature and high temperature. In particular, at the classical operating condition, i.e. 200 MV m−1 and 150 °C, the Ud (0.78 J cm−3) is nearly twice that of biaxially oriented polypropylene (BOPP) (0.4 J cm−3) and the η of 95% is achieved in the semi-aromatic PI. Based on the experimental data, the concept of charge transfer complex and simulation results, alicyclic structure in the main-chain of PI not only can avoid the formation of electron channels due to staggered stack of benzene rings, but also can increase the bandgap width, resulting in the increment of breakdown strength and the decrement of conductive loss. This work demonstrates that the semi-aromatic PI dielectrics containing alicyclic structure are ideal energy storage materials used in the extreme condition.