Alter the charge transport orientation of aromatic polyimide by induction effect to achieve superior high-temperature capacitance performance

Abstract

Aerospace, electric vehicles, and other particular application scenarios place higher demands on the applicable electric field and temperature of capacitors. Polyimide, as the most ideal and widely studied high-temperature capacitor dielectric material, has poor insulation performance under extreme conditions. The main reason is that many conjugated π-bonds on its aromatic rings provide channels for the movement of free electrons, this phenomenon is more intense in high-temperature and high-field environments, which accelerates the high-temperature performance degradation of polyimide. Herein, we propose a molecular structure strategy to design high-temperature capacitance performance polymer dielectrics based on the induction effect. Both the experimental and density functional theory calculation results indicate that the polar functional groups -CF₃ and –OCH₃ can lead to a strong induction effect, which changes the direction of electron transport on the aromatic ring, serve to weaken the free-sharing ability of electrons in the conjugated π bond, increases the energy levels of PI and induces the formation of local deep traps in the polymer films, which significantly restrains charge carrier transport, ultimately improves the high-temperature capacitance property for aromatic polyimide. The resultant polymer film exhibits an excellent discharged energy density (U_d) of 7.9 J/cm³ at 150 °C and 810.3 MV/m. Meanwhile, it maintains excellent stability at over 100,000 fatigue tests and 500 MV/m. Hopefully, it will provide theoretical and technical support for developing high-performance capacitors.