Significantly enhanced energy storage performance of polyimide dielectrics at high temperatures via manipulating crosslinked density

Aromatic polyimide (PI) film capacitors have attracted wide attention due to their good film-forming, outstanding high-temperature resistance, and good flexibility. However, high conductive loss gives rise to poor energy storage performance at high temperatures, originating from the conjugation effect of the benzene ring in the main chain. To improve the discharge energy density (Ud) and efficiency (η) of the Kapton polyimide (PI) film capacitor at high temperatures, 1, 3, 5-tris(4-aminophenyl)benzene was selected as a crosslinking agent to synthesize a series of cross-linked Kapton PI with different crosslinking agent content from 5 wt% to 30 wt%. The results showed that the 30 wt% cross-linked PI (PI/30) could achieve the maximal Ud of 5.87 J/cm3 and the η of 81.5 % at room temperature, which is much higher than that of pure Kapton (2.61 J/cm3 and 50.2 %) respectively. Importantly, the PI/30 film can obtain the Ud of 1.75 J/cm3 and the η of 70 % at 150 °C. Combining the experimental results with density functional theory (DFT) calculation, the crosslinking network can increase the bandgap width, decrease the inherent defects, construct the charge trap, and suppress conductivity loss, resulting in promoting Ud and η. This study explores in depth the relationship between chemical structure and dielectric properties of polyimide.