Tailoring High‐Temperature Low‐Loss Properties in Polyimide Films for Energy Storage Through Multiamino Crosslinking

ABSTRACT Organic film capacitors are extensively utilized in pulse power regulation, integrated circuit boards, and hybrid electric vehicles due to their exceptional electrical insulation properties, high power density, and facile processability. Nevertheless, conventional dielectric films exhibit critical limitations, including low energy density, restricted operational temperature ranges, and significantly elevated charge–discharge losses at high temperatures. These deficiencies manifest as compromised charge–discharge efficiency and diminished dielectric strength, necessitating urgent development of polymer dielectrics with enhanced energy storage density and thermal stability. Herein, we prepared a kind of crosslinked polyimide film, which can endure high heat resistance and maintain low loss at high temperatures. As a demonstration, hyperbranched polyamine‐terminated polymers (HBP) were self‐polymerized by 3,5‐aminobenzoic acid (DABA) and polymerized with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and 2‐(4‐aminophenyl)‐1H benzimidazole‐5‐amine (BIA) as a crosslinking agent. Crosslinked PI films were prepared by scraping, coating, and thermal imidization. The dielectric stability of the films was greatly improved after crosslinking, and the dielectric loss at high temperatures was significantly reduced from 1.17 to 0.071 at 250°C (@ f = 10 Hz). Besides, the discharge energy density ( U e ) of the film was increased from 1.98 to 4.28 J/cm 3 at room temperature, and the charge and discharge efficiency ( η ) was higher than 80%. In addition, the charge–discharge loss of the crosslinked film was reduced at 150°C, the energy density was increased from 1.14 to 1.63 J/cm 3 , and the efficiency was also increased from 19% to 49%. It is worth noting that the PI‐5‐3layer film exhibits excellent electrical insulation at 150°C, its discharge energy density reaches 2.01 J/cm 3 , and the discharge efficiency was 79.9% (at 418 MV/m). The thermal resistance of crosslinked PI film was significantly improved, with the T g increased from 357°C to 377°C, and the linear coefficient of thermal expansion (CTE) decreased from 32.5 to 12.8 ppm, which decrease of more than 60%. This work provides an efficient method to develop high‐temperature dielectric films.