Nanoscale microphase separation in soft-hard block copolyimides enables excellent high-temperature capacitive energy storage performance

Advanced polymer dielectrics are in high demand for building film capacitors with high-temperature tolerance and high energy density. Conventional polyimide is well known for high-temperature resistance, yet its capacitive energy storage performance is unsatisfactory. Herein, a new-type soft-hard block copolyimide film with high electrostatic energy storage density and low dielectric loss at high temperatures is reported. This copolymer film with optimized ratio of hard to soft segments exhibits nanoscale microphase separation structures, which act as a plethora of deep charge traps for enhancing the breakdown strength. The hard segments containing trifluoromethyl and sulfone groups show microphase separation and help to increase the dielectric constant to ~ 5. In addition, these hard segments not only widen the energy bandgap, but also increase the glass transition temperature of the copolymer. The optimized block copolyimide film exhibits high discharged energy densities (U d ) of 8.0 J cm −3 at room temperature and 6.02 J cm −3 at 150 °C, along with a high charge-discharge efficiency (η) of 90%. The maximum U d reaches 6.9 J cm −3 with η = 84.3%. The effect of microphase separation in the block copolyimide on enhancing the high-temperature capacitive energy storage performance is discussed in detail.