Superior discharged energy density in polyetherimide composites enabled by ultra-low ZnO@BN core-shell fillers

Abstract The primary strategy to increase dielectric constant and energy storage density is adding a high fraction of fillers with high dielectric constant to polymer matrix. Yet, it has not been very successful without encountering processing difficulties, lowered breakdown strength, and mechanical inflexibility. Herein, we introduce an unconventional approach using ultra-low fraction of zinc oxide core and boron nitride shell (ZnO@BN) filler with very high thermal conductivity dispersed in polyetherimide (PEI) for the same purpose. For the 0.1 vol.% core-shelled fillers, the PEI composite film exhibits a superior dischargeable energy density of 10.8 J/cm3 and a high efficiency of 92.1% at an electric field of 500 kV/mm. The polarization responses under high electric fields and simulation reveal the association with the increased interfacial polarization of the thermally conductive core-shelled structure. This strategy lays out a new route to further investigate of high energy density composite and capacitor technologies.