All-organic polyimide/Cl-HBC composite film with high breakdown strength and ultra-low dielectric loss

The combination of high breakdown strength and low dielectric loss has always been a challenge for the preparation of high energy storage density dielectric films. In this work, in order to optimize their dielectric performances, we develop a series of all-organic PI composite films by introducing perchlorinated hexa-peri-hexabenzocoronene (Cl-HBC) molecules with a concentration (0.01–0.1mol%) into PI film. Even at an ultra-low concentration, the Cl-HBC molecule with a quasi-two-dimensional structure would successfully induce the in-plane orientation of PI macromolecular chains and reduce their orientation confusion and molecular cavity. Thus, the existence of Cl-HBC obviously limits the chain mobility of PI in PI-Cl-HBC film under the electric field, which is supposed to reduce the dielectric loss of resulted films. Moreover, Cl-HBC molecules are equipped with a low Lowest Unoccupied Molecular Orbital (LUMO) of about −3.52eV and could work as an electron trap and block the conduction of electrons in the PI composite film. Here, the breakdown strength of the composite film was improved from 442 kV/mm (pure PI) to 539 kV/mm and the dielectric loss was reduced to 0.002. To our best knowledge, it is the first time to significantly enhance the dielectric strength and largely reduce its dielectric loss simultaneously by preparing PI composite film. Meanwhile, compared with pure PI, the energy storage density of composite film increases by 43% and 96% at room temperature and 150 °C, respectively.