High-temperature energy storage capability of flexible polyimide film incorporated with compatible covalent organic framework

Polymer film with the intrinsic breakdown and processability demonstrates great potential for film capacitor. Nevertheless, it's constrained by the deteriorated evolution in dielectric reliability and energy loss of polymer film under the elevated temperature. In this work, an imine-based covalent organic framework COF-300 has been synthesized via Uribe-Romo method, and the high-temperature electric displacement of COF-300/fluorinated polyimide (FPI) composite is investigated based on the tailored compatible interface between imide macromolecular structure and imine-based COF-300 filler. The presence of porous configuration reduces the dielectric constant and dielectric loss of FPI composite. The large electric displacement is achieved due to the interfacial polarization in composite, resulting in the enhanced energy storage capability. The 0.1 wt% COF-300/FPI film exhibits an energy density of 11.6 J/cm 3 with a charge-discharge efficiency of 93.1 % at 625 MV/m. The interfacial interactions between the COF-300 and the PI skeleton contribute to the strong constraint for the orientation and relaxation of active dipoles, and thus the high-temperature migrations of charge carriers are alleviated effectively. The 0.1 wt% composite retains outstanding high-temperature energy capability at 150 °C, for example, the energy density of 8.6 J/cm 3 with efficiency of 91.2 % at 475 MV/m is achieved. The resultant FPI film with the enhanced high-temperature dielectric reliability paves the path for the application of polymer capacitor.