High-temperature energy storage capability of flexible polyimide with the fluorinated pendant group

High-temperature film capacitor with large energy density and charge-discharge efficiency is urgent to be developed to fulfill the requirement of energy storage system. In this work, a semi-crystal polyimide (PI) with the fluorine-containing pendant group has been synthesized, and the high-temperature electrical displacement and breakdown behavior of PI film are investigated systematically. The evolution of crystal structure in PI film is evaluated by XRD and density function theory simulation. The lattice distortion caused by the large pendant group contributes to the free volume inside PI bulk. The optimized PI film demonstrates an energy density of 8.0 J cm-3 with a charge-discharge efficiency of 90% at 500 MV m-1 and 150 °C. The ultrahigh energy storage capability under high temperature is attributed to the combination of broad bandgap and free volume effect in the condense state. The presence of –CF3 effectively hinders the diffusion of charge carriers under the action of the applied field, which results in the enhanced dielectric reliability. This semi-crystal PI film with fluorinated pendant group illustrates the improved high-temperature energy storage performance, which sheds a light on the exploration of the depression of energy loss for polymer film capacitor.