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

Abstract

The development of high-temperature film capacitors with high energy density and charge–discharge efficiency is urgent in order to fulfill the requirements of energy storage systems. In this work, a semi-crystal polyimide (PI) with a fluorine-containing pendant group has been synthesized, and the high-temperature electrical displacement and breakdown behavior of the PI film are investigated systematically. The evolution of the crystal structure in the PI film is evaluated using XRD and density functional theory simulation. The lattice distortion caused by the large pendant group contributes to the free volume inside the bulk PI. 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 at high temperature is attributed to the combination of a broad bandgap and the free volume effect in the condensed state. The presence of –CF₃ effectively hinders the diffusion of charge carriers under the action of an applied field, which results in enhanced dielectric reliability. This semi-crystalline PI film with a fluorinated pendant group exhibits improved high-temperature energy storage performance, which sheds light on the exploration of the suppression of energy loss for polymer film capacitors.