Spirocyclic groups to induce significant enhancement of high-temperature energy storage performance in polyimide

With the development of modern power electronic systems, there is an urgent demand for polymer dielectric materials that can operate efficiently for a long time under high temperature and high electric field. In this study, a polyimide (PI)-derivative containing spirocyclic groups was designed. The spirocyclic groups possess a rigid three-dimensional structure, which can effectively destroy the conjugated plane of PI polymer to block intramolecular charge transfer. Meanwhile, the large steric hindrance of the spirocyclic groups increases the distance between molecular chains and disrupts π-π stacking, thus hindering intermolecular charge transport. These effects jointly widen the bandgap and reduce the carrier mobility of the PI derivative. The composite film obtained by blending this PI-derivative with conventional PI exhibits the maximum discharge energy density of 4.78 J/cm 3 with the charge-discharge efficiency of 87.5% under 550 MV/m at 150 °C, outperforming most high-temperature polymer dielectrics. This work provides a feasible strategy for the design of polymer dielectrics targeted at high-temperature energy storage applications.