Aiming at the problems of rapid growth in the high field conductivity

significant decrease in breakdown strength and energy storage density (Ue) of polyetherimide (PEI) at high temperature. Functional groups for chain blocking are utilized so as to solve these problems and realize the improvement of the energy storage performance at extremely high temperature. A series of N-PEI films are prepared by blocking PEI with the different content of Nadic anhydride (NA). The effects of NA contents on the thermal stability

dielectric and energy storage properties of the N-PEI films are studied. Combining high field conductivity and depolarization thermal stimulation current tests

the trap characteristics of N-PEI films are analyzed. In addition

the influence mechanism of NA on the energy storage properties of N-PEI films is elucidated. The results show that the appropriate content of NA blocking can ensure that N-PEI has a large molecular weight and a broad molecular weight distribution and reduces the free volume. Simultaneously NA can introduce new deeper traps which can effectively capture the free charges and shorten the hopping distance

thereby suppressing high temperature conductivity and improving the breakdown strength

which achieves the improvement in Ue and charge-discharge efficiency (η) at an ultra-high temperature. When the content of NA is 5 mol%

the N05 film achieves a Ue of 6.8 J/cm3 at room temperature with an η of 95.8%. It is inspiring that the N05 film can still achieve an Ue of 4.39 J/cm3 (η=90.9%) under 500 MV/m at 200℃

which is 109% higher than that of the traditional PEI (2.10 J/cm3). This article provides a new approach for the development of polymer dielectrics that are suitable for energy storage at high temperature.