Enhancing the high-temperature energy storage properties of PEI dielectrics by constructing trap-rich covalently...

Polymer films are ideal dielectric materials for energy storage capacitors due to their light weight and flexibility, but lower energy density and poor heat resistance greatly limit their application in high-temperature energy storage. Unlike the traditional method of solely adding wide-bandgap inorganic fillers to enhance energy density, in this study we constructed trap-rich hybrid covalently cross-linked networks in polyetherimide (PEI) via reactive polyhedral oligomeric silsesquioxane (POSS)-functionalized boron nitride nanosheets (BNNS@POSS), which not only serve as interfacial layers for dielectric transitions and insulating barriers but also create deeper traps and higher energy barriers in the region of cross-linked chains. This strategy based on the co-modulation of interfaces and traps achieved the compatibility of high polarization and high breakdown strength and improved energy storage performance. Therefore, the composite film BNNS@POSS/PEI with the addition of 5 wt% BNNS@POSS achieved a maximum discharge energy density and charge-discharge efficiency at 150 °C of 6.16 J cm^-3 and 89.92%, and maintained high values at 200 °C of 4.12 J cm^-3 and 88.38%, respectively. Moreover, the glass transition temperature (T_g) of the composite dielectrics increased by 20.2 °C. This work provides a promising candidate material and development directions for research in the field of high-temperature energy storage capacitors.