Superior high-temperature energy storage performance of Polyetherimide-Based dielectric composites via optimization of the spatial distribution of MgO nanoparticles

Polymer dielectric capacitors are ideal candidates for high-power density applications due to their high breakdown strength and exceptional flexibility. However, the significant increase in conduction loss predominantly caused by the Schottky and Poole-Frenkel (P-F) emission reduces the energy density (U_e ) and charge-discharge efficiency (η) of polymer at elevated temperature. This study presents a novel sandwiched MgO/polyetherimide (MgO/PEI) composite, in which insulation layers are placed near the electrodes to prevent charge injection, and the spatial distribution of MgO nanoparticles is optimized to construct deeper inner trap energy levels. This well-designed structure integrates the optimization of both the electrode/dielectric interface and the bulk phase of polymer dielectrics, thereby significantly regulating charge migration, suppressing conduction loss and improving the overall energy storage property at elevated temperatures. The optimized composite incorporating 5.0 wt% MgO in the polarization layer and 1.0 wt% MgO in the insulating layers achieves ultra-high U e of 6.1 J/cm 3 (η ~ 91.2%) at 150 ℃ and 4.0 J/cm 3 (η ~ 86.1%) at 200 ℃, respectively. Notably, the obtained performance in this study surpasses that of most previously reported polymer dielectrics. This work demonstrates the substantial potential of multilayer structures for application in dielectric polymer composites at elevated temperatures.