Improved high-temperature energy storage performance of sandwich PEI-based composites via introducing charge traps by differential functional fillers

With the rapid development of electric vehicles, aerospace technology, and other emerging applications, the demand for polymer film capacitors capable of operating under extreme conditions is increasing rapidly. However, the significant rise in conduction losses at high temperatures and high electric fields results in substantial deterioration in energy storage performance of polymer dielectrics. Thus, designing composite dielectrics in structural to effectively mitigate their conduction losses remains a critical challenge. This study introduces a typical sandwich-structured high-temperature polymer-based composite dielectric, incorporating surface-charged kaolinite nanosheets (KLNS) and the organic molecular semiconductor 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) with high electron affinity in different polyetherimide (PEI) layers, respectively. This construction introduces differential charge traps into the composites to modulate charge migration and capture the charges that injected from electrodes or excited in the dielectric. Experimental results demonstrate that this construction effectively reduces leakage current caused by Poole-Frenkel emission and hopping conduction, thereby suppressing the conduction losses of composites at high temperatures. Consequently, the sandwich-structured composite exhibits an excellent high-temperature stability in electrical properties and the optimized composite filled with 0.2 wt% KLNS in the middle layer and 0.5 wt% NTCDA in the outer layers achieves an ultrahigh discharged energy density (U-e) of 5.0 J/cm(3) and a high efficiency (eta) of 88.7 % at 150 degrees C, representing improvements of 163 % and 41 % compared with pure PEI (U-e similar to 1.9J/cm(3), eta similar to 62.8 %), respectively. This study presents an effective strategy for designing composites with enhanced energy storage capabilities under high-temperature and high-electric-field conditions.