Enhancing high-temperature capacitor performance of alumina-polyimide nanocomposites induced by the microscopic interface charge trap

Nanofillers and polymer matrices are utilized to construct nanocomposites, offering a promising approach to enhance energy storage performance in harsh conditions. This strategy relies on structural design to introduce deep charge traps that regulate carrier transport within the material. However, comprehensive studies combining theoretical and experimental methods to elucidate how trap introduction by nanofillers improves capacitive performance remain limited. Here, we in-situ synthesized alumina (AO) nanosheets via a hydrothermal method and fabricated uniformly dispersed nanocomposites with polyimide (PI) as the matrix. Energy band theory revealed that AO nanosheets introduced deep charge traps at the PI-AO interface, substantially reducing leakage current density. High-resolution Kelvin probe force microscopy (KPFM) experimentally confirmed the presence of interfacial deep charge traps at the nanofiller/polymer interface. Thermally stimulated discharge current (TSDC) was further measured to characterize variations in trap depth and density among different materials. At 150 °C, the optimized nanocomposite achieved a high energy storage density of 2.72 J cm −3 with a charge–discharge efficiency exceeding 90 %, corresponding to approximately 448 % of the performance of pristine PI. This work bridges critical gaps between experimental observations and theoretical mechanisms, clarifying the role of interfacial charge traps in nanocomposite performance.