Modulating the charge trapping characteristics of PEI/BNNPs dilute nanocomposite for improved high-temperature energy storage performance

Flexible polymeric dielectrics with excellent energy density and high temperature resistance are essential in modern electronic communication and industrial systems. However, current polymeric dielectrics suffer from seriously deteriorated energy density with the increase of temperature, which is caused by the exceptionally increased leakage current under high voltage and high temperature. Here, based on the results of thermally stimulated depolarization current measurements and phase-filed simulations, we demonstrate that an ultralow (0.25-0.75%) volume fraction of high-insulative boron nitride nanoparticles (BNNPs) can generate deep traps and shorten the hopping distance for mobile charges in a polyetherimide (PEI) nanocomposite, thereby suppressing conduction loss and improving breakdown strength at 150 °C. In addition, it's found that the dielectric constant of the nanocomposites is remarkably enhanced at ultra-low loading of BNNPs compared to the pristine PEI. Accordingly, with the simultaneous enhancement of the dielectric constant and breakdown field strength, the PEI-based dilute nanocomposite film yields a high energy density of 4.2 J cm−3 and the ultrahigh charge-discharge efficiency of 90% at 150 °C. This work offers a facile and scalable approach to adjusting the charge transport and trapping behaviors of polymeric dielectrics for improved high temperature electrostatic energy storage performance, which is of significant importance for their practical applications in high-temperature electrical and electronic systems.