Excellent Stability in Polyetherimide/SiO 2 Nanocomposites with Ultrahigh Energy Density and Discharge Efficiency at High Temperature.

Polymer dielectrics with excellent thermal stability are the essential core material for thin film capacitors applied in a harsh-environment. However, the dielectric and mechanical properties of polymers are commonly deteriorated with temperature rising. Herein, polyetherimide (PEI)-based nanocomposites contained with SiO 2 nanoparticles (SiO 2 -NPs) are fabricated by a solution casting method. It is found that the introduction of SiO 2 -NPs decreases the electric conductivity and significantly enhances the breakdown strength of the nanocomposites, especially under high temperatures. As a result, the 5 vol% PEI/SiO 2 -NPs nanocomposite film displays a superior dielectric energy storage performance, e.g., a discharged energy density of 6.30 J cm -3 and a charge-discharge efficiency of 90.5% measured at 620 MV m -1 and 150 °C. In situ scanning Kelvin probe microscopy characterization indicates that the charge carriers can be trapped in the interfacial regions between the polymer matrix and the SiO 2 -NPs till the temperature reaches as high as 150 °C. This work demonstrates an effective strategy to fabricate high-temperature dielectric polymer nanocomposites by embedding inorganic nanoparticles and provides a method for directly detecting charge behavior at the nanoscale inside the matrix.