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 SiO2 nanoparticles (SiO2‐NPs) are fabricated by a solution casting method. It is found that the introduction of SiO2‐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/SiO2‐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 SiO2‐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.
Larger energy density is desirable for the nanocomposites as the potential dielectrics in energy storage capacitor. It is necessary to overcome the contradiction between dielectric permittivity and breakdown strength in...
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