Roll‐to‐Roll Manufactured Polyetherimide Nanocomposite With Different Diameters of SiO₂ Nanoparticles Exhibiting Improved High‐Temperature Dielectric Energy Storage Performance

To enhance the high-temperature energy storage performance of the polymer-based dielectric film, inorganic nanofillers with large band gaps are much more effective and have been widely adopted. However, the impact of nanoparticle diameters on the dielectric properties of polymer nanocomposites has been less studied. Herein, silicon dioxide nanoparticles (SiO₂-NPs) with varying diameters (20, 60, 120, 200 nm) prepared by the sol-gel method are incorporated in the PEI matrix to form PEI/SiO₂ nanocomposites. The characterization results reveal a distinct correlation between the dielectric properties of polyetherimide (PEI) composites and the diameters of SiO₂-NPs. Leakage current density analysis and breakdown strength simulations indicate that SiO₂-NPs with smaller diameters generate more deep traps that impede the transport of charge carriers, especially under high temperatures. Notably, PEI/20 nm-SiO₂ exhibits a high discharged energy density of 4.4 J cm^-3 with an efficiency of 90% at 150 °C. Furthermore, PEI/SiO₂ films with 10 µm in thickness are manufactured by a large-scale solution casting process. The continuously prepared PEI/20 nm-SiO₂ film exhibits a discharged energy density of 3.2 J cm^-3 with an efficiency of 90% at 150 °C. This study not only provides a strategy for the design of high-performance dielectric polymer composites but also offers a large-scale high-temperature dielectric film for practical use.