A Facile In Situ Surface‐Functionalization Approach to Scalable Laminated High‐Temperature Polymer Dielectrics with Ultrahigh Capacitive Performance

High‐temperature dielectric materials for capacitive energy storage are in urgent demand for modern power electronic and electrical systems. However, the drastically degraded energy storage capabilities owing to the inevitable conduction loss severely limit the utility of dielectric polymers at elevated temperatures. Herein, a new approach based on the in situ preparation of oxides onto polyimide (PI) films to high‐temperature laminated polymer dielectrics is described. As confirmed by computational simulations, the charge injection at the electrode/dielectric interface and electrical conduction in dielectric films are substantially depressed via engineering the in situ prepared oxide layer in the laminated composites. Consequently, ultrahigh dielectric energy densities and high efficiencies are simultaneously achieved at elevated temperatures. Especially, an excellent energy density of 1.59 J cm−3 at a charge–discharge efficiency of above 90% has been achieved at 200 °C, outperforming the current dielectric polymers and composites. Together with its excellent discharging capability and cyclic reliability, the laminate‐structured film is demonstrated to be a promising class of polymer dielectrics for high‐power energy storage capacitors operating at elevated temperatures. The facile preparation method reported herein is readily adaptable to a variety of polymer thin films for energy applications under extreme environments. Laminated high‐temperature polymer dielectrics composed of an in situ prepared wide‐bandgap oxide layer and polyimide are prepared for the first time. Ultrahigh capacitive performance is obtained at 200 °C, far outperforming the current polymer and polymer composite dielectrics including the polymer films coated with physically/chemically deposited inorganic layer.