Sandwiched Polymer Nanocomposites Reinforced by Two‐Dimensional Interface Nanocoating for Ultrahigh Energy Storage Performance at Elevated Temperatures

Abstract Polymer‐based dielectrics are essential components in electrical and power electronic systems for high power density storage and conversion. A mounting challenge for polymer dielectrics is how to maintain their electrical insulation at not only high electric fields but also elevated temperatures, in order to meet the growing needs for renewable energies and grand electrifications. Here, a sandwiched barium titanate/polyamideimide nanocomposite with reinforced interfaces via two‐dimensional nanocoatings is presented. It is demonstrated that boron nitride and montmorillonite nanocoatings can block and dissipate injected charges, respectively, to present a synergetic effect on the suppression of conduction loss and the enhancement of breakdown strength. Ultrahigh energy densities of 2.6, 1.8, and 1.0 J cm −3 are obtained at 150 °C, 200 °C, and 250 °C, respectively, with a charge‐discharge efficiency >90%, far outperforming the state‐of‐the‐art high‐temperature polymer dielectrics. Cyclic charge‐discharge tests up to 10 000 times verify the excellent lifetime of the interface‐reinforced sandwiched polymer nanocomposite. This work provides a new pathway to design high‐performance polymer dielectrics for high‐temperature energy storage via interfacial engineering.