High‐Performance Polymers Sandwiched with Chemical Vapor Deposited Hexagonal Boron Nitrides as Scalable High‐Temperature Dielectric Materials

Polymer dielectrics are the preferred materials of choice for power electronics and pulsed power applications. However, their relatively low operating temperatures significantly limit their uses in harsh‐environment energy storage devices, e.g., automobile and aerospace power systems. Herein, hexagonal boron nitride ( h ‐BN) films are prepared from chemical vapor deposition (CVD) and readily transferred onto polyetherimide (PEI) films. Greatly improved performance in terms of discharged energy density and charge–discharge efficiency is achieved in the PEI sandwiched with CVD‐grown h ‐BN films at elevated temperatures when compared to neat PEI films and other high‐temperature polymer and nanocomposite dielectrics. Notably, the h ‐BN‐coated PEI films are capable of operating with >90% charge–discharge efficiencies and delivering high energy densities, i.e., 1.2 J cm −3 , even at a temperature close to the glass transition temperature of polymer (i.e., 217 °C) where pristine PEI almost fails. Outstanding cyclability and dielectric stability over a straight 55 000 charge–discharge cycles are demonstrated in the h ‐BN‐coated PEI at high temperatures. The work demonstrates a general and scalable pathway to enable the high‐temperature capacitive energy applications of a wide range of engineering polymers and also offers an efficient method for the synthesis and transfer of 2D nanomaterials at the scale demanded for applications.