Ferroelectric polymer nanocomposites with boron nitride nanosheets exhibit greatly improved energy densities and higher charge–discharge efficiencies.

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 , 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.

The demand for a new generation of high-temperature dielectric materials toward capacitive energy storage has been driven by the rise of high-power applications such as electric vehicles, aircraft, and pulsed power systems where the power electronics are exposed to elevated temperatures. Polymer dielectrics are characterized by being lightweight, and their scalability, mechanical flexibility, high dielectric strength, and great reliability, but they are limited to relatively low operating temperatures. The existing polymer nanocomposite-based dielectrics with a limited energy density at high temperatures also present a major barrier to achieving significant reductions in size and weight of energy devices. Here we report the sandwich structures as an efficient route to high-temperature dielectric polymer nanocomposites that simultaneously possess high dielectric constant and low dielectric loss. In contrast to the conventional single-layer configuration, the rationally designed sandwich-structured polymer nanocomposites are capable of integrating the complementary properties of spatially organized multicomponents in a synergistic fashion to raise dielectric constant, and subsequently greatly improve discharged energy densities while retaining low loss and high charge-discharge efficiency at elevated temperatures. At 150°C and 200 MV m −1 , an operating condition toward electric vehicle applications, the sandwich-structured polymer nanocomposites outperform the state-of-the-art polymer-based dielectrics in terms of energy density, power density, charge-discharge efficiency, and cyclability. The excellent dielectric and capacitive properties of the polymer nanocomposites may pave a way for widespread applications in modern electronics and power modules where harsh operating conditions are present.electrical energy storage | dielectric | polymer nanocomposites | capacitors | high temperature F ilm capacitors store electrical energy in dielectric materials in the form of an electrostatic field between two electrodes. They possess the highest power density (on the order of megawatts) and the best rate capability (on the order of microseconds) among the electrical energy storage devices and are critical for power electronics, power conditioning, and pulsed power applications (1-3). For instance, DC bus capacitors are essential components in the power inverters of electric vehicles for the conversion of direct current to alternating current, which is required to drive the vehicle's motor. Compared with ceramics, polymeric materials offer inherent advantages for capacitors, including their light weight, facile processability, scalability, high breakdown strength, and graceful failure mechanism (1-5). However, dielectric polymers often suffer from low operating temperatures, which fall short of the emerging demands for energy storage and conversion in harsh environments commonly present in automobile, aerospace power systems, and advanced microelectronics (6, 7). For example, to accommodate biaxially oriented polypropylen...