Dielectric capacitors are the key components in advanced electronics and electrical systems owing to their highest power density among the electrical energy devices. [1][2][3][4][5][6][7] While ceramic dielectrics are of large dielectric constants and high thermal stability, [8][9][10][11][12] polymer dielectrics possess high tolerance to voltage, great reliability, scalability, and light weight, and therefore are preferred for high-energy-density high-power film capacitors. [13][14][15][16][17] However, the current polymer dielectrics are unable to match the temperature requirements of the emerging applications of electrical energy storage and conversion in harsh environments [18][19][20][21][22] because of their inherently poor thermal stability. For example, while the near-engine-temperature in electric vehicles can reach to above 120 °C, [23] the operating temperature of biaxially oriented polypropylene (BOPP), which is the best commercially available polymer dielectric and currently used in power inverters of electric vehicles, is below 105 °C. [24] The wide bandgap semiconductors like silicon carbide (SiC) and gallium nitride that are well positioned to replace traditional silicon power devices boost the operating temperatures of next-generation capacitors beyond 150 °C. [19] To address these urging needs, a variety of engineering polymers with high thermal stability, such as polyimides (PIs) and fluorene polyesters (FPEs), have been exploited as high-temperature dielectric materials. [20,25] Unfortunately, all the polymers show poor charge-discharge efficiencies under elevated temperatures and high applied fields, [26] which is due to sharply increased electrical conduction attributable to various temperature-and field-dependent conduction mechanisms, e.g., charge injection at the electrode/dielectric interface. [27,28] Ceramic dielectrics are relatively insensitive to temperature and able to maintain the energy-storage performance throughout a broad temperature range, [8][9][10][11][12] but they still suffer from considerable energy loss under high electric fields and elevated temperatures. [29] More recently, the addition of 2D wide bandgap nanostructures such as boron nitride nanosheets (BNNSs) into the polymer has been demonstrated to effectively reduce the conduction loss and largely improve the charge-discharge High-temperature capability is critical for polymer dielectrics in the nextgeneration capacitors demanded in harsh-environment electronics and electrical-power applications. It is well recognized that the energy-storage capabilities of dielectrics are degraded drastically with increasing temperature due to the exponential increase of conduction loss. Here, a general and scalable method to enable significant improvement of the high-temperature capacitive performance of the current polymer dielectrics is reported. The high-temperature capacitive properties in terms of discharged energy density and the charge-discharge efficiency of the polymer films coated with SiO 2 via plasma-enhanced chemical...

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Ferroelectric polymers are being actively explored as dielectric materials for electrical energy storage applications. However, their high dielectric constants and outstanding energy densities are accompanied by large dielectric loss due to ferroelectric hysteresis and electrical conduction, resulting in poor charge-discharge efficiencies under high electric fields. To address this long-standing problem, here we report the ferroelectric polymer networks exhibiting significantly reduced dielectric loss, superior polarization and greatly improved breakdown strength and reliability, while maintaining their fast discharge capability at a rate of microseconds. These concurrent improvements lead to unprecedented charge-discharge efficiencies and large values of the discharged energy density and also enable the operation of the ferroelectric polymers at elevated temperatures, which clearly outperforms the melt-extruded ferroelectric polymer films that represents the state of the art in dielectric polymers. The simplicity and scalability of the described method further suggest their potential for high energy density capacitors.

The discovery of ferroelectric phenomenon in polymers in early 1970s has aroused tremendous research interests in these soft materials with intriguing physical properties, and led to a broad range of applications. Since then the understanding of physical origin of ferroelectricity in these macromolecules has been fast deepened by virtue of the rapid development of ferroelectric polymer science, which in turn has enabled better design of ferroelectric polymers with improved performance. Over the last two decades, as boosted by the increasing demand for advanced energy technologies, great progress has been made in understanding and developing new ferroelectric polymers toward energy-related applications. This trend article summarizes the important aspects and recent advances in the research area of ferroelectric polymers, covering from understanding of material fundamentals, through synthesis and processing techniques, to applications in energy conversion and storage.

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