Biaxially oriented polypropylene (BOPP) is one of the most commonly used commercial capacitor films, but its upper operating temperature is below 105 °C due to the sharply increased electrical conduction loss at high temperature. In this study, growing an inorganic nanoscale coating layer onto the BOPP film's surface is proposed to suppress electrical conduction loss at high temperature, as well as increase its upper operating temperature. Four kinds of inorganic coating layers that have different energy band structure and dielectric property are grown onto the both surface of BOPP films, respectively. The effect of inorganic coating layer on the high‐temperature energy storage performance has been systematically investigated. The favorable coating layer materials and appropriate thickness enable the BOPP films to have a significant improvement in high‐temperature energy storage performance. Specifically, when the aluminum nitride (AlN) acts as a coating layer, the AlN‐BOPP‐AlN sandwich‐structured films possess a discharged energy density of 1.5 J cm−3 with an efficiency of 90% at 125 °C, accompanying an outstandingly cyclic property. Both the discharged energy density and operation temperature are significantly enhanced, indicating that this efficient and facile method provides an important reference to improve the high‐temperature energy storage performance of polymer‐based dielectric films.

Commercial biaxially oriented polypropylene (BOPP) film capacitors have been widely applied in the fields of electrical and electronic engineering. However, due to the sharp increase in electrical conduction loss as the temperature rises, the energy storage performance of BOPP films seriously degrades at elevated temperatures. In this study, the grafting modification method is facile and suitable for large-scale industrial manufacturing and has been proposed to increase the high-temperature energy storage performance of commercial BOPP films for the first time. Specifically, acrylic acid (AA) as a polar organic molecular is used to graft onto the surface of commercial BOPP films by using ultraviolet irradiation (abbreviated as BOPP−AA). The results demonstrate that the AA grafting modification not only slightly increases the dielectric constant, but also significantly reduces the leakage current density at hightemperature, greatly improving the high-temperature energy storage performance. The modified BOPP−AA films display a discharged energy density of 1.32 J/cm 3 with an efficiency of >90% at 370 kV/mm and 125 °C, which is 474% higher than that of the pristine BOPP films. This work manifests that utilizing ultraviolet grafting modification is a very efficient way to improve the high-temperature energy storage performance of commercial BOPP films as well as provides a hitherto unexplored opportunity for large-scalable production applications.

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