Significantly Improved High‐Temperature Energy Storage Performance of BOPP Films by Coating Nanoscale Inorganic Layer

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. The inorganic coating layers are successfully grown onto the surface of BOPP films using magnetron sputtering technique. The barrier height at the electrode/dielectric interface is significantly improved, leading to the effectively suppressed conduction loss at elevated temperature. An impressive discharged energy density of 1.5 J cm−3 with energy efficiency of 90% is achieved for AlN‐BOPP‐AlN capacitor films at 125 °C.