Significant improvement in high-temperature energy storage performance of polymer dielectrics via constructing a surface polymer carrier trap layer

Polymer dielectrics are preferred materials for high-energy-storage metalized film capacitors. However, the state-of-the-art commercial capacitor dielectrics represented by biaxially oriented polypropylene (BOPP) can hardly fulfill the practical requirements of the harsh operating environments of electronics and electrical-power equipment. In this work, a facile, high-efficiency strategy is proposed for fabricating polymeric films with excellent high-temperature capacitive performance. This strategy involves coating the surface of BOPP films with parylene polymers by chemical vapor deposition. The addition of a parylene polymer layer with deep trap energy levels and high melting temperatures significantly improves the temperature resistance of BOPP and effectively suppresses leakage current, resulting in excellent capacitive properties at elevated temperatures and high electric fields. The maximum discharged energy density (U_e) of the modified BOPP films is 10.10 J cm⁻³ with a charge-discharge efficiency (η) > 90% at 30 °C, and it reaches 5.52 J cm⁻³ with an η of over 90% at 120 °C. This method offers unprecedented opportunities for the development of scalable polymer dielectrics with high energy storage and low loss at high temperatures due to its non-damaging nature, precise thickness control, low temperature, and readily scaled-up conformal deposition.