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.

Polymer-based nanodielectrics have been intensively investigated for their potential application as energy storage capacitors. However, their relatively low energy density (U_e) and discharging efficiency (η) may greatly limit their practical usage. In present work, high insulating two-dimensional boron nitride nanosheets (BNNS), were introduced into a linear dielectric polymer (P(VDF-TrFE-CTFE)-g-PMMA) matrix to enhance the energy storage performance of the composite. Thanks to the surface coating of polydopamine (PDA) on BN nanosheets, the composite filled with 6 wt% coated BNNS (mBNNS) exhibits significantly improved breakdown strength (E_b) of 540 MV/m and an energy density (U_e) of 11 J/cm³, which are increased by 23% and 100%, respectively as compared with the composite filled with the same content of pristine BNNS. Meanwhile, η of both composites is well retained at around 70% even under a high voltage of 400 MV/m, which is superior to most of the reported composites. This work suggests that complexing polymer matrix with linear dielectric properties with surface coated BNNS fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency.