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The urgent demand for next-generation high-temperature film capacitors with excellent energy storage properties originates from electrical-power applications under harsh environments. However, the state-of-the-art commercial capacitor dielectric biaxially oriented polypropylene (BOPP) suffers from a rapid decline in energy density and charge–discharge efficiency at elevated temperatures due to remarkably increased leakage current and reduced breakdown strength. Here, we report a scalable high-temperature capacitor film based on grafted polypropylene, in which the polar methyl methacrylate group is uniformity grafted by a facile and green water-solid phase suspension grafting method. The polypropylene is continuously grafted, melt cast, extruded, and biaxially stretched to form thin and uniform capacitor films, which are compatible with the present capacitor film industrial production line with high productivity. The grafted group keeps excellent interaction with the polypropylene during the biaxial stretching process without producing any perceptible defects. The experimental result and density functional theory simulation indicate that the grafted group can serve as a deep trap impeding the transit of charge carriers, leading to a one-order-of-magnitude decrease in the leakage current and a remarkable increase in breakdown strength from 537 MV m−1 of commercial BOPP to 764 MV m−1 of the grafted polypropylene at 125 °C. Consequently, the maximum discharged energy density above 90% efficiency of the grafted polypropylene (4.5 J cm−3) is significantly enhanced with respect to commercial BOPP (0.1 J cm−3). The approach reported in this work provides the possibility for large-scale production of capacitor films with high energy storage density under elevated temperature and high electric field. [ABSTRACT FROM AUTHOR]

Carbon neutrality is a state of dynamic equilibrium in carbon dioxide emissions. In insulation material aspect, polypropylene (PP) with grafted side chain segments possesses recyclability and may have better electrical property under high temperature compared with traditional norecyclable insulation insulation material like cross-linked polyethylene, which will reduce the carbon emission and help carbon neutrality processing. However, focused on the ideal grafted PP chain, the bandgap ( E g ) parameter is no longer suitable for describing the electrical properties of this system for the small grafting ratio. The induced grafted monomer might generate new band energy level and reduce the bandgap but with improvement on the electrical properties, which is not consistent with the positive correlation of the bandgap and the electrical properties. Alternatively, the trap depth, as one of the important electrical performance parameters, can reflect its influence on conductivity and breakdown. In this paper, the trap depth of the grafted PP chain is predicted by machine learning method with recursive feature elimination-based fingerprints. The paper analyzes the influence of different component groups and the ratioes of PP monomers on the charge trap depth. The grafted monomers with strong positive correlations on the electron/hole trap depth are given, and the electrical conductivity of PP-g-VK polymer has been tested for validation from the side. This paper provides a predictable parameter for the analysis of grafted systems and accelerates future predictions of performance parameters such as conductivity and breakdown strength. [ABSTRACT FROM AUTHOR]