Ultrahigh Energy Density Achieved at High Efficiency in Dielectric Capacitors by Regulating α-Phase Crystallization in Polypropylene Films with Fluorinated Groups

Polypropylene (PP)-based dielectric film capacitors cannot meet the rapid development requirements of electromagnetic energy equipment because of their low energy storage density (Ue). The development of new dielectric materials is hampered by the trade-off between high energy storage properties and thin film processibility for capacitors. This study proposes a strategy to improve the comprehensive energy storage properties of PP films by reconciling the trade-offs not only between their polarity and crystallinity but also between their energy storage and processing performance. In this approach, a trifluoroethyl methacrylate (TFEMA) modified PP film is fabricated at the kilogram scale. The TFEMA units regulate PP crystallization in the alpha-phase, resulting in improved mechanical, dielectric, and energy storage performance. The optimal PP-g-TFEMA film exhibits a remarkable breakdown strength (Eb) of 865 MV m-1 and a record Ue of 8.2 J cm-3 at over 90% discharge efficiency. The promising thin film processibility, excellent self-healing, and long-term reliability of PP are finely preserved in the aluminum (Al) coated PP-g-TFEMA film. These findings present a novel avenue to significantly increase the Ue of film capacitors for long-term service not only in academia but also in industry. Incorporating fluorinated groups serve as heterogeneous nuclei accelerates the crystallization of PP chains, while effectively improving the mechanical, dielectric, high electric field resistance, energy storage, andlong-lifespan performances, thereby effectively resolving the trade-off between the high energy storage properties and thin film processibility for capacitors. image