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 (U_e). 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 α-phase, resulting in improved mechanical, dielectric, and energy storage performance. The optimal PP-g-TFEMA film exhibits a remarkable breakdown strength (E_b) of 865 MV m⁻¹ and a record U_e 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 U_e of film capacitors for long-term service not only in academia but also in industry.