Simultaneous Enhancement of the Energy Storage Density and the Self-Healing Properties via Interface Grafting for Metallized Film Capacitor Application

Metallized film capacitors (MFCs) are widely applied in power systems and electronic engineering. Driven by the urgent demand for MFC miniaturization, it has been a hotspot and a challenge to modify the dielectric material to simultaneously achieve a high energy storage density, an excellent discharge efficiency, and processability for scalable manufacturing. However, less attention has been paid to the self-healing performance, which is another key property determining the reliability of MFCs. Therefore, the present study proposes an interface-grafted polypropylene/poly(methyl methacrylate) (PP/PMMA) bilayer film. The PMMA layer minimizes the carbon residue of self-healing products, thereby reducing leakage current at self-healing points. Functional groups grafted onto the PP layer help construct a self-assembled molecular structure at the PP/PMMA interface, introducing barriers for charge carriers’ transportation and thus enhancing breakdown strength. Consequently, the acrylic acid (AA)-grafted PP/PMMA film achieves an energy storage density of 9.15 J/cm³ with a discharge efficiency of 92.5%. This interface also reduces the equivalent conductivity at the self-healing point by 86.4% compared to the pristine PP film. Moreover, the interface grafting demonstrates excellent feasibility for large-scale production and improved interlayer adhesion, facilitating the industrial transition from resins to films and the subsequent capacitor manufacturing.