Enhancing the Polarization and Breakdown Performance of Three-Layer Linear Polymer Films through Modulating the Dielectric Properties of the Inner Layer for Improved Energy Density

In high-voltage thin film capacitor applications, linear polymers have attracted considerable interest owing to their superior insulating properties. In this study, poly(methyl methacrylate) (PMMA) was chosen as the outer layers of a three-layer architecture because of its favorable thermal and chemical stability and reliable dielectric performance. The intermediate dielectric layer comprises a polymer blend of poly(vinylidene fluoride) (PVDF) and PMMA, designed to exploit PVDF's strong polarization to tune the composite film's dielectric response. We investigated how tuning the inner layer's dielectric properties influences the internal electric-field distribution and interfacial polarization characteristics of the three-layer structure, and we identified the optimal structural configuration for maximizing energy storage performance. Experimental results demonstrate that increasing the PVDF content in the inner layer markedly enhances interfacial polarization within the three-layer film. Concomitantly, the local electric field intensity in the middle layer decreases, whereas the field in the outer PMMA layers correspondingly increases, effectively redistributing the electric field. By optimizing the inner-layer dielectric properties, a three-layer film containing 30 wt % PVDF in the central layer achieved a discharge energy density of 15.3 J/cm³ under an applied field of 680 kV/mm.