In Situ Engineering of Sheet-Like Domains in All-Organic Dielectric Films for Enhanced Capacitive Energy Storage

Polypropylene (PP) dielectric films dominate commercial dielectric capacitors, but their intrinsically low polarizability has become a major bottleneck for next-generation high-energy-density dielectric films. Although current modification strategies can enhance polarization, these improvements frequently result in increased dielectric loss, diminished breakdown strength, or inadequate compatibility with biaxial film processing techniques. Here, this bottleneck is addressed through in situ engineering of sheet-like domains in a PP/poly(methyl methacrylate)/poly(vinylidene fluoride) (PP/PMMA/PVDF) ternary system. During biaxial stretching, the droplet-like PMMA/PVDF dispersed phase is reconstructed into sheet-like domains extending along the film plane, converting biaxial deformation from a manufacturing step into a morphology-engineering strategy. The resulting layered architecture can enhance the interfacial polarization, suppress through-thickness charge transport, and mitigate local electric-field concentration while maintaining the high-breakdown-tolerance semicrystalline framework of PP. Consequently, the optimized film delivers a discharged energy density of 5.1 J/cm³ at 650 MV/m with an efficiency above 90%, together with good large-area uniformity and stable cycling performance. More importantly, this work identifies post-deformation dispersed-phase geometry as a decisive design variable in all-organic dielectric films, providing a practical route toward high-performance polymer dielectric materials.