Engineering High‐Performance Polymer Dielectrics via Sea‐Island Phase Separation: Synergizing Toughness, Energy Density, and Low Dielectric Loss

ABSTRACT In modern electronics and power systems, high‐performance dielectric capacitors with metallized films are indispensable for efficient energy storage and power delivery. However, commercially available polymers like BOPP and PVDF are limited by inherent structural defects, restricting their ability to achieve high energy density and low energy loss. Glassy polymers, which offer a promising balance between these attributes, are severely restricted by their brittleness, complicating film casting and coil winding processes crucial for capacitor applications. To address these challenges, we introduced non‐polar hydroxyl‐terminated polybutadiene monomers into glassy polymers to construct distinct sea‐island structures. This approach enhances the dielectric constant through interface polarization and significantly improves material toughness. These structures concentrate stress, enable plastic deformation, inhibit crack propagation, and demonstrate self‐healing capabilities. Additionally, the reverse electric field generated by interface polarization traps charges, preventing further electron migration and delaying the decline in breakdown strength. Our results show a releasing efficiency of 89.5%, a discharge energy of 10.48 J/cm 3 at 550 MV m −1 , and a fracture elongation of 27.3%. This study pioneers a novel strategy to decouple the trade‐offs between high energy density, low energy loss, and enhanced toughness through the strategic construction of sea‐island structures, opening new avenues for advanced dielectric materials.