Flexible Unusual Ternary‐Component Graded‐Modulus Dielectric Films with High‐Density Capacitive Energy Storage

ABSTRACT Polypropylene (PP) is widely used in film capacitors but is limited by an intrinsic trade‐off between dielectric permittivity and breakdown strength, capping energy density around 3 J cm − 3 . This limitation is overcome by introducing a liquid silicone rubber (LSR107) interphase and BaTiO 3 (BT, diameter 5 nm) nanofiller into PP via one‐step melt extrusion, creating a ternary nanocomposite with a hierarchical interphase‐regulated structure. LSR107 selectively localizes in the amorphous/low‐crystallinity regions of PP and around BT‐rich regions, forming a compliant LSR107‐rich interphase that alleviates local electric‐field concentration, while BT provides a moderate permittivity increase. The optimized composite achieves a discharged energy density of 5.89 J cm − 3 at 96% charge–discharge efficiency and a high breakdown field (∼640 kV/mm). Remarkably, it retains >480% elongation at break and shows no performance degradation over 1 00 000 charge–discharge cycles. This soft–hard interphase design circumvents the traditional permittivity–breakdown compromise, yielding a melt‐processable dielectric film compatible with roll‐to‐roll manufacturing for high‐frequency capacitors and flexible electronics.