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

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 BaTiO₃ (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.