Heterogeneous Interface Engineering with In‐Situ Aligned Polyamide Fibrils for High‐Energy‐Density Polypropylene Dielectric Films

The inherently low dielectric constant constrains the discharged energy density of polypropylene (PP)-based dielectrics, making it challenging to meet the growing demand for lightweight, efficient, and cost-effective dielectric capacitors. In this work, highly aligned polyamide 6 (PA6) submicron fibrils were in situ fabricated in the PP matrix via the "melt blending-hot stretching-quenching-annealing" technique, where the PA6 submicron fibrils could effectively serve as the heterogeneous nucleation sites for promoting the formation of PP crystals. As a result, the well-defined PA6 submicron fibrils and PP crystalline structure not only provided extensive interfacial areas to increase the interfacial polarization, but also significantly increased the propagation path of electric trees to improve the breakdown strength. The PP/PA6 dielectric films exhibited a remarkable maximum discharged energy density of 5.8 J cm^{- 3} with a high energy efficiency of 88.9% at 700 MV m^-1. This work demonstrates that heterogeneous interface engineering provides a viable route to simultaneously achieve high energy density and high efficiency in PP-based dielectric films, thereby promoting the scalable fabrication of high-performance all-organic dielectric capacitors.