Synergistic Effect of Polar Phase and Hierarchical Interface Engineering on Enhancing Energy Storage Performance in BNT/PVDF Composites

Sandwich-structured polyvinylidene fluoride (PVDF) composites with Bi0.5Na0.5TiO3 (BNT) fillers (0.05–0.5 wt %) were developed via molecular defect engineering and interfacial design to enhance energy storage. Using modified PVDF as the matrix, excellent dispersion of BNT was achieved through deep eutectic solvent (DES), while hydrogen bonding enhanced the interlayer connections. The composites achieved nearly complete polar phase crystallization after annealing. The multilayer architecture creates dielectric gradient interfaces that homogenize electric fields, inhibit charge accumulation, and extend the breakdown pathways. Optimized 0.5 wt % BNT composites demonstrate a breakdown strength of 504 MV/m and discharged energy density of 12.7 J/cm3, outperforming most PVDF-based materials. Concurrently, the design ensures 87% peak discharge efficiency, maintaining >80% efficiency under electric fields >400 MV/m due to reduced hysteresis and enhanced interfacial polarization. This work provides a scalable approach to eco-friendly dielectric materials through hierarchical structure–property optimization, advancing high-efficiency energy storage technology.