Breakthrough Energy Storage Density in Bi_0.5Na_0.5TiO₃-Based Films via Synergistic Enhancement of Polarization and...

Dielectric capacitors are indispensable for high-power energy storage systems due to their rapid charge-discharge capabilities, environmental sustainability, and exceptional power density. As a prototypical lead-free relaxor ferroelectric material, bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, NBT) is considered a promising candidate for dielectric capacitors owing to its large polarization. However, the inherent contradiction between high polarization and high breakdown strength (E_b) limits the energy storage performance of NBT-based film capacitors, severely restricting their application in high-pulsed-power systems. In this work, a synergistic strategy is proposed to optimize the polarization performance and achieve outstanding energy storage capabilities. From the introduction of Bi(Mg_0.5Zr_0.5)O₃ (BMZ) into NBT-based films, a structural transition is realized from large-scale ferroelectric domains to small-sized, highly dynamic polar nanoregions (PNRs), accompanied by significant grain densification and reduced grain size. Consequently, this approach effectively reduces remnant polarization (P_r) and minimizes the leakage current. In the optimized 0.7NBT-0.3BMZ films, simultaneous enhancements in polarization behavior and E_b are achieved, yielding an ultrahigh W_rec of 74.0 J cm^-3 and maximum polarization (P_max) of 110 μC cm^-2 at a high E_b of 2273 kV cm^-1. Furthermore, the excellent temperature stability (20-200 °C), frequency stability (50-5000 Hz), and cycling stability (1-10⁵ cycles) with the variation of W_rec < ±4% and efficiency (η) < ±3% are also achieved in the 0.7NBT-0.3BMZ films. This work achieves simultaneous enhancement of polarization and E_b in lead-free film capacitors, offering a breakthrough strategy to advance dielectric energy storage devices with superior performance.