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 (Bi0.5Na0.5TiO3, 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 (Eb) 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(Mg0.5Zr0.5)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 (Pr) and minimizes the leakage current. In the optimized 0.7NBT-0.3BMZ films, simultaneous enhancements in polarization behavior and Eb are achieved, yielding an ultrahigh Wrec of 74.0 J cm-3 and maximum polarization (Pmax) of 110 μC cm-2 at a high Eb 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 Wrec Eb in lead-free film capacitors, offering a breakthrough strategy to advance dielectric energy storage devices with superior performance.
Zhang et al. (2026) studied this question.