Unlocking Superior Energy Storage: Multiscale Optimized BNT‐Based Capacitors for Low‐Field Applications

Achieving superior energy storage performance in dielectric materials under low electric fields remains a challenge. Most recent advancements require high fields that limit device applicability. Developing dielectric capacitors with high recoverable energy density (Wrec), efficiency (η), and energy-storage coefficient (Wrec/E) at low/moderate fields is critical for safer, compact, and durable electronics. To address this, lead-free BNT-based {(1-x)(Bi0.5Na0.5)(Ti0.7Zr0.3)O3-x(Sr0.7Bi0.2)TiO3} is optimized, abbreviated as (1-x)BNZT-xSBT, solid solutions using multi-scale regulations to achieve a giant Wrec/E. This approach modulates the rhombohedral (R)/tetragonal (T) phase ratio, refines grains, and induces polymorphic polar nanoregions (PNRs) through a macrodomain-to-nanodomain transition. SBT incorporation also raises activation energy, broadens band-gap energy, and suppresses interfacial polarization, enhancing breakdown strength. The optimized 0.7BNZT-0.3SBT ceramic delivers an exceptionally high Wrec/E of 0.021 mC cm-2 and Wrec of ≈4.3 J cm-3 at 204 kV cm-1, surpassing most recently developed dielectric bulk ceramics. Although a high η ≈ 97.52% is achieved at x = 0.4, all energy storage parameters are best at x = 0.3. Additionally, the material shows excellent stability across a wide temperature (≈160 °C) and frequency (≈150Hz) range and strong fatigue resistance (≈104 cycles). These findings highlight the potential and effectiveness of this BNT-based ceramic for highly efficient capacitors in low electric field applications.