Multiscale synergistic design for enhanced energy storage performance in Bi_0.5Na_0.5TiO₃-based lead-free dielectrics under various electric fields

Dielectric capacitors have been recognized as promising devices for advanced pulse power systems due to their high-power density and fast charge-discharge rates. The dielectrics must simultaneously achieve large energy storage density and high efficiency to support the rapid development of dielectric capacitors. Among the various dielectric ceramics investigated so far, the Bi_0.5Na_0.5TiO₃ (BNT)-based lead-free relaxor ferroelectric has recently become increasingly attractive for dielectric energy storage owing to its high spontaneous polarization and temperature corresponding to the peak of maximum permittivity (T_m) in dielectric constant spectroscopy. Extensive efforts have been devoted to developing high-performance BNT-based ceramics in extreme conditions, and significant progress has been made. To meet the application demands of energy storage devices across diverse electric fields, it is imperative to understand the fundamental principles of energy storage and devise targeted optimization strategies for BNT-based ceramics. This review provides an overview of energy storage theory and essential determinants governing capacitive performance of dielectric materials, encompassing polarization response, breakdown characteristics, relaxation behavior, and dielectric properties. Furthermore, we elucidate tailored multiscale design strategies to optimize the energy storage capability of BNT-based ceramics across various electric field (E-field) regions:  low E-field (< 300 kV/cm), moderate E-field (300 - 500 kV/cm), and high E-field (˃ 500 kV/cm). We further present the developmental progress and future outlook of BNT-based ceramics for advanced electrostatic capacitor applications.