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 a large energy storage density and high efficiency to support the rapid development of dielectric capacitors. Among the various dielectric ceramics investigated thus far, the Bi_0.5Na_0.5TiO₃ (BNT)-based lead-free relaxor ferroelectric (RFE) 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 the 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.

The simultaneous achievement of high recoverable energy storage density (W_rec) and high efficiency (η) under moderate electric fields remains a critical challenge for dielectric ceramic capacitors in modern electronic systems, despite their ultrahigh power density and rapid charge-discharge capabilities. Here, we propose a strategy to construct strongly polarizable nanodomains, enabling excellent energy storage performance (ESP) under moderate electric fields in Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics. Compositional modulation by multiple cations, together with a regulative proportion of rhombohedral (R) and tetragonal (T) phases, enhances random fields, weakens interdomain interactions, forms strongly polarizable nanodomains, and elevates the breakdown strength (E_b) without sacrificing the intrinsic high polarity of the matrix. Consequently, the optimized 0.98(BNSB)_0.985S_0.01T–0.02CMN ceramic exhibits an ultrahigh maximum polarization (P_max) of 65.8 μC/cm², with slim polarization–electric (P–E) field loops. Owing to these features, the optimized bulk ceramic achieves a record W_rec of 6.11 J/cm³ and an impressive η of 86% at an E_b of 330 kV/cm. Moreover, this sample also presents outstanding temperature/frequency stability and charging–discharging performance. These findings suggest that the (BNSB)_1–1.5yS_yT–0.02CMN component has immense potential for advanced pulse power capacitors under a moderate applied electric field and further offers a valid avenue for exploring high-performance lead-free dielectric materials.