With the ever-increasing demand for energy, research on energy storage materials is imperative. Thereinto, dielectric materials are regarded as one of the potential candidates for application in advanced pulsed capacitors by reason of their ultrahigh energy-storage density, low energy loss, and good thermal stability. Among the numerous dielectric materials for energy storage, sodium bismuth titanate (Bi_0.5Na_0.5TiO₃, BNT) with high saturation polarization, as one of the successful alternatives to lead-based materials, has been extensively studied. However, degraded dielectric and ferroelectric properties as a consequence of chemical alterations usually produced by inhomogeneity in microstructure and composition due to the ion volatilization during preparing, thus affecting performance of devices. Hence, this review served to encompass the current state and progress on the optimization of energy storage performance in lead-free BNT-based materials over the past few years, including ceramics, multilayer ceramics, thin films, and thick films, involved in solid solution modification, metal/metallic oxide doping, process optimization and other related aspects to optimize energy storage performance. Furthermore, some prospective approach in the improvement of energy storage performance for BNT-based materials were also provided in this work according to the existing theoretical and experimental results, to impel their practical application.

Na_0.5Bi_0.5TiO₃ (NBT)-based ceramics are promising lead-free candidates for energy-storage applications due to their outstanding dielectric and ferroelectric properties derived from large polarization. However, the high coercive field and large remnant polarization are unfavorable for practical applications, and thus NBT-based ceramics with relaxation behavior via doping/forming solid solutions with other elements/components have been widely studied. In this work, BaTiO₃ (BT) was introduced to the 0.94Na_0.5Bi_0.5TiO₃-0.06Bi(Mg_2/3Nb_1/3)O₃ system by a conventional solid-state reaction to form a homogeneous solid solution of 0.94[(1−x)Na_0.5Bi_0.51TiO₃-xBaTiO₃]-0.06Bi(Mg_2/3Nb_1/3)O₃ (BNT-100xBT-BMN). As the BT content increased, the proportion of the rhombohedral R3c phase increased while that of the tetragonal P4bm phase decreased, leading to the maximum P_max (38.29 μC/cm²) and E_b (80 kV/cm) obtained in BNT-7BT-BMN (x = 0.07) composition. Specifically, the optimal energy storage properties of W_rec ~ 1.02 J/cm³ and η ~ 62.91% under 80 kV/cm were obtained in BNT-7BT-BMN ceramics, along with good temperature stability up to 200 °C, which are promising factors for future pulse power applications.

Over the past decades, Na_0.5Bi_0.5TiO₃ (NBT)-based ceramics have received increasing attention in energy storage applications due to their high power density and relatively large maximum polarization. However, their high remnant polarization (P_r) and low breakdown field strength are detrimental for their practical applications. In this paper, a new solid solution (1−x)Na_0.5Bi_0.5TiO₃–xCaHfO₃ (x = 0.04, 0.08, 0.12, 0.16) was constructed by introducing CaHfO₃ into NBT, and thus was prepared using a conventional solid-state reaction. With the addition of CaHfO_3, the disorder of the structure increased, A-site vacancies formed, and thus oxygen vacancies were suppressed due to the replacement of the Na⁺ by Ca²⁺, resulting in the enhanced relaxation behavior and the reduced P_r, the refined grain, and improved breakdown strength. Furthermore, an optimal recoverable energy storage density (W_rec) of 1.2 J/cm³ was achieved in 0.92Na_0.5Bi_0.5TiO₃–0.08CaHfO₃ ceramics under the breakdown strength of 140 kV/cm, which is mainly attributed to the resultant defect of Na⁺ vacancy_.