Excellent energy storage properties with ultrahigh W_rec in lead-free relaxor ferroelectrics of ternary Bi_0.5Na_0.5TiO₃-SrTiO₃-Bi_0.5Li_0.5TiO₃ via multiple synergistic optimization

Advanced energy storage capacitors play important roles in modern power systems and electronic devices. Next-generation high/pulsed power capacitors will rely heavily on eco-friendly dielectric ceramics with high energy storage density (W_rec), high efficiency (η), wide work temperature range and stable charge-discharge ability, etc. Lead-free Bi_0.5Na_0.5TiO₃ (BNT) based relaxor ferroelectric (RFE) ceramics are considered as one of the most promising candidates for energy storage capacitors. However, the application fields of them are greatly limited by their relatively low W_rec (generally <5 J/cm³). In this paper, excellent energy storage properties characterized by a great breakthrough in W_rec are achieved in a novel BNT system, (1-x)BNT-x(0.7SrTiO₃-0.3Bi_0.5Li_0.5TiO₃)+0.5 at.%Nb₂O₅ (x = 0, 0.1, 0.2, 0.3, 0.4), by synergistically constructing highly dynamic polar nanoregions (PNRs) and nanodomains, ultrafine grains (submicron size) and intrinsic conduction. Of great importance, the x = 0.4 ceramic exhibits an ultrahigh W_rec of 8.63 J/cm³ as well as a high efficiency (ƞ) of 89.6 % under a giant electric field of 520 kV/cm, due to coexistence of ultrahigh polarization difference (ΔP=P_max −P_r) and high dielectric breakdown electric strength (E_b). Furthermore, excellent temperature stability (20−180 °C), frequency stability (1 − 500 Hz), and cycling stability (1 − 10⁵ times) with the variation of W_rec < ±4 % and η < ±3 % are also found in the x = 0.4 ceramic. These results demonstrate that it is a very promising lead-free dielectric capacitor with enormous energy storage applications.