Synchronous realization of remarkable energy-storage density and efficiency in (Na_0.5Bi_0.5)_0.75Sr_0.25TiO₃-based lead-free ceramics at moderate electric fields

Lead-free dielectric ceramics, as vital components of eco-friendly advanced pulse power systems, have encountered challenges for simultaneously achieving excellent energy-storage density (W_rec) and efficiency (η) at moderate electric fields. To address this issue, a novel class of (1-x)(Na_0.5Bi_0.5)_0.75Sr_0.25TiO₃-x(K_0.5Ag_0.5)_0.97Bi_0.01NbO₃ (NBST-xKABN, x = 0, 0.05, 0.10 and 0.15) relaxor ferroelectric ceramics are designed and synthesized in this work. K⁺-Bi³⁺ ion pairs are introduced into NBST-xKABN ceramics to alter charge distribution and destroy local structural symmetry of A-site. Thereby, large saturation polarization is maintained, which assists in energy storage at lower electric fields and minimizing the likelihood of aging failure in energy-storage devices that operate at high electric fields. Moreover, the incorporation of KABN strengthens breakdown strength of ceramics via reducing grain size and improving density and electrical uniformity (simulated by COMSOL). Along with the enhanced relaxor behavior induced by compositional inhomogeneity and ionic disorder, NBST-0.10KABN ceramics synchronously obtain W_rec of 5.3 J/cm³ and high η of 90.0 % at a moderate electric field of 330 kV/cm. The optimum composition also exhibits satisfactory temperature (30–130 °C) and frequency (1–100 Hz) stability, accompanied by large power density (P_D) of 38.2 MW/cm³ and rapid discharge rate t_0.9 of 34.8 ns. This work offers an achievable tactic to develop dielectric ceramics with remarkable comprehensive energy-storage properties at moderate electric fields, so as to satisfy requirements of energy-storage capacitors in harsh circumstances.