Potassium–sodium niobate based lead-free ceramics: novel electrical energy storage materials

Abstract

The development of lead-free bulk ceramics with high recoverable energy density (W_rec) is of decisive importance for meeting the requirements of advanced pulsed power capacitors toward miniaturization and integration. However, the W_rec (<2 J cm⁻³) of lead-free bulk ceramics has long been limited by their low dielectric breakdown strength (DBS < 200 kV cm⁻¹) and small saturation polarization (P_s). In this work, a strategy (compositions control the grain size of lead-free ceramics to submicron scale to increase the DBS, and the hybridization between the Bi 6p and O 2p orbitals enhances the P_s) was proposed to improve the W_rec of lead-free ceramics. (K_0.5Na_0.5)NbO₃–Bi(Me_2/3Nb_1/3)O₃ solid solutions (where Me²⁺ = Mg and Zn) were designed for achieving large P_s, and high DBS and W_rec. As an example, (1 − x)(K_0.5Na_0.5)NbO₃–xBi(Mg_2/3Nb_1/3)O₃ (KNN–BMN) ceramics were prepared by using a conventional solid-state reaction process in this study. Large P_s (41 μC cm⁻²) and high DBS (300 kV cm⁻¹) were obtained for 0.90KNN–0.10BMN ceramics, leading to large W_rec (4.08 J cm⁻³). The significantly enhanced W_rec is more than 2–3 times larger than that of other lead-free bulk ceramics. The findings in this study not only provide a design methodology for developing lead-free bulk ceramics with large W_rec but also could bring about the development of a series of KNN-based ceramics with significantly enhanced W_rec and DBS in the future. More importantly, this work opens a new research and application field (dielectric energy storage) for (K_0.5Na_0.5)NbO₃-based ceramics.