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

Abstract

A design methodology for developing lead-free bulk ceramics with large recoverable energy storage density was proposed in this study.

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)NbO ₃–Bi(Me _2/3Nb _1/3)O ₃ solid solutions (where Me ²⁺ = 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)NbO ₃– xBi(Mg _2/3Nb _1/3)O ₃ (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)NbO ₃-based ceramics.