Significantly enhanced energy storage density and efficiency of lead-free K_0.5Na_0.5NbO₃-based relaxor ferroelectric ceramics

The development of dielectric ceramics for energy storage has received great research attention due to high power density and extremely high charge–discharge speed in recent years. Herein, the lead-free (1-x)(0.92K_0.5Na_0.5NbO₃-0.08Sr_0.7Bi_0.2TiO₃)-xBi(Zn_0.5Zr_0.5)O₃ [(1-x)(0.92KNN-0.08SBT)-xBZZ] ceramics were prepared. The enhanced energy storage performance in the x = 0.15 sample, with large recoverable energy storage density (W_rec) of 3.35 J/cm³ and high energy efficiency (η) of 81.9%, which can export satisfactory in temperatures (25–150 °C) and frequencies (1–100 Hz). It is revealed that the introduction of BZZ can enhance relaxor behaviors and decrease grain size, which are supported by the dielectric tunability, polarization hysteresis, and microstructure. Also, a superfast discharge speed (t_0.9 = 27.2 ns) and a high power density (P_D = 26.04 WM/cm³), with minimal fluctuation of ≤ 5.6%, are examined ranging from 20 °C to 120 °C. These characteristics render 0.85(0.92KNN-0.08SBT)-0.15BZZ ceramic promising candidate for high power energy storage applications.