Developing a novel high performance NaNbO3-based lead-free dielectric capacitor for energy storage applications

The development of dielectric capacitors with high recoverable energy density, high energy storage efficiency, short discharge time, and good temperature stability is of great importance for meeting the demands of integration and miniaturization of energy storage devices. Learning from the advantages of relaxor ferroelectrics for energy storage applications and the relationship between their grain size and breakdown strength, we develop a novel lead-free NaNbO3-based (xBa0.6(Bi0.5K0.5)0.4TiO3–(1 − x)NaNbO3, abbreviated as xBBKT–NN) relaxor ferroelectric in this study. The XRD results reveal that the average structure of xBBKT–NN ceramics belongs to the pseudo-cubic phase due to cation disorder distribution. All compositions display a fine-grain microstructure and relaxor ferroelectric characteristics. The composition with x = 0.32 shows optimal comprehensive energy storage properties, including the highest recoverable energy density of 2.75 J cm−3 and a favorable energy storage efficiency of 78.3%. The improvement of energy storage properties is mainly related to the enhanced relaxor behavior. Additionally, pulse charge–discharge analysis was also carried out to estimate the practical discharge performance of the x = 0.32 ceramic. An extremely short discharge time (<100 ns) and relatively high thermal stability (20–100 °C) were also observed in the x = 0.32 ceramic. These results not only show that the lead-free xBBKT–NN ceramics are a novel relaxor ferroelectric for energy storage applications, but also demonstrate that a combination of fine-grain engineering and relaxor behavior is an effective method to develop high performance dielectric materials.