Ultrahigh Energy Storage Characteristics of Sodium Niobate-Based Ceramics by Introducing a Local Random Field

Lead-free ceramic capacitors are widely applied for novel pulse power supply systems owing to their environmental friendliness, high power density, and fast charge–discharge characteristics. Nevertheless, the simultaneous achievement of a higher recoverable energy storage density (W rec) and efficiency (η) is still challenging and must be investigated. To obtain a dielectric capacitor with a high W rec and η, the energy storage characteristics can be improved by reducing the residual polarization and increasing the breakdown strength. In this work, the doping modification of the NaNbO3 (NN) ceramics is used to produce a local random field to improve the electrical breakdown strength, obtaining a lead-free dielectric capacitor with high energy storage characteristics. According to this strategy, Bi­(Ni0.67Ta0.33)­O3 is added to NN, and an ultrahigh E b is obtained so that the ceramics have ideal W rec and η values. 0.85NN–0.15Bi­(Ni0.67Ta0.33)­O3 has a very high W rec (5.53 J cm–3) and η (82.0%) at 575 kV cm–1. Furthermore, the energy storage characteristics of the ceramics exhibit good thermal stability and frequency stability that are superior to those of most of the lead-free dielectric capacitors reported to date. In particular, the 0.85NN–0.15 Bi0.5Na0.5TiO3 (0.85NN–0.15BNT) ceramic also allows an ultrafast discharge time (t 0.9 = 27.5 ns), large current density (C D = 506.42 A cm–2), and higher power density (P D = 35.45 mW cm–3). These results indicate that (1 – x)­NN–xBNT ceramics are promising for applications in lead-free dielectric ceramic capacitors with a high energy storage density and conversion efficiency.