Significant increase in comprehensive energy storage performance of potassium sodium niobate-based ceramics via synergistic optimization strategy

K0.5Na0.5NbO3 (KNN)-based ceramics are considered as one of the most promising lead-free dielectric ceramics owing to relatively high dielectric breakdown strength (DBS) resulted from their unique submicron grains. Unfortunately, it has been difficult to increase recoverable energy-storage density (W-rec) and energy-storage efficiency (eta) simultaneously at present. Herein, we propose a synergistic optimization strategy, namely, simultaneously enhancing DBS by tailoring grain size to submicron scale and inducing the temperature range between the maximum dielectric permittivity temperature (T-max ) and the Burns temperature (T-B) to room temperature, for solving the bottleneck. (1- x)K0.5Na0.5NbO3- xBi(Ni0.5Zr0.5)O-3(KNN-BNZ) ceramics were chosen as an example to illustrate the validity of this strategy. An ultrahigh W-rec of 8.09 J.cm(-3) was obtained at the optimum composition of x = 0.15 under the electric field of 870 kV .cm(-1), which is much higher than those of other reported KNNbased ceramics. Most importantly, this high W-rec was accompanied by a high eta of 88.46%, which is superior to those of other KNN-based ceramics and very important for practical applications. The excellent comprehensive energy storage performance was resulted from the polar nanoregions, which is confirmed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), piezo-force microscopy (PFM) and first order reversal curve (FORC) distributions. The work not only finds out novel KNN-based ceramics with excellent comprehensive energy storage properties, but also provides a remarkable designing strategy for exploring a series of novel lead-free dielectric ceramics with high energy storage properties for practical applications in the future.