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 (Wrec) and energy-storage efficiency (η) 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 (Tmax) and the Burns temperature (TB) to room temperature, for solving the bottleneck. (1-x)K0.5Na0.5NbO3-xBi(Ni0.5Zr0.5)O3 (KNN-BNZ) ceramics were chosen as an example to illustrate the validity of this strategy. An ultrahigh Wrec 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 KNN-based ceramics. Most importantly, this high Wrec was accompanied by a high η 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.