Enhanced comprehensive energy storage properties of lead-free KNN based ceramics through composition optimization strategy.

• Excellent recoverable energy density W rec value (∼8.25 J/cm3) and a high η (∼71.26 %) are simultaneously obtained at a high BDS of 840 kV/cm. • KNN-0.075BLN-NN ceramics show good comprehensive energy storage performances and good mechanical properties simultaneously. • The phase field simulation is used to study the characteristic of electric breakdown and the effect of grain size on the breakdown strength. As one of the most potential lead-free dielectric capacitors in pulsed power systems, K 0.5 Na 0.5 NbO 3 (KNN)-based ceramic possesses comparatively high dielectric breakdown strength (BDS) due to its particular submicron grains. Nonetheless, it is hard to improve both the energy efficiency η and the recoverable energy density W rec of potassium sodium niobate ceramic at the same time. Herein, a composition optimization strategy is used, Bi(Li 0.5 Nb 0.5)O 3 (BLN) as a second component and NaNbO 3 (NN) as a third component are introduced into KNN-based ceramic. It is corroborated that BLN content facilitates the growth of polar nano-regions (PNRs), and then strengthens the relaxation behavior, lows the remnant polarization P r and upgrades the maximum polarization P max value of the ceramic. A transition from ferroelectricity to relaxation ferroelectricity occurred and an ultrahigh W rec of 10.03 J/cm3 with a η of 64.15 % and the BDS of 1140 kV/cm are gained in KNN-0.100BLN-NN ceramic, W rec of 8.25 J/cm3, η of 71.26 % and the BDS of 840 kV/cm are obtained in KNN-0.075BLN-NN ceramic. Besides, the KNN-0.075BLN-NN ceramic exists not only fine energy storage properties, but also high hardness and good temperature and frequency stability, confirming it's a feasible material to be applied in pulsed power systems. [ABSTRACT FROM AUTHOR]