Significantly improved energy storage performances of K_0.5Na_0.5NbO₃ lead-free ceramics via a composition optimization strategy

Ceramic dielectric materials for energy storage have been widely investigated because of the superior advantages of a rapid charge/discharge speed and ultra-high power density. However, there are no significant breakthroughs in integrative energy storage density and efficiency improvements. In this work, a composition optimization scheme for boosting the synergistic energy storage performances of K0.5Na0.5NbO3 (KNN)-based ceramics has been proposed, namely diminishing the grain size to the sub-micron scale for enhancing the breakdown strength (BDS) and generating nanodomains for reducing the remanent polarization (P-r) by incorporating the Bi3+ ion and (Mg2/3Ta1/3)(3+) multiple ions into the A-site and B-site of the KNN matrix. As a result, it is confirmed that an ultrahigh recoverable energy storage density (W-r) of 6.14 J cm(-3) and a high energy storage efficiency (& eta;) of 87% are realized simultaneously for the (1 - x)K0.5Na0.5NbO3-xBi(Mg2/3Ta1/3)O-3 (KNN-BMT) ceramics at x = 0.15 under 720 kV cm(-1), which surpass most other reported lead-free ceramics. Moreover, the outstanding thermal and frequency stability associated with variation rates of W-r and & eta; below 10% is verified. All these merits indicate that the doped Bi(Mg2/3Ta1/3)O-3 component leads to optimized energy storage performances. This work may attract significant attention in exploring ceramic dielectric capacitors with excellent properties for energy storage applications.