Significantly improved energy storage performances of K0.5Na0.5NbO3 lead-free ceramics via a composition optimization strategy

Abstract

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 K_0.5Na_0.5NbO₃ (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 (Mg_2/3Ta_1/3)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 (η) of 87% are realized simultaneously for the (1 − x)K_0.5Na_0.5NbO₃–xBi(Mg_2/3Ta_1/3)O₃ (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 η below 10% is verified. All these merits indicate that the doped Bi(Mg_2/3Ta_1/3)O₃ 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.