Ultrahigh energy storage performance in BNT-based binary ceramic via relaxor design and grain engineering

Dielectric capacitors attract much attention for advanced electronic systems owing to their ultra-fast discharge rate and high power density. However, the low energy storage density (W_rec) and efficiency (η) severely limit their applications. Herein, Bi_0.5Na_0.5TiO₃-K_0.5Na_0.5NbO₃ binary ceramic is developed to obtain excellent energy storage performance with strong relaxor behavior, together with large polarization and distorted lattice calculated by first-principles calculations. The atomic-scale local structure analysis of 0.75Bi_0.5Na_0.5TiO₃–0.25K_0.5Na_0.5NbO₃ ceramic reveals distorted polarization distribution and small polar nanoregion related with the enhanced relaxation and low hysteresis. Finite element analysis demonstrates ultrafine grain and increased grain boundary density following hot-pressing sintering are crucial factors in significantly enhancing the breakdown strength (E_b). As a result, ultrahigh W_rec of 12.39 J/cm³ and η of 87.1 % are achieved at a superhigh E_b of 713 kV/cm. Encouragingly, excellent performance of temperature, frequency and fatigue stability at 400 kV/cm are obtained, and high power density of ∼ 306 MW/cm³ as well as fast discharge speed of ∼ 23.3 ns are also realized. This work proposes a simple binary design with strong relaxor behavior, and highlights the potential of grain engineering to achieve outstanding energy storage performance with great stability and excellent charge-discharge property for pulse power devices.