Boosting High Electric Breakdown Strength for Excellent Energy Storage Performance in Bi_0.5Na_0.5TiO₃-Based Lead-Free Ceramics via a High Entropy Strategy

High-performance dielectric capacitors featuring large recoverable energy storage density (W_rec) and high discharge efficiency (η) are beneficial to realize the device miniaturization, lightweight property, and sustainability of advanced pulse power systems. The obtainment of a high electric breakdown strength (E_b) is crucial for improving the energy storage performance of dielectric materials. However, as for Bi_0.5Na_0.5TiO₃ (BNT) lead-free relaxor ferroelectric ceramics, the relatively lower E_b directly limits their electrical performance improvement and practical applications. Herein, a popular high entropy strategy was employed to rationally design and prepare the (Bi_0.5Na_0.5)_x(Sr_0.25Ba_0.25La_0.25K_0.25)_(1-x)TiO₃ (BNSLBKT-x) lead-free relaxor ferroelectric ceramics based on the BNT matrix. Encouragingly, the BNSLBKT-0.2 high-entropy ceramic exhibits a high E_b of 510 kV/cm, and this can be ascribed to the refined grains and enhanced activation energy. Moreover, it is confirmed that the polar nanoregions (PNRs) exist in the BNSLBKT-0.2 ceramic by the piezoresponse force microscopy (PFM) and transmission electron microscopy (TEM) characteristics, further strengthening relaxation behaviors and decreasing remanent polarization (P_r). It is anticipated that a high W_rec of 4.6 J/cm³ and a good η of 86% are obtained in this BNSLBKT-0.2 high-entropy ceramic. More importantly, the BNSLBKT-0.2 ceramic displays excellent frequency stability of capacitive energy storage at 10-1000 Hz and good temperature stability at 20-140 °C. The fast discharge rate (τ_0.9 = 0.26 μs) and the high P_D of 49.2 MW/cm are also achieved in this BNSLBKT-0.2 ceramic. The findings demonstrate that this high entropy design is an effective strategy for developing dielectrics with excellent energy storage capability to meet the requirements of modern dielectric capacitor applications.