Boosting High Electric Breakdown Strength for Excellent Energy Storage Performance in Bi0.5Na0.5TiO3-Based Lead-Free Ceramics via a High Entropy Strategy

High-performance dielectric capacitors featuring large recoverable energy storage density (Wrec) 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 (Eb) is crucial for improving the energy storage performance of dielectric materials. However, as for Bi0.5Na0.5TiO3 (BNT) lead-free relaxor ferroelectric ceramics, the relatively lower Eb directly limits their electrical performance improvement and practical applications. Herein, a popular high entropy strategy was employed to rationally design and prepare the (Bi0.5Na0.5)x(Sr0.25Ba0.25La0.25K0.25)(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 Eb 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 (Pr). It is anticipated that a high Wrec 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 (τ0.9 = 0.26 μs) and the high PD 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.