Remarkable energy storage performance of BiFeO₃-based high-entropy lead-free ceramics and multilayers

Electrostatic energy storage capacitors featuring fast charge–discharge capability play an indispensable role in pulsed power capacitors. However, the inverse correlation between polarization and dielectric breakdown strength (E_b) is the main obstacle limiting the access to high recoverable energy storage density (W_rec) and high efficiency (η). In this work, we designed a series of novel (1-x)BiFeO₃-x(Ba_0.2S_r0.2Ca_0.2Bi_0.2Na_0.2)TiO₃ (BF-xBSCBNT, x = 0.4–1.0) high-entropy lead-free relaxor ferroelectric ceramics. The synergy of refined grain size, broadened band gap, and core–shell microstructure is well-investigated by experimental results and phase-field simulations. High polarization difference is achieved by the strengthened relaxation behavior and the dominated polar nanoregions (PNRs). Both high W_rec of 6.0 J/cm³ and η of 81.1 % are achieved in the BF–0.8BSCBNT ceramics. In particular, a remarkable W_rec of 12.1 J/cm³ with a η of 86.1 % are obtained in the multilayer ceramic capacitors (MLCCs) fabricated from the x = 0.8 composition. Excellent temperature stability (<4.0 % in the range of 25–140 °C) and frequency stability (<6.2 % in the range of 1–500 Hz) are also achieved in MLCCs. The excellent energy storage performance demonstrates that high-entropy strategy is effective to develop novel lead-fee ceramics and devices for energy storage applications.