MgO–Driven High-Entropy Engineering in (Bi _0.5 Na _0.5 )TiO ₃ –Based Ceramics for Superior Energy Storage Performance

High-performance dielectric capacitors are essential for advancing the miniaturization of pulsed power devices. High-entropy design has recently emerged as a potent strategy for developing ceramics with superior energy storage properties. In this study, a series of lead-free (Bi 0.5 Na 0.5 )TiO 3 -based energy storage ceramics were designed via MgO-driven high-entropy engineering. Initially, (Ca 0.5 Ba 0.5 )(Zr 0.5 Hf 0.5 )O 3 (CBZH) was introduced into (Bi 0.5 Na 0.5 )TiO 3 -(Sr 0.7 Bi 0.2 )TiO 3 (BNT-SBT) to raise configurational entropy and disrupt long-range ferroelectric order. Subsequently, MgO was deliberately incorporated into the BNT-SBT-CBZH system to activate and intensify high-entropy effects. The MgO doping drives the phase evolution from the rhombohedral to tetragonal phase, refines grains, widens the bandgap, promotes the formation of polar nanoregions, and simultaneously enhances relaxation behavior. These MgO-enabled modifications work synergistically to maintain a high polarization difference while significantly increasing the breakdown strength ( E b ). Consequently, an outstanding recoverable energy density ( W rec ∼ 8.30 J/cm 3 ) and high efficiency (η ∼ 85.0%) are achieved in 10 mol % MgO-doped high-entropy ceramic under a large E b of 647 kV/cm, along with good thermal stability, frequency stability, and charge–discharge capability. This work demonstrates that the MgO-driven high-entropy engineering offers an effective pathway for developing lead-free dielectric ceramics with superior comprehensive energy storage properties.