Ultrahigh Energy Storage in Relaxor Ferroelectric Ceramics with Core–Shell Grains

The achievement of record-high energy storage performance in relaxor-ferroelectric bulk ceramics represents a major advancement in the field of dielectric capacitors. Nonetheless, a trade-off between breakdown strength and polarization has typically limited the optimization of overall performance. Here, guided by a rational composition design, K_0.5Na_0.5NbO₃-based bulk ceramics are fabricated with grain core–shell structures and polymorphic nanodomains, leading to a synergistic enhancement of breakdown strength and polarization. This results in an unprecedented recoverable energy density of ≈20.4 J·cm⁻³ and an energy efficiency of ≈90% at an electric field of ≈1020 kV·cm⁻¹. Additionally, the ceramics exhibits excellent charge–discharge performance, including a high discharge energy density of ≈6.0 J·cm⁻³ and an ultrashort discharge time of ≈42 ns at 500 kV·cm⁻¹, along with superior reliability and stability. These advancements are expected to provide valuable insights for the exploration and utilization of advanced dielectric materials.