Outstanding Energy Storage Performance in High-Hardness (Bi0.5K0.5)TiO3-Based Lead-Free Relaxors via Multi-Scale Synergistic Design

Lead-free dielectric ceramics with ultrahigh energy storage performance are the best potential stocks used in next-generation advanced pulse power capacitors. Here, an ultrahigh recoverable energy storage density W rec of ≈7.57 J cm −3 and a large efficiency η of ≈81.4% are first realized in (Bi 0.5 K 0.5 )TiO 3 (BKT)-based relaxor ferroelectric ceramics with an ultrahigh Vickers hardness H v ≈ 8.63 Gpa by adding BaTiO 3 and NaNbO 3 in order to synergistically design the domain and microstructure in multiscale, leading to the existence of ultrasmall polar nanoregions, ultrafine grain size, compact grain boundaries, dense microstructure, and large band gap E g simultaneously. Encouragingly, an excellent energy storage temperature stability ( W rec ≈ 4.31 ± 0.25 J cm −3 , η ≈ 86 ± 5%, 20–200 °C), frequency stability ( W rec ≈ 5.14 ± 0.12 J cm −3 , η ≈ 81.3 ± 1.2%, 5–100 Hz), and excellent charge/discharge performance (power density P D ≈ 103.2 MW cm −3 , discharge energy density W D ≈ 2.4 J cm −3 , discharge rate t 0.9 ≈ 130 ns) are also achieved in BKT-based ceramics. The results demonstrate that BKT-based ceramics can be very competitive lead-free relaxors for energy storage capacitors in pulsed power devices.