Ultrahigh energy-storage density of a lead-free 0.85Bi0.5Na0.5TiO3–0.15Ca(Nb0.5Al0.5)O3 ceramic under low electric fields

Ultrahigh recoverable energy storage density ( W rec = 4.41 J cm −3 ) and efficiency ( η = 88%) at low electric field (210 kV cm −1 ), over wide frequency (10–100 Hz) and temperature (20–200 °C) were achieved simultaneously for 0.85Bi 0.5 Na 0.5 TiO 3 -0.15Ca(Nb 0.5 Al 0.5 )O 3 ceramics.