• 0.90(BNT-ST)-0.10BNN ceramic possesses a desired W rec of 4.1 J/cm 3 and η of 83.15% at 250 kV/cm. • W rec and η are both insensitive to thermal stimulus over 25–120 °C. • 0.90(BNT-ST)-0.10BNN ceramic exhibits a fast discharge speed ( t 0.9 = 62.4 ns). • The improved properties are explained by first order reversal curve distribution. The electrical and electronic devices become more and more integrated and miniaturized. It is necessary to develop high performance lead-free energy storage ceramics. In this work, new relaxor ferroelectric (1-x)(0.76Bi 0.5 Na 0.5 TiO 3 -0.24SrTiO 3 )-xBi(Ni 2/3 Nb 1/3 )O 3 ceramics were prepared by the traditional solid-state reaction method. Particularly, the 0.90(BNT-ST)-0.10BNN ceramic exhibits the excellent recoverable energy storage density ( W rec = 4.1 J/cm 3 ) and efficiency ( η = 83.15%) under a low electric field (250 kV/cm). The 0.90(BNT-ST)-0.10BNN ceramic has excellent stability between 25 °C and 120 °C. In addition, an ultrahigh power density of 49.8 WM/cm 3 and a fast charge-discharge rate ( t 0.9 = 62.4 ns) can be obtained simultaneously. These properties indubitably reflect that the (1-x)(BNT-ST)-xBNN ceramics have a great potential for the applications of high energy storage capacitors.