Multilayer pulsed power ceramic capacitors require that dielectric ceramics possess not only large recoverable energy storage density (W-rec) but also low sintering temperature (<950 degrees C) for using the inexpensive metals as the electrodes. However, lead-free bulk ceramics usually show low W-rec (<2 J/cm(3)) and high sintering temperature (>1150 degrees C), limiting their applications in multilayer pulsed power ceramic capacitors. In this work, large W-rec (similar to 4.02 J/cm(3) at 400 kV/cm) and low sintering temperature (940 degrees C) are simultaneously achieved in 0.9(K0.5Na0.5)NbO3-0.1Bi(Mg2/3Nb1/3)O-3-1.0 mol% CuO ceramics prepared using transition liquid phase sintering. W-rec of 4.02 J/cm(3) is 2-3 times as large as the reported value of other (Bi0.5Na0.5)TiO3 and BaTiO3-based lead-free bulk ceramics. The results reveal that 0.9(K0.5Na0.5)NbO3-0.1Bi(Mg2/3Nb1/3)O-3-1.0 mol% CuO ceramics are promising candidates for fabricating multilayer pulsed power ceramic capacitors.