The micrometer scale grain size and large remnant polarization of Bi0.5Na0.5TiO3 (BNT) ferroelectric ceramics severely constrain the breakdown strength and energy efficiency, respectively, restricting their energy storage application despite their large polarization. Hereby, superior energy storage performance is reported by a synergistic strategy of introducing Sr0.7Bi0.2TiO3 (SBT) relaxor ferroelectrics and a solution combustion synthesis (SCS) method. The BNT-SBT solid-solution ceramics are comparatively investigated by the two methods, conventional sintering (CS) and SCS. An ultrafine average grain size of ∼ 0.39 μm was obtained in the SCS-derived ceramic, and thus exhibits an ultra-high critical electric field of 548 kV/cm, and a high recoverable energy density of ∼ 5.69 J/cm3. Those key energy storage parameters are superior to those of the previous reported samples prepared by the CS method. Meanwhile, a high energy efficiency ∼90%, a large power density of ∼ 130.44 MW/cm3 (at 320 kV/cm), and an ultrafast discharge time of ∼ 61.7 ns are also achieved. This study indicates that grain engineering combing with chemical design is an effective way to enhance the dielectric energy storage performance.