Ferroelectric materials are considered to be the most competitive energy storage materials for applications in pulsed power electronics due to excellent charge–discharge properties. However, the low energy storage density is the primary problem limiting their practical application. In this study, (1$-x$)Na${}_{0.5}$Bi${}_{0.5}$TiO₃ – $x$Sr${}_{0.7}$La${}_{0.2}$TiO₃[(1$-x$)NBT–$x$SLT] ferroelectric ceramics are found to exhibit excellent energy storage performances through a synergistic strategy. As the SLT concentration increases, the relaxation characteristic increases significantly and the breakdown strength increases dramatically from 150 kV/cm to 220 kV/cm. The recoverable energy storage density of the 0.55NBT–0.45SLT ceramic is 2.86 J/cm³ with an energy storage efficiency of 88% under an electric field of 220 kV/cm. Furthermore, the ceramic with$x$ = 0.45 mol exhibited excellent energy storage stability in the ranges of 20–180${}^{\circ }$C (temperature) and 1–125 Hz (frequency). These excellent properties demonstrate the potential of (1$-x$)NBT–$x$SLT ceramics when used as dielectric capacitors in pulsed power systems.Ferroelectric materials are considered to be the most competitive energy storage materials for applications in pulsed power electronics due to excellent charge–discharge properties. However, the low energy storage density is the primary problem limiting their practical application. In this study, (1$-x$)Na${}_{0.5}$Bi${}_{0.5}$TiO₃ – $x$Sr${}_{0.7}$La${}_{0.2}$TiO₃[(1$-x$)NBT–$x$SLT] ferroelectric ceramics are found to exhibit excellent energy storage performances through a synergistic strategy. As the SLT concentration increases, the relaxation characteristic increases significantly and the breakdown strength increases dramatically from 150 kV/cm to 220 kV/cm. The recoverable energy storage density of the 0.55NBT–0.45SLT ceramic is 2.86 J/cm³ with an energy storage efficiency of 88% under an electric field of 220 kV/cm. Furthermore, the ceramic with$x$ = 0.45 mol exhibited excellent energy storage stability in the ranges of 20–180${}^{\circ }$C (temperature) and 1–125 Hz (frequency). These excellent properties demonstrate the potential of (1$-x$)NBT–$x$SLT ceramics when used as dielectric capacitors in pulsed power systems.