Abstract In this study, (1‐ x )Bi 0.5 Na 0.46 Li 0.04 TiO 3 ‐ x Bi 0.9 Sm 0.1 ScO 3 (BNLT‐ x BSS) relaxation ferroelectric ceramics were successfully prepared by conventional solid phase method. Multiscale analyses such as XRD and EDS confirmed that these ceramics form a solid solution with a single‐phase perovskite structure. As the doping amount of Bi 0.9 Sm 0.1 ScO 3 increases, a smaller grain size is obtained at x = 0.1, and the breakdown strength increases to 350 kV/cm, resulting in a higher W rec = 5.92 J/cm 3 , η = 82.2%. In addition, these ceramics demonstrate other excellent properties: (1) Thermal stability, with W rec of 2.85 ± 0.06 J/cm 3 and η of 86 ± 1.2% in the temperature range of 35°C–200°C; (2) Frequency stability, with W rec of 2.9 ± 0.05 J/cm 3 and η of 85.8 ± 1.1% in the frequency range of 5–150 Hz; (3) Fast charge/discharge rate, t 0.9 is about 0.18 µs. The comprehensive experiments show that the ceramic can be used as a pulse capacitor in high‐temperature environments and has great development potential.