Display omitted •A novel Bi1/2K1/2TiO3-based ergodic relaxor ceramic was designed and prepared .•The ceramic displayed large Wrec (3.07 J/cm3) and high η (>88%).•The variation of Wrec is less than ±2% between 30 and 150 °C. Relaxor ferroelectrics are attractive for the high energy storage density. However, the polarization responses of most relaxor ferroelectrics are sensitive to temperature, thus leading to thermal-dependent energy storage properties. In this work, 0.5Bi1/2K1/2TiO3–0.5SrTiO3 (0.5BKT–0.5ST) and 0.95(0.5Bi1/2K1/2TiO3–0.5SrTiO3)–0.05Bi(Zn1/2Ti1/2)O3 (BKT–ST–0.05BZT) ceramics were prepared using the solid-state reaction method. Both compositions showed an average cubic structure, with a relaxor-type dielectric anomaly. The rather low remanent polarization and delayed saturated polarization indicated the formation of the ergodic polar nano regions. Benefitting from the Bi(Zn1/2Ti1/2)O3 modification, the recoverable energy storage density (Wrec) reached 3.07 J/cm3 because of the enhanced polarization and increased bandgap. Meanwhile, BKT–ST–0.05BZT exhibited a high storage efficiency (η > 88%). When the specimen was heated from 30 °C to 150 °C, Wrec under the maximum electric field Em of 150 kV/cm varied from 1.58 to 1.63 J/cm3 (＜ ±2%).