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Achieving high energy storage density (ESD), energy storage efficiency (η) and exceptional stability is deemed the foremost challenge for the application of lead-free dielectric energy storage materials. Relaxor ferroelectric (REF) ceramics are one of the most promising candidate materials for energy storage materials by virtue of their low remnant polarization, hysteresis, and high permittivity. Here, we demonstrated that excellent energy storage properties (high recoverable energy storage density Wrec of 5.23 J cm−3 and 5.47 J cm−3 with high η of 89.7% and 90.6%) are achieved in Hf-modified (0.7Ba0.55Sr0.45–0.3Bi0.5Na0.5)TiO3 (BSBNT) relaxor ferroelectric ceramics. Analysis of a first order reversal curve (FORC) and piezoresponse force microscopy (PFM) indicate that the incorporation of Hf can effectively inhibit the polarization nonlinearity and reduce the size of polar nanoregions, resulting in improved energy density and efficiency. Additionally, the introduction of Hf greatly enhances the breakdown strength by improving the electric insulation, suppressing the electronic transition and boosting the bandgap. For practice application, the (0.7Ba0.55Sr0.45–0.3Bi0.5Na0.5)(Ti0.85Hf0.15)O3 ceramics also show excellent temperature (−95 to 125 °C) and frequency (1–1000 Hz) stability at 250 kV cm−1. Meanwhile, the energy storage properties (ESPs) of ceramics can maintain stability even after 106 hysteresis cycles. This work provides a feasible approach that can be employed to develop high-performance lead-free capacitors in high-power electronics and pulse power systems. [ABSTRACT FROM AUTHOR]