Next-generation advanced high/pulsed power capacitors urgently require dielectric materials with outstanding energy storage performance. Bi_0.5Na_0.5TiO₃-based lead-free materials exhibit high polarization, but the high remanent polarization and large polarization hysteresis limit their applications in dielectric capacitors. Herein, high-entropy perovskite relaxor ferroelectrics (Na_0.2Bi_0.2Ba_0.2Sr_0.2Ca_0.2)(Ti_1−x%Zr_x%)O₃ are designed by adding multiple ions in the A-site and replacing the B-site Ti⁴⁺ with a certain amount of Zr⁴⁺. The newly designed system showed high relaxor feature and slim polarization–electric (P–E) loops. Especially, improved relaxor feature and obviously delayed polarization saturation were found with the increasing of Zr⁴⁺. Of particular importance is that both high recoverable energy storage density of 6.6 J/cm³ and energy efficiency of 93.5% were achieved under 550 kV/cm for the ceramics of x = 6, accompanying with excellent frequency stability, appreciable thermal stability, and prosperous discharge property. This work not only provides potential dielectric materials for energy storage applications, but also offers an effective strategy to obtain dielectric ceramics with ultrahigh comprehensive energy storage performance to meet the demanding requirements of advanced energy storage applications.

Both sustainable development in environment and safety of high-power systems require to develop a novel lead-free dielectric capacitor with high energy density (W_rec) at low applied electric field. In this work, a remarkably high W_rec of 2.9 J/cm³ accompanying with energy storage efficiency of 56% was achieved in Ag_0.9Sr_0.05NbO₃ ceramic at a low applied electric field of 190 kV/cm, by improving anti-ferroelectricity and introducing relaxor behaviour. The improved anti-ferroelectric stability was attributed to the decreased tolerance factor and average electronegativity difference, while the relaxor behaviour was associated with the increased disordered local structure by Sr-doping. Moreover, the Ag_0.9Sr_0.05NbO₃ ceramics also exhibited outstanding temperature stability in energy density with small variation less than 5% over 20–140 ℃. The results indicate that the Ag_0.9Sr_0.05NbO₃ ceramic is a promising candidate for low-electric-field driving capacitors.