Ultrahigh energy storage density in (Bi_0.5Na_0.5)_0.65Sr_0.35TiO₃-based lead-free relaxor ceramics with excellent temperature stability

High-performance dielectric ceramic capacitors are considered as one of the great hopeful apparatuses to solve the energy crisis and environmental pollution. However, the low energy storage density severely limits their further development. Herein, an ultrahigh recoverable energy density (W_rec) of 8.46 J/cm³ with excellent efficiency of 85.9% under 522 kV/cm is obtained in 0.90(Bi_0.5Na_0.5)_0.65Sr_0.35TiO₃-0.10Bi(Mg_0.5Zr_0.5)O₃ ceramic by the synergistic effect of delayed polarization saturation and improved breakdown field (E_b). The introducing of Bi(Mg_0.5Zr_0.5)O₃ induces the quenched random field and increases the number of high dynamic polar nano-domains, which inhibits the forming of the long-range polar order and suppresses the early polarization saturation. Besides, the refined grains and compact structure reduce the oxygen vacancies concentration and enhance the activation energy, giving rise to higher E_b. Furthermore, the ceramic for x = 0.10 also displays outstanding thermal stability at 0–200 °C (with W_rec > 4.74 J/cm³ at 200 ℃ and the variation being only ~12.4%) due to the stable local structure and temperature-insensitive dielectric constant. Our work shows that the 0.90(Bi_0.5Na_0.5)_0.65Sr_0.35TiO₃-0.10Bi(Mg_0.5Zr_0.5)O₃ is a powerful competitor in next-generation energy storage materials and high temperature dielectric ceramic capacitors.