Superior energy storage performance with a record high breakdown strength in bulk Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ceramics via multiple synergistic strategies

A high breakdown strength (E_b) together with a large maximum polarization (P_m) is essential for achieving a high recoverable energy density (W_rec) in energy storage dielectric ceramics. However, meeting the urgent need for practical applications remains a challenge due to the intrinsic properties of bulk dielectric ceramics. Herein, a composition and structure optimization strategy combined with a two-step sintering (TSS) process is proposed to design and fabricate (1−x)Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃−xBi(Mg_1/2Sn_1/2)O₃ (BCZT-BMSx-TSS) lead-free ceramics. Highly dynamic locally polar nano-regions (PNRs) are formed via composition optimization, exhibiting a very high P_m and energy storage efficiency (η). Compared to the traditional one-step sintering (OSS) process, the TSS process results in a composition with finer grain size and higher density, dramatically increasing E_b. As a result, an ultrahigh energy storage performance with W_rec ∼ 10.53 J cm⁻³ and η ∼ 85.71% is achieved for the BCZT-BMSx-TSS (x = 0.08) ceramic which is attributed to a record high E_b ∼ 830 kV cm⁻¹ and a large P_m ∼ 44.66 μC cm⁻². Complex impedance spectroscopy revealed that the activation energies of the bulk and grain boundary counterparts significantly increased, suggesting an increase in insulation resistance and a decrease in oxygen vacancies, which is the main reason for the high E_b value. In addition, excellent thermal/frequency stability is achieved in both energy density and efficiency, along with good charge–discharge performance. These findings suggest that BCZT-based lead-free ceramics have the potential for practical use in the future.