The development and use of high-performance and environmentally friendly energy storage capacitors are urgently demanded. Despite extensive research efforts, the performance of existing lead-free dielectric ceramics is barely satisfactory. In this work, a novel lead-free 0.78NaNbO₃–0.22Bi(Mg_2/3Ta_1/3)O₃ (0.22BMT) linear-like relaxor ferroelectric with ultrahigh energy storage capability and ultrahigh efficiency was designed and synthesized via a local random field strategy. To our satisfaction, an ultrahigh recoverable energy density (W_rec, 5.01 J cm⁻³) and an ultrahigh energy efficiency (η) of 86.1% were achieved simultaneously, which are superior to those of other reported lead-free systems. In addition, excellent temperature, frequency and fatigue stabilities (variation of W_rec < 8% over 20–200 °C, W_rec < 3% after 1–100 Hz and 10⁴ cycles) were observed. More importantly, the 0.22BMT ceramic exhibited a large current density (C_D ∼ 537.9 A cm⁻²), an extremely high power density (P_D ∼ 37.7 MW cm⁻³), and an ultrafast discharge time (t_0.9 ∼ 23 ns). The impedance analysis demonstrated that the introduction of BMT was beneficial for the improvement of the insulation ability and breakdown strength (E_b) of the 0.22BMT ceramic. Additionally, nonisovalent Mg²⁺ and Ta⁵⁺-filled Nb⁵⁺ on the B-site with low average electronegativity generated a random local field, which enhanced the ion bonding, destroyed the long-range order and led to decreased remnant polarization (P_r). These results indicate that this new strategy is a feasible and efficacious means to simultaneously achieve ultrahigh W_rec, superior η and excellent thermal stability in NN-based lead-free ceramics. Furthermore, this work has further broadened the scope of research and the application of the NN-based ceramics.

NaNbO ₃ -based (NN) energy storage ceramics exhibit high breakdown electric field strength ( E _b ) with large recoverable energy storage density ( W _rec ).

Ceramic dielectric capacitors have a broad scope of application in pulsed power supply devices. Relaxor behavior has manifested decent energy storage capabilities in dielectric materials due to its fast polarization response. In addition, an ultrahigh energy storage density can also be achieved in NaNbO₃ (NN)-based ceramics by combining antiferroelectric and relaxor characteristics. Most of the existing reports about lead-free dielectric ceramics, nevertheless, still lack the relevant research about domain evolution and relaxor behavior. Therefore, a novel lead-free solid solution, (1−x)NaNbO₃−xBi(Zn_0.5Sn_0.5)O₃ (abbreviated as xBZS, x = 0.05, 0.10, 0.15, and 0.20) was designed to analyze the domain evolution and relaxor behavior. Domain evolutions in xBZS ceramics confirmed the contribution of the relaxor behavior to their decent energy storage characteristics caused by the fast polarization rotation according to the low energy barrier of polar nanoregions (PNRs). Consequently, a high energy storage density of 3.14 J/cm³ and energy efficiency of 83.30% are simultaneously available with 0.10BZS ceramics, together with stable energy storage properties over a large temperature range (20–100 °C) and a wide frequency range (1–200 Hz). Additionally, for practical applications, the 0.10BZS ceramics display a high discharge energy storage density (W_dis ≈ 1.05 J/cm³), fast discharge rate (t_0.9 ≈ 60.60 ns), and high hardness (H ≈ 5.49 GPa). This study offers significant insights on the mechanisms of high performance lead-free ceramic energy storage materials.