Synergistic relaxor doping and multilayer engineering unlocking superior energy storage in lead-free NaNbO₃-based ceramic capacitors

The urgent need for sustainable and green energy storage has intensified the demand for high-performance, lead-free dielectric capacitors that couple high power density with ultra-fast charge-discharge characteristics. Herein, a novel lead-free relaxor antiferroelectric ceramic, (1-x)[0.9NaNbO₃-0.1BiFeO₃]-xBi(Mg_2/3Nb_1/3)O₃ (NN-BF-BMN), was designed by incorporating BMN as a third component to the NN-BF matrix. This synergistic approach of BMN incorporation demonstrates inducing relaxor antiferroelectric characteristics, enhancing polarization response and enabling superior energy storage performance. Resultantly, the 0.9(NN-BF)-0.1BMN bulk ceramic achieves an excellent recoverable energy density (W_rec) of 7.3 J/cm³ and a high efficiency (η) of 86.6% under an electric field (E_b) of 720 kV/cm. The optimized composition with x = 0.10 was further selected for multilayer ceramic capacitors (MLCCs) fabrication via tape casting. The MLCCs revealed a breakthrough in energy storage performance, exhibiting an ultrahigh W_rec of 12.2 J/cm³ with an outstanding η of 89.6% at a high E_b of 920 kV/cm along with thermal stability across the broader temperature range from 30 to 150 °C with little variation in W_rec (<7.1%) and η (<5.7%). Furthermore, a robust discharge time (t_0.9 = 19.2 ns), and ultra-high current density (C_D = 1598.7 A/cm²) along with substantial power density (P_D = 263.8 MW/cm³) represent a promising lead-free environmentally friendly candidate​ for next-generation advanced pulsed power applications.