Ultrahigh energy-storage in lead-free ceramic capacitors via local structure design

Dielectric capacitors are crucial energy-storage modules in pulsed- and high-power devices. However, the simultaneous enhancement in recoverable energy density (W_rec) and efficiency (η) still remains challenge owing to the restrictive relationship between the maximum polarization (P_max), remanent polarization (P_r) and electric breakdown strength (E_b). To address this, we propose a strategy of local polar structure design in BiFeO₃-based ceramics. By incorporating NaNbO₃ to create embedded, persistent polar nanoregions within a weakly polar matrix, we achieve a giant polarization difference ΔP (56.4 μC cm^-2), a low P_r (3.6 μC cm^-2) and a large E_b (66 kV mm^-1), endowing an ultrahigh W_rec of 14.5 J cm^-3 and a high η of 88%. The local structure, directly visualized via the 2D/3D atomic displacement mapping, enables a high P_max under an applied field and a low P_r at zero field, a mechanism explicitly validated by phase-field simulation. Meanwhile, the optimized microstructure and enhanced insulating property contribute to a giant E_b. This work provides insights to overcome the paradox between multiple parameters and paves a feasible route for the cutting-edge energy-storage applications.