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 (Wrec) and efficiency (η) still remains challenge owing to the restrictive relationship between the maximum polarization (Pmax), remanent polarization (Pr) and electric breakdown strength (Eb). 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 Pr (3.6 μC cm-2) and a large Eb (66 kV mm-1), endowing an ultrahigh Wrec 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 Pmax under an applied field and a low Pr at zero field, a mechanism explicitly validated by phase-field simulation. Meanwhile, the optimized microstructure and enhanced insulating property contribute to a giant Eb. This work provides insights to overcome the paradox between multiple parameters and paves a feasible route for the cutting-edge energy-storage applications.