Giant Capacitive Energy-Storage in BaTiO₃-Based Fine-Grained Relaxors via Local Polarization Enhancement

Pb-free dielectric energy storage capacitors are core components in advanced pulse-power electronic systems and devices. However, the relatively low energy density (W_rec) for the industrial pillar BaTiO₃ (BT)-based capacitors remains a significant obstacle for their cutting-edge applications, due to their low intrinsic polarization and breakdown strength (E_B). Herein, through chemical composition and local structure design, a giant W_rec of 15.1 J cm^-3 along with a high efficiency (η) of 85% is demonstrated in a BT-based relaxor bulk ceramic. This is achieved by introducing rare A-site polarization enhancement substitution (Bi_0.5Na_0.5)²⁺ ions in combination with B-site fastest relaxation alternative (Zn_1/3Nb_2/3)⁴⁺ ions to enhance local polarization and refine grain structure. Atomic-level local structure analysis has revealed that the diversified atomic polar displacement vectors, characterized by largely extended magnitude and heterogeneous directions, assemble into highly polarizable clusters at several unit-cells scale. Consequently, it exerts a large polarization difference (ΔP) of 49 µC cm^-2 and a high E_B of 90 kV mm^-1. Moreover, a giant power density (677 MW cm^-3), high discharge energy density (3.9 J cm^-3), and excellent stability are achieved. This study overcomes the current W_rec bottleneck of ≈10 J cm^-3 in BT-based bulk ceramics, presenting an approach to optimize the energy storage performance of Pb-free relaxors.