Achieving high energy storage density under moderate electric field in K_0.5Na_0.5NbO₃ ceramics via multiple synergistic optimization strategies

Currently, research on energy storage technologies primarily focuses on dielectric capacitors, supercapacitors, batteries, and solid oxide fuel cells. Lead-free ceramic-based dielectric capacitors are considered highly promising materials for advanced pulsed power applications due to their distinct advantages, including high power density, rapid charge/discharge rates, and environmental friendliness. However, achieving high recoverable energy densities (W_rec > 5 J/cm³) typically requires the application of large external electric fields (>400 kV/cm), which pose significant risks to electrically insulated systems and hinder the further advancement of ceramic capacitors. Guided by multiple synergistic strategies, this study achieves a high W_rec of 6.0 J/cm³ with simultaneous an exceptional energy storage efficiency (η) of 71 % at moderate electric fields of 400 kV/cm is achieved in the (Sr_0.7La_0.2)(Mg_1/3Ta_2/3)O₃ (SLMT) modified K_0.5Na_0.5NbO₃ ceramic. The outstanding W_rec can primarily be attributed to its ultra-high polarization difference (ΔP) of approximately 42.2 μC/cm², which results from the approximate core-shell structure with varying levels of polarization. Additionally, the incorporation of SLMT enhances the ceramics' dense microstructures, fine grains, and high intrinsic resistivity, thereby improving their breakdown electric field. This study highlights the potential of 0.91KNN-0.09SLMT ceramic as a promising dielectric material for advanced energy storage capacitors operating under moderate electric fields.