Synergistic enhancement of energy storage performance in BNT-based ceramics through the co-doping of multiple A-site ions

The pursuit of high-performance energy storage (ES) materials has placed (Bi_0.5Na_0.5)TiO₃ (BNT)-based ceramics at the forefront of research, owing to their exceptional dielectric properties and environmentally friendly composition. This study explores the synergistic enhancement of ES performance in BNT-based ceramics achieved through A-site co-doping with Ca²⁺, Sr²⁺, and Ba²⁺ ions. By integrating electrical testing with thermodynamic analysis, we unveil the mechanisms by which ion doping influences the electrical properties, ES parameters, and free energy of these materials. Our findings reveal that the co-doping strategy significantly widens the band gap and reduces the free energy of BNT-based ceramics, leading to remarkable improvements in recoverable energy density (W_rec) and energy storage efficiency (η). Additionally, the application of the viscous polymer process (VPP) enhances grain refinement, densification, and dielectric breakdown strength, culminating in the development of 0.4BNT-0.6(Ba_0.15Sr_0.55Ca_0.3)TiO₃ (VPP) ceramics with an ultrahigh W_rec of 7.34 J/cm³ and η of 84.4% at 540 kV/cm. These samples are noteworthy for their remarkable thermal stability, which allows them to sustain steady ES performance across a wide operating temperature range of 20–140 °C. This work demonstrates the transformative potential of multi-doping strategies and advanced processing techniques in tailoring the properties of BNT-based ceramics. The insights presented here provide a robust framework for the design of next-generation lead-free ES materials, offering a promising pathway for sustainable ES applications.