Enhanced energy storage properties under low electric fields in (Bi0.5Na0.5)TiO3-based relaxor ferroelectrics via a synergistic optimization strategy

•A synergism strategy was adopted based on complex-ion substitution and tape casting.•Achieving a high Wrec of 4.30 J/cm3 at a low E of 230 kV/cm in lead-free ceramics.•Superior thermal & frequency stability and fast discharge speed were also obtained.•Mechanisms for the substantially enhanced energy storage properties were visualized. Lead-free dielectric ceramics with high energy storage performance (ESP) are strongly desired for pulse power capacitor applications. However, low recoverable energy storage density (Wrec) under low electric fields seriously hinders their applications in miniatured and integrated electronic devices. In this work, we adopted a synergism strategy to develop (Bi0.5Na0.5)0.7Sr0.3Ti(1-x)(Al0.5Nb0.5)xO3 (BNST-xAN) ceramics with substantially enhanced low-field ESP through combining composition design and tape-casting approaches. Complex-ion substitution of (Al0.5Nb0.5)4+ for Ti4+ shifted the temperature of maximum dielectric constant towards room temperature direction, made relaxor behavior stronger and promoted formation of highly dynamic nanodomains, thus reducing the remanent polarization. Besides, refined submicron grains and improved densification behavior were achieved in those ceramics fabricated by tape casting, further increasing the breakdown strength. Consequently, a large Wrec of 4.30 J/cm3 was achieved at a low electric field of 230 kV/cm at x = 0.10, which is superior to previously reported lead-free energy storage ceramics under low electric fields. Moreover, our ceramics exhibited brilliant thermal endurance (20–140 °C) and frequency stability (0.2–200 Hz) together with fast discharge speed. These characteristics suggest the great potential of the BNST-0.10AN ceramic for low-field and high-performance energy storage capacitor applications.