As a critical research direction in dielectric energy storage applications, achieving a synergistic balance between a high breakdown strength (E_b) and high polarization remains a significant challenge for lead-free relaxor ferroelectrics. In this work, we proposed a rational chemical design strategy by simultaneously doping A- and B-site ions into classical BaTiO₃ (BT) ferroelectrics, breaking the long-range ordered polarization, increasing the maximum polarization (P_m), reducing the remnant polarization (P_r), and improving the E_b. An ultrahigh recoverable energy storage density (W_rec) of 15.3 J/cm³, accompanied by a high energy storage efficiency (η) of 82.4%, was finally achieved at 1150 kV/cm. Impedance spectroscopy and microstructure analyses reveal enhanced activation energies for both grains and grain boundaries, as well as multiphase coexistence and formation of polar nanoregions (PNRs). This collectively contributes to an elevated breakdown strength while maintaining robust polarization. This study presents a promising pathway to achieve advanced energy storage performance in lead-free dielectric systems.

Dielectric pulse capacitors are of great concerns due to the fast charge/discharge rate and high-power density over traditional counterparts. However, energy-storage capacitor in power converters typically works at a large DC-biased voltage, where the energy-storge density (W_dis) and efficiency (η) will dramatically decay, thus fatally blocks its further applications. Herein, we proposed a synergistic strategy to achieve a comprehensively improved energy storage property in Bi_1-xNa_xTiO₃-NaNbO₃ based ceramics. Configuration of chemical composition optimization, A-site vacancy engineering, grain size refinement, and sample thickness reduction were designed in the ceramics. Finally, an optimum W_dis of 8.04 J/cm³ and an ultrahigh η of 85% was achieved for the 0.50 (0.95Bi_0.52Na_0.44TiO₃-0.05SrZrO₃)-0.50NaNbO₃ composite under a breakdown strength of 630 kV/cm, along with a stable DC-biased capacitance retention. Additionally, a superior performance stability was affirmed in a wide temperature/frequency range (25–150 ℃ and 1–100 Hz, respectively). It also exhibits an impressive ability in fatigue resistance after being subjected to up to 10⁶ cycles, which enable it to be a suitable candidate for high energy density storage devices.