Boosting energy storage performance in Na_0.5Bi_0.5TiO₃-based lead-free ceramics modified by a synergistic design

Na_0.5Bi_0.5TiO₃-based relaxor ferroelectric ceramics have attracted widespread attention due to their potential applications in energy storage capacitors for pulse power system. We herein propose a synergistic strategy of introduction of 6s² lone pair electrons, breaking the long-range ferroelectric order, and band structure engineering for high performance energy storage by introducing Bi(Mg_0.5Sn_0.5)O₃ (BMS) with weak ferroelectric active cations into 0.7Na_0.5Bi_0.5TiO₃-0.3SrTiO₃ (BNT-ST) to form BNT-ST-BMS ceramics. The doped ceramics display the excellent dielectric stability versus temperature and frequency. The suitable BMS doping can increase the band gap of the BNT-ST ceramic and effectively avoids early dielectric breakdown and polarization saturation. The BNT-ST-BMS ceramic in the composition of x = 0.08 exhibits an outstanding recoverable energy storage density (W_rec) of 5.99 J/cm³, together with a good efficiency (ƞ) of 76% as well as an excellent dielectric stability versus temperature (Δε_r/ε_r(150°C) ≤ ±15%) and frequency. The findings in this work demonstrate that the BNT-ST-BMS ceramics have exceptional potential as candidate materials for pulse power and high voltage capacitors applications, and provide a path for the development of the other lead-free energy storage materials.