Domain engineered lead-free Bi_0.5Na_0.5TiO₃-Bi(Ni_0.5Hf_0.5)O₃ relaxor ferroelectric ceramics for energy storage with low electric field applications

Lead-free materials for energy storage are increasingly receiving attention due to their exceptional properties of high charging and discharging rates, high power density, and eco-friendliness. In this work, (1−x)Bi_0.5Na_0.5TiO₃-xBi(Ni_0.5Hf_0.5)O₃ (BNT-BNH, x = 0.05, 0.10, 0.15 and 0.20) ceramics were prepared for electrostatic energy storage. P-E loops results show that the introduction of Ni²⁺ and Hf⁴⁺ induces the formation of polar nanoregions (PNRs) and the phase transition from ferroelectric to relaxor ferroelectric in BNT ceramics. Transmission Electron Microscopy directly confirm the increase of crystal plane spacing implies a good solid solution of BNT-BNH, and the number of spherical PNRs increases significantly with increasing the BNH content. Herein, a recoverable energy storage density of 2.68 J/cm³ and relative efficiency of 72.1 % are achieved for 0.8BNT-0.2BNH ceramics under 210 kV/cm. The 0.8BNT-0.2BNH ceramics also exhibit a fast discharge rate (t_0.9 = 76 ns), high current density (403.1 A/cm²), and high power density (12.85 MW/cm³), which illustrates that BNT-BNH material systems have good application potential in electrostatic energy storage.