Toward high-end lead-free ceramics for energy storage: Na_0.5Bi_0.5TiO₃-based relaxor ferroelectrics with simultaneously enhanced energy density and efficiency

The utilization of relaxor ferroelectrics is thought to be a feasible approach to enhance energy storage performance due to the low remnant polarizations and slim hysteresis. Herein, environment-friendly (1-x)(Bi_0.5Na_0.5)TiO₃-xSr(Ti_0.5Zr_0.5)O₃ bulk ceramics have been developed, where the synergistic effect of enhanced relaxor-ferroelectricity and grain refinement with increasing x value boosts excellent energy storage performance, with impressive energy density (W_rec) of 4.2 J/cm³ accompanied by satisfactory energy efficiency (η) of 75.1%. Together with high thermal stability of the energy storage density of 2.0–2.1 J/cm³ (with minimal variation of ≤ ±5%) over 25–150 °C at 150.0 kV/cm due to the enhancement of thermal insensitivity, which is evidenced by simulation based on thermal conduction model. Additionally, an extraordinary fast discharge rate (t_0.9) of 54.6 ns and a high power density (P_d) of 35.4 MW/cm³ can be achieved in the x = 0.20 ceramic sample. This discovery provides new opportunities to lead-free dielectric materials with a high energy density and efficiency for capacitive electrical energy storage.