Realizing high comprehensive energy storage performance in lead-free bulk ceramics: Via designing an unmatched temperature range

The study of lead-free dielectric ceramics for capacitors has become one of the most active academic research areas in advanced functional materials owing to the environmental regulations. A large recoverable energy storage density (W_rec), a high energy storage efficiency (η) and good temperature stability in lead-free dielectric ceramics are highly desired simultaneously to meet the requirements of light weight and integration of dielectric capacitors in pulsed power devices. Unfortunately, a large W_rec of lead-free dielectric ceramics is usually achieved at the cost of η, and vice versa, hindering their practical applications. More importantly, despite the considerable efforts made so far to develop a large amount of lead-free bulk ceramics for dielectric capacitor applications, there is still a lack of scientific and feasible guidelines on how to design new material systems with a large W_rec, a high η and excellent thermal stability. Herein, we propose a new strategy to tailor the temperature region between the temperature corresponding to the maximum dielectric permittivity (T_m) and the Burns temperature (T_B) of relaxor ferroelectrics to room temperature via composition optimization, to explore lead-free bulk ceramics with high comprehensive energy storage properties. A large W_rec of 3.51 J cm^-3 and a high η of 80.1% are simultaneously obtained in 0.86NaNbO₃-0.14(Bi_0.5Na_0.5)HfO₃ (0.86NN-0.14BNH) ceramics under an electric field of 350 kV cm^-1, leading to an excellent comprehensive energy storage performance in lead-free bulk ceramics. Furthermore, both the W_rec and η of 0.86NN-0.14BNH ceramics show good temperature stability over 20 °C to 200 °C at 280 kV cm^-1, which is superior to that of other lead-free bulk ceramics. Most importantly, this work provides significant guidelines for designing new high-performance bulk ceramics for electrical energy storage applications.