Simultaneously enhanced energy density and discharge efficiency of (Na0.5Bi0.5)0.7Sr0.3TiO3-La1/3(Ta0.5Nb0.5)O3 lead-free energy storage ceramics via grain inhibition and dielectric peak flattening engineering

Abstract

Energy storage ceramics are widely favored for their rapid charging/discharging speed, good temperature stability and large power density. Nevertheless, most lead-free energy storage ceramics can achieve excellent energy storage density (W_t) only under extremely high breakdown electric field and usually possess inferior efficiency (η). In this research, neoteric (1 − x)(Na_0.5Bi_0.5)_0.7Sr_0.3TiO₃-xLa_1/3(Ta_0.5Nb_0.5)O₃ (NBST-xLTN) ceramics were designed by grain inhibition and dielectric peak flattening engineering to enhance W_t and η simultaneously under a low electric field (≤150 kV cm⁻¹). In particular, in one aspect, multiple co-doping of the elements La³⁺, Ta⁵⁺ and Nb⁵⁺ as excellent grain growth inhibitors reduces the concentration of oxygen vacancies and refines the grain size to increase the breakdown strength. In another aspect, partial ion substitution in the A/B sites of BNST ceramics breaks the ferroelectric long-range order to generate polar nanoregions, resulting in a remarkable decrease in remanent polarization. Moreover, the incorporation of LTN distorts the lattice, causing a shift towards room temperature and flattening of dielectric peaks to promote the temperature/frequency stabilities significantly. Ultimately, the ultrahigh η of 92.49%, promising W_t of 2.09 J cm⁻³ and large W_rec of 1.94 J cm⁻³ under 148 kV cm⁻¹ are achieved concurrently accompanied by the optimistic temperature, frequency and cyclic stabilities in the BNST-0.025LTN ceramic. Besides, outstanding power and current densities (P_D and C_D) of 67.86 MW cm⁻³ and 848.29 A cm⁻² are procured in the BNST-0.025LTZ ceramic under a low electric field of 160 kV cm⁻¹. The present strategies of grain inhibition and dielectric peak flattening engineering provide an effective approach to exploit novel lead-free ceramics with excellent energy storage properties.