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 (Wt) only under extremely high breakdown electric field and usually possess inferior efficiency (η). In this research, neoteric (1 - x)(Na0.5Bi0.5)0.7Sr0.3TiO3-xLa1/3(Ta0.5Nb0.5)O3 (NBST-xLTN) ceramics were designed by grain inhibition and dielectric peak flattening engineering to enhance Wt 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 Wt of 2.09 J cm-3 and large Wrec 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 (PD and CD) 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.