Simultaneously enhanced energy density and discharge efficiency of (Na 0.5 Bi 0.5 ) 0.7 Sr 0.3 TiO 3 -La 1/3 (Ta 0.5 Nb 0.5 )O 3 lead-free energy storage ceramics via grain inhibition and dielectric peak flattening engineering.

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 0.5 Bi 0.5 ) 0.7 Sr 0.3 TiO 3 - x La 1/3 (Ta 0.5 Nb 0.5 )O 3 (NBST- x LTN) 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 La 3+ , Ta 5+ and Nb 5+ 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.