Tungsten and oxygen co-doped stable tetragonal phase Na3SbS4 with ultrahigh ionic conductivity for all-solid-state sodium batteries

Development of sodium solid electrolytes with high ionic conductivity and good interface stability towards Na metal plays a dominant role in achieving stable all-solid-state sodium batteries. Herein, WS 2 -doped Na 3- x Sb 1- x W x S 4 and WO 2 -doped Na 3- x Sb 1- x W x S 4–2 x O 2 x ( x  = 0.025, 0.05, 0.075, 0.1) solid electrolytes are successfully synthesized by melt-quenching method followed by an annealing procedure. Compared with 0.98 mS cm −1 for pristine Na 3 SbS 4 , the dramatically enhanced room temperature ionic conductivities of 10.37 and 8.49 mS cm −1 are achieved for Na 2.95 Sb 0.95 W 0.05 S 4 and Na 2.95 Sb 0.95 W 0.05 S 3.9 O 0.1 , respectively. In addition, it is found that the introduction of oxygen in Na 3 SbS 4 through W and O co-doping can alleviate the deteriorative Na/solid electrolyte interface induced by W substitution. The modified interface stability is demonstrated by the suppressed increase of Na plating/striping voltage and impedance for the symmetric Na/Na 2.95 Sb 0.95 W 0.05 S 3.9 O 0.1 /Na cells. Moreover, in contrast with rapid capacity decay for TiS 2 /Na 2.95 Sb 0.95 W 0.05 S 4 /Na battery, the batteries employing Na 2.95 Sb 0.95 W 0.05 S 3.9 O 0.1 exhibit stable cyclic performance and good rate capability. This work provides a W and O co-doping strategy for preparing Na 3 SbS 4 solid electrolytes with simultaneously enhanced ionic conductivity and interface stability.