High ionic conductivity and stable phase Na11.5Sn2Sb0.5Ti0.5S12 for all-solid-state sodium batteries

The quaternary antimony (Sb)-based sulfide sodium solid electrolyte Na 11 Sn 2 SbS 12 with good moisture stability is attractive for practical application in all-solid-state sodium batteries . However, the Na 11 Sn 2 SbS 12 exhibits low room temperature ionic conductivity and it is difficult to obtain pure phase due to the limited solubility of Sb in the Na 11 Sn 2 SbS 12 crystal structure. Herein, titanium (Ti)-doping Na 11+ x Sn 2 Sb 1- x Ti x S 12 ( x  = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0) materials are systematically investigated, and the highest room temperature ionic conductivity of 1.01 mS cm −1 is achieved when x  = 0.5 (Na 11.5 Sn 2 Sb 0.5 Ti 0.5 S 12 ), which is 3 times higher than that of pristine Na 11 Sn 2 SbS 12 . X-ray diffraction and alternating current impedance analyses reveal that the substitution of Sb with Ti can prevent the formation of the NaSbS 2 impurity, determining high ionic conductivity. Meanwhile, the Na 11.5 Sn 2 Sb 0.5 Ti 0.5 S 12 demonstrates good air stability with limited H 2 S gas evolution. Besides, the activation energy , electronic conductivity and electrochemistry stability window for Na 11.5 Sn 2 Sb 0.5 Ti 0.5 S 12 are also evaluated. Moreover, a high reversible capacity and stable cyclic performance of TiS 2 based all-solid-state sodium battery using Na 11.5 Sn 2 Sb 0.5 Ti 0.5 S 12 are demonstrated, showing an initial discharge capacity of 177.6 mAh g −1 at 0.1C with a capacity retention of 83.5% based on the second discharge capacity after 50 cycles at 25 °C.