Highly conductive Na2.804Sb0.879W0.046S3.7F0.075 with moisture tolerance enables stable all-solid-state sodium batteries

The low ionic conductivity of sodium solid electrolytes and the instability with moisture and sodium metal are the main challenges for the development of all-solid-state sodium batteries. In this work, a Na 3 SbS 4 solid electrolyte with coexisting W and F dopants (Na 2.804 Sb 0.879 W 0.046 S 3.7 F 0.075 ) is synthesized and achieves a high ionic conductivity of 11.13 mS cm −1 . Density-functional-theory calculations indicate that both the reduced Na-vacancy formation energy and Na-ion diffusion barrier by such co-doping strategy contribute to the improved ionic conductivity. Furthermore, although the promoted H 2 O dissociation by W doping results in the extremely low stability of Na 2.95 Sb 0.95 W 0.05 S 4 in moisture, the added F dopant dramatically increases the energy costs for H 2 O adsorption and dissociation, effectively inhibiting the hydrolysis of Na 2.804 Sb 0.879 W 0.046 S 3.7 F 0.075 . Moreover, the NaF layer formed at the interfaces of Na/Na 2.804 Sb 0.879 W 0.046 S 3.7 F 0.075 /Na symmetric cell significantly ameliorates the interfacial instability caused by W, realizing four times longer stable cycle time to 800 h. As a result, the TiS 2 /Na 2.804 Sb 0.879 W 0.046 S 3.7 F 0.075 /Na battery shows an initial reversible capacity of 173.3 mAh g −1 , with a capacity retention of 85 % after 100 cycles at 0.1 C.