Aqueous-solution synthesis of Na₃SbS₄ solid electrolytes for all-solid-state Na-ion batteries

Room-temperature-operable all-solid-state Na-ion batteries (ASNBs) using sulfide Na-ion solid electrolytes (SEs) are promising because of their potential for greater safety, lower cost, and acceptable performance. Despite extensive developments in the area of sulfide Na-ion SEs, their poor chemical stability and prospects for wet-chemical synthesis have been overlooked to date. Herein, the scalable synthesis of Na₃SbS₄via aqueous-solution routes using precursors of Na₂S, Sb₂S₃, and elemental sulfur for ASNBs is described. With no concerns about the evolution of toxic H₂S gas, the aqueous-solution-synthesized Na₃SbS₄ exhibits high ionic conductivities (0.1-0.2 mS cm^-1 at 25 °C). Importantly, the homogeneity of the aqueous solutions enables the creation of uniform Na₃SbS₄ coatings on FeS₂. Fe₂S/Na-Sn ASNBs, employing the aqueous-solution-synthesized Na₃SbS₄ and the Na₃SbS₄-coated FeS₂ for the SE layer and positive electrode, respectively, demonstrate a high charge capacity of 256 or 346 mA h g^-1 with good reversibility at 30 °C, highlighting their potential for practical applications.