Sodium solid electrolyte combining high conductivity with electrochemical stability

All-solid-state sodium-ion batteries are a promising technology for large-scale energy storage owing to the abundance and low cost of sodium resources; however, their practical implementation is hindered by the lack of solid electrolytes that simultaneously exhibit high room-temperature ionic conductivity and robust electrochemical stability. This study reports the development of a chlorine-substituted Na₃SbS₄ solid electrolyte synthesized via a liquid-phase method suitable for mass production. Partial substitution of sulfur with chlorine in Na₃SbS₄ increases the room-temperature ionic conductivity from 0.3 to 0.9 mS cm⁻¹, representing a threefold enhancement without the need for post-processing such as ball milling. Structural analysis and visualization of ion-conduction pathways reveal that Cl substitution weakens the local electrostatic interactions between Na and S/Cl, forming a crystal framework that enables three-dimensional Na-ion diffusion, with particularly facilitated transport along the crystallographic c-axis. Furthermore, the Cl-substituted Na₃SbS₄ demonstrates superior electrochemical stability in contact with Na metal anodes, attributed to reduced interfacial resistance and the beneficial effects of heavy Cl doping. These findings establish a key design principle for tailoring solid electrolytes that combine high ionic conductivity with improved interfacial stability and suggest that integrating this material with liquid-phase coating technologies could advance high-capacity, long-life all-solid-state Na-ion batteries.