Formation of Passivate Interphases by Na₃BS₃-Glass Solid Electrolytes in All-Solid-State Sodium-Metal Batteries

Interphase formation at the interface between a solid electrolyte and negative electrode is one of the main factors limiting the practical use of all-solid-state sodium batteries. Sulfide-type solid electrolytes with group 15 elements (P and Sb) exhibit high ductility and ionic conductivity, comparable to those of organic liquid electrolytes. However, the electronically conductive interphase formed at the interface between Na₃PS₄ and sodium metal increases the cell resistance and deteriorates its electrochemical properties. Contrarily, Na₃BS₃, containing boron as an electrochemically inert element, forms an electronically insulating thin passivate interphase, facilitating reversible sodium plating and stripping. Sodium-metal symmetric cells with Na₃BS₃ exhibit steady operation over 1000 cycles. Thus, reduction-stable solid electrolytes can be developed by substitution with an electrochemically inert element versus sodium.