The present invention provides an electrochemical cell having an negative electrode compartment and a positive electrode compartment. A solid alkali ion conductive electrolyte membrane is positioned between the negative electrode compartment and the positive electrode compartment. A catholyte solution in the positive electrode compartment includes a halide ion or pseudohalide ion concentration greater than 3M, which provides degradation protection to the alkali ion conductive electrolyte membrane. The halide ion or pseudohalide ion is selected from chloride, bromide, iodide, azide, thiocyanate, and cyanide. In some embodiments, the electrochemical cell is a molten sodium rechargeable cell which functions at an operating temperature between about 100° C. and about 150° C.