Degradation protection of solid alkali ion conductive electrolyte membrane

A method for protecting a solid alkali ion conductive electrolyte membrane from degradation comprising:

• obtaining an electrochemical cell comprising:
• an negative electrode compartment comprising an anode;
• a positive electrode compartment comprising a cathode for holding an aqueous catholyte solution, the positive electrode compartment comprising a cathode positioned to contact the catholyte solution, wherein the catholyte solution comprises a halide ion or pseudohalide ion concentration greater than 3M;
• and
• a solid alkali ion conductive electrolyte membrane positioned between the negative electrode compartment and the positive electrode compartment;
• and
• operating the electrochemical cell, wherein the presence of halide or pseudohalide ions protects the solid alkali ion conductive electrolyte membrane from degradation.

A molten sodium secondary cell, comprising:

• a negative electrode, which electrochemically oxidizes to release sodium ions during discharge and electrochemically reduces sodium ions to sodium metal during recharging;
• a positive electrode compartment comprising a positive electrode disposed in an aqueous liquid positive electrode solution, wherein the aqueous liquid positive electrode solution comprises a halide ion or pseudohalide ion concentration greater than 3M;
• and
• a solid sodium ion conductive electrolyte membrane that separates the negative electrode from the liquid positive electrode solution,
• wherein the negative electrode is molten and in contact with the conductive electrolyte membrane as the cell operates, and wherein the cell functions at an operating temperature between about 100° C. and about 150° C.