Chemical Stability of Sodium Beta″‐Alumina Electrolyte in Sulfur/Sodium Polysulfide Melts

Immersion of sodium β''‐alumina electrolyte in sodium polysulfide and pure sulfur melts, at Na/S battery operation temperatures, showed that the electrolyte was chemically attacked by the melts, and that the extent of degradation was affected by a number of factors, including surface morphology and chemistry of the electrolyte, melt composition, impurity contamination, etc. The corrosion reactions mostly initiated and concentrated on defected areas, and were catalyzed by the presence of impurities such as water, moist air, oxygen, etc. The corrosion power of sodium polysulfide melts increased with the sulfur content in the range of to . The reaction products, formed at the interface, were believed to be , , , , , , etc. Precipitation of crystallized sulfates occurred on preferred areas after saturation. Corrosion products of transition metals also deposited on the electrolyte surface. As a result, a partly insulating layer was formed on the electrolyte surface during immersion, which was a mixture of sulfates, carbonates, and sulfides of transition metals.