The Corrosion of Aluminum in Sodium Polysulfides and Sulfur at 350°C

Abstract

Materials selection for the current collector in the positive electrode of the sodium/sulfur cell has received significant attention in the literature [see Ref.(1) for a recent review]. Aluminum is one of the materials that many investigators have claimed to be compatible with the positive electrode environments (sodium polysulfide/sulfur) but this metal cannot be used as a current collector because its corrosion scale is an electronically insulating film of AI~S3 (1-5): In addition, the post-test analysis of sodium/sulfur cells constructed with an aluminum spacer in the container compression seal has shown extensive corrosive attack of the aluminum, with significant quantities of crystalline NaA1S2 dispersed throughout the polysulfide/graphite fiber matrix of the positive electrode (6). We have now completed a series of static corrosion tests of aluminum in various sodium polysulfides (i.e., Na2S3, Na2S4, Na2S,) and sulfur at 350~ The results clearly show that aluminum is not compatible with the discharged state of the positive electrode of the sodium/sulfur cell and that the corrosion product is only AI2Sa when the corrosion environment is sulfur. Experimental

Enhanced corrosion resistance of hypo-eutectic Al–1Mg– x Si alloys against molten sodium attack in high temperature sodium sulfur batteries

“…A preliminary experiment conducted by the present authors showed that the corrosion of Al-1Mg-xSi alloys by sulfur in a vapor phase at 350 • C is negligible, and it agrees with the results from a previous similar study [20]. Corrosion of aluminum alloys, and the alloys with protective coatings exposed to catholytic melts (molten sulfur and sodium polysulfides) has been intensively studied by earlier NaS cell developers targeting at mitigating significant corrosion inside the cell container which may also result in a catastrophic failure of the cell [20][21][22][23].…”