Investigation of the wetting behavior of Na and Na alloys on uncoated and coated Na-v""-alumina at temperatures below 150 °C

Insufficient wetting of Na on Na-beta"-alumina is responsible for an increased interfacial polarization in Na-batteries if the operating temperature is below 270-300 A degrees C. In this study, Na alloys (Na-Sn, Na-Bi and Na-In) on the ceramic surface are examined on their capability to improve the wetting with molten sodium at medium temperatures and thereby enabling operation of the cell at temperatures in the range of 105 to 150 A degrees C. Metallic coatings with Bi or Sn confirm this improvement at a temperature of 115 A degrees C. The overpotential of a symmetrical Naa",Na-beta"-aluminaa",Na cell is determined by galvanostatic cycling and electrochemical impedance spectroscopy and then associated to contact angle measurements. As a result, both the alloys and the metallic coatings have a positive impact on wetting and reduction of the overpotential during galvanostatic cycling.