STABILITY OF SODIUM ELECTRODEPOSITED FROM A ROOM-TEMPERATURE CHLOROALUMINATE MOLTEN-SALT

Room temperature molten salts consisting of 1-methyl-3-ethylimidazoliu m chloride (MEIC) and aluminum chloride (AlCl3) have been examined as possible electrolytes for a room temperature design of the sodium/iron (II) chloride battery. This work examines the conditions required to a chieve efficient reduction and oxidation of sodium from a sodium chlor ide buffered, neutral melt. Two substrates were examined, tungsten and 303 stainless steel, using both cyclic voltammetry and chronopotentio metry. Melts were protonated using a closed electrochemical cell to al low quantification of the effect of dissolved HCl on the efficiency of the sodium couple. A threshold of approximately 6 Torr HCl partial pr essure was observed for sodium plating-stripping. Below this threshold , the sodium couple was not observed. The results show that the sodium plating-stripping efficiency increases with increasing current densit y; however, the efficiency reaches a maximum and is adversely affected by high overpotentials and extended exposure of the sodium to the mel t. It appears that some passivation occurs as even a very thin layer o f plated sodium exhibits a steady open-circuit voltage over long perio ds in the melt.