Abstract
Room temperature molten salts consisting of 1‐methyl‐3‐propylimidazolium chloride and aluminum chloride have been examined as possible electrolytes for a room temperature design of the sodium/metal chloride battery; however, the coulombic efficiency of the sodium couple is less than 95%. This work examines the reduction and oxidation efficiency of the sodium couple from a 1‐methyl‐3‐propylimidazolium chloride/aluminum chloride neutral melt. Most of the work was performed on a tungsten substrate using cyclic voltammetry. The coulombic efficiency of the sodium couple was improved by treating the melt with gaseous HCl using a closed electrochemical cell which allowed for quantification of the effect of HCl on the electrochemical behavior of sodium. Thionyl chloride was also found to induce sodium plating and stripping in 1‐methyl‐3‐propylimidazolium chloride/aluminum chloride melts. Optical microscopy was used to examine the surface of the tungsten electrode during sodium deposition, open‐circuit periods, and sodium stripping. In comparison to the stability of sodium in two other imidazolium melts, (1,2‐dimethyl‐3‐propylimidazolium chloride and 1‐methyl‐2‐ethylimidazolium chloride) the 1‐methyl‐3‐propylimidazolium chloride system was found to have the widest stability window.