PLATING AND STRIPPING OF SODIUM FROM A ROOM-TEMPERATURE 1-METHYL-3-PROPYLIMIDAZOLIUM CHLORIDE MELT

Room temperature molten salts consisting of 1-methyl-3-propylimidazoli um chloride and aluminum chloride have been examined as possible elect rolytes for a room temperature design of the sodium/metal chloride bat tery; however, the coulombic efficiency of the sodium couple is less t han 95%. This work examines the reduction and oxidation efficiency of the sodium couple from a 1-methyl-3-propylimidazolium chloride/aluminu m chloride neutral melt. Most of the work was performed on a tungsten substrate using cyclic voltammetry. The coulombic efficiency of the so dium couple was improved by treating the melt with gaseous HCl using a closed electrochemical cell which allowed for quantification of the e ffect of HCl on the electrochemical behavior of sodium. Thionyl chlori de was also found to induce sodium plating and stripping in 1-methyl-3 -propylimidazolium chloride/aluminum chloride melts. Optical microscop y was used to examine the surface of the tungsten electrode during sod ium deposition, open-circuit periods, and sodium stripping. In compari son to the stability of sodium in two other imidazolium melts, (1,2-di methyl-3-propylimidazolium chloride and 1-methyl-2-ethylimidazolium ch loride) the 1-methyl-3-propylimidazolium chloride system was found to have the widest stability window.