LiAlCl4/SO2 electrolytes were observed, by infrared spectroscopy, to contain hydroxychloroaluminate impurities, which would react with metallic Lithium in a battery. These hydroxyl contaminants were removed by reaction with chlorine, and the products were identified to be HCl and a chlorosulfanatoaluminate species. A simple method is suggested for the routine purification of these electrolytes.