The fundamental chemical behavior of the AlCl3/SO2Cl2 catholyte system was investigated using Al-27 NMR spectroscopy, Raman spectroscopy, and single-crystal X-ray diffraction. Three major Al-containing species were found to be present in this catholyte system, where the ratio of each was dependent upon aging time, concentration, and/or storage temperature. The first species was identified as [Cl2Al(mu-Cl)](2) in equilibrium with AlCl3, The second species results from the decomposition of SO2Cl2 which forms Cl-2(g) and SO2(g), The SO2(g) is readily consumed in the presence of AlCl3 to form the crystallographically characterized species [Cl2Al(mu-O2SCl)](2) (1). For 1, each Al is tetrahedrally (T-d) bound by two terminal Cl and two mu-O ligands whereas, the S is three-coordinated by two mu-O ligands and one terminal Cl. The third molecular species also has T-d-coordinated Al metal centers but with increased oxygen coordination. Over time it was noted that a precipitate formed from the catholyte solutions. Raman spectroscopic studies show that this gel or precipitate has a component that was consistent with thionyl chloride. We have proposed a polymerization scheme that accounts for the precipitate formation, Further NMR studies indicate that the precipitate is in equilibrium with the solution.