Spectroelectrochemical Studies on the Reduction of

The electrochemical reduction of thionyl chloride in dimethyl sulfoxide and of the thionyl chloride-lithium tetra-chloroaluminate system has been studied using spectroelectrochemical techniques. Results indicate that the reduction mechan ism of SOCI2 in the LiAICI4-SOCI2 solution is essentially the same as that in DMSO. The key intermediate species in this reduction is shown to be SO § wh ich is p roduced upon reduction of SOCI2 by a one-electron transfer, fol lowed by the dechloridation process. This species then undergoes a series of following reactions to produce the final reduction products, S and SQ, via other intermediates such as SO and $20. At very negative potentials, reduction products of S and SO2 are shown to be produced. A l though thionyl chloride has long been an important reagent for introducing chlorine a toms into organic molecules, studies of its electrochemical reduction were initiated only after it became important as the catholyte in lithium-thionyl chloride batteries. The eleetochemical re-duction of SOCI2 has received much interest in the battery communi ty because of its importance in high energy den-sity l ithium batteries. 1-4 However, the batteries are known to have safety prob lems in connection with short-circuit-ing, forced-discharge (reversal), casual storage, and/or ex-posure to the env i ronment of a partially discharged cell. I W i th a high cell discharge rate, excessive cell heating gen-erated by accidental short-circuiting may cause explosion. To avoid cell explosion, low pressure venting (i00 to 200 psi) has been introduced to cool the cells enough not to reach a critical temperature. Explosions during casual storage and/or exposure to the env i ronment of a partially discharged cell may be due to the reaction of unstable chemicals fo rmed during the discharge. I For this reason, some investigators have been studying the SOCI2 reduction to identify intermediate species. Based on postulated inter-mediate species, several cell reaction mechan isms have been proposed. A l though papers have been publ ished on the subject, 5-19 little is known about the reduction of SOC12 except the overall stoichiometry established a