Iodine Mediator with Anomalously High Redox Potential and Its Application to a Catalytic Cycle for Lithium Carbonate Decomposition toward Future Lithium Reproduction

• Published in: Journal of physical chemistry. C Vol. 123; no. 7; pp. 3944 - 3950
• Main Authors: Shiga, Tohru, Kondo, Hiroki, Kato, Yuichi, Hase, Yoko
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.02.2019
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b09967

Lithium carbonate (Li2CO3) is observed in conventional lithium-ion batteries in which cell performance has been reduced. In this paper, a catalyst to electrochemically decompose Li2CO3 was investigated to develop a Li reproduction technology. It has been accepted that iodine with a redox potential below 3.5 V vs Li+/Li cannot decompose Li2CO3, because the decomposition potential of Li2CO3 is 3.82 V vs Li+/Li. Here, we observed that the redox potential of iodine in trimethyl phosphate (TMP) and dimethyl sulfoxide (DMSO) solutions increased up to 4.0 V, and thus Li2CO3 could be chemically decomposed by iodine in these solvents. This unexpectedly high redox potential may be caused by deviation of the electric charges on two iodine atoms due to a 1:1 complex formation of iodine with the solvent. Reaction pathways are discussed with respect to the chemical decomposition of Li2CO3 by iodine. We combined the chemical decomposition behavior with the redox couple of iodine species. A double-chamber type cell with carbon paper as cathode in catholyte that dissolved iodine and suspended Li2CO3 powders was constructed to substantiate a catalytic cycle for Li2CO3 decomposition. The cell was demonstrated to be rechargeable due to the decomposition of Li2CO3.