Lithium/Sulfur Cell Discharge Mechanism: An Original Approach for Intermediate Species Identification

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• 作者：C茅line Barchasz ; Florian Molton ; Carole Duboc ; Jean-Claude Lepr锚tre ; S茅bastien Patoux ; Fannie Alloin
• 刊名：Analytical Chemistry
• 出版年：2012
• 出版时间：May 1, 2012
• 年：2012
• 卷：84
• 期：9
• 页码：3973-3980
• 全文大小：444K
• 年卷期：v.84,no.9(May 1, 2012)
• ISSN：1520-6882

文摘

The lithium/sulfur battery is a promising electrochemical system that has a high theoretical capacity of 1675 mAh g^鈥?, but its discharge mechanism is well-known to be a complex multistep process. As the active material dissolves during cycling, this discharge mechanism was investigated through the electrolyte characterization. Using high-performance liquid chromatography, UV鈥搗isible absorption, and electron spin resonance spectroscopies, we investigated the electrolyte composition at different discharge potentials in a TEGDME-based electrolyte. In this study, we propose a possible mechanism for sulfur reduction consisting of three steps. Long polysulfide chains are produced during the first reduction step (2.4鈥?.2 V vs Li⁺/Li), such as S₈^{2鈥?/sup> and S₆2鈥?/sup>, as evidenced by UV and HPLC data. The S₃鈥⑩€?/sup> radical can also be found in solution because of a disproportionation reaction. S₄2鈥?/sup> is produced during the second reduction step (2.15鈥?.1 V vs Li+/Li), thus pointing out the gradual decrease of the polysulfide chain lengths. Finally, short polysulfide species, such as S₃2鈥?/sup>, S₂2鈥?/sup>, and S2鈥?/sup>, are produced at the end of the reduction process, i.e., between 2.1 and 1.9 V vs Li+/Li. The precipitation of the poorly soluble and insulating short polysulfide compounds was evidenced, thus leading to the positive electrode passivation and explaining the early end of discharge.}