Potential-Dependent Generation of O2‿/sup> and LiO2 and Their Critical Roles in O2 Reduction to Li2O2 in Aprotic Li–O2 Batteries

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• 作者：Yelong Zhang ; Xinmin Zhang ; Jiawei Wang ; William C. McKee ; Ye Xu ; Zhangquan Peng
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：February 25, 2016
• 年：2016
• 卷：120
• 期：7
• 页码：3690-3698
• 全文大小：447K
• ISSN：1932-7455

文摘

Discharging of the aprotic Li–O₂ battery relies on the oxygen reduction reaction (ORR) producing Li₂O₂ in the positive electrode, which remains incompletely understood. Here, we report a mechanistic study of the Li-ORR on a model system, i.e., an Au electrode in a Li⁺ dimethyl sulfoxide (DMSO) electrolyte. By spectroscopic identification of the reaction intermediates coupled with density functional theory calculations, we conclude that the formation of O₂^– and LiO₂ in the Li-ORR critically depends on electrode potentials and determines the Li₂O₂ formation mechanism. At low overpotentials (> 2.0 V vs Li/Li⁺) O₂^– is identified to be the first surface intermediate, which diffuses into the bulk electrolyte and forms Li₂O₂ therein via a solution-mediated disproportionation mechanism. At high overpotentials (ca. 2.0–1.6 V vs Li/Li⁺) LiO₂ has been observed, which can rapidly transform to Li₂O₂ by further electro-reduction, suggesting a surface-mediated mechanism. The solution-mediated Li₂O₂ formation that can account for the widely observed toroid-shaped discharged Li₂O₂ particles has also been thoroughly examined. Thus, O₂^– formation controls the overall reaction onset potential, and LiO₂ formation demarcates the change from a solution- to surface-mediated reaction mechanism. The new findings and improved understandings of the Li-ORR in DMSO will contribute to the further development of aprotic Li–O₂ batteries.