Theoretical Evidence for Low Charging Overpotentials of Superoxide Discharge Products in Metal鈥揙xygen Batteries

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• 作者：Byungju Lee ; Jinsoo Kim ; Gabin Yoon ; Hee-Dae Lim ; In-Suk Choi ; Kisuk Kang
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：December 22, 2015
• 年：2015
• 卷：27
• 期：24
• 页码：8406-8413
• 全文大小：405K
• ISSN：1520-5002

文摘

Li鈥搊xygen and Na鈥搊xygen batteries are some of the most promising next-generation battery systems because of their high energy densities. Despite the chemical similarity of Li and Na, the two systems exhibit distinct characteristics, especially the typically higher charging overpotential observed in Li鈥搊xygen batteries. In previous theoretical and experimental studies, this higher charging overpotential was attributed to factors such as the sluggish oxygen evolution or poor transport property of the discharge product of the Li鈥搊xygen cell; however, a general understanding of the interplay between the discharge products and overpotential remains elusive. Here, we investigated the charging mechanisms with respect to the oxygen evolution reaction (OER) kinetics, charge-carrier conductivity, and dissolution property of various discharge products reported in Li鈥搊xygen and Na鈥搊xygen cells. The OER kinetics were generally faster for superoxides (i.e., LiO₂ and NaO₂) than for peroxides (i.e., Li₂O₂ and Na₂O₂). The electronic and ionic conductivities were also predicted to be significantly higher in superoxide phases than in peroxide phases. Moreover, systematic calculations of the dissolution energy of the discharge products in the electrolyte, which mediate a solution-based OER reaction, revealed that the superoxide phases, particularly NaO₂, exhibited markedly low dissolution energy compared with the peroxide phases. These results imply that the formation of superoxides instead of peroxides during discharge may be the key to improving the energy efficiency of metal鈥搊xygen batteries in general.