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Comparative kinetic study of redox mediators for high-power lithium–oxygen batteries

Abstract

The use of redox mediators (RMs) effectively reduces the high polarization of lithium-oxygen batteries by mediating the electrochemical formation and decomposition of the discharge products. As the electrochemical reactions are mediated by RMs, the power capability of the system would be critically dependent on the intrinsic kinetic properties of the RM in mediating the reaction. Herein, we performed a comparative kinetic study for several reported oxygen evolution reaction RMs by probing the RM-assisted charging process with respect to the rate of chemical decomposition of discharge product and the diffusivity of the RM in the controlled lithium-oxygen cells. It was found that the overall kinetics of RMs have a positive correlation with the redox potential of the RM, and, the multi-redox RMs can display distinct properties depending on its oxidation states. Among RMs investigated, DMPZ2+ (5,10-dihydro-5,10-dimethylphenazine) exhibit the highest reaction rate of lithium peroxide decomposition, while the mass diffusion rate is highest for TEMPO+ (2,2,6,6-tetramethyl-1-piperidinyloxy). Additionally, the choice of electrolytes is shown to greatly affect the rate capability of the RM-assisted charge, and thus be carefully considered. This study suggests the importance of understanding the kinetics of RMs and provides guidelines for achieving an optimized RM/electrolyte combination to realize high-power lithium–oxygen batteries.

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Publication details

The article was received on 04 Jan 2019, accepted on 10 Feb 2019 and first published on 11 Feb 2019


Article type: Paper
DOI: 10.1039/C9TA00096H
Citation: J. Mater. Chem. A, 2019, Accepted Manuscript

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    Comparative kinetic study of redox mediators for high-power lithium–oxygen batteries

    Y. Ko, H. Park, B. Lee, Y. Bae, S. park and K. Kang, J. Mater. Chem. A, 2019, Accepted Manuscript , DOI: 10.1039/C9TA00096H

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