Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen.

Authors:
Dr. Won-Jin Kwak, PhD
Dr. Won-Jin Kwak, PhD
Pacific Northwest National Laboratory
Richland, WA | United States
Hun Kim
Hun Kim
Sungkyunkwan University School of Medicine
Yann K Petit
Yann K Petit
Institute for Chemistry and Technology of Materials
Christian Leypold
Christian Leypold
Institute for Chemistry and Technology of Materials
Trung Thien Nguyen
Trung Thien Nguyen
Hanyang University
Nika Mahne
Nika Mahne
Institute for Chemistry and Technology of Materials
Paul Redfern
Paul Redfern
Indiana University
United States
Larry A Curtiss
Larry A Curtiss
Northwestern University
United States

Nat Commun 2019 03 26;10(1):1380. Epub 2019 Mar 26.

Department of Energy Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

Non-aqueous lithium-oxygen batteries cycle by forming lithium peroxide during discharge and oxidizing it during recharge. The significant problem of oxidizing the solid insulating lithium peroxide can greatly be facilitated by incorporating redox mediators that shuttle electron-holes between the porous substrate and lithium peroxide. Redox mediator stability is thus key for energy efficiency, reversibility, and cycle life. However, the gradual deactivation of redox mediators during repeated cycling has not conclusively been explained. Here, we show that organic redox mediators are predominantly decomposed by singlet oxygen that forms during cycling. Their reaction with superoxide, previously assumed to mainly trigger their degradation, peroxide, and dioxygen, is orders of magnitude slower in comparison. The reduced form of the mediator is markedly more reactive towards singlet oxygen than the oxidized form, from which we derive reaction mechanisms supported by density functional theory calculations. Redox mediators must thus be designed for stability against singlet oxygen.

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Source
http://dx.doi.org/10.1038/s41467-019-09399-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6435713PMC
March 2019
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