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.
Kwak W-J, Kim H, Petit YK, et al. Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen. Nature Communications. 2019;10. doi:10.1038/s41467-019-09399-0
Kwak, W.-J., Kim, H., Petit, Y. K., Leypold, C., Nguyen, T. T., Mahne, N., … Sun, Y.-K. (2019). Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen. Nature Communications, 10. https://doi.org/10.1038/s41467-019-09399-0
Kwak, Won-Jin, Hun Kim, Yann K. Petit, Christian Leypold, Trung Thien Nguyen, Nika Mahne, Paul Redfern, et al. “Deactivation of Redox Mediators in Lithium-Oxygen Batteries by Singlet Oxygen.” Nature Communications 10 (2019). https://doi.org/10.1038/s41467-019-09399-0.
W.-J. Kwak et al., “Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen,” Nature Communications, vol. 10, 2019.
Kwak W-J, Kim H, Petit YK, Leypold C, Nguyen TT, Mahne N, Redfern P, Curtiss LA, Jung H-G, Borisov SM, Freunberger SA, Sun Y-K. 2019. Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen. Nature Communications. 10.
Kwak, Won-Jin, et al. “Deactivation of Redox Mediators in Lithium-Oxygen Batteries by Singlet Oxygen.” Nature Communications, vol. 10, 1380, Springer Nature, 2019, doi:10.1038/s41467-019-09399-0.
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