Advances in Understanding Oxygen Reduction in the Metal-O2 Battery
Authors: Jovanov Zarko P , Chen Yuhui , Johnson Lee , Bruce Peter G. 
Published: February 2020

Li-ion and related battery technologies will be important for years to come. However, we must explore alternatives if we are to have any hope of meeting the long-term needs for energy storage. One such alternative is the metal-O2 battery; the theoretical specific energy of typical aprotic metal-O2batteries exceeds that of Li-ion, but many obstacles hinder realization of this technology.[1-4] Overcoming these hurdles will require an understanding of the fundamental electrochemistry at the positive electrode within aprotic metal-air batteries.[5-12]

Recently interest in the Na-O2 battery has grown due to the relatively low polarization during cycling and the high rates.[13, 14] This is despite the lower specific energy of this battery chemistry.[15] A number of groups have shown promising results with this system.[16-18] An important area of contention is the nature of the discharge product, which, unlike the lithium system that forms Li2O2, may form the superoxide, peroxide or oxide. The discharge product in the metal-O2 battery directly influences the specific capacity and ease of charge. Therefore, it is important to understand the mechanism such that this can be controlled.

We have combined a range of electrochemical, spectroscopic and microscopy methods to investigate the mechanism of electrochemical O2 reduction. The results of these studies will be presented, along with the implications for the future of rechargeable metal-O2 batteries.

References:

1. Bruce, P.G., et al., Li-O2 and Li-S batteries with high energy storage. Nature Materials, 2012. 11(1): p. 19-29.

2. Lu, Y.C., et al., Lithium-oxygen batteries: bridging mechanistic understanding and battery performance. Energy & Environmental Science, 2013. 6(3): p. 750-768.

3. Girishkumar, G., et al., Lithium−air battery: promise and challenges. The Journal of Physical Chemistry Letters, 2010. 1(14): p. 2193-2203.

4. Li, F., T. Zhang, and H. Zhou, Challenges of non-aqueous Li-O2 batteries: electrolytes, catalysts, and anodes. Energy & Environmental Science, 2013. 6(4): p. 1125-1141.

5. Adams, B.D., et al., Current density dependence of peroxide formation in the Li-O2 battery and its effect on charge. Energy & Environmental Science, 2013. 6(6): p. 1772-1778.

6. Horstmann, B., et al., Rate-Dependent Morphology of Li2O2 Growth in Li–O2 Batteries. The Journal of Physical Chemistry Letters, 2013. 4(24): p. 4217-4222.

7. Hummelshoj, J.S., A.C. Luntz, and J.K. Norskov, Theoretical evidence for low kinetic overpotentials in Li-O2 electrochemistry. The Journal of Chemical Physics, 2013. 138(3): p. 034703-12.

8. McCloskey, B.D., et al., On the mechanism of nonaqueous Li–O2 electrochemistry on C and its kinetic overpotentials: Some implications for Li–air batteries. The Journal of Physical Chemistry C, 2012. 116(45): p. 23897-23905.

9. Mitchell, R.R., et al., Mechanisms of Morphological Evolution of Li2O2 Particles During Electrochemical Growth. The Journal of Physical Chemistry Letters, 2013. 4(7): p. 1060–1064.

10. Trahan, M.J., et al., Studies of Li-Air Cells Utilizing Dimethyl Sulfoxide-Based Electrolyte. Journal of The Electrochemical Society, 2013. 160(2): p. A259-A267.

11. Jung, H.G., et al., A transmission electron microscopy study of the electrochemical process of lithium-oxygen cells. Nano Letters, 2012. 12(8): p. 4333-5.

12. Zhai, D., et al., Disproportionation in li-o2 batteries based on a large surface area carbon cathode. Journal of the American Chemical Society, 2013. 135(41): p. 15364-72.

13. Hartmann, P., et al., A rechargeable room-temperature sodium superoxide (NaO2) battery. Nature Materials, 2013. 12(3): p. 228-232.

14. McCloskey, B.D., J.M. Garcia, and A.C. Luntz, Chemical and Electrochemical Differences in Nonaqueous Li-O-2 and Na-O-2 Batteries. Journal of Physical Chemistry Letters, 2014. 5(7): p. 1230-1235.

15. Das, S.K., S. Lau, and L.A. Archer, Sodium-oxygen batteries: a new class of metal-air batteries. Journal of Materials Chemistry A, 2014. 2(32): p. 12623-12629.

16. Hartmann, P., et al., Discharge and Charge Reaction Paths in Sodium–Oxygen Batteries: Does NaO2Form by Direct Electrochemical Growth or by Precipitation from Solution? The Journal of Physical Chemistry C, 2015. 119(40): p. 22778-22786.

17. Xia, C., et al., The critical role of phase-transfer catalysis in aprotic sodium oxygen batteries. Nat Chem, 2015. 7(6): p. 496-501.

18. Lutz, L., et al., High Capacity Na–O2 Batteries: Key Parameters for Solution-Mediated Discharge. The Journal of Physical Chemistry C, 2016. 120(36): p. 20068-20076.

Figure 1