The Aprotic Lithium-Air Battery: New Insights into Materials and Reactions

In the long term high-volume applications such as electric vehicles and the storage of electricity from renewables require a step change in energy density, material sustainability and cost that stepwise improvement of current Li-ion technology based on intercalation electrodes cannot hope to deliver. Radical new approaches are required, motivating ambitious and potentially game-changing research ‘beyond intercalation chemistries’. One such alternative is the Li-air(O₂) battery; its theoretical specific energy exceeds that of Li-ion, but many hurdles face its realization.[1-3] First, the processes that occur in the cell on discharge and charge need to be understood to use such knowledge to address the hurdles.

The discharge reaction in the cathode of the nonaqueous Li-O₂ cell involves reduction of O₂ and the formation of solid Li₂O₂; the process is reversed on charge, O₂ + 2 Li⁺ + 2 e^– « Li₂O₂. It is now understood that parasitic reactions are a major cause for overpotentials on discharge and charge and limited cycle life. These are both caused by decomposition of many electrolytes and the cathode. Poor electron transport in Li₂O₂ is recognized as a major factor limiting its achievable amount during discharge (that is, achievable capacity) and the rate and overpotentials at which it can be formed and decomposed during cycling[4-6]. A further major challenge is extended cyclability at desirable deep discharge. We will discuss recent insights into the mechanism of Li₂O₂ formation and decomposition, of parasitic reactions and novel electrode and electrolyte materials.

[1]                 P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nature Mater. 11 (2012) 19.

[2]                 J. Christensen, P. Albertus, R.S. Sanchez-Carrera et al., J. Electrochem. Soc. 159 (2012) R1.

[3]                 Y.-C. Lu, B.M. Gallant, D.G. Kwabi et al., Energy Environ. Sci. 6 (2013) 750.

[4]                 Y. Chen, S.A. Freunberger, Z. Peng, O. Fontaine, P.G. Bruce, Nature Chem. 5 (2013) 489.

[5]                 A. Dunst, V. Epp, I. Hanzu, S.A. Freunberger, M. Wilkening, Energy Environ. Sci. 7 (2014) 2739.

[6]                 L. Johnson, C. Li, Z. Liu et al., Nature Chem. 6 (2014) 1091