Solvating Additives and Their Role in Increasing the Capacity of Nonaqueous Li-O2 Batteries

The passivation of Li-O2 battery cathode by the electronically insulating Li₂O₂ limits the maximum attainable capacity in these batteries.[1] We show that electrolyte additives, such as tiny amounts of water, which activate solution-mediated growth of Li₂O₂, make it possible to circumvent this fundamental limitation and enable high capacity Li-O2 batteries. Design rules for choosing these solvent additives are presented.[2] 

1. V. Viswanathan, K. Thygesen, J.S. Hummelshøj, J. K. Nørskov, G. Girishkumar, B.D. McCloskey, A. Luntz,  J. Chem. Phys., 135, 214704 (2011).
2. N. B. Aetukuri, B. D. McCloskey, Jeannette M. García, L. E. Krupp, V. Viswanathan and A. C. Luntz, Nature Chemistry., DOI: 10.1038/nchem.2132 (2014).

Figure 1: Proposed mechanism for the growth of Li₂O₂ toroids in the presence of water. The deposition of Li₂O₂ in a Li-O₂ cell is shown, schematically, to proceed via a surface electrochemical growth process. The presence of a additive (water in our experiments) that solvates LiO₂^* to Li⁺ and O₂^- triggering a solution mechanism.  Design rules for additive engineering are presented in the contour plot.