Influence of Electrolyte Li+ Ion Concentration on the Growth of Li2O2 Discharge Products

Organic Li-air battery is represented as the most promising energy-storage technology due to its ultra-high theoretical energy density.1,2 However, how to realize the advantage of high energy density has become one of the most important and urgent challenges. In our opinion, discharge process could be considered as fulfilling Li2O2 crystals in the pores of air cathode. Since supersaturation is the key driving force to influence the insoluble sedimentation process3, the growth of discharge products could be tailored by the activity of Li+ ions and/or reductive species. Therefore discharge products are possible to grow tri-dimensionally, instead of a thin layer, by adjusting Li+ ion concentration in the electrolytes.

In this work, it is investigated the influence of electrolyte Li+ ion concentrations on discharge behavior. As shown in Fig.1, the discharge behaviour could be divided into 3 regions as electrolyte concentration increases from 10-3 M to 5 M. The first region is ranged from 10-3 to 1 M, where discharge capacities are monotonic augmenting. It only delivers 2211 mAh gcarbon-1 at 10-3 M, and quickly ramps to 3013, 6055, and 7529 mAh gcarbon-1 at 10-2, 10-1 and 1 M separately. At 2 and 3 M, the discharge capacity hovers at an extremely high level, 12250 and 13245 mAh gcarbon-1 respectively. As the concentration further increases to 4 M and 5 M, the discharge capacity slumps severely to less than 4000 mAh gcarbon-1. The capacity variation is up to ~600% as a result of the tailoring effect of Li+ ion concentration in the electrolytes. The probable mechanism and further discussion will be presented in the conference.

Reference
1. P.G. Bruce.; S.A., Freunberger, L.J. Hardwick, J. M. Tarascon, Nature Mater. 2012, 11, 19;
2. G. Girishkumar, B. McCloskey, A.C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett. 2010, 1, 2193.
3. H.J. Scheel, T. Fukuda, Crystal Growth Technology John Wiley & Sons, Ltd. 2003.