batteries have a major obstacle regarding the large overpotential upon charging that results from the low conductivity of the discharge product.1-3
Thus, various redox mediators (RMs) have been widely studied to reduce the overpotential upon the charging process; this should help promote the oxidation of Li2
. However, since RMs degrade the Li-metal anode through a parasitic reaction between the RM and the Li metal, a solution is needed to rectify this phenomenon. Here, we propose an effective method to prevent the migration of the RM toward the anode side of the lithium metal by using a modified separator with a negatively-charged polymer. When DMPZ (5,10-dihydro-5,10-dimethylphenazine) is used as the RM, we find that the modified separator suppressed the migration of DMPZ toward the counter electrode of the Li-metal anode; this is investigated by a visual redox couple diffusion test, morphological investigation, and X-ray diffraction study. This advanced separator effectively maximizes the catalytic activity of the redox mediator. Li–O2
batteries using both a high concentrated DMPZ and the modified separator exhibit improved performances and maintain 90% of the round-trip efficiency up to the 20th cycle.
1. B. D. McCloskey, R. Scheffler, A. Speidel, D. S. Bethune, R. M. Shelby, and A. C. Luntz, J. Am. Chem. Soc., 2011, 133, 18038–18041.`
2. S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Bardé, and P. G. Bruce, Angew. Chem. Int. Ed. Engl., 2011, 50, 8609–8613.
3. S. Meini, N. Tsiouvaras, K. U. Schwenke, M. Piana, H. Beyer, L. Lange, and H. A. Gasteiger, Phys. Chem. Chem. Phys., 2013, 15, 11478–11493