Monday, 20 June 2016
Riverside Center (Hyatt Regency)
B. G. Kim and J. W. Choi (Korea Advanced Institute of Science and Technology)
Lithium-oxygen batteries (Li-O2) have lately received considerable attention because of their exceptional potential gravimetric energies, i.e., 3~5 times compared to those of conventional lithium ion batteries. In spite of the unparalleled theoretical gravimetric energy, lithium-oxygen batteries are still under research because of their insufficient cycle lives. This shortcoming is associated with several entangled fading mechanisms [1,2]: partly irreversible nature of the air-cathode, electrolyte evaporation, unstable lithium anode interface, etc. While the reversibility in air-cathodes has been recently improved significantly by the deepened understanding on the electrode-electrolyte reaction and the integration of diverse catalysts, the stability of the lithium anode interface has received relatively much less attention. The destabilization of the lithium anode interface by crossover of water and oxygen from the air-cathode side can indeed cause as fatal degradation for the cycle life as the irreversibility of the air-cathodes [3]. Here we report that cheap poreless polyurethane separator can effectively prevent this crossover while allowing the selective diffusion of lithium ions by high electrolyte uptake of the polyurethane separator through the interchain space. The polyurethane separator also protects lithium anodes from redox mediators, lithium iodide, used to enhance the reversibility of the air-cathode reaction. Based on the lithium anode protection, a consistent capacity of 600 mAh/g is preserved for more than 200 cycles. This study reveals that in most operation conditions, the destabilization of the lithium anode is more critical for the cycle life than the poor reversibility of air-cathode reaction. The present study can also be readily applicable to many other rechargeable batteries that suffer from similar interfacial degradation by side products from the other electrode.
Fig. 1. Comparative schematic illustration of lithium-oxygen cells with (a) conventional polyolefin porous PE separator and (b) poreless PU separator. (c) The cycling performance of the PE, PU, PE+LiI, and PU+LiI cells at a current density of 200mA/g with a fixed capacity of 600 mAh/g. The inset shows XRD spectra and color changes of the Li metals of PE and PU cells after 70 and 100 cycles, respectively.
References
[1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J.-M. Tarascon, Nat. Mater. 11 (2012) 19-29.
[2] L. Grande, E. Paillard, J. Hassoun, J.-B. Park, Y.-J. Lee, Y.-K. Sun, S. Passerini, B. Scrosati, Adv. Mater. 27 (2015) 784-800.
[3] R. S. Assary, J. Lu, P. Du, X. Luo , X. Zhang, Y. Ren, L. A. Curtiss, K. Amine, ChemSusChem 6 (2013) 51-55.
