Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2012.
for Adv. Mater., DOI: 10.1002/adma.201204018
Enhanced Power an
d Rechargeability of a Li?O2 Battery Based on a Hierarchical-Fibril CNT Electrode Hee-Dae Lim, Kyu-Young Park, Hyelynn Song, Eui Yun Jang, Hyeokjo Gwon, Jinsoo Kim, Yong Hyup Kim, Márcio D. Lima, Raquel Ovalle Robles, Xavier Lepró, Ray H. Baughman, and Kisuk Kang*
Submitted to Supporting Information
Figure S1. SEM images of highly aligned CNT fibrils at various magnifications. The twodimensional CNT sheets were cross-stacked with a 90° shift (inset of Figure S1d: TEM image of one string of a multi-wall CNT).
Figure S2. AFM images of a CNT fibril. One sheet of the CNT fibril was composed of hundreds of CNT bundles, and each bundle was made up of many CNT strings. One bundle of CNT is ~5 μm in thickness and 150 nm in height.
Figure S3. HR-TEM images of CNT strand. The MWNTs is 10-15 nm thick and composed of about 8-9 walls.
Figure S4. (a) The SEM image of single CNT sheet. (b) The thickness of the non-woven CNT powder electrode.
Figure S4a shows the SEM image of the single CNT sheet which is about 1.4 ?m thick. The thickness of the air electrode that is comprised of 10 sheets of CNT fibrils is approximately 14 ?m. The air electrode with non-woven CNT also has a similar thickness about 15 ?m (Figure RS4b). We also measured the loading densities of two electrodes and found they are 0.016 mg cm-2 for the aligned CNT electrode and 0.0166 mg cm-2 for the non-woven CNT electrode, respectively. This indicates that the porosities of the two electrodes are comparable and the primary difference of two electrodes comes from the distribution of pores and their individual sizes. This measurement strongly supports that the enhanced electrochemical performances were mainly originated from the unique electrode structure. Because the woven CNT electrode has uniform pores within the aligned structure, it is much beneficial to the facile accessibilities of oxygen and Li ions compared to the random pores of non-woven CNT electrode even in the same volume.
Figure S5. Cycle stability and Coulombic efficiency of Li?O2 cells at ultra-high current densities of 4,000 mA g?1 and 5,000 mA g?1.
Figure S6. Electron diffraction patterns of (a) an as-prepared electrode and (b) the electrode after the first discharge. The formation of Li2O2 was detected after the discharge.
Figure S7. EDS mapping of the CNT string after the first discharge: (a) original TEM image, (b) carbon elemental map, and (c) oxygen elemental map. EDS mapping was used to demonstrate the uniform coating of the discharge products on the CNT surface. The oxygen elemental mapping was thicker than that of the carbon, which indicates the uniform formation of an oxide on the entire CNT surface.
Figure S8. SEM images of the air electrode based on a woven CNT after 100 cycles at various magnifications. Many small beads were produced after 100 cycles. Nevertheless, it is worthwhile to note that the overall structure was maintained after many cycles.
Figure S9. (a) The HR-TEM image of the bead-like discharge products and (b) the electron diffraction patterns at the white rectangular region. It demonstrates that the particles were composed of Li2O2.
Figure S10. The TEM image of the bead-like discharge products. (a) The EDS and (b) the EELS spectra.
The figure above demonstrates that the bead particles were composed of oxygen element, while the F and P were from residual electrolyte and Ni was from Ni grid for TEM observation (Figure S10a). Because Li is not detected by EDS, we additionally investigated the existence of lithium through EELS spectra (electron energy loss spectroscopy, Figure S10b). The peak near ~56 eV confirms the existence of lithium in the bead particle. [1,2] These elemental analyses reveal again that the beads are Li2O2.
Submitted to  K. Rana, G. Kucukayan-Dogu, H. S. Sen, C. Boothroyd, O. Gulseren, E. Bengu, J. Phys. Chem. C 2012, 116, 11364.  X. H. Liu, J. W. Wang, Y. Liu, H. Zheng, A. Kushima, S. Huang, T. Zhu, S. X. Mao, J. Li, S. Zhang, W. Lu, J. M. Tour, J. Y. Huang, Carbon 2012, 50, 3836.