The Influence of Carbon Cathode in Rechargeable Li-O2 Batteries Based on a LiNO3-Litfsi/DMSO Electrolytes

Abstract

Rechargeable Li-O2 batteries have been considered one of the most promising candidates as the power source for electric vehicles due to their extremely high energy density [1,2]. In spite of this great prospect, there are still many obstacles such as the degradation of the electrode, huge polarization, low energy efficiency and poor reversibility [3]. Thus, developing stable and effective cathode catalysts is important as they can be utilized to decrease the polarization and increase the reversibility. Carbon materials are known to advantageous air electrodes for Li-O2 batteries with nonaqueous electrolyte due to their good conductivity and site of reversible electrode reaction. However, the influence of carbon materials on electrochemical performance in Li-O2 batteries is not clear. Furthermore, recent research focused on selecting a combination of lithium salt and electrolytes by challenge in improving the electrochemical performance of Li-O2 batteries. In this study, we select four different kinds of carbon materials such as multi-walled carbon nanotubes (MWCNTs), CMK-3, Graphene nanosheets (GNSs), and KB as air electrodes and further examine their electrochemical performance in Li-O2 batteries with 0.7 M LiNO3-0.3 M LiTFSI/DMSO electrolytes. We find that the Li-O2 cell with a MWCNTs electrode in a 0.7 M LiNO3-0.3 M LiTFSI/ DMSO electrolyte demonstrates good rate performance and cycle stability comparison with other carbon electrodes. The result shows that the Li-O2 cell based on MWCNTs electrodes with a cut-off capacity of 1000 mAg-1 at 500 mAg-1 can undergo around 90 cycles without obvious capacity loss. Even when the discharge depth is increased to 2000 mAhg-1, stable cycling is maintained for 45 cycles with a charge potential below 4.0 V vs. Li/Li+. Moreover, when the rate performance of Li-O2 cell with MWCNTs electrodes is examined at different current densities from 200, 400, 500, and 1000 mAg-1 with a cut-off capacity of 2000 mAhg-1, interestingly, the discharge voltage is not drastically increased even the current density is 1000 mAg-1. And then, the chare voltage remains at around 3.85 V, which is similar to the current density of 200 mAg-1 (about 3.82 V). Therefore, these results demonstrate that the MWCNTs maintain excellent activity and stability of catalysts toward the reversible formation-decomposition of Li2O2. Reference [1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon, Nat. Mater. 2012, 11, 172– 172 [2] J. Lu, L. Li, J.-B. Park, Y.-K. Sun, F. Wu, K. Amine, Chem. Rev. 2014, 114, 5611 – 5640. [3] L. Grande, E. Paillard, J. Hassoun, J.-B. Park, Y.-J. Lee, Y.-K. Sun, S. Passerini,