Exploration of Side Reactions Based on Graphite-Li2O2 Redox Couple for Lithium Oxygen Battery

Abstract

In recent years, lithium oxygen batteries (LOBs) have been considered as one of most promising energy storage systems for long-range electric vehicles and smart grid due to its high energy density.1-3 However, there are many fundamental scientific problems hinder it’s realization from theory to practice, including the sluggish oxygen evolution reaction (OER), the instability of electrode/electrolyte and the contamination of H2O/CO2/N2 in air. The instability of electrode and electrolyte always leads to serious side reactions which result in high charge overpotential and poor cycle life. In the study of LOBs, Li metal is usually used as the anode material to achieve high energy densities because Li is the lightest and most electropositive metal. Besides, the amount of Li metal is always far enough in our battery system. Thus, the electrochemical performance obtained with excess amount of Li metal could not reflect the true performance of our battery due to the existing side reactions which will constantly consume the lithium sources.4 To solve this problem, we used a graphite-Li2O2 redox couple for LOBs. Fig. 1 shows the typical charge-discharge profiles of Li-graphite, Li-O2 and graphite-Li2O2 batteries. Further, we systematically investigated the side reactions occurred in this battery system and evaluated its impact on the cycle performance of LOBs. Graphite has been widely used as anode material in commercial lithium ion battery, and has also been investigated in lithium sulfur and lithium oxygen batteries.4-6 In our cases, we used LISICON protected graphite as anode to avoid the contamination of O2. Lithium peroxide-carbon composites were used as cathode and acted as the only lithium source for LOB. The battery was cycled at different C-rates and the cathode was measured by multiple analysis methods including SEM, TEM, Raman/FTIR, HNMR etc. Reference 1. Abraham, K. M.; Jiang, Z. J. Electrochem. Soc. 1996, 143, (1), 1-5. 2. Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nat. Mater. 2012, 11, (1), 19-29. 3. Luntz, A. C.; McCloskey, B. D. Chem. Rev. 2014, 114, (23), 11721-50. 4. Chun, J.; Kim, H.; Jo, C.; Lim, E.; Lee, J.; Kim, Y. ChemPlusChem 2015, 80, (2), 349-353. 5. Agostini, M.; Scrosati, B.; Hassoun, J. Adv. Energy Mater. 2015, 5, (16), 1500481. 6. Bhargav, A.; Fu, Y. J. Electrochem. Soc. 2015, 162, (7), A1327-A1333. Figure 1