Oxygen Reduction Pathways in the Li-O2 Battery: Understanding Solvent-Water Interactions

Abstract

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that exceeds the capacity of Li-ion batteries. We must explore alternatives to Li-ion if we are to have any hope of meeting the long-term requirements for energy storage. One such alternative technology is the Li-air (O2) battery; its theoretical specific energy exceeds that of Li-ion five-fold, but many obstacles face its realisation.1–4 It is assumed that H2O in the Li-O2 battery will result in irreversible formation of LiOH and thus gas streams must be dried before entering the battery. Projections have suggested that this would sacrifice one third of the pack weight to a gas filtration unit required to bring atmospheric H2O content to functional levels (<1 ppm).5–9 Understanding the specific solvent properties that are associated with H2O tolerance, or distinct lack of, can guide rational selection of solvents able to tolerate wet air streams and reduce the requirements of the gas filtration unit, increasing the practical energy density.Here we consider competition between reversible 2e- O2 reduction and proton coupled irreversible 4e- O2 reduction. The predisposition to favour one of these O2 reduction pathways is largely solvent dependent. We have combined a range of methods including cyclic voltammetry, operando pressure analysis, NMR, FTIR, Raman, UV-vis spectroscopy and SEM to investigate the O2 reduction pathways in four common Li-air electrolytes containing H2O.10 H2O concentrations spanning 0–36% were employed to understand the onset and of the irreversible 4e- O2 reduction process across these solvents, with specific solvent properties being attributed to their performance. The results of these studies will be presented, along with their implications on rational future solvent development for rechargeable Li-O2 battery electrolytes. Reference s : [1] X. Gao, Y. Chen, L. Johnson and P. G. Bruce, Nat. Mater. 15 (2016) 882–888.[2] N. Feng, P. He and H. Zhou, Adv. Energy Mater. 6 (2016) 1502303.[3] L. Ma, T. Yu, E. Tzoganakis, K. Amine, T. Wu, Z. Chen and J. Lu, Adv. Energy Mater. 8 (2018) 1–13.[4] D. Aurbach, B. D. McCloskey, L. F. Nazar and P. G. Bruce, Nat. Energy 1 (2016) 16128.[5] K. G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu and V. Srinivasan, Energy Environ. Sci. 7 (2014) 1555-1563.[6] P. Tan, W. Shyy, T. S. Zhao, R. H. Zhang and X. B. Zhu, Appl. Energy 182 (2016) 569–575.[7] C. Shu, J. Wang, J. Long, H. K. Liu and S. X. Dou, Adv. Mater. 31 (2019) 1–43.[8] A. Dai, Q. Li, T. Liu, K. Amine and J. Lu, Adv. Mater. 31 (2018) 1805602.[9] D. G. Kwabi, T. P. Batcho, S. Feng, L. Giordano, C. V. Thompson and Y. Shao-Horn, Phys. Chem. Chem. Phys., 18 (2016) 24944–24953.[10] H. Guo, W. Luo, J. Chen, S. Chou, H. Liu and J. Wang, Adv. Sustain. Syst. 2 (2018) 1700183.