Limited Stability of Ether-Based Solvents in Lithium–Oxygen Batteries

Abstract

Li–O₂ batteries offer the tantalizing promise of a specific energy much greater than current Li ion technologies; however, many challenges remain before the development of commercial energy storage applications based on the lithium–oxygen couple can be realized. One of the most apparent limitations is electrolyte stability. Without an electrolyte that is resistant to attack by reduced oxygen species, optimizing other aspects of the redox performance is challenging. Thus, identifying electrolyte decomposition processes that occur early in the redox process will accelerate the discovery process. In this study, ATR–FTIR was used to examine various reported Li–O₂ electrolytes taken directly from the cell separators of cycled electrochemical cells. Specifically, we examined, 1 M LiPF₆ in propylene carbonate (PC), 1 M LiCF₃SO₃ in tetraethyleneglycoldimethylether (TEGDME), and 1 M LiCF₃SO₃ in a siloxane ether (1NM3) and looked for soluble decomposition products. Each electrolyte was tested using a regular Li–O₂ cathode with no catalyst and either an O₂ atmosphere or an Ar atmosphere and a Li metal anode as well as in a Li–Li symmetric cell. The 1NM3 electrolyte was found to form soluble decomposition products under all cell conditions tested, and a decomposition pathway has been proposed. It was also found that 1NM3 and TEGDME were consumed as part of the charging process in a working Li–O₂ cell, even at moderate voltages in the absence of O<sub>2.</sub