Autoxidation in amide-based electrolyte and its suppression for enhanced oxygen efficiency and cycle performance in non-aqueous lithium oxygen battery

In spite of several desirable properties such as high stability against superoxide anion and low vapor pressure, N-methyl-2-pyrrolidone (NMP) electrolyte is reported not suitable for use in lithium-oxygen (Li-O₂) batteries because of severe degradation upon cycling and low oxygen efficiency. In this work, we find that NMP electrolyte is reactive with O₂ gas in the presence of lithium metal and such O₂-consuming reaction (i.e., autoxidation) is a possible cause for the poor performance in Li-O₂ batteries with NMP electrolyte. The autoxidation of NMP is verified by direct measurement of the depletion of O₂ gas in the hermetically sealed symmetric Li/Li cells via in-situ gas pressure analysis. In-situ differential electrochemical mass spectroscopy (DEMS) experiment reveals that the autoxidation resulted in significant O₂ consumption upon discharge, very low O₂ efficiency upon charge, and eventually fast capacity fading. Lithium nitrate (LiNO₃), which provides a protective layer on the surface of lithium metal, is employed to suppress the autoxidation, leading to significantly enhanced oxygen efficiency and cycle life.