LAUSR

Abstract 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-O 2 ) batteries because of severe degradation upon cycling and low oxygen efficiency. In this work, we find that NMP electrolyte is reactive with O 2 gas in the presence of lithium metal and such O 2 -consuming reaction ( i.e., autoxidation) is a possible cause for the poor performance in Li-O 2 batteries with NMP electrolyte. The autoxidation of NMP is verified by direct measurement of the depletion of O 2 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 O 2 consumption upon discharge, very low O 2 efficiency upon charge, and eventually fast capacity fading. Lithium nitrate (LiNO 3 ), 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.