The instability of the electrolyte is believed to be one of the reasons affecting the electrochemical performance of the today's Li–O2 batteries. Aim of this study is to give new insights about the stability of LiTFSI-Tetraglyme as electrolyte for Li–O2 batteries. Thus the electrochemical behavior of Li–O2 cells comprised of Super-P based cathode coated on gas diffusion layer, lithium anode and LiTFSI-Tetraglyme electrolyte is investigated by galvanostatic cycling and impedance spectroscopy. The reversibility of the formation/dissolution of Li2O2 in the carbon cathode upon discharge/charge is suggested by impedance outcomes and confirmed by ex situ XRD measurements. The chemical degradation of the liquid aprotic electrolyte is investigated via gas chromatography with headspace injection, which allows detecting decomposition products generated during the galvanostatic charge/discharge of Li–O2 batteries.