Insight on the Li₂S electrochemical process in a composite configuration electrode

A novel, low cost and environmentally sustainable lithium sulfide-carbon composite cathode, suitably prepared by combining polyethylene oxide (PEO), LiCF₃SO₃ and Li₂S-C powders is presented herein. The cathode is characterized in a lithium-metal cell employing a solution of LiCF₃SO₃ salt in dioxolane-dimethylether (DOL:DME) as the electrolyte. The detailed NMR investigation of the diffusion properties of the electrolyte is reported in order to determine its suitability for the proposed cell. The addition of LiNO₃ to the electrolyte solution allows its practical application in a lithium sulfur cell using an Li₂S-C-based cathode characterized by a specific capacity of about 500 mA h g^-1 (with respect to the Li₂S mass). The cell holds its optimal performances for over 70 cycles at a C/5 rate, with a steady state efficiency approaching 99%. The X-ray diffraction patterns of the cell upon operation suggest the reversibility of the Li₂S electrochemical process, while the repeated electrochemical impedance spectroscopy (EIS) measurements indicate the suitability of the electrode-electrolyte interface in terms of low and stable cell impedance. Furthermore, the EIS study clarifies the activation process occurring at the Li₂S cathode during the first charge process, leading to a decrease of cell polarization during the following cycles. The data reported here shed light on important aspects which should be considered for the efficient application of a Li₂S cathode in lithium batteries.