Characteristics of Li2S8-tetraglyme catholyte in a semi-liquid lithium–sulfur battery

• Li2S8–TEGDME catholyte is used in a safe, semi-liquid lithium–sulfur cell.
• The cell is characterized by remarkable safety and non-flammability.
• The 2 V-cell shows a capacity ranging from 430 mAh g−1S to 700 mAh g−1S.
• The cell stability is affected by the voltage cut-off as demonstrated by XPS.
• LiNO3-addition to the catholyte stabilizes the cell under extended voltage limits.

In this paper we exploit the use of a Li2S8-containing electrolyte based on a non-flammable TEGDME in a semi-liquid lithium cell, characterized by a configuration usually employed in conventional lithium ion batteries. The cell, using a sulfur-free, Super P carbon electrode shows a capacity varying from 430 mAh g−1 s to 700 mAh g−1S. The cycling tests show that the stability of the cell is strongly affected by the voltage cutoff directly controlling the electrochemical process, in particular the polysulfide shuttle reaction. In this respect, XPS measurement shows the deposition of Li2S2 salt at the lithium electrode surface as the cell voltage cutoff is enlarged, thus suggesting that the use of the reduced voltage and capacity regimes may lead to higher stability. Under the best control regime, the 2 V cell delivers a capacity of 530 mAh g−1S, with extremely low polarization and cycling stability extended up to 100 charge–discharge cycles. Furthermore, we demonstrate that enhanced performances may be effectively reached by adding LiNO3 salt to the electrolyte solution to form a stable, protective SEI film on the lithium surface, thus avoiding the shuttle process and increasing the cell efficiency, even under a full voltage cutoff range, i.e. extending from 1 V to 3 V.