Disiloxane with nitrile end groups as Co-solvent for electrolytes in lithium–sulfur batteries – A feasible approach to replace LiNO ₃

The lithium-sulfur battery is a leading candidate for a new-generation Li-ion battery, because of its high theoretical capacity and abundance of sulfur. Yet, the flammability of either the organic-carbonate or ether-based electrolytes used in such battery systems is of concern. Moreover, the oxidation of Li ₂ S leads to the formation of polysulfides (Li ₂ S _3-8 ), which dissolve in the electrolyte and initiate a shuttle mechanism, which results in low Coulombic efficiency and growth of a thick SEI on the anode. Therefore, various electrolyte additives, like LiNO ₃ , are added to the electrolyte. Unfortunately, the nitrate additive is gradually consumed and the “shuttle effect” resumes. Here we present a LiNO ₃ -free electrolyte consisting of nitrile-functionalized disiloxane (TmdSx-CN) with dissolved LiTFSI as a candidate electrolyte for lithium-sulfur batteries. We have examined the effect of TmdSx-CN as a co-solvent along with 1,3-dioxolane (DOL) on the performance of Li/S cells. It was found that LiNO ₃ -free TmdSx-CN:DOL electrolyte mitigates the polysulfide shuttle. The cell containing this electrolyte yields an average capacity of 700 mAh g ⁻¹ and 96% Coulombic efficiency for more than 100 cycles. Moreover, 87.5% energy efficiency, which is similar to the LiNO ₃ -based control cell. We expect that our preliminary results will encourage the further use of siloxane-based electrolytes in metallic-lithium battery systems, and specifically, in lithium-sulfur batteries.