Ionic liquid electrolytes for enhancing the performance of lithium–sulfur batteries: a new approach to mitigating polysulfide dissolution and shuttle effects

Abstract

Despite the potential for a greater energy density than lithium-ion batteries, polysulphide dissolution, the polysulphide shuttle effect, and lithium metal instability impede the commercialization of lithium–sulfur (Li–S) batteries. To overcome these obstacles, this study investigates ionic liquids (ILs) as electrolytes, with a particular emphasis on mixed-anion ILs and high concentrations of lithium salt. As demonstrated by undetectable levels in Raman and UV spectroscopy, our results demonstrate that trimethyl-isobutyl phosphonium (P111i4FSI) with 30 mol% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) efficiently inhibits polysulphide dissolution. With a specific capacity of 625 mA h g⁻¹ (based on sulphur) and a 60% capacity retention after 200 cycles, this electrolyte dramatically enhances Li–S battery performance. These findings show how high-concentration IL electrolytes may stabilise lithium interfaces and reduce polysulfide-related problems, bringing Li–S battery technology closer to real-world uses.