From Fluorinated to All-Fluorine-Free Systems: Hückel Anion-Based Electrolytes for Lithium–Sulfur Batteries with Enhanced High C-Rate Sulfur Utilization

High Resolution Image Download MS PowerPoint Slide Lithium–sulfur (Li–S) batteries are considered a promising alternative to conventional lithium-ion systems; however, their practical deployment is still limited by insufficient sulfur utilization, polysulfide shuttling, and capacity fading. In this work, two complementary modification strategies for Li–S batteries are systematically investigated. First, obtaining simple, easy-to-prepare, and low-cost model cathodes enables the simulation of cycling of the cell with different sulfur availability through a comparative assessment of conductive carbon blacks (Super P, Ketjen Black EC-300-JD, and Vulcan XC-72), NaCMC binder, and sulfur content. The influence of electrode formulation, sulfur loading, electrolyte-to-sulfur (E/S) ratio, and conductive carbon type on electrochemical performance is evaluated, enabling the identification of an optimized model cathode. In the second part of the study, electrolyte optimization is explored using a series of Hückel anion-based lithium salts, including fluorine-free candidates. The electrochemical performance of lithium 4,5-dicyano-2-(n-heptafluoropropyl)imidazolide (LiHDI), lithium 4,5-dicyano-2-(pentafluoroethyl)imidazolide (LiPDI), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), and lithium 2,4,5-tricyanoimidazolide (LiTIM) is benchmarked against the conventional LiTFSI-based electrolyte. The investigated salts generally deliver higher discharge capacities, particularly at elevated charge rates, and exhibit improved capacity retention during prolonged cycling. The combined cathode and electrolyte engineering approach demonstrates enhanced electrochemical stability and reduced capacity decay, indicating that Hückel anion-based electrolytes represent a viable direction for further optimization of Li–S battery systems.