Exploring Fluoropyridine Electrolytes in Li–S Batteries: Balancing Performance and Stability across Temperatures

A novel high-donor 3-fluoropyridine (3FPy) electrolyte has been introduced for use in Li–S batteries, demonstrating an inhibition effect on the polysulfide shuttle, even without the addition of LiNO₃. In this study, fluoropyridine electrolytes, including 2-fluoropyridine (2FPy) and 3FPy electrolytes, are studied using electrochemical analysis, mass spectrometry (MS), and high-performance liquid chromatography (HPLC) methods. Collision-induced dissociation spectra revealed that Li⁺ preferentially solvates with different fluoropyridines, with 2FPy exhibiting a stronger interaction due to ortho-fluorine’s influence, compared to 4FPy and 3FPy. However, MS and HPLC analyses showed that 2FPy is reactive with polysulfides, while 3FPy offers high solubility for polysulfides and sulfur without reacting with them at room temperature. Despite 3FPy performing well at room temperature, further electrochemistry studies at elevated (60 °C) and reduced (0 °C) temperatures reveal the challenges. At high temperatures, LiNO₃ is essential to suppress the polysulfide shuttle; and at low temperatures, the performance with the 3FPy electrolyte significantly lags behind that of the ether-based electrolyte.