Fluorinated electrolytes for lithium–sulfur and beyond-lithium metal–sulfur batteries

Metal–sulfur batteries, particularly lithium–sulfur (Li–S) systems, have attracted significant attention due to their high theoretical energy densities, low cost, and sustainability benefits arising from sulfur’s abundance and non-toxicity. Despite extensive research, their practical deployment remains limited by persistent challenges such as polysulfide shuttling and metal anode degradation, which collectively lead to poor coulombic efficiency and limited cycle life. These issues are further intensified in emerging systems employing sodium, potassium, magnesium, calcium, and siliconbased anodes. Fluorinated electrolytes have emerged as a promising approach to address these limitations. Fluorination enhances oxidative stability, suppresses polysulfide dissolution, promotes stable solid–electrolyte interphase (SEI) formation, and improves safety. Although widely studied in lithium-ion and lithium-metal batteries, fluorinated electrolytes remain underexplored in metal–sulfur systems, despite growing evidence of their potential to mitigate key degradation pathways. This review provides a mechanism-focused analysis of fluorinated electrolytes for metal–sulfur batteries, with a particular emphasis on Li–S systems. It begins by assessing the limitations of conventional electrolytes and examines how fluorinated solvents, salts, and additives influence polysulfide solubility, electrode interfacial stability, and overall electrochemical performance. The discussion then extends to emerging non-lithium metal–sulfur systems, where fluorinated electrolytes can improve stability. Environmental and economic considerations are addressed, followed by an outlook on key parameters and target goals for realizing practical metal–sulfur batteries by leveraging fluorinated electrolytes. By connecting electrolyte design to specific failure mechanisms, this review establishes a framework for targeted materials development and outlines future directions for advancing high-performance, practical metal–sulfur batteries.