Ultralow Concentration Nonflammable Electrolytes Mediated by Intermolecular Interactions for Safer Potassium‐Ion Sulfur Batteries

Abstract Designing electrolytes that are compatible with graphite anodes and possess flame‐retardant features is strongly demanded in potassium‐ion batteries (PIBs) to inhibit solvent co‐insertion and graphite exfoliation, and also stabilize the highly active potassium‐based species (e.g., KC₈). Herein, a nonflammable electrolyte is designed by introducing the fluoroethers to stabilize graphite anodes, particularly at an ultralow concentration (<0.43 m) that is rarely reported before. It is discovered that intermolecular interactions can form between the 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (i.e., HFE) diluent and trimethyl phosphate (TMP) flame‐retardant by electronegative fluorine (δ⁻F) and electropositive hydrogen (δ⁺H). The intermolecular interactions can change the potassium ion (K⁺) solvation structure (e.g., weakening the K⁺‐TMP interaction), and then determine the properties of the K⁺‐solvent‐anion complex at the electrode interface. a molecular interfacial model is presented with a new coordination mechanism involving the diluent to elucidate the relationship between the intermolecular interactions and electrode performance (i.e., K⁺‐solvent co‐insertion, or reversible K⁺ (de)intercalation) at the molecular scale, facilitating the design of high safety and high energy density potassium‐ion sulfur batteries. This study sheds light on the importance of intermolecular interactions to tune electrolyte properties and also opens new avenues for designing electrolytes for safe and practical PIBs.