Electrolyte Intermolecular Interaction Mediated Nonflammable Potassium-Ion Sulfur Batteries

The design of electrolytes that are compatible with graphite electrodes and incorporate flame-retardant properties in potassium-ion batteries (PIBs) can not only facilitate their commercialization but also improve the safety reliability. However, it remains challenging, particularly in propylene carbonate (PC)-based electrolytes. Herein, we achieved a highly reversible K⁺ (de)intercalation with graphite in PC-based electrolytes by introducing the fluoroethers. We identified the strength of interactions formed between fluoroethers (e.g., 1,1,2,2-tetrafluoroethy-2,2,3,3-tetrafluoropropyl ether (HFE), 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFTFE)) and PC by heteronuclear overhauser effect spectroscopy. We find that the interaction between HFE and PC is stronger, which can significantly weaken the K⁺-PC interaction, contributing to a reversible K⁺ (de)intercalation and also endowing electrolyte nonflammable features. The kinetic and thermodynamic properties of K⁺-solvent-anion complexes in the proposed interfacial model can elucidate the electrolyte and electrode stability, enabling the as-designed potassium-ion sulfur batteries to show high performance. This discovery offers a fresh perspective for designing and advancing electrolytes in PIBs and beyond.