Sulfolane-Graphite Incompatibility and Its Mitigation in Li-ion Batteries

The non-flammability and high oxidation stability of sulfolane (SL) make it an excellent electrolyte candidate for lithium-ion batteries (LIBs). However, its incompatibility with graphitic anode prevents the realization of these advantages. To understand how this incompatibility arises on molecular level so that it can be suppressed, we combined theoretical calculation and experimental characterization and reveal that the primary Li⁺ solvation sheath in SL is depleted of fluorine source. Upon reduction, SL in such fluorine-poor solvation sheath generates insoluble dimer with poor electronic insulation, hence leading to slow but sustained parasitic reactions. When fluorine content in Li⁺-SL solvation sheath is increased via salt concentration, a high stability LiF-rich interphase on graphite can be formed. This new understanding of the failure mechanism of graphite in SL-based electrolyte is of great significance in unlocking many possible electrolyte solvent candidates for the high-voltage cathode materials for next-generation LIBs.