Synergistic Solvent Design for Fluorine‐Free Electrolytes in High‐Performance Lithium‐Ion Batteries

Abstract The development of fluorine‐free electrolytes offers a promising route for more environmentally sustainable lithium‐ion batteries (LIBs). However, the low solubility of fluorine‐free lithium salts in conventional carbonate solvents limits this progress. Additionally, while strongly coordinating solvents enhance salt dissolution, their use can lead to co‐intercalation in graphite, complicating electrolyte design. Herein, lithium bis(oxalate)borate (LiBOB) is chosen as lithium salt, and a synergistic electrolyte design strategy is employed, combining a strongly coordinating solvent (tris(2‐methylpropyl) phosphine oxide, TMP) and weakly coordinating solvent (dimethyl carbonate, DMC). This approach enables the use of fluorine‐free lithium salts while ensuring compatibility with graphite by modulating the primary coordination shell. Furthermore, this solvation structure enables the formation of an inorganic‐dominated cathode electrolyte interphase (CEI) on the LiMn ₂ O ₄ (LMO) and a solid electrolyte interphase (SEI) on the graphite, improving lithium‐ion conductivity and overall electrochemical performance. Additionally, compared to lithium hexafluorophosphate (LiPF ₆ ), fluorine‐free lithium salt minimized the formation of HF by‐products, suppressing transition metals (TMs) dissolution. As a result, 1 Ah LMO||graphite pouch cell with fluorine‐free electrolyte retains 92.8% of its capacity after 200 cycles, demonstrating excellent cycling stability and delivering high‐rate capacity of 0.8486 Ah at 2 C, compared to 84.8% retention and 0.652 Ah with the conventional electrolyte.