Developing Quasi-Solid-State Ether-Based Electrolytes with Trifluorotoluylation Ionic Liquids for High Voltage Lithium Metal Batteries

The practical application of quasi-solid-state ether-based electrolytes is hindered by lithium dendrite formation and poor oxidation stability, which reduce the cycle life and energy density of the battery. Here, taking advantage of the ionic liquids’ high ionic interactions and structural flexibility in forming an optimized electrode/electrolyte interface, a pyrrolidinium-based ionic liquids with trifluorotoluylation cationic segment is designed and developed. The oxidation of anions in the electrolytes is induced to form a robust inorganic LiF-rich interphase at the cathode, thereby effectively achieving high oxidation stability and suppressing the dissolution of transition metal ions. In addition, the LiF interphases derived from the trifluorotoluylation cations increase the modulus of the anode interface and suppress the growth of lithium dendrites. Therefore, the Li-LiFePO₄, Li-LiCoO₂, and Li-LiNi_0.8Co_0.1Mn_0.1O₂ full cells with the optimized electrolytes demonstrate remarkable performance improvements at high current density (10 C), a wide voltage range of 4.5 V, a high mass loading of 11.1 mg cm⁻², and a wide temperature range of −20–80 °C. Furthermore, a 2.66 Ah-level pouch cell with a high-energy-density of exceeding 356 Wh kg^‒1 and excellent cyclic stability demonstrates the potential of the strategy in providing a path for the practical application of quasi-solid-state ether-based electrolytes in high-energy-density batteries.