High‐Entropy Non‐Flammable Ionic Liquid/Dimethoxymethane Composite Electrolyte for High‐Performance Lithium‐Ion Batteries

The development of high-energy-density and high-safety lithium-ion batteries requires advancements in electrolytes. This study proposes a high-entropy ionic liquid/ether composite electrolyte, which is composed of N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PMP-TFSI) ionic liquid, dimethoxymethane (DME), lithium difluoro(oxalato)borate (LiDFOB), fluoroethylene carbonate (FEC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). In this electrolyte, a unique coordination structure forms, where Li⁺ is surrounded by a highly complex environment consisting of DME, FEC, TTE, TFSI^-, DFOB^-, and PMP⁺. The effects of this solution structure on the solid-electrolyte interphase chemistry and Li⁺ desolvation kinetics are examined. The proposed electrolyte has low flammability, high thermal stability, negligible corrosivity toward an Al current collector, and the ability to withstand a high potential of up to 5 V. Importantly, this electrolyte is highly compatible with graphite and SiO_x anodes, as well as a high-nickel LiNi_0.8Co_0.1Mn_0.1O₂ cathode. Operando X-ray diffraction data confirm that the co-intercalation of DME and PMP⁺ into the graphite lattice, a long-standing challenge, is eliminated with this electrolyte. A 4.5-V LiNi_0.8Co_0.1Mn_0.1O₂//graphite full cell with the proposed high-entropy electrolyte is shown to have superior specific capacity, rate capability, and cycling stability, demonstrating the great potential of the proposed electrolyte for practical applications.