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

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Abstract 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 0.8 Co 0.1 Mn 0.1 O 2 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 0.8 Co 0.1 Mn 0.1 O 2 //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.

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