Ionic Liquid Reinforcing Ether Coordination of Localized High Concentration Electrolyte Enables High‐Voltage Lithium Metal Batteries

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The decomposition of 1,2-dimethoxyethane (DME) in localized high-concentration electrolytes (LHCEs) under high voltage produces fragile and unstable organic fragments at the cathode/electrolyte interphase, which greatly damages the cycling performance of high-energy-density lithium metal batteries. Herein, a robust strategy is proposed by adding ionic liquid of 1-Methyl-1-propyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₃TFSI) as co-solvent into the bulk electrolyte to significantly improve the stability of solvated DME through reinforcing the ion-dipole interaction between TFSI⁻ and DME. The Pyr₁₃TFSI can balance the interaction among the electrolyte components to reduce the dynamic de-coordinated DME molecules and promote the formation of anion-derived cathode electrolyte interphase with excellent electrochemical stability and high Li⁺ transport dynamics. The Li||LiNi0.8Co0.1Mn0.1O₂ coin cells with Pyr₁₃TFSI exhibit capacity retention of 76.1% after 1800 cycles at 1 C rate (4.5 V), and 77.1% after 800 cycles at a high cut-off voltage of 4.6 V. Furthermore, the cells using Li anode with the thickness of 50 µm and high LiNi0.8Co0.1Mn0.1O₂ loading of 18.68 mg cm⁻² can operate for 175 cycles with high-capacity retention of 73.35%. This work demonstrates that modulating the interactions among electrolyte components using ionic liquid can optimize the coordination chemistry for advanced high-energy density Li metal batteries.