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

Abstract 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 (Pyr 13 TFSI) 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 Pyr 13 TFSI 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||LiNi 0.8 Co 0.1 Mn 0.1 O 2 coin cells with Pyr 13 TFSI 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 LiNi 0.8 Co 0.1 Mn 0.1 O 2 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.