Ordering the Coordination Environment of Solvated Ionic Liquid Gel Electrolytes: Pathway to High-Efficiency 4.5 V Lithium Metal Batteries.

Solvated ionic liquids (SILs) are promising candidates for lithium metal battery (LMB) electrolytes owing to their facile synthesis and high safety. However, the high-voltage stability and ionic conductivity of ether-based SILs are compromised by their chaotic coordination structure, characterized by bulky solvation shells and poor oxidation stability. Here, optimizing electrolyte performance is proposed by incorporating weakly coordinating fluoroethylene carbonate (FEC) and a hydrogen-bond (H-bond)-rich polymer into SILs. FEC occupies the second solvation shell, suppressing large-volume solvation structures and improving ion transfer kinetics, while H-bonds anchor TFSI^-, reducing its competitive coordination and suppressing its diffusion. This dual approach inhibits the formation of chaotic structures, leading to the development of a SIL-FEC (SILF) based H-bond gel electrolyte (SFHE) for LMBs, which exhibits high Li⁺ conductivity and superior oxidative stability. The resulting electrolyte exhibits a high Li⁺ transference number of 0.65. Furthermore, Li/SFHE/LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) battery can operate stably at a high cut-off voltage of 4.5 V, achieving an impressive capacity retention of ≈80% after 400 cycles at 1C. Additionally, the Li/SFHE/LiFePO₄ (LFP) retains 81.8% capacity after 450 cycles at a high rate of 3C at 60 °C. This work provides a strategy for achieving high-voltage LMBs by ordering electrolyte micro-solvation structures.