Imidazolium-Based Ionic Liquid as a Solid Electrolyte Interphase-Forming Additive for Lithium Metal Anodes

The notorious lithium (Li) dendrite formed due to the poor protection of a solid electrolyte interphase (SEI) is the major obstacle to the practical utilization of lithium metal batteries (LMBs). The high reduction potential and nitrogen-containing character of imidazolium-based ionic liquids (ILs) make them a promising candidate for SEI-forming additives. Herein, an imidazolium-based IL, 1-octyl-3-methylimidazole hexafluorophosphate (Im1(8)PF₆), is used as an additive to regulate Li deposition by forming a Li₃N-rich SEI on metallic Li anodes. A stable Coulombic efficiency (CE) of 97.4% in Li||Cu cells and a constant polarization voltage lower than 25 mV in Li||Li symmetric cells have been achieved. The Li||LiFePO₄cell exhibits a high capacity retention rate and improved rate performance. These results demonstrate that Im1(8)PF₆has extensive application prospects as a dendrite-suppressing additive in LMBs.