A Competitive Solvation of Ternary Eutectic Electrolytes Tailoring the Electrode/Electrolyte Interphase for Lithium Metal Batteries

The development of electrolytes with high safety, high ionic conductivity, and the ability to inhibit lithium dendrites growth is crucial for the fabrication of high-energy-density lithium metal batteries. In this study, a ternary eutectic electrolyte is designed with LiTFSI (TFSI = bis(trifluoromethanesulfonyl)imide), butyrolactam (BL), and succinonitrile (SN). This electrolyte exhibits a high ion conductivity, nonflammability, and a wide electrochemical window. The competitive solvation effect among SN, BL, and Li⁺ reduces the viscosity and improves the stability of the eutectic electrolyte. The preferential coordination of BL toward Li⁺ facilitates the formation of stable solid electrolyte interphase films, leading to homogeneous and dendrite-free Li plating. As expected, the LiFePO₄/Li cell with this ternary eutectic electrolyte delivers a high capacity retention of 90% after 500 cycles at 2 C and an average Coulombic efficiency of 99.8%. Moreover, Ni-rich LiNi_0.8Co_0.1Al_0.1O₂/Li and LiNi_0.8Co_0.1Mn_0.1O₂/Li cells based on the modified ternary eutectic electrolyte achieve an outstanding cycling performance. This study provides insights for understanding and designing better electrolytes for lithium metal batteries and analogous sodium/potassium metal batteries.