“Dragging” effect induced formation of AGGs-rich solvation structures in lithium metal batteries

The chemically homogeneous and mechanically robust solid electrolyte interphase (SEI) is a prerequisite for the realization of high-efficiency and long-life lithium metal batteries (LMBs). The performance of SEI is considerably influenced by the solvation structure of Li⁺ which can be precisely regulated by the interaction between electrolytes. In this study, new mechanism of the “dragging” effect on Li⁺ by diluents located outside the first solvation shell of Li⁺ was described by investigating diluent-Li⁺ interaction and diluent-anion interaction in a locally concentrated ionic liquid electrolyte (LCILE) based on lithium bis(fluorosulfonyl)imide (LiFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr₁₃FSI) and 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFE). A drag force on Li⁺ arising from the relatively powerful Li⁺-TFETFE interaction effectively contributes to the combination of Li⁺ with anion, creating a solvation structure rich in aggregate ion pairs (AGGs), which assists in the construction of high-quality SEI. With the exceptional lithium dendrite inhibition ability and Li⁺ transport characteristics of SEI, the lithium stripping/plating Coulombic efficiency is up to 99.2 % over 750 cycles at 1.0 mA cm⁻² and Li/LFP cells achieves a remarkable capacity retention of 82.4 % for 100 cycles. This study presents a new viewpoint for diluents to modulate the solvation structure and provides a new strategy for the development of electrolytes suitable for next-generation high-performance LMBs.