Performance-enhanced lithium metal batteries through ionic liquid based electrolytes and mechanism research derived by density functional theory calculations

Metallic lithium (Li) has been researched extensively in recent years due to its high theoretical specific capacity and its extremely low redox potential . However, uncontrolled Li dendrites growth during the charging process can lead to safety problems and shortens the life of lithium metal batteries (LMBs). Our recent work has discovered that an ionic liquid (IL), namely, N-methyl, (2-methoxyethyl)-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([MEMP][TFSI]), can significantly improve the cycling performance when added into the conventional electrolyte. Compared with LMBs with no ionic liquids (ILs), those with mixed electrolytes containing [MEMP][TFSI] can increase the effective cycle number by as much as 84.6%. Li metal anode with mixed electrolytes containing [MEMP][TFSI] presents low and stable polarization, excellent cycle performance, uniform Li deposit, and thinner Li layer, as well as low interfacial impedance. Density functional calculations are carried out and demonstrate that the addition of [MEMP][TFSI] enhances the interaction between Li and oxygen as well as the charge transfer from the Li, which prevents Li deposit growth at the Li metal anode surface and also enables a more stable battery cycling performance. The key findings of this study provide a useful method to research the molecular engineering of electrolyte components by experiments and by density functional theory (DFT) calculations.