The effects of lithium salt and solvent on lithium metal anode performance

In this study, the effects of lithium salts (i.e. LiPF6, LiClO4 and LiN(SO2CF3)2) and solvents (i.e. carbonate and ether type) on the Li metal anode electrochemical performance are systematically studied. It is found that LiN(SO2CF3)2, denoted as LiTFSI, in 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) as electrolyte offers the best performance with a cycle life of 1100 h under the capacity of 2 mAh/cm2 and current density of 2 mA/cm2. Lithium stripping/plating produces porous loose lithium powders rather than dendrites. Both lithium salts and solvents have influences on the lithium powder nucleation and growth. In the LiTFSI-DOL/DME system, lithium metal after stripping/plating has a relative flat and dense surface, which concomitantly brings in a low charge transfer resistance, low solid electrolyte interphase resistance, and elongated cycle life. A high Li+ transference number and a high Li+-solvent interaction force are beneficial to an even Li+ flux and a stable Li-electrolyte interface. This study sheds light on the importance of electrolytes for high performance lithium metal anodes.