Effects of Carbonate Solvents and Lithium Salts in High-Concentration Electrolytes on Lithium Anode

Lithium (Li) metal is considered an ideal anode material for Li-ion batteries. However, traditional carbonate-based solvents exhibit poor compatibility with the Li anode. High-concentration electrolytes (HCEs) are promising in the improvement of the behavior of the Li anode. To determine suitable HCE formulations, we revealed the effects of various carbonate solvents and Li salts in HCEs on the Li anode in terms of electrochemical performance, morphology, and surface chemical components. After screening six carbonates and four Li salts, the results suggested that ethylene carbonate (EC) and lithium bis(fluorosulfonyl)imide (LiFSI) were suitable in HCEs for the Li anode. The EC1–2 (molar ratio of LiFSI to EC is 1:2) electrolyte exhibited great cycling stability for up to 250 cycles at a high average Coulombic efficiency of 97.1% at a current density of 1 mA cm −1 with a fixed capacity of 0.5 mAh cm −2 . This was demonstrated as the formation of large Li with uniform nodule-like morphology and dense structure. In addition, the surface components on the Li anode were observed to have been highly contributed by the FSI-anion decomposition with the least EC reduction, providing an anion-derived surface with rich Li-F content.