| Summary: | Lithium Metal Battery (LMB) has attracted much attention to realize higher energy of rechargeable battery. However, LMB has not been commercialized due to its low safety and poor cycle performance. Recently, the highly concentrated (3–5 mol dm−3) electrolytes have been utilized, because of oxidation stability and thermal stability. So, in this study, lithium bis(fluorosulfonyl) imide (LiFSI)/ethylene carbonate (EC) electrolytes with different concentrations were investigated. With increasing concentration, amount of non-coordinating free EC solvent and FSI− ion decreased, leading to high stability of both the solvent and anion. In addition, the volume expansion of lithium metal was more suppressed with increasing the concentration of the electrolyte, leading to better contact between lithium metal and the separator without any free voids. XPS results showed that the SEI layer consisted of several inorganic components with high Li+ ion conductivity, such as Li-F, Li-N, Li2-S2 and Li2-S. Such SEI layer enabled more stable dissolution and deposition of lithium metal. In conclusion, the best molar ratio between LiFSI and EC was found to be 1 : 2.0 in this study.
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