Due to growing demand for electric vehicles (EVs) and energy storage systems (ESS), it is essential to meet the requirement for high energy density of Li secondary batteries. In this sense, an electrode chemistry matching high-Ni cathode materials and thin Li metal anode has been investigated most actively under high voltage operation. As a result, there are a variety of degradation issues on both electrodes like high-resistance cathode electrolyte interphase (CEI) as well as solid electrolyte interphase (SEI) on the anode, electrolyte depletion, or Li dendritic growth. Thus, advanced electrolytes containing functional additives are extensively being developed to mitigate those stresses occurred in the high-energy-density Li-metal secondary batteries (LMSBs). Especially, to minimize the amount of expensive additives, many research groups have made much effort in discovering new or multi-functional additives for LMSBs.

In this work, we report a bis(2-fluoroethyl) carbonate (B-FEC) as a new fluorine-based linear carbonate electrolyte additive to stabilize the SEI even in the high voltage conditions (4.5 V cut-off). To confirm the role of B-FEC on electrochemical properties, we evaluated its electrochemical properties with Li/Li symmetric cells as well as LiNi_0.6Co_0.2Mn_0.2O₂ (NCM 622)/Li cells with or without B-FEC. Also, various analysis data were also gathered to check the morphological and compositional changes caused by B-FEC through SEM, XPS, etc.