Bifunctional carbon monofluoride (CFx) coating on a separator for lithium-metal batteries with enhanced cycling stability

Herein, we suggest a new way to improve the cycling stability of the lithium-metal battery by using a separator coated by carbon monofluoride (CFx). CFx has been used as a cathode material for a lithium primary battery and is converted to LiF and carbon during the discharge process. The CFx-coated separator with 5 μm thickness is obtained by casting a CFx-containing slurry on a bare polyethylene separator and the CFx-coated separator is characterized in a LiCoO2 (LCO) // Li cell. The CFx-coated separator enables a better cycling stability up to 200 cycles than the bare separator due to its dual functions: 1) capturing cobalt ions dissolved from the LCO cathode and 2) formation of a thin and stable SEI layer containing LiF on the lithium metal anode. Employment of the CFx-coated separator also leads to much suppressed dendritic growth of lithium and stable interfacial resistance during the cycle. [Display omitted] •We prepare a separator coated with carbon monofluoride (CFx) for Li-metal battery.•The CFx on the separator is converted to LiF and carbon in the 1st discharge process.•The cobalt ions dissolved from the LCO cathode are captured by the CFx coating layer.•A thin and stable SEI layer containing LiF is formed on the lithium metal anode.•The bifunctions of the CFx-coating enables good cycling stability of a LCO//Li cell.