Enhanced cycling, safety and high-temperature performance of hybrid Li ion/ Li metal batteries via fluoroethylene carbonate additive

Hybrid graphite/Li metal anode has been proved to be a feasible approach to enlarge the energy density of Li-ion batteries. However, there is still a gap between the electrochemical performance of the hybrid Li-ion/Li metal batteries (HLI-LMBs) and the practical requirements. In this work, the cycling, safety and high-temperature performance of the HLI-LMBs have been successfully enhanced via adding fluoroethylene carbonate (FEC) in the electrolyte. It is found that FEC can facilitate the formation of a LiF-rich SEI layer on the surface of Li metal, which effectively suppresses the formation of Li dendrites and enables uniform deposition of Li metal on the surface of graphite. The LiF-rich SEI layer can restrain the exothermal reaction between Li metal and electrolyte under short-circuit. Moreover, the LiF-rich SEI slows down the reaction of anode with electrolyte and largely suppresses the Li dendrite formation at high temperature, improving the high-temperature performance of the HLI-LMBs. This work sheds the light on the critical roles of electrolyte additive and can serve as a guideline for the development of high-performance HLI-LMBs.