Nonflammable functional electrolytes with all-fluorinated solvents matching rechargeable high-voltage Li-metal batteries with Ni-rich ternary cathode

Abstract A nonflammable functional electrolyte with fluoroethylene carbonate (FEC) and ethyl difluoroacetate (EFA) solvents is developed to match the rechargeable Li-metal batteries (LMBs) with LiNi0.8Co0.1Mn0.1O2 cathode (NCM811). The NCM811/Li LMBs with 1 M LiPF6-FEC/EFA electrolyte exhibit an enhanced cycling retention of 74% after 150 cycles and an average coulombic efficiency of ~99.9% at 1 C under a charging cut-off voltage of 4.4 V. In contrast, the capacity retention and average coulombic efficiency of NCM811/Li LMBs with fluorocarbonate-based electrolyte are 28% and 99.5%, and the batteries with carbonate-based electrolyte are 8% and 97.2%, respectively. This FEC/EFA-based electrolyte also shows comparable low-temperature performance to carbonate-based electrolyte and is superior to fluorocarbonate-based electrolyte. It is indicated that this all-fluorinated solvent system can facilitate the formation of a durable and highly fluorinated interfacial layer on both cathode and Li-metal anode. Especially, the FEC/EFA-based electrolyte promotes the uniform Li deposition with less Li dendrites and lower polarization in the Li-metal anode, which reduces the decomposition of the electrolyte and enables stable cycling of LMBs. This FEC/EFA-based electrolyte shows promising prospects in the application of high-performance LMBs, and it also provides a novel idea for the design of all-fluorinated high-performance electrolyte to advance the commercialization of LMBs.