Resolving the Phase Instability of a Fluorinated Ether, Carbonate-Based Electrolyte for the Safe Operation of an Anode-Free Lithium Metal Battery

The anode-free full cell architecture (Cu parallel to NMC111) is an essential milestone for boosting the energy density of lithium metal batteries (LMBs). The LiPF6 dissolved in fluorinated carbonate (fluoroethylene carbonate (EEC)) and partially fluorinated ether (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE)) solvents has been reported to be a fluorinated electrolyte in the development of LMBs because of their wide electrochemical windows, nonflammable characteristics, and stable LiF-rich solid electrolyte interface. However, its phase instability and high viscosity limit its practical application. In this work, an advanced ethyl methyl carbonate (EMC)-based fluorinated electrolyte (1 M LiPF6 in FEC/TTE/EMC (3:5:2 by vol.) is developed, which is free of phase instability and has higher ionic conductivity, oxidative stability, and nonflammability. It has a higher oxidation potential of >5.3 V and better rate capabilities than the EMC-free electrolyte for lithium metal batteries (Li parallel to NCM111). Meanwhile, the ternary electrolyte also enhances the cycling performance of anode-free lithium metal batteries (AFLMBs) within the potential range of 2.5-4.5 V at room temperature. The Cu parallel to NMC111 cell with 1 M LiPF6 in FEC/TTE/EMC (3:5:2 by vol.) electrolyte delivers superior capacity retention of 40% and average Coulombic efficiency (av CE) of 98.30% for 80 cycles with a cutoff voltage of 4.5 V at the charge and discharge current densities of 0.2 and 0.5 mA/cm(2), respectively. Hence, we develop a robust nonflammable electrolyte free of phase instability having wider oxidative stability, high rate capability, and good cyclic performance using an anode-free full cell configuration (Cu parallel to NMC111).