Efficient Low-Temperature Cycling of Lithium Metal Anodes by Tailoring the Solid-Electrolyte Interphase

Operation of Li-ion batteries below -20 degrees C is hindered by low electrolyte conductivity and sluggish solid-state diffusion in electrodes. Li metal anodes show promise for low-temperature operation, but few electrolyte compositions exhibit high conductivity at reduced temperature while also allowing Li electrodeposition/stripping with high Coulombic efficiency. Here, we show that the Coulombic efficiency of Li metal anodes can be substantially improved at low temperatures (-60 degrees C) by tailoring the solid-electrolyte interphase (SEI) structure through the use of two classes of electrolyte solvents: cyclic carbonates and ethers. Cryogenic transmission electron microscopy and other methods show that fluoroethylene carbonate (FEC) induces temperature-dependent changes in the chemistry and structure of the SEI to be abundant with LiF and Li2CO3, while O-17 nuclear magnetic resonance and molecular dynamics calculations show that FEC affects the solvation behavior and SEI formation process this new in electrolyte system. Our results demonstrate the promise of rechargeable Li-metal batteries to enable energy storage over a broad temperature range.