Rational electrolyte solvent screening for high-energy lithium metal batteries at low temperatures

Weakening the solvation ability has shown great potential in electrolyte solvent design to promote the cycling performance of Li-metal batteries, yet suffers from sluggish kinetics and uncontrolled Li dendrite formation, particularly at low temperatures. Herein, we propose a guideline for rational electrolyte solvent screening, where the restrained electrostatic potential of the coordinated O is proposed as one descriptor to quantify the solvation effect, followed by introducing the dipole moment as a correction descriptor to optimize solvents' sensitivity to the electric fields and interphase stability. Under the guidance of this screening principle, a class of asymmetric fluorinated ethers is rationally designed, of which the 3,3,3-trifluoropropyl-1-methyl ether with moderate restrained electrostatic potential of the coordinated O and dipole moment is identified to mediate a stable six-membered chelating structure with Li⁺, significantly promoting Li kinetics and reversibility from 30 to -60 °C. Coupled with its good anodic stability, this single-salt single-solvent electrolyte enables the 50 μm Li | |4.0 mAh cm^-2 LiNi_0.8Mn_0.1Co_0.1O₂ coin-cells maintaining > 90% capacity after 200 cycles at benign and low temperatures. A practical Li-metal pouch-cell delivers a high specific energy (based on the mass of all components) of 345.3 Wh kg^-1 over 40 cycles at -40 °C.