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 LiNi0.8Mn0.1Co0.1O2 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. Li-metal batteries suffer from sluggish kinetics at low temperatures. Here, authors propose a guideline for rational electrolyte solvent screening and design a class of asymmetric ethers, which bestows the Li metal pouch cell with a high specific energy of 345.3 Wh kg−1 over 40 cycles at −40 °C.