Weak-Coordination Electrolyte Enabling Fast Li+ Transport in Lithium Metal Batteries at Ultra-Low Temperature.

Lithium metal batteries (LMBs) are promising for next-generation high-energy-density batteries owing to the highest specific capacity and the lowest potential of Li metal anode. However, the LMBs are normally confronted with drastic capacity fading under extremely cold conditions mainly due to the freezing issue and sluggish Li+ desolvation process in commercial ethylene carbonate (EC)-based electrolyte at ultra-low temperature (e.g., below -30 °C). To overcome the above challenges, an anti-freezing carboxylic ester of methyl propionate (MP)-based electrolyte with weak Li+ coordination and low-freezing temperature (below -60 °C) is designed, and the corresponding LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathode exhibits a higher discharge capacity of 84.2 mAh g-1 and energy density of 195.0 Wh kg-1 cathode than that of the cathode (1.6 mAh g-1 and 3.9 Wh kg-1 cathode ) working in commercial EC-based electrolytes for NCM811‖ Li cell at -60 °C. Molecular dynamics simulation, Raman spectra, and nuclear magnetic resonance characterizations reveal that rich mobile Li+ and the unique solvation structure with weak Li+ coordination are achieved in MP-based electrolyte, which collectively facilitate the Li+ transference process at low temperature. This work provides fundamental insights into low-temperature electrolytes by regulating solvation structure, and offers the basic guidelines for the design of low-temperature electrolytes for LMBs.