A bifunctional fluorinated ether co-solvent for dendrite-free and long-term lithium metal batteries

The employment of localized high concentration electrolytes (LHCEs) has been demonstrated as an effective strategy for the fabrication of next-generation high-energy-density lithium metal batteries. However, the low ionic conductivity of LHCEs and their parasitic side reactions with lithium metal anodes severely hinder the cycling stability of lithium metal batteries. Herein, a partially fluorinated ether of bis (2,2-difluoroethyl) ether (BDE) is proposed as a bifunctional co-solvent to form novel LHCEs for realizing dendrite-free and long-term lithium metal batteries. The BDE co-solvent serves as a diluent to improve the ionic conductivity up to 6.4 mS/cm by dissociating lithium salt via weak interaction and decreasing the electrolyte viscosity. In addition, the BDE co-solvent could promote the formation of uniform lithium fluoride (LiF)-rich solid electrolyte interphase (SEI) to suppress the dendrite deposition by regulating the solvation shell structure, resulting in high Coulombic efficiency of 99.6%. As a result, the assembled full cell exhibits outstanding cycling stability (97% capacity retention after 200 cycles @0.5 C) with high areal capacity (2 mAh/cm²) and high rate capability (2 C) under practical conditions (50 µm Li, lean electrolyte: 3 g/Ah). We also demonstrate the real application of electrolyte with a commercial cathode in 320-mAh-level pouch cells.