Toward Understanding\nthe Effect of Fluoride Ions on\nthe Solvation Structure in Lithium Metal Batteries: Insights from\nFirst-Principles Simulations

Regulating the structure and composition of the lithium-ion\n(Li+) solvation shell is crucial to the performance of\nlithium\nmetal batteries. The introduction of fluorine anions (F–) into the electrolyte significantly enhances the cycle efficiency\nand the interfacial stability of lithium metal anodes. However, the\neffect of dissolved F– on the solvation shell is\nrarely touched in the literature. Herein, we investigate the evolution\nprocessing of the fluorine-containing solvation structure to explore\nthe underlying mechanisms via first-principles calculations. The additive\nF– is found to invade the first solvation shell\nand strongly coordinate with Li+, liberating the bis(trifluoromethanesulfonyl)\nimide anion (TFSI–) from the Li+ local\nenvironment, which enhances the Li+ diffusivity by altering\nthe transport mode. Moreover, the fluorine-containing Li+ solvation shell exhibits a higher lowest unoccupied molecular orbital\nenergy level than that of the solvation sheath without F– additives, suggesting the reduction stability of the electrolyte.\nFurthermore, the Gibbs free energy calculations for Li+ desolvation reveal that the energy barrier of the Li+ desolvation process will be reduced because of the presence of F–. Our work provides new insights into the mechanisms\nof electrolyte fluorinated strategies and leads to the rational design\nof high-performance lithium metal batteries.