Toward Understanding the Effect of Fluoride Ions on the Solvation Structure in Lithium Metal Batteries: Insights from First-Principles Simulations

Regulating the structure and composition of the lithium-ion (Li+) solvation shell is crucial to the performance of lithium metal batteries. The introduction of fluorine anions (F-) into the electrolyte significantly enhances the cycle efficiency and the interfacial stability of lithium metal anodes. However, the effect of dissolved F- on the solvation shell is rarely touched in the literature. Herein, we investigate the evolution processing of the fluorine-containing solvation structure to explore the underlying mechanisms via first-principles calculations. The additive F- is found to invade the first solvation shell and strongly coordinate with Li+, liberating the bis(trifluoromethanesulfonyl) imide anion (TFSI-) from the Li+ local environment, which enhances the Li+ diffusivity by altering the transport mode. Moreover, the fluorine-containing Li+ solvation shell exhibits a higher lowest unoccupied molecular orbital energy level than that of the solvation sheath without F- additives, suggesting the reduction stability of the electrolyte. Furthermore, 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 of electrolyte fluorinated strategies and leads to the rational design of high-performance lithium metal batteries.