Tuning Fluorination of Carbonates for Lithium-Ion Batteries: A Theoretical Study

It is critical to design the solvents or additives to provide high oxidation stability of electrolyte and good solid-electrolyte interphase (SEI) in lithium secondary batteries. In this work, we used quantum chemical calculations to evaluate carbonates with various fluorinated patterns to satisfy the requirements of antioxidation, stabilize SEI films, and modify solvation structures. The thermodynamic cycle method was used to calculate the oxidation and reduction potentials of a series of fluorinated linear (dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) and cyclic carbonates (ethylene carbonate, propylene carbonate, and 2,3-butanediol cyclic carbonate) vs Li⁺/Li. Both quantity and position of fluorine substitutions have a significant impact on the oxidation and reduction potentials according to correlation analyses. The instinctive causes for the potential change were the influence of the fluorinated position on the frontier orbital. We further studied lithium-ion coordinated fluorinated carbonates and found that the binding energy is mostly determined by electrostatic interaction according to the energy decomposition analysis. Fluorination will weaken the coordination ability of carbonates, which is demonstrated by their electrostatic potential distributions. Furthermore, it was found that the linear carbonate fluorinated at the α-position under reduction reaction easily produces LiF in situ, which was beneficial to the construction of good SEI. Finally, we provide some suggestions for the development of fluorinated carbonates based on the theoretical studies in this work.