Formation Mechanism and Regulation of LiF in a Solid Electrolyte Interphase on Graphite Anodes in Carbonate Electrolytes

LiF plays an important role in stabilizing solid electrolyte interphases (SEIs) on graphite anodes of commercialized lithium-ion batteries (LIBs) that adopt 1 M LiPF6 in carbonate solvents as base electrolytes. To construct LiF-rich SEIs, various strategies have been developed, including replacing carbonates with F-containing solvents, applying F-containing additives, and using LiPF6 with ultrahigh concentrations. However, these efforts add cost to battery manufacturing or are at the expense of battery rate capability. In this work, we propose new strategies based on the insight into the formation mechanism of LiF. It is found that LiPF6 presents higher reduction activity than carbonate solvents and prefers to be reduced under the coordination of carbonate solvents, generating LiF that contributes to the main component of SEIs on graphite. Among various carbonate solvents, EC is the most beneficial for the formation of LiF because of its strong ability to combine LiPF6. Additionally, the content of LiF in SEIs can be controlled by applying pulse potentials. Therefore, LiF-rich SEIs can be achieved by regulating solvent compositions and graphite anode potentials. This new strategy not only provides a facile solution to the construction of stable SEIs but is also beneficial for designing stabler SEIs on graphite anodes to further improve the performances of LIBs.