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

LiFplays 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 baseelectrolytes. To construct LiF-rich SEIs, various strategies havebeen developed, including replacing carbonates with F-containing solvents,applying F-containing additives, and using LiPF6 with ultrahighconcentrations. However, these efforts add cost to battery manufacturingor are at the expense of battery rate capability. In this work, wepropose new strategies based on the insight into the formation mechanismof LiF. It is found that LiPF6 presents higher reductionactivity than carbonate solvents and prefers to be reduced under thecoordination of carbonate solvents, generating LiF that contributesto the main component of SEIs on graphite. Among various carbonatesolvents, EC is the most beneficial for the formation of LiF becauseof its strong ability to combine LiPF6. Additionally, thecontent of LiF in SEIs can be controlled by applying pulse potentials.Therefore, LiF-rich SEIs can be achieved by regulating solvent compositionsand graphite anode potentials. This new strategy not only providesa facile solution to the construction of stable SEIs but is also beneficialfor designing stabler SEIs on graphite anodes to further improve theperformances of LIBs.