Dynamic in situ fourier transform infrared measurements of chemical bonds of electrolyte solvents during the initial charging process in a Li ion battery

Solvation/desolvation and the solid electrolyte interphase (SEI) formation at a graphite electrode during the initial charging process were investigated using in situ Fourier transform infrared spectroscopy (FTIR) measurements. These measurements were developed by applying a diamond attenuated total reflectance (ATR) crystal, which probed the electrolyte solvents at the surface of the graphite electrode and provided successive FTIR spectra with high signal-to-noise ratio. The charging process was performed in the Li(reference)/electrolyte/graphite(working)/Cu cell at a voltage ranging from 3.2 to 0.0001 V vs. Li/Li+. The measurement elucidated the change in the chemical bond of the electrolyte solvents. In an early stage, the amounts of solvated and desolvated solvents changed, providing evidence that the Li+ ions were intercalated into the graphite layer. The formation of the Li alkyl carbonate that forms the SEI layer was facilitated toward the end of the charging process. Measurements were also obtained of the electrolyte with a vinylene carbonate additive, and the contribution of the additive to the electrolyte solvent reduction was investigated.