Chemical reaction of lithium surface during immersion in LiClO4 or LiPF6/DEC electrolyte

Chemical reactions of lithium with diethyl carbonate (DEC) containing 1.0 mol dm(-3) LiClO4 or LiPF6 (LiClO6/DEC or LiPF6/DEC) were studied by using in situ Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopies. The in situ FTIR spectra for both electrolytes show a penetration of the DEC electrolyte into the native surface film on lithium foils at the initial period of immersion. In the case of LiClO4/DEC, the DEC solvent contacts the lithium metal, and then reacts directly with lithium metal to form reductive decomposition products of DEC, such as lithium alkylcarbonate, lithium alkoxide, and Li2CO3. When LiPF6/DEC was used as the electrolyte, the native surface film was gradual ly etched and then changed to a LiF/Li2O bilayer surface film. The in situ FTIR spectra showed no formation of decomposition products of DEC. This means that the surface film consisting of LiF/Li2O was highly effective in suppressing the direct chemical reactions of DEC with lithium metal.