Figure 3. (a) Voltage profile at first cycle, (b) Voltage
profile at 80th cycle,
(c) Cycling performance, and (d) Coulombic efficiency of baseline, CM10,
CM20, CM30, and CM40 samples with NMC622 full-cells.
FT-IR Spectroscopy was further performed to evaluate the formation of
the SEI layer on the anode surface by analyzing the vibrational state of
chemical bonds. Figure 4 exhibits similar qualitative spectra
but differentiates quantitatively in peak intensity, indicating the
heterogenous formation of the SEI layer. In general, there are three
main frequency regions observed, and each of these regions is associated
with typical group frequencies:
4000 – 3000 cm-1 assigned for the O – H stretching,
3000 – 1750 cm-1 for the C – H stretching, and 1700
– 800 cm-1 for the C = O stretching regions, as
earlier reported by Guorong V. Zhuang et al. [27] The wavenumber
region of 2800 – 2000 cm-1 might represent the
CO2 molecular absorbed by LiOH or Li2O,
which happens during sample reservation and testing process
(Figure 4 ). In addition, the SEI layer was reported to be
composed of Li2CO3 and lithium alkyl
carbonate (ROCO2Li) compounds due to the decomposition
of ethyl carbonate (EC) electrolyte. [28] Thereby, IR fingerprints
of these samples proved the present of
Li2CO3 on the electrode surface by the
broad band of 920 – 800 cm-1 and the double peak at
1520 – 1380 cm-1 wavelength. It can be observed that
the peak intensity of Li2CO3 also
increases with the longer contact duration, which is consistent with the
explanation of the thick SEI layer. Additionally, three wavelength
regions including 1820 – 1740 cm-1, 1100 – 1000
cm-1, and 780 – 600 cm-1 represent
organic carbonate from ROCO2Li compounds was observed
and also increased with the contact time. [28]