Defects in Li₄Ti₅O₁₂induced by carbon deposition: an analysis of unidentified bands in Raman spectra

Abstract

Raman spectroscopy was shown to be sensitive to the presence of diluted low-concentration defects in both pristine and carbon-coated lithium titanate.

Clarification on the Gassing Behavior of Carbon‐Coated Li4Ti5O12 at Elevated Temperature: Importance of Coating Coverage

“…Higher (1.7) and Lower value (0.6) I C / I LTO ratio in LTO/C‐3 h (Figure 5d) ensures that all the LTO particles′ surface is completely covered with carbon coating. Since our XRD (Figure 3b) shows the presence of oxygen vacancy, and the HRTEM image (Figure 3c) shows that the coating is uniform for LTO/C‐3 h. One possible way to intercept the broadened distribution of I C / I LTO ratio in LTO/C‐3 h is due to the induced oxygen vacancy on the surface, other than the carbon coating non‐uniformity, which also affects the Raman response from the LTO [50] (Figure S4). The structural heterogeneity of the carbon deposited on the surface of the LTO is important for the electrochemical performance of the materials.…”

“…HRTEM will just allow us to examine and visualize qualitatively a highlighted area of the particle, which is indeed not sufficient to claim and quantify the efficacy of the carbon coverage. We have previously introduced that Raman spectroscopy (RS) is a facile and cost‐effective tool that has been used for in‐line quality control for the application of coating layers [50,52,53] . Spatial RS measurements (SRS) are measured to get 100 Raman spectra for each sample with a 1 μm step size in XY plane of 10 μm ×10 μm area to give localized information about the coating coverage on the surface the LTO.…”

“…The magnified image of the 111 peak (Figure 3b) shows a shift in LTO/C‐3 h due to the oxygen vacancy. Since the coating process takes place in a reducing atmosphere, which is also favorable for oxygen vacancy formation on the surface of the LTO [32,50,51] . The Raman spectra of LTO contains a set of six bands (Figure 3c) with major bands centered at 231 cm −1 (which is F 2g vibrations in TiO 6 octahedral), 341 cm −1 (F 2g vibrations in LiO 6 octahedral), 421 cm −1 (E g vibrations in LiO 4 tetrahedral), and 668 cm −1 (A 1g vibrations in TiO 6 octahedral).…”

“…Since the coating process takes place in a reducing atmosphere, which is also favorable for oxygen vacancy formation on the surface of the LTO. [32,50,51] The Raman spectra of LTO contains a set of six bands (Figure 3c) with major bands centered at 231 cm À 1 (which is F 2g vibrations in TiO 6 octahedral), 341 cm À 1 (F 2g vibrations in LiO 6 octahedral), 421 cm À 1 (E g vibrations in LiO 4 tetrahedral), and 668 cm À 1 (A 1g vibrations in TiO 6 octahedral). In comparison, the two minor bands are located at 258 cm À 1 (attributed to F 2g vibrations in TiO 6 octahedral) and 737 cm À 1 (so-called A 1g shoulder).…”

“…We have previously introduced that Raman spectroscopy (RS) is a facile and cost-effective tool that has been used for in-line quality control for the application of coating layers. [50,52,53] Spatial RS measurements (SRS) are measured to get 100 Raman spectra for each sample with a 1 μm step size in XY plane of 10 μm × 10 μm area to give localized information about the coating coverage on the surface the LTO. Instead of discussing just the intensity from carbon and LTO separately, the I C /I LTO ratio is used, which is the relative Raman intensity of the carbon layer.…”