## 3 Results and Discussion  
### Material Characterization  
The elemental analysis results are presented in Table 1. The main element contents in the SiO\({}_{2}\)-coated NMC622 powder remained unchanged after calcination at 500 \({}^{\circ}\)C. Si concentration was very close to theoretical calculation results, 0.270 wt.%, and C content did not increase-which means the expected reaction, the transformation from TEOS to SiO\({}_{2}\), was completed. The XRD patterns of the pristine and coated NMC622 materials in a range of 10-80\({}^{\circ}\) are presented in Figure 1. All the main reflexes are indexed and coincide well to the R\(\overline{3}\) m space group. Both diagrams display a single phase with \(\alpha\)-NaFeO\({}_{2}\) structure. The reflexes of (006)/(102) and (108)/(110) split obviously, indicating that both samples are highly crystallized with layered structure. The lattice parameters, obtained through Rietveld refinement with fitting range between 3-120\({}^{\circ}\), are shown in Table 2. The r\({}_{1}\) factor, defined by (I\({}_{006}\) + I\({}_{102}\))/I\({}_{101}\), is an indicator of the hexagonal ordering; r\({}_{1}\) < 0.6 shows a well-defined hexagonal ordering [15]. The I\({}_{003}\)/I\({}_{104}\) factor indicates the cation mixing in the lattice of NMC622 material; I\({}_{003}\)/I\({}_{104}\) > 1.2 is an index of no obvious cation mixing [16]. The lattice parameters were calculated by fitting the measured curves, and the lower R factors (R\({}_{\text{wp}}\), R\({}_{\text{p}}\)) and \(\chi^{2}\) confirm the refinement results are reliable. The lattice parameters of the coated material did not change \begin{table}
\begin{tabular}{l c c c c c c} \hline
**Sample** & **Li** & **Ni** & **Mn** & **Co** & **O** & **Si** & **C** \\ \hline Pristine & & & & & & & \\ NMC622 & & & & & & & \\ \hline SiO\({}_{2}\)-coated & & & & & & & \\ NMC622 & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Elemental analysis results of pristine and SiO\({}_{2}\)-coated NMC622 material by ICP-OES, HE, and C/S analyzer. significantly compared to that of the pristine ones. Additionally, no reflexes from SiO\({}_{2}\) were detected because of the low amount of SiO\({}_{2}\) coating and amorphous structure [12]. All the analysis results of XRD imply that the layered structure of NMC622 powder did not change after SiO\({}_{2}\) coating. Figure 2 shows the surface morphology of the pristine and the SiO\({}_{2}\)-coated NMC622 particles at different magnifications. Approximately 200-500 nm primary NMC622 particles with rough surface formed secondary spherical particles whose size is distributed in 5-15 \(\upmu\)m compactly. After SiO\({}_{2}\) coating, the NMC622 particles were covered by nano-sized particles which were formed by SiO\({}_{2}\), especially the boundaries between primary particles. The SiO\({}_{2}\)-coated NMC622 particles were analyzed further in TEM (Figure 3). A 30-50 nm thin layer was formed on the particle surface after SiO\({}_{2}\) coating. The existence of Si is determined through elemental mapping with EDX suggests that the expected SiO\({}_{2}\) coating was successful. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample** & **a (Å)** & **c (Å)** & **c/a** & **V (Å)** & **I\({}_{\text{00}}\)/I\({}_{\text{104}}\)** & **r\({}_{\text{1}}\)** & **R\({}_{\text{p}}\) (\%)** & **X\({}^{\text{2}}\)** & **R\({}_{\text{wp}}\) (\%)** \\ \hline Pristine & 2.8666 & 14.222 & 4.961 & 101.22 & 1.690 & 0.497 & 0.647 & 5.76 & 0.996 \\ NMC622 & (8) & (8) & (4) & (1) & & & & & & \\ \hline SiO\({}_{2}\)-coated & 2.8671 & 14.220 & 4.959 & 101.23 & 1.731 & 0.491 & 0.668 & 4.79 & 1.045 \\ NMC622 & (2) & (1) & (7) & (4) & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Lattice parameters and cation mixing indicators of pristine and SiO\({}_{2}\)-coated NMC622 powders. Figure 1: XRD patterns of (**a**) pristine and (**b**) SiO\({}_{2}\)-coated NMC622 powders and their Rietveld refinement results.