## 4 Conclusions  
In this work, the wet coating method was applied on a commercialized NMC622 material for the first time, and a significant improvement of electrochemical performance was obtained. It was shown that the long-term cyclability of commercial NMC622 was significantly enhanced, even at relatively higher discharge rates (2 C), via a simple coating method. This can increase the cycle life of commercially available Li-Ion batteries without decreasing their rate performance. An amorphous SiO\({}_{2}\) layer was formed on the NMC622 material surface successfully, which did not change the base material due to the coating process. The SiO\({}_{2}\) coating layer can reduce the side reactions between material surface and the electrolyte, especially at the first 200 cycles, where most capacity fading occurs. The capacity retention of coated NMC622 is visibly improved even after up to 700 cycles. EIS measurement shows that the SiO\({}_{2}\)-coated material has less charge transfer resistance. XRD patterns reveal that after long-term cycling, NMC622 with an SiO\({}_{2}\) coating layer still has very good crystallinity. Compared to previous work [9; 12; 13] the application of SiO\({}_{2}\) coating on synthesized NMC622 did not show obvious improvement in the first 50 cycles, but the coating method is still beneficial for long-term cycling. To summarize, SiO\({}_{2}\) coating is an effective and facile surface modification method, even for commercialized NMC622 material, for long-term cycle capability and therefore longer service life.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Uncycled Pristine** & **Cycled Pristine** & **Cycled SiO\({}_{2}\)-Coated** \\  & **NMC622** & **NMC622** & **NMC622** \\ \hline Crystalline size (Å) & \(470\pm 48\) & \(253\pm 72\) & \(452\pm 54\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: The crystallite size obtained by calculation of full width of half maximum (FWHM).  
Figure 9: Ex-situ XRD of the pristine and SiO\({}_{2}\)-coated NMC622 electrodes after 700 cycles.  
**Supplementary Materials:** The following are available online at [[http://www.mdpic.com/2076-3417/9/18/3671/s1](http://www.mdpic.com/2076-3417/9/18/3671/s1)]([http://www.mdpic.com/2076-3417/9/18/3671/s1](http://www.mdpic.com/2076-3417/9/18/3671/s1)), Figure S1: Comparison of rate capability between pristine and SiO\({}_{2}\)-coated NMC622; Figure S2: EIS measurements of the pristine and SiO\({}_{2}\)-coated NMC622 of both samples after formation cycles; Figure S3: Electrodes (diameter 15 mm) of (**a**) pristine and (**b**) SiO\({}_{2}\)-coated NMC622 material after 700 cycles; Table S1: The full width of half maximum (FWHM) of the main reflexes and crystallite size obtained by fitting the XRD patterns.  
**Author Contributions:** Conceptualization, N.Z. and M.J.; methodology, N.Z., M.J., and X.L.; investigation, X.L.; writing--original draft preparation, X.L.; writing--review and editing, N.Z., M.J., and W.P.; supervision, H.J.S.; funding acquisition, M.J.  
**Funding:** This research was funded by the Austrian Ministry for Transport, Innovation and Technology (BMVIT).  
**Acknowledgments:** [PERSON], [PERSON], [PERSON], and [PERSON] are greatly acknowledged for the SEM, XRD analysis, and scientific discussion. In addition, the support for chemical analysis (Bergfeldt) by the Karlsruhe Nano Micro Facility (KNMF, [[http://www.knmf.kit.edu/](http://www.knmf.kit.edu/)]([http://www.knmf.kit.edu/](http://www.knmf.kit.edu/))), a Helmholtz research infrastructure at KIT, is gratefully acknowledged.  
**Conflicts of Interest:** The authors declare no conflicts of interest.