## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**pH**} & **Residual Alkaline** & **First Discharge** & **First Discharge** & **Discharge** & **Discharge** & **110 Cycles** \\  & & **(Li+CO\% +** & **Capacity at** & **Emciency (\%)** & **Capacity at 1 C** & **Capacity** \\  & & **LiOH\%)** & **0.2 C (mAh/g)** & **(mAh/g)** & **Retention (\%)** \\ \hline NCA & 12.70 & 3.99\% & 183.1 & 88.6\% & 173.0 & 89.31\% \\ NCA-0.25-400 \({}^{\circ}\)C & 11.86 & 1.78\% & 181.1 & 83.1\% & 166.3 & 88.03\% \\ NCA-0.25-500 \({}^{\circ}\)C & 11.80 & 1.48\% & 184.5 & 83.8\% & 172.3 & 94.67\% \\ NCA-0.25-600 \({}^{\circ}\)C & 11.82 & 1.38\% & 184.1 & 84.3\% & 168.6 & 92.88\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical and chemical properties of the pristine NCA sample and NCA-0.25 samples at different calcination temperatures from 400 \({}^{\circ}\)C to 600 \({}^{\circ}\)C.  
Figure 5: TEM micrographs of the pristine NCA (**a**) and NCA-0.25 (**b**), EDS pattern of the pristine NCA (**c**) and NCA-0.25 (**d**). Figure 6c shows the cycling performances for 100 cycles at 1C in the voltage range of 3.0-4.3 V and it shows that NCA exhibits a rapid discharge capacity fading after 100 cycles and a low capacity retention of 89.31%. The lower capacity retention suggests that electrode materials may react with electrolyte and generate particles on the surface, which hinder the lithium ions intercalation. In contrast, NCA-0.25-500 \({}^{\circ}\)C shows a better cyclic performance with a lower discharge fading after 100 cycles and a relatively high capacity retention of 94.67%. This indicates that LiAlO\({}_{2}\) modification can restrain the capacity degradation effectively. To examine the rate capabilities of raw NCA and NCA-0.25-500 \({}^{\circ}\)C, discharge capabilities were taken at 0.2 C, 1 C, 2 C, 5 C and 8 C. As shown in Figure 6d, compared to NCA, NCA-0.25-500 \({}^{\circ}\)C show better discharge capacity and cycle stability as the discharge rate increased. This is especially so when the discharge capacities of NCA-0.25-500 \({}^{\circ}\)C is 139.8 mAh/g at 8 C rate, which is 15% higher than NCA. This is mainly due to the more stable structure during cycling of NCA with the coating layer, which can protect the particle from the side reactions on the surface. Therefore, LiAlO\({}_{2}\) modification can improve the discharge capacities and cyclic stability. The electrochemical impedance spectra (EIS) of the samples are shown in Figure 7. Figure 7a shows electrochemical impedance spectroscopy and equivalent circuit of samples before discharge [20]. Figure 7b shows electrochemical impedance spectroscopy and equivalent circuit of samples after 25 charge-discharge cycles at 1 C. The circuit elements of Rs, Rf, Rct, CPE,Ws and Wo represent the internal resistance of the cell, the surface film resistance (the resistance of SEI film), the charge-transfer resistance, constant phase element, the Li\({}^{+}\) diffusion in finite thin layer impedance, and the Warburg electrode bulk, respectively [21]. As can be seen from Figure 7a, the assembled cell displays a single semicircle at the higher frequency and a straight line at low frequency, which corresponds to the surface film resistance and Warburg resistance. It can be seen from Figure 7a that there is no charge-transfer resistance due to the fact that the anode has no electrochemical reaction before charge-discharge [22]. Table 3 shows the impedances of LiAlO\({}_{2}\) modified samples drastically decreased compared to the raw material. This phenomenon illustrates that LiAlO\({}_{2}\) modification is beneficial to charge migration on the electrode interface and could decrease the battery internal impedance. Figure 6: Charge and discharge profiles at the first cycle at 0.2 C (**a**) and at the 110 th cycle at 1 C (**b**) of the as-prepared samples; the cycle performances at 1 C (**c**) and rate capability (**d**) of the as-prepared samples. After 25 cycles, it can be seen that in EIS the charge-transfer resistance is formed.