## 3 Results and Discussion
### Electrochemical Performance  
Table 4 shows the first cycle performance and capacity retention after the testing program. LN670 had the highest first cycle efficiency (91.3%) and discharge capacity (231 mAh/g), one of the highest ever reported for LiNiO\({}_{2}\). [17; 18; 19]. Higher and lower lithiation temperatures produced lower capacities and lower efficiency, but the lowest lithiation temperature also showed improved capacity retention. In Table 6, the discharge capacity results from previously published research articles are presented for comparison. As can be seen in Table 6, results of [PERSON] et al. [17] show the highest first cycle capacity of 246.6 mAh/g. There are, however, some differences in the electrochemical testing conditions between our work and the work of [PERSON] et al. For example, lower current and higher testing temperatures used in the article of [PERSON] et al. can increase the first cycle capacity. Table 7 shows the rate performance of the LiNiO\({}_{2}\) materials. Cells were charged at 0.1 C to 4.3 V and at a constant voltage until 0.02 C was reached. Cells were subsequently discharged at different rates (0.2 C, 0.33 C, 0.5 C, 1 C, and 2 C). Results indicate the best results were produced by the LN670 sample regardless of the discharge rate. Figure 5a shows the first cycle charge and discharge voltage curves for the different LNO samples. Figure 5b shows the discharge voltage curves at different C rates for sample LN670. Up to 0.5 C voltage, the plateaus are clearly different, but at 1 C and 2 C, the plateaus start fading. Figure 5c shows the charge and discharge curves for cells charged to different cut-off voltages. Cut-off voltages of 4.3 V \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Testing Conditions**} \\
**Result (mAh/g)** & **Current (mA/g)** & **Voltage Range (V)** & **T (\({}^{\circ}\)C)** & **Ref.** \\ \hline
231.7 & 20 & 4.3–2.6 & 25 & This article \\
246.6 & 18 & 4.3–2.7 & 30 & [16] \\
220.2 & 22.5 & 4.3–3.0 & 25 & [18] \\
199 & 21 & 4.27–2.6 & & [17] \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The first cycle discharge capacities and testing conditions from reference articles. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Charge 0.1 C + 0.02 C \(\rightarrow\)-3.3 V–\(>\)DC 3.0 V**} \\
**Sample** & **DC 0.2 C** & **DC 0.33 C** & **DC 0.5 C** & **DC 1 C** & **DC 2 C** \\  & **mAh/g** & **mAh/g** & **mAh/g** & **mAh/g** & **mAh/g** \\ \hline LN650 & 215.5 & 210.2 & 206.0 & 201.3 & 195.3 \\ LN670 & 217.4 & 211.6 & 207.1 & 202.9 & 196.5 \\ LN690 & 208.3 & 201.7 & 197.0 & 191.8 & 185.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Rate performances of the tested samples. Figure 4: SEM images of LN650, LN670, and LN690 at magnitudes of 5000\(\times\) and 75,000\(\times\). and 4.2 V show similar voltage plateaus, but cells with 4.15 V and 4.1 V the highest voltage plateau vanish. Figure 5d shows the cyclability curves for cells with different cut-off voltages, indicating that the 4.3 V and 4.2 V cut-off voltages possess a similar capacity and capacity retention, while 4.15 V and 4.1 V bear a lower capacity but excellent capacity retention. [PERSON] et al. [17] presented similar results, claiming that a better capacity retention was due to a lower level of particle cracking for cells with lower voltage cut-offs. Table 8 shows the excess lithium before (LN670) and after the washing procedure (LN670-W). Results showed that washing effectively reduced the lithium from the particle surfaces. Figure 6 shows pouch cell discharge capacity retention during the cycles. The unwashed sample capacity was higher at the beginning but decreased quickly. A high amount of residual lithium on the unwashed particle surfaces can react with electrolytes and produce gases, causing bad contacts in the cell [18; 20; 21]. The washing procedure can remove lithium from the LiNiO\({}_{2}\) structure, which might explain the lower capacity at the beginning of the tests [18].