## 4 Discussion
The energy density of an entire cell tends to be lower when anode and separator are taken into account, with about 370 Wh/L to 430 Wh/L energy density for cells with 100 \(\upmu\)m to 250 \(\upmu\)m cathodes [18]. The cathode of 91 \(\upmu\)m thickness has almost 1300 Wh/L, about 300 Wh/L more energy density, compared to the results from [PERSON] et al., of NMC 111 [6], which is due to the higher specific capacity of NMC 622. Figure 7b shows the improvement of energy density for cells with structured cathodes in comparison to cells with unstructured cathodes having the same thicknesses. For structured cathodes, a 100% to 400% higher energy density is observed at 1C to 5C. As for 151 \(\upmu\)m cathode, the enhancement is more significant at 1C to 3C. Although cells with structured cathodes having a line pitch distance of 200 \(\upmu\)m showed higher discharge capacity with increasing discharge rate comparing to cells having other line pitch distances, it is unnecessary to pursue higher power simply by decreasing the pitch distance, because that leads to a dramatic active mass loss, which in turn would increases the total battery manufacture cost. Therefore, the selection of pitch distance and electrode thickness should be related to specific demands of applications. For the stationary storage application, unstructured thick film electrodes are preferred, while for high powered usage, such as in electrical vehicles, laser structuring has great potential. Besides, thick film electrode and 3D electrode concepts ensure higher capacity as well as higher power, at intermediate C-rates around C/2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pitch Distance (\(\upmu\)m)** & \begin{tabular}{c} **Final Thickness** \\ **without Al Foil** \\ **(\(\upmu\)m)** \\ \end{tabular} & \begin{tabular}{c} **Areal Capacity** \\ **(\(\upmu\)m)** \\ \end{tabular} & \
\begin{tabular}{c} **Area of Cathodes** \\ **for a 52-Ah Pouch** \\ **Cell 1 (m\({}^{2}\))** \\ \end{tabular} &
\begin{tabular}{c} **Number of the** \\ **Cathodes (21 cm \(\times\)** \\ **24 cm)** \\ \end{tabular} \\ \hline unstructured & 91 & 3.6 & 0.73 & 14 \\
200 & 91 & 3.1 & 0.85 & 17 \\
400 & 91 & 3.3 & 0.78 & 15 \\
600 & 91 & 3.5 & 0.75 & 15 \\ unstructured & 151 & 5.6 & 0.47 & 9 \\
200 & 151 & 5.1 & 0.51 & 10 \\
400 & 151 & 5.3 & 0.49 & 10 \\
600 & 151 & 5.4 & 0.48 & 10 \\ unstructured & 250 & 9.4 & 0.28 & 6 \\
200 & 250 & 8.5 & 0.30 & 6 \\
400 & 250 & 8.9 & 0.29 & 6 \\
600 & 250 & 9.0 & 0.29 & 6 \\ \hline \hline \end{tabular} \({}^{1}\) The NMC 622 cathodes were assumed to be double-coated in the calculations.  
\end{table} 
Table 2: The total area and quantity of NMC 622 cathodes required to fabricate a 52-Ah pouch cell. Figure 7: (**a**) Ragone plots for cells containing cathodes with different thicknesses, and (**b**) the increase of volumetric energy density of cells with structured cathodes in comparison to cells with unstructured cathodes with the same thickness at different C-rates. The CV analyses of cells with NMC 622 cathodes in Figure 5 show only one redox couple from 3 V to 4.3 V, which corresponds to the oxidation and reduction of Ni\({}^{2+}\)/Ni\({}^{4+}\)[19]. The oxidation peak of NMC 622 cathode appears at 3.8 V under 0.02 mV/s scan rate and gradually rises with increasing scan rate. The result is similar to the study by [PERSON] et al. [20]. Furthermore, CV is used to determine the chemical diffusion coefficient of lithium-ions (D\({}_{\text{CV}}\)) in cathode materials during charge and discharge process using the Randles-Sevcik equation [21]:  
\[I_{p} =0.4463\left(\frac{F^{3}}{R\cdot T}\right)_{0}^{3/2}\cdot A\cdot C_{0} \cdot D_{\text{CV}}^{1/2}\cdot v^{1/2} \tag{2}\]  
In this equation, \(I_{p}\) is the maximum current from CV measurement during charge or discharge, \(F\) is [PERSON]'s constant, \(R\) is the gas constant, \(T\) is the absolute temperature, \(z_{0}\) is the number of transferred electrons, \(A\) is the electrode area, and \(C_{0}\) is the total amount of lithium-ions in an NMC 622 particle before delithiation.