## 4 Discussion
Upon cycling, active materials suffer from a volume expansion and contraction with lithium intercalation and deintercalation. The change in volume can induce severe strain accumulation in the thick electrode, leading to increased internal stress [16]. Especially at high C-rates above 1C, the rapid volume change will lead to crack formation or a fracture in the cathode laminate. Those cracks can cause particle isolation, resulting in capacity loss of the electrode. For commercial applications, power density and energy density are more practical to characterize electrochemical cell performance. Since cathodes with 200 \(\upmu\)m pitch distance show great improvement of rate capability for each thickness, the volumetric energy density of cells containing structured cathodes with 200 \(\upmu\)m pitch distance and cells with unstructured cathodes were calculated from galvanostatic measurements and were plotted versus the power density (Figure 7a). In order to be more consistent with the practical situation in the battery industry, the calculation of volumetric energy density with respect to cathode side was carried out using the total volume of the electrode material plus half of the volume of current collector and separator, since double-coated cathodes and anodes are mostly used in industry. This Ragone chart reveals that the energy density decreases with higher power density, especially for thick electrodes, and the energy density drops dramatically with increasing power. Clearly, there is a trade-off between energy density and power density controlled by the electrode thickness. At 100 W/L to 400 W/L, a cell with a 250 \(\upmu\)m unstructured cathode has the highest energy density of about 1400 W/L, which is due to the decrease of current collector fraction with increasing electrode thickness. Meanwhile, all unstructured cathodes have 100 to 200 Wh/L more energy density compared to structured cathodes, which means that for low power application (C-rate below C/2), the improvement of lithium-ion diffusion with 3D structures in electrode is insufficient to compensate the mass loss of electrode materials owing to laser structuring. However, laser structured cathodes show higher energy density with increased power when power density reached a threshold. For cathodes with 151 \(\upmu\)m and 250 \(\upmu\)m thicknesses, the turning point is 400 W/L, and 600 W/L, respectively. The cells with structured cathode of 91 \(\upmu\)m thickness begin to show higher energy densities, at 3000 W/L, which is significantly delayed in comparison to cells with other cathodes, indicating that laser structuring technique is very suitable for improving the electrochemical performance of cells with thick cathodes at higher C-rates. Furthermore, when the inactive components, such as current collector and separator are taken into account, the production cost of battery with thick film electrode will be significantly reduced. Table 2 shows the total area and quantity of NMC 622 cathodes that are required for the production of 52-Ah automobile cells using an electrode design of 21 cm \(\times\) 24 cm, as suggested by [PERSON] et al. [17]. The area of cathodes decreases from 1.45 m\({}^{2}\) to 0.56 m\({}^{2}\) with increasing film thickness from 91 \(\upmu\)m to 250 \(\upmu\)m, allowing for using half of the separators as well as the current collectors. For cells with 91 \(\upmu\)m cathodes, 14 to 17 cathode sheets are needed, while only six sheets will be packed into the cells with cathodes having a thickness of 250 \(\upmu\)m. As a result, the cost of electrode cutting and welding will be decreased. Besides, the difference of required area for 52-Ah cell between structured NMC 622 cathodes and unstructured NMC 622 cathodes is less distinct (the differences for cathodes with thicknesses of 91 \(\upmu\)m and 250 \(\upmu\)m are 0.12 m\({}^{2}\)-0.02 m\({}^{2}\) and 0.02 m\({}^{2}\)-0.01 m\({}^{2}\), respectively).