## 3 Results and Discussion
The details of the calibration curve were reported previously [12]. By charging the cell, the S-parameter of the anode increases approximately 3.18%, and that of the cathode decreases  
Figure 2: (**a**) Compton scattering X-ray energy spectrum obtained from the cathode (blue line), separator (black line), and anode (red line) of the fresh VL2020 cell. (**b**) The internal structure of the cell obtained from the Compton scattering intensity (white filled circle) and S-parameter (red filled circle). The background colors correspond to the regions of each component of the cell. approximately 1.25%. Here, the lithium composition on the cathode changes from 0.124 \(\pm\) 0.190 to 0.723 \(\pm\) 0.190 with the discharge; the lithium composition on the anode changes from 0.046 \(\pm\) 0.031 to 0.270 \(\pm\) 0.031 with the charge. From the above, we observe a clear variation in the fresh cell in the charged and discharged states via the Compton scattering intensity and S-parameter. On the other hand, the aged cell produces a different response with charge and discharge compared with the fresh cell. Figure 4a,b depicts the Compton scattering intensity distribution, and Figure 4c,d depicts the S-parameter distribution of the charged and discharged states in the aged cell, respectively. The state of charge on the cell changed by a constant current with 2 mA. However, in the aged cell, a clear variation in the distribution at the charged and discharged states is not observed in both the Compton scattering intensity and S-parameter distributions. The averaged S-parameter and corresponding lithium composition of both electrodes do not show a significant change, as summarized in Table 2. Comparing these distributions of the aged cell with those of the fresh cell, we observe that the anode expanded and the separator shrank in the aged cell. Hence, the region under the anode also shows a difference in distribution. [PERSON] et al. reported that the capacity loss of the cell is induced by \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Averaged S-Parameter** & **Lithium Composition** \\ \cline{2-4}  & **Charged State** & **Discharged State** & **Charged State** & **Discharged State** \\ \hline Cathode & 1.574 \(\pm\) 0.006 & 1.592 \(\pm\) 0.006 & 0.124 \(\pm\) 0.095 & 0.723 \(\pm\) 0.095 \\ \hline Anode & 1.392 \(\pm\) 0.006 & 1.349 \(\pm\) 0.006 & 0.270 \(\pm\) 0.029 & 0.046 \(\pm\) 0.031 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The averaged S-parameter and corresponding lithium composition in the charged and discharged states in the fresh cell. Figure 3: In the fresh cell: (**a**) The Compton scattering intensity distribution in the charged state. (**b**) The Compton scattering intensity distribution in the discharged state. (**c**) The S-parameter distribution in the charged state. (**d**) The S-parameter distribution in the discharged state. the expansion of the LiAl alloy electrode [32]. Interestingly, a region with a low Compton scattering intensity and high S-parameter value appears near the interface between the cathode and separator. The correlation between the Compton scattering intensity and the S-parameter in the fresh and aged cells is shown in Figure 5, depicting the change in the internal structure of the aged cell. In the fresh cell, the distributions between the Compton scattering intensity and S-parameter in the charged state of the cathode, separator, and anode are concentrated at the region around 0.5 in the Compton scattering intensity and 1.5 for the S-parameter, around 0.35 in the Compton scattering intensity and 2.3 for the S-parameter, and around 0.45 in the Compton scattering intensity and 1.4 for the S-parameter, respectively, as shown in Figure 5a. The distributions in the discharged state of the fresh cell display the same trends as the charged state, as shown in Figure 5b.