## 9 Industrial Applications (_Operando_ Observation of Electrolyte Distribution)
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **CXI** & **X-ray Microscope [68]** & **7-T MRI [69]** \\ \hline Spatial & 6.5 μm & \textless{}40 nm & 0.1 mm \\ \multirow{2}{*}{Acquisition time} & \multirow{2}{*}{5 s/image} & \multirow{2}{*}{A few min/image} & \multirow{2}{*}{5 min/image} \\ \cline{1-1} \cline{5-5} Sensitivity & & 1000 & 1 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of CXI and other detecting methods for ion distribution in electrolyte. Figure 16: (**a**) Schematic of experimental setup of CXI system for in situ observation of LIB behavior. (**b**) Schematic of LIB cell, where WE is LiFePO\({}_{4}\) composite electrode, CE is Li electrode, and electrolyte is 1 M LiClO\({}_{4}\) dissolved in carbonate solvent (EC:DEC = 12 \(v/v\)). Continuous phase map of electrolyte in region indicated by red dashed line was analyzed [70]. Reproduced with permission from ref [70]. Copyright 2022 Springer Nature. Figure 17: (**a**) Constant-current (0.06 mA, C/2 rate) charging profile and (**b**) corresponding extracted phase maps of electrolyte. Since \(\Delta p\) is estimated as change from initial image of t = 0 s (without an applied current), change in \(\Delta p\) reflects change in electrolyte density from the initial state caused by charging. (**c**) \(\Delta p\) profiles of x-axis averaged over y-axis in (**b**) [71]. (Reproduced with permission from ref [71]. Copyright 2018 American Chemical Society.) SOC: state of charge. Figure 18: (**a**) Fast charge/discharge cycle (0.36 mA, 3C rate, five cycles) and potential profiles of first cycle, (**b**) corresponding extracted phase maps of electrolyte, and (**c**) \(\Delta p\) profile of x-axis direction charge (points A to F) and discharge (points G to L) [71]. Reproduced with permission from ref [71]. Copyright 2018 American Chemical Society. LAB observations have also been performed using a LAB model cell with a galvanostat (GS), using the same procedure as for LIB [72]. A lead-oxide (PbO\({}_{2}\)) cell was used as the positive electrode, a lead (Pb) cell was used as the negative electrode, and a 37 wt% dilute sulfuric acid solution (H\({}_{2}\)SO\({}_{4}\) aq.) was used as the electrolyte. Observations were performed during charging and discharge using 17.8-keV SR. The exposure time was set to 5 s, and a phase map was obtained using the fringe scanning method with five steps. The phase shift is defined as the change from the initial state (before charging/discharging (t = 0, open circuit voltage). Figure 19a shows a phase map of the LAB cell obtained before a current was applied; the two electrodes are blacked out because X-rays do not penetrate such electrodes. Before X-ray phase imaging measurement, the electrodes were fully charged, i.e., the SOC was set to 100%. Figure 19b shows the charge-discharge curve at 50 mA constant current (C/2 rate) and the corresponding phase maps obtained at points A to H (the corresponding SOC and actual capacitance are also shown). \(\Delta p\) decreased overall when discharge started (A to C), and it increased gradually when charging switched (C to D). When charging switched to deep discharging, \(\Delta p\) decreased substantially (D\(-\)F), and when deep discharging switched back to charging, \(\Delta p\) in the lower region of the electrolyte increased, whereas \(\Delta p\) in the upper region remained virtually unchanged (F\(-\)H). These results indicate that the difference in electrolyte density between the upper and lower regions increases during charging; i.e., electrolyte stratification becomes apparent. The horizontal \(\Delta p\) difference was very small, and the horizontal density distribution was negligible at low rates of charge and discharge (C/2 rate). The high sensitivity temporal and spatial resolution of CXI enable visualization and quantification of not only vertical electrolyte stratification behavior during high-speed charge-discharge but also local differences in reaction rates in the horizontal direction.