Fig. shows the XRD pa5erns of the pris-ne FMO thin film and that aQer lithia-on. The XRD pa5erns exhibited peaks corresponding to the FMO thin film, as well as those of the LATP substrate and Pt current collector. The peaks of the FMO thin film agreed with the P21/a monoclinic FMO , and exhibited polycrystalline nature. On the other hand, the h00 peaks were more prominent compared to that of the powder XRD pa5ern of FMO, indica-ng a localized a-axis orienta-on of the FMO thin film on the LATP substrate, in agreement with a previous report . AQer lithia-on, while no changes were observed in the peaks of the LATP substrate and Pt current collector, the posi-ons of the FMO peaks, par-cularly the 200, 400, 1 " 14 , 3 " 14 , and 402 " peaks, no-ceably shiQed to lower Q values, consistent with those in the literature for the lithia-on of FMO in liquid electrolytes . In the following analysis, we focused on the main peak (1 " 14, 3 " 14, and 402 " peak) of FMO, which exhibited the most significant changes during lithia-on, to track the lithia-on/delithia-on reac-on of the FMO thin film on the solid electrolyte.