Fig. presents the voltage curve of the FMO thin film during lithia-on with the charging current density of 1.0 µA/cm 2 (~0.3C). The horizontal axis corresponds to the voltage against the reference FMO electrode, while the ver-cal axis denotes the areal capacity of the FMO thin film. The charge capacity of approximately 3.2 µAh/cm 2 agreed well with the theore-cal capacity of FMO, sugges-ng that the FMO thin film was almost fully lithiated during charging. As shown in this figure, the voltage of the FMO thin film gradually changed with lithia-on, and no dis-nct poten-al plateaus were confirmed, in contrast to the lithia-on in liquid electrolytes . Fig. shows the evolu-on of the main peak of the FMO thin film during lithia-on. Throughout the lithia-on process, essen-ally a single FMO main peak was observed. The posi-on of the FMO main peak gradually shiQed towards lower Q values during lithia-on, finally reaching the peak posi-on of Li2FMO. Figs. and show the voltage curve and peak evolu-on of the FMO thin film during delithia-on with the same (dis)charging rate, respec-vely. The evolu-ons of the voltage and main peak of the FMO thin film during delithia-on were generally symmetric to those during lithia-on.