(1 0 3) to lower 2 θ angles (30.25 °) as seen in Figure b. The fluorination of the active material is followed by a symmetry lowering from I4/mmm to P4/nmm . No ex-situ XRD analysis was performed for potentials below 0.2 V. At this cutoff potential, the pristine oxide phase had already disappeared, as evidenced in Figure as the cutoff capacity rises. This result is supported by the linear change in lattice parameters reported in Figure for potential cutoffs comprised in the range 0.2-1 V. Such results are in line with previous experimental observations on the electrochemical fluorination of LaSrMnO4Fx up to x=1, reporting a clear two phases domain up to at least x = 0.75 . Rietveld analysis of the active material's lattice parameters reveals that during the prolonged plateau from 1.2 V to 3 V the active material undergoes no significant structural changes, suggesting that the composition of the fluorinated phase remain stable. Previous studies showed that around this potential, fluorination of the carbon additive occurs. These findings differ from those reported by Nowroozi et al. As it has been reported previously, the Ruddlesden-Popper type structure with first-row transition metals shows redox-catalytic activity for oxidative fluorination of carbon, leading to poor cycling performance . Upon discharging the cell to 0.6 V, 0.3 V, and 0 V, the XRD pattern shows no significant changes (see A plateau characteristic for a two-phases domain is observed around -0.2 V, and the XRD pattern acquired at this cut off confirms that defluorination occurs within this range. To validate this result, an XRD measurement is taken at the beginning of the plateau using a capacity cutoff instead of a potential cut-off. The cell charged up to 15 mAh/g shows the onset of defluorination, evidenced by small peaks of the defluorinated phase at 31.01 °. When discharging down to -0.2 V, a minor peak from a residual fluorinated phase at 30.29 ° was observed along with the presence of 3.7(2) wt % of the fluorinated residual phase (P4/nmm) and 22.0 (3) wt% of oxide phase (I4/nmm). These results confirm that in a certain voltage range fluoride insertion/deinsertion into LaSrMnO4 proceeds via a typical two-phases reaction. The residual peaks originating from the fluorinated phase disappear when the cell is discharged to -0.5 V. Beyond this point, discharging the cell to lower potentials, e.g., down to -1.2 V, does not result in significant changes in the XRD pattern or in the unit cell lattice parameters. Unlike the charging process, in which the LaSrMnO4F phase with P4/nmm symmetry is formed, it fully reverts to the initial parent LaSrMnO4 phase with I4/mmm symmetry at -0.5 V during the discharging process with the lattice parameters a~3.8038(3) Å, c~13.1505 (15) Å and a volume of 190.27(3) Å . Discharging the cell to lower potentials, e.g., down to -1.2 V, does not lead to significant changes in the XRD pattern. Nevertheless, the reflections appear to become asymmetric, shifting towards the lower angles which implies that some changes may have been induced in the material. But at this potential, the LaSrMnO4F phase disappears, leaving only the parent phase LaSrMnO4. At a discharging capacity of ~ 55 mAh/g, the reduction of the Mn 3+ transition metal ion is more pronounced than its oxidation during the preceding charging of LaSrMnO4. This reduction leads to a decrease in the c lattice parameter and expansion along the a-axis, as illustrated in Figure . This result confirms that F⁻ insertion and de-insertion occur with high reversibility, while maintaining the structural stability of LaSrMnO4 throughout the fluorination and defluorination processes. The charging and discharging analysis revealed the presence of monophasic and biphasic domains during the fluorination and defluorination of the active material. To further investigate the relative stability of various fluorinated phases during these processes, a formation energy convex hull was constructed. This involved calculating the total energy for various compositions in the LaSrMnO₄Fₓ system, with x ranging from 0 to 2 in increments of 1 /16 fluoride ions. This systematic approach generated 32 distinct fluoride ion compositions, with a total of 148 unique configurations explored across the concentration range. These supercells where ELaSrMnO4Fx is the lattice energy of the configuration LaSrMnO4Fx, ELaSrMnO4F2 is the lattice energy of LaSrMnO4F2, and ELaSrMnO4 is the lattice energy of LaSrMnO4. The formation energy of each F-interstitial configuration is plotted in Figure . The graph indicates that the composition LaSrMnO4F1 is stable, in agreement with the structural analysis conducted during the charging and discharging processes in this study, as well as chemical fluorination performed with a gas mixture of 10 % F2/ 90 % N2 in previous works . Additionally, the graph shows that the composition LaSrMnO4F~1.8 is also stable, in agreement with the structural analysis conducted in previous work , as well as chemical fluorination performed with AgF2 as fluorinating agent . discharging. When examining the cell stopped at 15 mAh/g with a capacity cut-off, the onset of defluorination is evident. At this point, the fluorinated phase is still dominant, as the cell is at the beginning of the plateau, but a two-phases domain persists.