Upon charging beyond 10 mAh g -1 within the first region, the orthorhombic #1 phase fraction is found to decrease significantly. In addition, a tetragonal phase as well as another orthorhombic phase (labeled as orthorhombic #2) appear. The tetragonal phase possesses cell parameters which appear to be fairly independent on the state of charge, in contrast to what is found for the orthorhombic #1 and #2 phases. The orthorhombic #2 and the tetragonal phase show an increase of c-axis; in addition, the orthorhombic #2 phase shows increase of the splitting of the a/b-lattice parameters at an overall increased cell volume as compared to the original state after heating. These changes remind about the structural distortions found for orthorhombic La2NiO3F2 , and we interpret this structural behavior as being induced by the fluoride-ions accumulating with in the interstitial layers at a low content and inducing an orthorhombic distortion to be accommodated therein. The maximum of the overall amount of the orthorhombic phases is found between 30-40 mAh g -1 , for which these phases amount to approximately 50 % of the total RP-type phases. Considering that carbon side reactions mainly occurs above 1.2 V and not in this potential range, one can estimate that the orthorhombic phases contain a maximum of 1 F per formula unit, further supported by the absence of a large increase of the c-axis, i.e. possess a maximum composition of La2Ni0.75Co0.25O4.08F1. Upon further charging to a higher cut-off capacity, i.e. up to 160 mAh g -1 , an additional phase can be observed within the X-ray diffractograms (Figure ) with an indicative reflection at 29°. Schematic illustrations of fluorinated and non-fluorinated La2Ni0.75Co0.25O4.08 state has been shown in Figure . From the Rietveld refinements, it was found that this phase can be refined within a monoclinic RP-type phase (the crystal system is indicated from the splitting of the reflections), for which we took the structural model with symmetry C2/c as previously observed for La2NiO4F1.7 from electron diffraction . The relative weight fraction (Figure ) of this phase was found to increase with increased charging between 40 mAh g -1 to 160 mAh g - 1 . As can be seen from Figure , this monoclinic phase has an increased volume per La2Ni0.75Co0.25O4.08 unit by about ~28 Å³ compared to the tetragonal, orthorhombic #1 and orthorhombic #2 phases. This volume change is indicative for highly fluorinated phase with all interstitial sites occupied by fluoride ions and mainly originates from the large increase of the c-axis length to ~ 15.275(3) Å, whereas the a/b parameters contract due to shortened (Co/Ni)-O bonds from the oxidation process (Figure ). The chemical formula for this phase is likely close to La2Ni0.75Co0.25O4.08F1.92-𝛿 (see also XAS analysis reported in section 3.3 ). We note that on charging, a change of the relative weight fraction of the monoclinic phase occurs, whereas its unit cell volume remains mainly constant (Figure ). This can be interpreted in the sense that this phase is saturated with fluoride ions already once it starts to In order to understand the electrochemical defluorination behavior of the parent RP-type phases, the parent oxide was first charged to 130 mAh g -1 followed by discharging to different discharge capacities (20, 40, 60, 130 and 180 mAh g -1 ) Figure a and subsequent ex-situ XRD analysis (see Figure . For the sample discharged to 20 mAh g -1 , it is found that the monoclinic phase is still the major phase present along with the relatively lower weight fractions of the tetragonal, orthorhombic #1 and orthorhombic #2 phases. The major indicative reflection of the monoclinic phase at 29° is still visible for the discharged state of 20 mAh g -1 (see Figure ), and no significant changes are observed for the lattice parameters. Upon discharging to 40 mAh g -1 , the indicative reflection of the monoclinic phase is no longer visible and only the tetragonal and two orthorhombic modifications are found. For high coulombic efficiency (an absence of side reactions on charging), the discharge capacity of 40 mAh g -1 would correspond to the charging capacity of 90 mAh g -1 . Interestingly, there is a clear difference between the relative weight fractions of the different phases at this stage shown in Figure a. For charging to 90 mAh g -1 , the main phase was found to be the monoclinic phase along with relative lower weight fractions of the other phases; however, for reaching a comparable state on discharging, the monoclinic phase is completely absent. This also suggests the possible overlapping of side reactions along with the charging of the parent RP oxide phase. Such side reactions can be attributed to carbon fluorination which is well known for FIBs .