(a) The in situ PDF data of iron oxyfluoride ( Fe(1−x)IIFexIIIOxF2−x , x = 0.6) during the first discharge–charge cycle. Characteristic peaks of the rock salt intermediate are indicated by arrows. Relative peak intensities are indicated by colors. (b) Evolution of phase composition in Fe(1−x)IIFexIIIOxF2−x (x = 0.6) during cycling. (c) Characteristic atomic pairs in rutile, rocksalt, and body-centered-cubic metal and their corresponding PDF peaks. (d) PDF patterns of Fe_0.9Co_0.1OF and FeOF at pristine state, charged state after the 1^st cycle, and charged state after the 100^th cycle. (e) PDF patterns of Fe_0.9Co_0.1OF and FeOF at discharged state after the 1^st cycle and discharged state after the 100^th cycle. (f) Percentages of metal and rocksalt phases in Fe_0.9Co_0.1OF and FeOF obtained by fitting PDF results.^[48,49]