Figure 4: In situ XRD patterns collected for a Na3V2(PO4)2F3/Na cell.
From: Insertion compounds and composites made by ball milling for advanced sodium-ion batteries
XRD patterns (a) and the corresponding electrochemical curve (b) is shown. The percentage of each phase and their unit cell volumes are shown in c,d, respectively. Error bars represent standard deviation obtained from the Rietveld refinement. Note that the Na4V2(PO4)2F3 phase mainly forms at the beginning of the process (within the 1.4–0.8 V domain) and then the Na-uptake appears self-limiting for reasons explained with the text. For time >20 h the amount of Na4V2(PO4)2F3 within the accuracy of the measurements still increases, while the cell is already in its oxidation mode.
