Afterwards, in region IV, the phase transition from Na2V2(PO4)3 to Na3V2(PO4)3 occurred rapidly. Finally, in region V (reduction down to 1 V vs. Na + /Na), a biphasic reaction between Na3V2(PO4)3 and Na4V2(PO4)3 is observed. When the pristine Na3V2(PO4)3 phase re-appears during discharge, the reaction mainly occurs through a two-phase reaction mechanism but a slight peak-shift to lower angles (Figure ) and an increase of V/Z were observed, which indicates that a partial solid solution mechanism is also involved. This behavior is typically observed in Na3V2(PO4)3 and other electrode materials, such as, Na3Al0.5V1.5(PO4)3, 51 Na4MnCr(PO4)3, 52