Using equation 5, we compare the voltages for the intercalation of sodium at a high sodium content in the cubic and rhombohedral phases. Due to differences in the unit cell size, in the case of the rhombohedral phase, the voltage calculation concerns the range from Na The intercalation potentials for the last sodium insertion step in rhombohedral and cubic Prussian White were calculated to be at 2.5 V and 2.77 V, respectively. These results agree reasonably well with the experiment but slightly underestimate measured open circuit voltages, which becomes apparent when comparing with experimental values of 2.8-3.3 V.