Within this energy difference window, there also exist several polymorphs. Some of the polymorphs are layered, with pure NiO 6 octahedra arranged in a single layer of rather than two consecutive layers as in Li 2 Ni 2 O 3 . This suggests that the structural feature of NiO 6 units arranged in two consecutive layers is stabilized by excess Li. Figure shows that the average potential window is between 2.6 -4.8 V, but the low voltage part dominates, which is not a desirable feature for a cathode. We note that the calculated voltages may contain systematic errors, since the voltages from DFT calculations is sensitive to the choice of functional and that not all the structural transformations can be captured or correctly predicted.