Li + /Li (Figure ). As is typical for Wadsley-Roth phases, the lithium insertion profile can be (Figure ). The impact of lower cut-off voltage was also evaluated (Figure , Supplementary Figure ). Unlike most battery materials, Wadsley-Roth phases do not have well-defined voltage or capacity limits and many exhibit reversible multi-electron redox over a sufficiently wide potential window. As with virtually all intercalation materials, the reversibility is linked to the capacity that is cycled and thus the operating potential window. This phenomenon is observed for NaNb7O18, albiet more weakly than for some Wadsley-Roth compositions. Even in compounds with a section of relatively flat plateau such as H-Nb2O5, NaNb13O33, Nb12MoO33, TiNb24O62, and TiNb2O7, there is diffraction intensity continuously between the two end-members; PNb9O25 may be the best example of a sharp two-phase transition. The slope has been correlated to the block size in the niobium tungsten oxides, but in previous work and on the body of data summarized here, we propose that the slope is most related to the degree of cation mixing over the octahedral sites, which give rise to a continuous distribution of lithium orderings and redox energies. In fact, block size itself trends with the degree of cation mixing as WO3 is added to Nb2O5 in niobium tungsten oxide Wadsley-Roth phases because block size trends with oxygen-to-metal ratio.