Cycling within a narrower voltage window (Figure ), combined with the overpotential, result in a spike at the start of charge at moderate C-rates. On the other hand, the major redox peaks of Nb18W8O69 (1.6-1.7 V) shift minimally up until ≥20C rate even as the initial overpotential increases. Overpotential scales with current density and resistance; the asymmetry shows that this effect is more pronounced on lithium extraction. For clarity we note that, due to the large particle sizes and small accessible surface areas, we do not ascribe the high-rate performance to capacitive or 'pseudocapacitive' effects. Overall, bulk morphologies of Nb18W8O69 appear to (de)intercalate lithium with rapid kinetics like in the Nb16W5O55 cs phase.