Nb18W8O69. The C/2 discharge curves of the three versions of Nb18W8O69 were nominally identical (Figure ), but the irreversible capacity and cycling performance differed (Figure ). Nb18W8O69 exhibits similar rate performance to its neighboring cs structure Nb16W5O55 up to 20C with similar Nb14W3O44, and Nb12WO33, . Cells were cycled between 3.0 V and a lower voltage cutoff (Vmin) of either 1.2 or 1.0 V, with capacity retention being worse for the wider potential window as expected (Figure ). The different preparations of Nb18W8O69 all showed the same first cycle