Nb18W8O69 (9Nb2O5·8WO3) is the tungsten-rich end-member of the Wadsley–Roth crystallographic shear (cs) structures within the Nb2O5–WO3 series. It has the largest block size of any known, stable Wadsley–Roth phase, comprising 5 × 5 units of corner-shared MO6 octahedra between the shear planes, giving rise to 2 × 2 nm2 blocks. Rapid lithium intercalation is observed in this new candidate battery material and 7Li pulsed field gradient nuclear magnetic resonance spectroscopy—measured in a battery electrode for the first time at room temperature—reveals superionic lithium conductivity with Li diffusivities at 298 K predominantly between 10–10 and 10–12 m2·s–1. In addition to its promising rate capability, Nb18W8O69 adds to our understanding of the large family of high-performance Wadsley–Roth complex metal oxides
