Structural Insights into the Lithium Ion Storage Behaviors of Niobium Tungsten Double Oxides

Niobium-based transitional metal oxides are emerging as promising fast-charging electrodes for lithium-ion batteries. Although various niobium-based double oxides have been investigated (Ti–Nb–O, V–Nb–O, W–Nb–O, Cr–Nb–O, etc.), their underlying structure–property relationships are still poorly understood, which hinders the structural optimization for Nb-based electrodes. In this work, niobium tungsten oxides (WNb2O8, W3Nb14O44, and W10.3Nb6.7O47) featured with different structural openings are selected as model systems to investigate the role of crystal structures in their lithium ion storage behaviors. The three crystal structures showed different voltage windows to maintain the stable and high-rate lithium ion (de)intercalation. In detail, WNb2O8 exhibits a wide stability window (cutoff voltage below 0.5 V vs Li/Li+), benefiting from its evenly distributed quadrilateral tunnels. In contrast, W3Nb14O44 and W10.3Nb6.7O47, with larger structural openings, required higher cutoff voltages (1.0 and 1.3 V vs Li/Li+, respectively) to maintain their structural stabilities during lithium (de)insertion. The best rate performance is found in W10.3Nb6.7O47 crystals, benefiting from its large pentagonal tunnels that offered a low lithium intercalation barrier and possible two-dimensional lithium ion pathways. Despite a medium-sized tunnel opening, the Wadsley–Roth structure of W3Nb14O44 shows the highest lithium storage capability and specific capacity due to its abundant lithium intercalation sites. We expect that our systematic investigation of the three representative structures could offer more inspiration for the future structural optimization of Nb-based electrodes toward different energy storage systems.