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

Abstract

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.

Insight into the Fast‐Rechargeability of a Novel Mo1.5W1.5Nb14O44 Anode Material for High‐Performance Lithium‐Ion Batteries

“…Additionally, based on the proposed local lattice structure of the MoO 4 tetrahedron (Figure 2j), an HAADF image simulation was performed on Dr. Probe simulation software, which also further confirms the occupation of Mo 6+ at the tetrahedral sites (Figure 2k). As expected, the aforementioned observation is obviously different from the previously reported WNO HAADF images with similar brightness and little contrast between the octahedral and tetrahedral sites, [ 2a,27 ] further implying the lower electron density of t 1 site in MWNO due to the occupation of Mo 6+ . Therefore, the AC‐STEM study above is in line with the NPD refinement results, confirming the exact lattice structure of MWNO, that is, the majority of the Mo 6+ ‐dopant fully occupies the t 1 site, and the remaining Mo 6+ cations may possibly reside on the o 1– o 4 sites.…”

“…This is in line with the previous studies. [ 2a,27 ] Additionally, MWNO exhibits a significantly reduced Li + diffusion energy barrier of the Path III, which indicates that the Mo 6+ /W 6+ doping can benefit the Li + diffusion between the layers. Therefore, these results share coherence with the GITT result and clearly unravel that Li + can transport easily and rapidly in MWNO, benefitting its rate‐capacity.…”

Nb-Based Mixed Oxides As Anodes for Metal-Ion Capacitors: Progress, Challenge, and Perspective

“…When the molar ratio of WO 3 to Nb 2 O 5 is less than 1, the W−R shear structure is exhibited, and the tunnels are rectangular. When the molar ratio is greater than or equal to 1, a tetragonal TB with triangle, quadrilateral, and pentagonal tunnels is presented 64. Therefore, the abundant large-scale channels and large intercalation spacing endow micron-scale NBMOs of TB structure with high ion diffusion rate and rate capability.…”

Conductive LaCeNb6O18 with a Very Open A‐Site‐Cation‐Deficient Perovskite Structure: A Fast‐ and Stable‐Charging Li+‐Storage Anode Compound in a Wide Temperature Range

“…[4] Second, large anion/cation ratios are achieved, leading to open crystal structures, such as shear ReO 3 structures (Ti 2 Nb 10 O 29 , Nb 14 W 3 O 44 , Nb 16 W 5 O 55 , and Ni 2 Nb 34 O 87 ) and tungsten bronze structures (Nb 18 W 16 O 93 and T-Nb 2 O 5 ), [1d,5] which enable not only fast Li + diffusivity but also significant intercalationpseudocapacitive behavior. However, the shear ReO 3 structures are still insufficiently open, and the tungsten bronze structures are insufficiently stable after deep lithiation, [6] more or less limiting their fast-and stable-charging capability.Here, we design and explore LaCeNb 6 O 18 (LCNO) as a fastand stable-charging niobium-based anode compound, which owns the following characteristics. First, the unpaired electrons in conductive Ce 3+ enable its fast electron conduction.…”