Structure–Property Relationships in High-Rate Anode Materials Based on Niobium Tungsten Oxide Shear Structures

Abstract

Nb16W5O55 emerged as a high-rate anode material for Li-ion batteries in 2018 [Griffith et al., Nature 2018, 559 (7715), 556–563]. This exciting discovery ignited research in Wadsley–Roth (W–R) compounds, but systematic experimental studies have not focused on how to tune material chemistry and structure to achieve desirable properties for energy storage applications. In this work, we systematically investigate how structure and composition influences capacity, Li-ion diffusivity, charge–discharge profiles, and capacity loss in a series of niobium tungsten oxide W–R compounds: (3 × 4)-Nb12WO33, (4 × 4)-Nb14W3O44, and (4 × 5)-Nb16W5O55. Potentiostatic intermittent titration (PITT) data confirmed that Li-ion diffusivity increases with block size, which can be attributed to an increasing number of tunnels for Li-ion diffusion. The small (3 × 4)-Nb12WO33 block size compound with preferential W ordering on tetrahedral sites exhibits single electron redox and, therefore, the smallest measured capacity despite having the largest theoretical capacity. This observation signals that introducing cation disorder (W occupancy at the octahedral sites in the block center) is a viable strategy to assess multi-electron redox behavior in (3 × 4) Nb12WO33. The asymmetric block size compounds [i.e., (3 × 4) and (4 × 5) blocks] exhibit the greatest capacity loss after the first cycle, possibly due to Li-ion trapping at a unique low energy pocket site along the shear plane. Finally, the slope of the charge–discharge profile increases with increasing block size, likely because the total number of energy-equivalent Li-ion binding sites also increases. This unfavorable characteristic prohibits the large block sizes from delivering constant power at a fixed C-rate more so than the smaller block sizes. Based on these findings, we discuss design principles for Li-ion insertion hosts made from W–R materials.

A V-doped W3Nb14O44 anode in a Wadsley–Roth structure for ultra-fast lithium-ion half/full batteries

“…In order to investigate the intercalation pseudocapacitive behavior of V-WNO, the electrochemical kinetics obtained from the CV curves were further analysed based on the eqn (2), 36 where the b -value is the criterion to evaluate the contribution of the pseudocapacitance: i v = av b …”

“…Among them, niobium tungsten oxides with crystallographic shear structures, such as Nb 18 W 8 O 69 , 1,5,27–31 Nb 14 W 3 O 44 , 32–35 Nb 12 WO 33 36–38 and Nb 9 W 8 O 47 39 recently have attracted much attention at the micrometer-sized level. Grey's group 1 proved that micrometre-sized Nb 14 W 3 O 44 with suitable host lattice can be used even at extremely high rate.…”

“…Nb 14 W 3 O 44 ,[32][33][34][35] Nb 12 WO 33[36][37][38] and Nb 9 W 8 O 47 39 recently have attracted much attention at the micrometer-sized level. Grey's group 1 proved that micrometre-sized Nb 14 W 3 O 44 with suitable host lattice can be used even at extremely high rate.…”

Significantly enhanced supercapacitor performance of W3Nb14O44 by introducing serine and histidine-functionalized and boron-doped graphene quantum dots

“…For example, (4 Â 4)-Nb 14 W 3 O 44 has a considerably larger discharge capacity than (3 Â 4)-Nb 12 WO 33 , (4 Â 4)-Nb 14 W 3 O 44 , and (4 Â 5)-Nb 16 W 5 O 55 . 9 Several strategies have been developed to synthesize niobium tungsten oxide, including the solid-state reaction, 10 the sol-gel method, 11 the electrospinning method, 12 and a hybrid with conductive carbon materials. 13 The solid-state reaction involves mixing Nb 2 O 5 with WO 3 at a certain molar ratio and subsequent annealing.…”

“…For example, (4 × 4)-Nb 14 W 3 O 44 has a considerably larger discharge capacity than (3 × 4)-Nb 12 WO 33 , (4 × 4)-Nb 14 W 3 O 44 , and (4 × 5)-Nb 16 W 5 O 55 . 9…”