Niobium Metal Oxide

Abstract

The present invention relates to niobium metal oxide, niobium metal oxide secondary particles, a method for preparing the same, and a working electrode and an electrochemical cell comprising the niobium metal oxide secondary particles. The niobium metal oxide is represented by the formula (I): Nb x M y O z wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo, x is 2 to 18, z is 2.5x+3y, and x / y is 1 to 3, and the crystal structure of the niobium metal oxide is a tetragonal tungsten bronze structure having four or eight pentagonal channels per unit cell, a portion of the pentagonal channels being filled with -Nb-O-Nb-O- strings, and the remaining portion of the pentagonal channels being optionally intercalated with lithium.

Description

[Technical Field]

[0001] Related Applications This application claims priority to and the benefit of UK Patent Application No. 2218984.9, filed December 15, 2022 (15.12.2022), the contents of which are hereby incorporated by reference in their entirety.

[0002] The present invention relates to niobium metal oxide, niobium metal oxide secondary particles, and methods for preparing the same, as well as working electrodes and electrochemical cells comprising niobium metal oxide secondary particles. [Background technology]

[0003] Fast-charging lithium-ion batteries are important for energy storage in a variety of technological areas, from electric vehicles and grid storage cells to handheld devices and backup systems. Various known niobium metal oxides (NMOs) are used as fast-charging working electrode materials, such as niobium tungsten oxide (NWO, Griffith et al.). These materials have good high-rate performance and capacity retention even at high charging rates.

[0004] Most known NMOs have structures that can be derived from simple ReO3-type structures, such as block structures or tetragonal tungsten bronze (TTB).

[0005] These NMO phases are typically synthesized by solid-state methods, in which solid precursor metal oxides are milled and / or mixed to form fine powders. Such methods are known for niobium tungsten oxide (Roth et al., 1965); niobium molybdenum oxide (Ekstrom et al., 1971), niobium titanium oxide (Wadsley et al., 1961), and niobium chromium oxide (Yang et al., 2017), among others. The fine powders are then calcined at high temperatures to form NMO. Because the powders are not homogeneous, metal ion diffusion must occur throughout the multiple crystallites within a particle (intra-particle cation diffusion) and throughout the particle (inter-particle cation diffusion), requiring high temperatures for the calcination step, typically exceeding 1,200°C. The higher the energy barrier for intra- and inter-particle ion diffusion, the higher the temperature required for synthesis. By using lower temperatures, a portion of the precursor remains unreacted. In an early attempt by Fiegel et al. to synthesize different NWO phases below 900 °C, the different phases coexisted and equilibrium was not reached even after 30 days.

[0006] NMO has also been synthesized using solution-based mixing methods (e.g., Kudo et al., 1988). In this case, solutions of metal oxide precursors are mixed before adding a precipitant to initiate precipitation of the dissolved precursors. For example, precipitation from salt precursors by hydrolysis is known, but the hydrolysis rate of Nb is significantly faster than that of W, resulting in the hydrolysis of Nb ions first, forming Nb2O5 islands, followed by the precipitation of WO3. These methods are known to result in non-simultaneous precipitation, meaning that the precipitation mixture is also poorly homogeneous, preventing uniform distribution of cations in the final product. For the same reasons mentioned above, high temperatures (e.g., above 1,200 °C) are then required for calcination to yield the desired block NMO phase.

[0007] The poor homogeneity and high synthesis temperatures result in complexes of structural variants with varying compositions within each crystallite. This is believed to be due to temperature gradients and irregular distribution of Nb and metal ions within the lattice (Krumeich, 2022). As a result, these materials generally crystallize in the form of rods, often with broad size distributions, variable aspect ratios, and irregular morphologies. For example, WO 2019 / 234248 describes the preparation of Nb by solid-state synthesis. 16 W5O 55 The synthesis of the product is described. The product is prepared by grinding together dry powders of Nb2O5 and WO2, and then calcining the mixture at 1200 °C. The resulting Nb 16 W5O 55 SEM images of the particles show irregular rod-like morphology (see Figure 1).

[0008] Therefore, the actual volumetric capacity and energy density of these NMO materials are limited. The poor packing density of NMO crystallites due to irregular particle morphology leads to voids between particles. These may also contribute to poor lithium ion conductivity and electrode kinetics. The poor contact between adjacent particles means that some particles intercalate lithium more or less readily, resulting in materials that are unstable at fast charge / discharge rates and poor capacity retention over many cycles at high rates.

[0009] The crystal structure of NMO synthesized by these known methods is also disordered. The cation occupancy between the Nb and M components is disordered within the crystal structure. This disorder leads to anisotropic lithium (de)intercalation during charge or discharge. The cation disorder also causes the crystal structure to expand and contract irregularly during (de)intercalation, making the material more susceptible to cracking. Cracking is particularly pronounced during rapid charge / discharge, when expansion and contraction occur most rapidly. Overall, this leads to poor electrochemical properties such as capacity retention, especially at high charge / discharge rates. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2019 / 234248 [Patent Document 2] Chinese Patent Application Publication No. 110304658 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, there is a need for improved NMO materials and related preparation methods that provide particles with improved electrochemical performance and volumetric energy density. [Means for solving the problem]

[0012] Most generally, the present invention provides a niobium metal oxide having a crystal structure comprising a tetragonal tungsten bronze with pentagonal channels (PC), where the PC is partially filled with -Nb-O-Nb-O- strings. The -Nb-O-Nb-O- strings in the PC provide cation ordering within the structure. A portion of the PC is filled with -Nb-O-Nb-O- strings, and the remaining portion is optionally intercalated with lithium.

[0013] Niobium metal oxides are represented by the formula (I) Nb x M y O z (I) where M is a metal, x is 2 to 18, z is 2.5x+3y, and x / y is 1 to 3, and the crystal structure of the niobium metal oxide is or includes tetragonal tungsten bronze with pentagonal channels, a portion of which is filled with -Nb-O-Nb-O- strings. If the pentagonal channels do not contain strings, they are optionally intercalated with lithium.

[0014] The NMO phases reported here act as high-rate anode materials, exhibiting excellent electrode kinetics, rate performance, and capacity retention, especially at high rates. These specific crystalline phases demonstrate highly symmetric and ordered morphologies. Furthermore, the cation ordering provided by the -Nb-O-Nb-O- strings promotes uniform lithium intercalation and results in uniform expansion and contraction of the crystalline structure during cell cycling. This new NMO phase also forms spherical secondary particles, as opposed to the irregular rod-like particles formed by known NMO phases.

[0015] In a first aspect of the present invention, a compound of formula (I) optionally intercalated with lithium is provided. Nb x M y O z (I) wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo, x is 2 to 18, z is 2.5x+3y, and x / y is 1 to 3; the crystal structure of the niobium metal oxide is a tetragonal tungsten bronze structure having four or eight pentagonal channels per unit cell; a portion of the pentagonal channel is filled with -Nb-O-Nb-O- strings, and the remaining portion of the pentagonal channel is optionally intercalated with lithium; Niobium metal oxide is provided.

[0016] The cation ordering provided by the pentagonal channels filled with -Nb-O-Nb-O- strings results in improved lithium intercalation of the niobium metal oxides of the present invention. During lithium intercalation and deintercalation, the niobium / metal cations in the niobium metal oxides are reduced and oxidized, respectively. Depending on the structure and metal components of the niobium metal oxide, preferential redox of the niobium or metal (e.g., tungsten) cations occurs during intercalation.

[0017] Because the provided structures are more ordered (e.g., due to pentagonal channels filled with -Nb-O-Nb-O- strings), preferential redox occurs for cations in the same lattice environment throughout the structure, meaning that the lattice expands and contracts uniformly during intercalation. This contrasts with known structures that do not have such cation ordering, in which the cations undergoing redox can exist in different lattice environments, resulting in non-uniform expansion and compression. The uniform expansion reduces cracking and structural defects during cell cycling, improving cell performance, especially at high rates.

[0018] Generally, the present invention also provides spherical niobium metal oxide secondary particles comprising agglomerates of primary particles.

[0019] In a second aspect of the present invention, there is provided niobium metal oxide secondary particles comprising agglomerates of niobium metal oxide primary particles such as the niobium metal oxide particles of the first aspect, the niobium metal oxide secondary particles having an average length of 1 to 5 μm and an aspect ratio of 1 to 1.5.

[0020] The highly regular particle shape of the particles (e.g., length of 1-5 μm and aspect ratio of 1-1.5) results in uniform packing of the particles. Preferably, the particles are highly symmetrical. Preferably, the particles are spherical.

[0021] Secondary particles can be formed from multiple primary particles of the niobium metal oxide of the first embodiment. Secondary particles are sometimes known as secondary agglomerates of the primary particles. The primary particles are believed to be tightly joined by NMO amorphous bridges between the primary particles. As a result, the interparticle distance of the primary particles is very low, allowing for easy ion diffusion. The strong amorphous NMO bridges are also believed to help retain the morphology of the secondary particles over many cycles at extremely fast charge / discharge rates.

[0022] The highly regular particle shape and packing also enable isotropic lithium (de)intercalation during charge and discharge. The uniform particle shape results in consistent coordination between adjacent particles (e.g., close-packed spheres have a coordination number of 12 with adjacent particles), meaning that lithium intercalation is consistent throughout the bulk material. This results in excellent high-rate performance.

[0023] The secondary particles have a very high packing efficiency due to their regular particle size, narrow particle size distribution, and preferred spherical shape.

[0024] The higher the packing efficiency, the denser the bulk material. The packing efficiency of spheres can be as high as the ideal close-packed structure for spherical particles, with a packing efficiency of about 74%. The bulk material exhibits particularly high density and good packing efficiency when calendered for use as an electrode for an electrochemical cell.

[0025] The higher the density (e.g., the higher the calendar density), the greater the number of lithium intercalation sites per unit volume of the electrode. Thus, the volumetric energy density of the electrode is increased as more lithium intercalation sites per unit volume are available.

[0026] Cationically ordered NMO crystal structures and secondary particles are typically not accessible via high temperature calcination. Instead, it has been found that low temperature calcination methods are required.

[0027] Generally, the present invention provides a method for preparing niobium metal oxide secondary particles, comprising the steps of: providing a precursor mixture of a Nb source and a M source; calcining the precursor mixture at a temperature of 550 to 1,100°C; wherein M is a metal other than Nb.

[0028] In a third aspect of the present invention, there is provided a method for preparing niobium metal oxide secondary particles such as the secondary particles of the second aspect, comprising the steps of: NbX aand MY b co-precipitating Nb oxide and M oxide from the solution; calcining the precipitate at a temperature of 550 to 1100°C; Including, wherein M is selected from Ti, Zr, V, Cr, W, and Mo; X and Y are independently one or more counter ions; and a and b are independently 2 to 6.

[0029] The method allows the preparation of the NMO phase of the first embodiment. By calcination at relatively low temperatures, PC can be partially filled with -Nb-O-Nb-O- strings, thus bringing cation ordering to the structure.

[0030] The method can also prepare secondary particles of the second embodiment. The secondary particles have a regular, preferably spherical, morphology that is believed to result from calcination at relatively low temperatures in the range of 550-1100°C, such as 800-900°C. Traditional high-temperature calcination (above 1200°C) results in loss of the spherical morphology.

[0031] The relatively low temperature calcination is believed to be possible due to the excellent cation mixing achieved by precipitation. Co-precipitation of metal cations results in atomic-scale mixing of cations in the precipitate. This contrasts with solid-state milling or mixing methods, where mixing occurs only on the μm or nm scale. Similarly, co-precipitation (e.g., by heating under solvothermal conditions using microwave heating in a sealed vessel) results in the simultaneous precipitation of both niobium oxide and metal (e.g., tungsten) oxide species in a homogeneous, atomic-scale mixed precipitate. This contrasts with known solution-based methods, where precipitation is non-co-precipitation, resulting in poor precipitate homogeneity.

[0032] Precipitation of NMO from its corresponding salt precursor is believed to occur via hydrolysis. The rate of hydrolysis is relatively high for Nb compared to W salts. As a result, when reacted under ambient conditions, hydrolysis of Nb salts occurs more rapidly, forming islands of NbO, leading to heterogeneity in the reaction mixture. In contrast, using a hydrothermal synthesis method (at high temperature and pressure), hydrolytic precipitation of Nb and W salts occurs simultaneously and more rapidly, improving homogeneity.

[0033] Furthermore, by using the co-precipitation process, various niobium-metal oxide compounds can be co-prepared with various metals such as Ti, Zr, V, Cr, W, and Mo. The thermal co-precipitation process is more chemically compatible than chemical precipitation methods that use precipitating agents to initiate precipitation.

[0034] The atomic-scale mixing achieved by this method means that the precipitate has a high degree of homogeneity of the two metal ions. Therefore, the need for metal ion diffusion is largely eliminated, and typically only intracrystallite metal ion diffusion is required. As a result, the energy barrier to ion rearrangement is relatively low (much lower than known solid-state synthesis methods). This allows for the use of much lower calcination temperatures, resulting in the specific niobium oxide phase of the first aspect of the present invention and the spherical secondary particles of the second aspect of the present invention.

[0035] The use of lower calcination temperatures has other advantages in terms of calcination equipment and energy usage. The lower the calcination temperature, the lower the total energy demand. This reduces manufacturing costs and the environmental impact of production. Calcination equipment (e.g., calciner and heat source) can also be less heat resistant, reducing capital costs.

[0036] In a fourth aspect, there is provided niobium metal oxide secondary particles comprising agglomerates of niobium metal oxide primary particles obtained or obtainable by the method of the third aspect.

[0037] In a fifth aspect, there is provided a working electrode for an electrochemical cell, the working electrode comprising the niobium metal oxide secondary particles of the second aspect or the fourth aspect.

[0038] In a sixth aspect, there is provided an electrochemical cell comprising the working electrode of the fifth aspect.

[0039] In an additional aspect, there is provided a lithium ion battery comprising one or more electrochemical cells of the sixth aspect.

[0040] In another aspect, there is provided a method of charging or discharging an electrochemical cell or a lithium-ion battery comprising the electrochemical cell of the sixth aspect, wherein the method of charging or discharging typically comprises intercalating lithium into the working electrode.

[0041] These and other aspects and embodiments of the present invention are described in further detail below.

[0042] The present invention will now be described with reference to the drawings listed below. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 10 shows an SEM image of a comparative Nb16W5O55 phase with irregular rod-like morphology prepared by the solid-state synthesis method of Comparative Example 8. [Figure 2] Figure 1 shows SEM images of precipitated NbCl5 and WCl6 prepared by the solvothermal method of Example 3. The images are taken after filtration and drying but before calcination. The images show varying magnification levels, with scale bars of (a) 20 μm, (b) 2 μm, and (c) 1 μm. [Figure 3]Figures 3(c)-(f) show additional SEM images of precipitated NbCl5 and WCl6 prepared by the solvothermal method of Example 3. The scale bar is 10 μm in (a) and (b). Figure 3(c)-(f) show SEM-EDS mapping images of precipitated NbCl5 and WCl6 prepared by the solvothermal method of Example 3. (c) shows SEM EDS mapping of Nb, (d) shows SEM EDS mapping of W, (e) shows SEM EDS mapping of O, and (f) is an overlay of Nb, W, and O. [Figure 4] Figure 1 shows SEM images at varying magnification levels of the NWO product prepared in Example 3 after calcination at 900°C, with scale bars (a) 20 μm, (b) 2 μm, and (c) 1 μm. [Figure 5] 1 shows transmission electron microscopy (TEM) images at varying magnification levels of the mixture of NWO phases prepared in Comparative Example 7. Scale bars are (a) 10 μm, (b) 20 μm, and (c) 50 μm. [Figure 6] FIG. 1 shows an EDS spectrum map of Nb18W6O63 prepared by Example 3. [Figure 7] FIG. 1 shows PXRD patterns over the 2θ range of 5 to 80° for the NWOs prepared in Example 1 (Nb:W=1, NbWO), Example 2 (Nb:W=2, NbWO), Example 2.5 (Nb:W=2.5, NbWO), and Example 3 (Nb:W=3, NbWO). [Figure 8] FIG. 1 shows PXRD patterns over the 2θ range of 5 to 30° for the NWOs prepared in Example 1 (Nb:W=1, NbWO), Example 2 (Nb:W=2, NbWO), Example 2.5 (Nb:W=2.5, NbWO), and Example 3 (Nb:W=3, NbWO). [Figure 9]Figure 9(a) shows PXRD patterns over the 10-80° 2θ range for NWO phases prepared in Examples 1, 2, 2.5, and 3 as well as Comparative Examples 4, 5, and 6. Figure 9b shows the same NWO phases over the 18-34° 2θ range. [Figure 10] FIG. 1 shows the PXRD of Comparative Example 7, which shows a mixture of NWO phases such as Nb16W5O55, Nb14W3O44, and Nb2WO8. [Figure 11] FIG. 1 shows the neutron diffraction patterns of NWO prepared in Example 1 (Nb:W=1, Nb2W2O11), Example 2 (Nb:W=2, Nb16W8O64), and Example 3 (Nb:W=3, Nb18W6O63). [Figure 12a] FIG. 1 shows the Rietveld refinement of Nb2W2O11 (Nb:W=1:1) prepared in Example 1. [Figure 12b] FIG. 1 is a diagram showing the crystal structure of Nb2W2O11 (Nb:W=1:1) prepared in Example 1. [Figure 13a] FIG. 1 shows the Rietveld refinement of Nb18W6O63 (Nb:W=3:1) prepared in Example 3. [Figure 13b] FIG. 1 shows the crystal structure of Nb18W6O63 (Nb:W=3:1) prepared in Example 3. [Figure 13c] This figure shows the relationship between the crystal structures of Nb2W2O11 (simple TTB unit cell) and Nb18W6O63 (supercell). The Nb2W2O11 unit cell is shown in the upper left, and the Nb18W6O63 supercell is shown in the center. [Figure 14] Figure 1 shows HR-STEM images of NWO prepared in (a) Example 1 (Nb:W=1, NbWO), (b) Example 2 (Nb:W=2, NbWO), and (c) Example 3 (Nb:W=3, NbWO). Scale bar is 10 nm. [Figure 15]Figure 1 shows HR-STEM images of NWO (Nb:W=3, Nb18W6O63) prepared in Example 3. (a) shows bright spots in HR-STEM demonstrating cation ordering in Nb18W6O63. (b) includes an overlay of the HRSTEM with the crystal structure. (c) shows one unit cell of the crystal structure. [Figure 16] Figure 1 shows HAADF-HRSTEM images of NWO (Nb:W=3, NbWO) prepared in Example 3. Images of NWO particles are shown before (a) and after (b) applying a band gap filter and thresholding. [Figure 17A] Figure 1 shows HAADF-HRSTEM images of NWO (Nb:W=1, Nb2W2O11) prepared according to Example 1. Images of NWO particles are shown before (a) and after (b) applying a band gap filter and thresholding. The scale bar is 5 nm. [Figure 17B] Figure 17B shows additional structural analysis of NWO (Nb:W = 1, Nb2W2O11) prepared in Example 1. Figure 17B(a) shows the Rietveld fit of the PXRD, Figure 17B(b) shows the TOF neutron diffraction pattern, and Figure 17B(c) shows the refined crystal structure of Example 1 viewed along the crystallographic a-axis (top) and c-axis (bottom). The PB site (magenta, 4h site) contains only Nb, the yellow octahedral site (8j) has equal probability of containing Nb and W atoms, while the cyan octahedral site (2c) is W-rich. Figure 17B(d) shows the HAADF-HR(S)TEM image along the c-axis with an overlay of the structural model (one unit cell) showing the atomic arrangement of Nb and W. For clarity, the second unit cell is depicted in Figure 17B(d) and the corresponding EDS maps of Figure 17B(e), Nb (red), Figure 17B(f), W (green), Figure 17B(g), and an overlay of Nb and W. [Figure 18]Figure 1 shows another HAADF STEM image of NbWO (prepared according to Example 3). The image has three sections (a-c) marked across the plane of atoms. The atomic line intensity profiles of sections (a-c) are shown along different planes of atoms in the HAADF STEM image. [Figure 19A] (a) Atomic resolution STEM-EDS image (scale bar is 5 nm) of Nb18W6O63 prepared in Example 3. The upper left image is a STEM image. The lower left is STEM-EDS mapping of Nb, and the lower right is STEM-EDS mapping of W. The upper right is an overlap of EDS mapping of Nb and W. (b) shows a closer view of the image in (a) (scale bar is 2 nm). [Figure 19B] Figure 1 shows HR(S)TEM-EDS data for a particle of Nb18W6O63. (a) STEM-HAADF image and corresponding STEM-EDS elemental maps of (b) Nb and (c) W; (d) overlay of elemental maps (b) and (c); (e) matched and summed STEM image (consisting of 1024 frames) from the same sample; and corresponding decomposition loadings of (f) Nb and (g) W obtained via NMF. NMF-based decomposition indicates the position of Nb and W atomic columns in the overlay (h) constructed from (f) and (g). All scale bars are 2 nm. [Figure 20] (a) TEM image of a primary particle of Nb16W8O64 perpendicular to the c-crystallographic axis, and (b) its corresponding fast Fourier transform. [Figure 21] (a) TEM image of a primary particle of Nb2W2O11 along the c crystallographic axis and (b) its corresponding fast Fourier transform. [Figure 22] (a) TEM image of a primary particle of Nb18W6O63 along the c crystallographic axis and (b) its corresponding fast Fourier transform. [Figure 23](a) TEM image of secondary particle lamellae of Nb18W6O63 (Example 3) prepared by FIB (focused ion beam) showing the network of primary particles. Scale bar is 1 μm. Figure 23(b) shows a closer view of the same TEM image; scale bar is 500 nm. [Figure 24] Figure 1 shows the electrochemical performance of the NWOs of Example 1 (Nb:W=1, NbWO) (bottom row) and Example 3 (Nb:W=3, NbWO) (top row) by measuring (a) the capacity at 1 C, 2 C, 5 C, 10 C, 20 C, and 1 C, and (b) the long-term cycling characteristics over 1000 cycles at 10 C for Example 1 (Nb:W=1, NbWO) (bottom row) and Example 3 (Nb:W=3, NbWO) (top row). [Figure 25] Figure 25 illustrates the structural modifications of the ReO3-type structure present in the crystalline structures of the present invention. Figure 25(a) shows the crystal shear (CS) or block structure, and Figure 25(b) shows the tetragonal tungsten bronze (TTB) structure found in the NWO materials of the present invention. The different channels are labeled T = trigonal, S = square / tetragonal, and P = pentagonal. [Figure 26] Figure 26 shows additional electrochemical characterization of the NWO anodes of the present invention. Galvanostatic discharge and charge curves are shown for Example 1 (NbWO5.5) in Figure 26(a), Example 2 (β-Nb2WO8) in Figure 26(b), and Example 3 (Nb3WO10.5) in Figure 26(c) at a range of different C-rates. Figure 26(d) shows the rate profile-based or gravimetric capacity for Examples 1, 2, and 3. Figure 26(e) shows the high-rate cycling capacity over 1000 cycles at 10 C for Examples 1, 2, and 3. [Figure 27] Figure 27 shows the PXRD patterns of Examples 1-3 after calcination at 800°C for 30 days during thermal stability testing. Figure 27(a) shows Example 1, Figure 27(b) shows Example 2, and Figure 27(c) shows Example 3. Figure 27(d) shows Example 3 with the Bragg positions of the decomposition products overlaid. [Figure 28A]FIG. 1 shows SEM images of Example 1 calcined at 800° C. for 30 days at different magnifications. [Figure 28B] Figure 1 shows SEM images at different magnifications of Example 2 calcined at 800°C for 30 days. The arrows point towards micron-sized particles believed to be the decomposition products NbWO and α-NbWO. [Figure 28C] FIG. 1 shows SEM images of Example 2 calcined at 800° C. for 30 days at different magnifications. DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention generally provides a niobium metal oxide having a crystal structure comprising a tetragonal tungsten bronze with pentagonal channels (PCs), where a portion of the PCs are filled with -Nb-O-Nb-O- strings, and the remaining PCs are optionally intercalated with lithium.

[0045] Niobium metal oxides typically have a crystalline structure with cation ordering, where a portion of the PCs are filled with -Nb-O-Nb-O- strings. The remaining PCs are either vacant or intercalated with lithium. The PCs are generally arranged in sets of four PCs interconnected by corner-sharing octahedra.

[0046] In a first aspect of the present invention, a compound of formula (I) optionally intercalated with lithium is provided. Nb x M y O z (I) wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo, x is 2 to 18, z is 2.5x+3y, and x / y is 1 to 3; the crystal structure of the niobium metal oxide is a tetragonal tungsten bronze structure having four or eight pentagonal channels per unit cell; a portion of the pentagonal channel is filled with -Nb-O-Nb-O- strings, and the remaining portion of the pentagonal channel is optionally intercalated with lithium; Niobium metal oxide is provided.

[0047] Niobium metal oxide phases with a tetragonal tungsten bronze structure have been previously reported, for example, by Sayagues et al. However, the cation ratios currently claimed for the niobium metal oxide and crystal structure were not reported. Sayagues et al. 12 O 32 described a tetragonal tungsten bronze (TTB)-type √2ax√2a superstructure in which all four pentagonal tunnels around the central square of the octahedron are filled with MO strings. Sayagues et al. did not describe cation ordering. In particular, they did not describe PC being selectively filled with Nb-O strings.

[0048] prepare niobium oxides by in situ gas reaction, as opposed to the solvothermal and low-temperature calcination of the present invention. Sayagues et al. also did not test the prepared NWOs as electrode materials.

[0049] Niobium metal oxide phases with similar Nb / M ratios have also been reported. However, these do not have the tetragonal tungsten bronze structure of the present invention. For example, the well-known Nb2WO8 phase has an Nb / W ratio of 2, whereas the Nb 16 W8O 64 (which also has a Nb / W ratio of 2). Nb2WO8 has a different structure from the Nb2WO8 of the present invention, in which the PC arrangement is 16 W8O 64 It crystallizes in an orthorhombic cell (space group, Pbcm) with a distorted structure different from that of NbWO (see Lundberg). Furthermore, the cation sites of NbWO are disordered, with equal probability that all sites will be occupied by Nb or W, rather than the ordered, filled cations seen in the present invention.

[0050] Furthermore, Chinese Patent Application Publication No. 110304658 discloses the preparation of Nb by co-precipitation of Nb and W precursors from ethanol, grinding the precipitate, and calcining. 18 W 16 O 93 The synthesis of irregular nanoparticles of Nb was described. The precipitation was carried out neither under solvothermal conditions nor using microwave-assisted heating. 18 W 16 O 93 The particles are a mix of "irregular nanoparticles, spindle-shaped nanospheres, and nanorods." The nanoparticles have a size of about 100 nm, and the nanorods have a size of 150 nm. The nanospheres have a size of 300-400 nm, and are secondary particles made of primary particles with a size of 50-200 nm. The particles described in CN110304658 are significantly smaller than the spherical secondary particles of the present invention, with a length of 1-5 μm. Furthermore, the Nb 18 W 16 O 93 does not have the specific crystal structure of the present invention and therefore the different morphology of the resulting particles.

[0051] Xia et al. ball-milled niobium oxide and tungsten oxide and calcined them at 1200°C to obtain Nb 18 W 16 O 93 describes the traditional synthesis of NWO by producing NbO. The co-precipitation and low-temperature calcination used in the present invention are not described. Xia et al. show that the shorter the calcination time, the smaller the particles. However, the produced Nb 18 W 16 O 93 The particles are irregular in shape and do not have the highly spherical morphology achieved by the present invention. The crystal structure described in Xia et al. is the well-known ReO3-type structure, and is not the crystal structure of the present invention.

[0052] We have developed new niobium metal oxide phases with a specific cation-ordered crystal structure in which pentagonal channels are partially filled with -Nb-O-Nb-O- strings. These phases are prepared by a novel solvothermal co-precipitation and low-temperature calcination method that facilitates the formation of these new NMO phases and their highly spherical secondary particles. These phases and particles are particularly suitable for use in working electrodes of electrochemical cells (e.g., lithium-ion cells), where they offer excellent volumetric capacity and volumetric energy density, as well as high-rate and long-term cycling performance.

[0053] Niobium Metal Oxide The present invention provides a compound of formula (I), optionally intercalated with lithium: Nb x M y O z (I) wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo, x is 2 to 18, z is 2.5x+3y, and x / y is 1 to 3; the crystal structure of the niobium metal oxide is a tetragonal tungsten bronze structure having four or eight pentagonal channels per unit cell; a portion of the pentagonal channel is filled with -Nb-O-Nb-O- strings, and the remaining portion of the pentagonal channel is optionally intercalated with lithium; Niobium metal oxide is provided.

[0054] Generally, niobium metal oxide refers to a metallic oxide comprising niobium, one or more other metals, and oxygen. Preferably, the niobium metal oxide is a binary metallic oxide comprising niobium, one other metal, and oxygen.

[0055] Niobium metal oxides are represented by the formula (I): Nb x M y O z It has.

[0056] Formula (I) can refer to NMO phases including Nb2O5 and MO3, such as Nb2O5 and WO3.

[0057] NMO includes niobium and any other suitable metal ("M" in formula (I)), such as a transition metal. The metal may be a Group 3, 4, or 5 metal, preferably a Group 4 or 5 metal, more preferably a Group 5 metal. Typically, the metal is selected from Ti, Zr, V, Cr, W, and Mo. Preferably, the metal is selected from Cr, W, and Mo, more preferably W and Mo, and even more preferably W.

[0058] The number of moles of Nb in NMO is defined by "x" in formula (I). x is 2 to 18, preferably 8 to 18, and more preferably 12 to 18. X may be 2, 16, or 18, preferably 16 or 18, and more preferably 18. X is typically an integer.

[0059] The number of moles of M in NMO is defined by "y" in formula (I). y may be 1 to 18, preferably 2 to 12, more preferably 4 to 10, and even more preferably 6 to 8. Preferably, y is 6. Y is typically an integer.

[0060] The number of moles of O in NMO is defined by "z" in formula (I). z is 2.5x + 3y. In view of the above, z may be 8 to 99, preferably 11 to 70, more preferably 45 to 64, and even more preferably 63 to 64. Z is typically an integer.

[0061] The molar ratio of Nb to M is defined by "x / y" in formula (I). The value of x / y may be the same as the ratio of Nb:M. x / y is 1 to 3, preferably 1.5 to 3, more preferably 2 to 3, and even more preferably 2.5 to 3. x / y can be selected from 1, 1.5, 2, 2.5, and 3, preferably 1.5, 2, 2.5, and 3, more preferably 2, 2.5, and 3, and even more preferably 2 and 3, and most preferably x / y is 3. Alternatively, x / y can be selected from 1, 2, and 3, preferably 2 and 3, and even more preferably 3.

[0062] In some embodiments, the niobium metal oxide is Nb 18 M6O 63 , Nb 16 M8O 64 , Nb2M2O 11 or a combination thereof. Preferably, the niobium metal oxide is Nb 18 M6O 63 , Nb 16 M8O 64 or a combination thereof, more preferably the niobium metal oxide is Nb 18 M6O 63 is.

[0063] In some embodiments, the niobium metal oxide is Nb 18 W6O 63 , Nb 16 W8O 64 , Nb2W2O 11 or a combination thereof. Preferably, the niobium metal oxide is Nb 18 W6O 63 , Nb 16 W8O 64 or a combination thereof, more preferably the niobium metal oxide is Nb 18 W6O 63 is.

[0064] Generally, the niobium metal oxides of the present invention are crystalline materials. In other words, NMOs have an ordered solid-state structure that includes a repeating pattern of ion positions in three-dimensional space. The smallest repeating structural unit is called a unit cell. The unit cell is repeated throughout the structure (by translation along the major axes of the unit cell) to define the crystalline structure.

[0065] A unit cell can be defined in terms of the lengths of its major axes and the angles between them. A unit cell can also be defined in terms of a space group or other symmetry within the unit cell.

[0066] The niobium metal oxide of the present invention has a crystal structure having a tetragonal tungsten bronze (TTB) type. TTB is a type of distorted ReO structure and is less symmetric than the ReO structure. The TTB structure is known in a variety of materials. Like the ReO crystal structure, TTB contains corner-sharing MO6 octahedra, with the MO6 octahedra typically oriented along the crystallographic c-axis.

[0067] The crystal structure may comprise a unit cell having space group P4 / mbm or a supercell having space group P4. Preferably, the crystal structure comprises a unit cell having space group P4 (referred to herein as a "supercell"). A supercell can be associated with a unit cell having space group P4 / mbm. The lattice parameters of the supercell coincide with the diagonal of the unit cell (see Figure 13c). Thus, if the unit cell has lattice parameter a x a, the supercell has lattice parameter equal to √2a x √2a. The lattice parameter c may be the same.

[0068] In some embodiments, the crystal structure comprises a unit cell having a space group P4 / mbm. In some embodiments, the crystal structure comprises a unit cell having a parameter a of 12-13 Å and a parameter c of 3.5-4.5 Å, preferably a parameter a of 12.2-12.5 Å and a parameter c of 3.7-4.3 Å, more preferably a parameter a of 12.2-12.3 Å and a parameter c of 3.8-4.0 Å, and even more preferably a parameter a of about 12.2 and a parameter c of about 3.9 Å. Specifically, the crystal structure may comprise a unit cell having a parameter a of 12.2210 Å and a parameter c of 3.9371 Å. In such embodiments, x / y may be 1. Preferably, the niobium metal oxide is Nb2W2O 11 etc.Nb2M2O 11 is.

[0069] In some embodiments, the crystal structure has a supercell with a parameter √2a of 17-18 Å and a c of 3.5-4.5 Å, preferably a parameter √2a of 17.2-17.6 Å and a c of 3.7-4.3 Å, more preferably a parameter √2a of 17.3-17.5 Å and a c of 3.8-4.0 Å, and even more preferably a parameter √2a of about 17.4 Å and a c of about 3.9 Å. Specifically, the crystal structure may have a unit cell with a parameter √2a of 17.4054 Å and a c of 3.9450 Å. In such embodiments, x / y may be 2 or 3. Preferably, the niobium metal oxide is Nb 18 W6O 63 , Nb 10 W4O 37 , or Nb 16 W8O 64 etc., Nb 18 M6O 63 , Nb 10 M4O 37 or Nb 16 M8O 64 is.

[0070] The TTB structure also contains "channels" throughout the structure. These channels are oriented perpendicular to the ab plane. The channel shapes are defined by the edges of the corner-sharing MO6 octahedron. Typically, TTB contains trigonal, tetragonal, and pentagonal channels. The parent ReO3 structure has only tetragonal channels. When TTB is a type of distorted ReO3 structure, eight of these tetragonal channels are distorted to form eight pentagonal channels and eight trigonal channels (Hyde et al.).

[0071] In the present invention, the TTB structure includes pentagonal channels (PCs), which are partially filled with -Nb-O-Nb-O- strings. The TTB structure may include four or eight PCs per unit cell. The TTB also includes four or eight trigonal channels per unit cell. The trigonal channels are typically unoccupied. The TTB also typically includes tetragonal channels.

[0072] A portion of the pentagonal channels is filled with -Nb-O-Nb-O- strings. By "partial," we mean that only a portion of the pentagonal channels are occupied with -Nb-O-Nb-O- strings. The remaining portion is either vacant or optionally intercalated with lithium. The pentagonal channels are typically not occupied by any metal (e.g., M) other than Nb from NMO, except when reversibly intercalated with lithium.

[0073] A -Nb-O-Nb-O- string refers to a string of -[Nb-O]- repeat units. A -Nb-O-Nb-O- string includes at least two repeat units, such as 5, 10, 20, 50, 100, 200, or 300 repeat units. The -Nb-O-Nb-O- is located on PCs connecting adjacent unit cells.

[0074] In some embodiments, the -Nb-O-Nb-O- strings fill 1 / 3 or more of the PC in the niobium metal oxide. In some embodiments, the -Nb-O-Nb-O- strings fill 1 / 2 or less of the PC in the niobium metal oxide. Preferably, the -Nb-O-Nb-O- strings fill 1 / 3 to 1 / 2 of the PC. In some embodiments, the Nb-O-Nb-O- strings fill about 1 / 3 or about 1 / 2 of the PC.

[0075] For example, x / y=1 (e.g., NMO is Nb2W2O 11 etc.Nb2M2O 11 When x / y is greater than 1, about 1 / 2 of the PC is filled with -Nb-O-Nb-O- strings in niobium metal oxide. When x / y is 2 (e.g., NMO is Nb 16 W8O 64 etc. Nb 16 M8O 64 When x / y=3 (e.g., NMO is Nb 16 W8O 64 etc. Nb 16 M8O 64 In the case where the niobium metal oxide is present, approximately half of the PC is filled with -Nb-O-Nb-O- strings.

[0076] In some embodiments, when half of the PCs are filled with -Nb-O-Nb-O- strings, two of the four PCs surrounding the 2 × 2 central block of the MO6 octahedron remain unoccupied. Preferably, the PCs are filled with -Nb-O-Nb-O- strings in an orderly manner, e.g., alternately. For example, two of the four PCs surrounding the 2 × 2 central block of the MO6 octahedron can be filled diagonally. The ordering is believed to be due to a reduction in cation-cation repulsion.

[0077] Preferably, the crystal structure exhibits cation ordering. In other words, it is ordered in the occupation of PCs. Filling PCs with only -Nb-O-Nb-O- strings is an example of cation ordering. Alternating filling of PCs (e.g., filling every other PC around a 2x2 central block of an MO6 octahedron) is also an example of cation ordering.

[0078] The niobium metal oxides of the present invention can intercalate lithium, for example, during cycling in a lithium-ion electrochemical cell. Lithium intercalation by the niobium metal oxides typically occurs by intercalating Li into the remaining tetragonal and / or pentagonal channels. In some embodiments, other species can optionally be present in the trigonal or tetragonal channels. Typically, the trigonal channels are unoccupied. Preferably, the tetragonal channels are unoccupied or optionally intercalated with lithium.

[0079] Intercalation typically refers to the reversible insertion of lithium into the crystal structure.

[0080] During lithium intercalation, the cations in the niobium metal oxide are reduced. During lithium deintercalation, the cations are oxidized. Depending on the structure and metal content of the niobium metal oxide, preferential redox of the niobium or metal (e.g., tungsten) cations occurs during intercalation.

[0081] Due to the cation ordering of the -Nb-O-Nb-O- strings of the present invention, the cation redox during (de)intercalation causes more uniform expansion and compression in the lattice. In other words, due to the cation ordering, redox occurs for cations in the same lattice environment throughout the structure. This is in contrast to known structures that do not have such cation ordering, in which the cations undergoing redox can exist in different lattice environments, resulting in non-uniform expansion and compression. Together with the 3D tunnel structure, the uniform expansion reduces cracks or other structural defects commonly observed in known crystalline shear / block structures without cation ordering.

[0082] The TTB structure also contains an octahedral moiety that forms an inner square, which is a square of octahedral moieties and is located within a set of four pentagonal channels interconnected by corner-sharing octahedra (see the overlaid inner square in Figure 15).

[0083] The inner square of the octahedral site is generally filled with -MOMO-strings and optionally some Nb defects (where M is as defined in formula (I)). The inner square of the octahedral site is filled completely or mainly with a mixture of -MOMO-strings. When x / y is 3, the inner square of the octahedral site is mainly -MOMO-strings with some Nb defects. This is due to a slight excess of Nb when x / y is 3. When x / y is 2, the inner square of the octahedral site is only -MOMO-strings.

[0084] Preferably, when M is W, the interior squares of the octahedral site are generally filled with a mixture of -WOWO- strings and optionally some Nb defects. When x / y is 3, the interior squares of the octahedral site are primarily -WOWO- strings with some Nb defects. When x / y is 2, the interior squares of the octahedral site are exclusively -WOWO- strings.

[0085] The TTB structure also contains an octahedral moiety that forms an outer square, which is a square of octahedral moieties located outside a set of four pentagonal channels interconnected by corner-sharing octahedra (see the overlaid outer square in Figure 15).

[0086] The outer square of the octahedral moiety is generally filled with -MOMO- strings. Preferably, when M is W, the outer square of the octahedral moiety is filled with -WOWO- strings.

[0087] The TTB structure contains an additional octahedral moiety that is not part of the inner or outer square.

[0088] The crystalline structure can be characterized using X-ray crystallography such as powder X-ray crystallography (PXRD). The crystalline structure can be characterized by having several 2θ values ​​in the PXRD diffraction pattern.

[0089] The niobium metal oxide may have a crystalline structure characterized by a powder X-ray diffraction (PXRD) pattern having two or more 2θ peaks, such as three or more, for example four or more peaks, selected from the group consisting of 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, and 32.60±0.2°, measured at a wavelength of Cu-Kα.

[0090] XRPD data can be obtained using any suitable diffractometer, such as a Panalytical Empyrean powder diffractometer. XRPD data can be obtained by exposing the NMO sample to Cu-Kα X-ray radiation. Cu-Kα has an energy of 8.04 keV, which corresponds to a wavelength of 1.5406 Å. Suitable XRPD details are provided in the Examples section.

[0091] Typically, the 2-theta peaks are within ±0.2°. Preferably, the 2-theta peaks are within ±0.1°, more preferably within ±0.05°.

[0092] In some embodiments, the crystalline structures of the present invention are characterized by having two or more 2θ peaks selected from the peaks at 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, and 32.60±0.2 degrees.

[0093] In some embodiments, the crystalline structure of the present invention is characterized by having three or more 2θ peaks, preferably four or more, five or more, six or more, seven or more, selected from the peaks at 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, and 32.60±0.2°.

[0094] In some embodiments, the crystalline structure of the present invention is characterized by having 2θ peaks at 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, and 32.60±0.2 degrees.

[0095] In one embodiment, the niobium metal oxide is Nb 18 W6O 63 or Nb 16 W8O 64 and the crystalline structure of the niobium metal oxide has two or more 2θ peaks selected from the peaks at 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, 32.60, 52.52±0.2°.

[0096] In one embodiment, the niobium metal oxide is Nb 18 W6O 63 and the crystalline structure of the niobium metal oxide has two or more 2θ peaks selected from the peaks at 10.15, 22.52, 22.83, 29.90, 26.08, 32.28, 52.52, 29.90, 32.50, 37.76, and 30.79±0.2°.

[0097] In one embodiment, the niobium metal oxide is Nb 16 W8O 64 and the crystalline structure of the niobium metal oxide has two or more 2θ peaks selected from the peaks at 10.17, 22.53, 22.87, 29.96, 26.12, 32.31, 52.58, 52.66, 37.80, 32.56, and 34.76±0.2°.

[0098] In one embodiment, the niobium metal oxide is NbWO 11 and the crystalline structure of the niobium metal oxide has two or more 2θ peaks selected from the peaks at 10.23, 16.11, 22.52, 22.83, 27.90, 29.90, 26.08, 32.28, 52.52, 29.90, 32.50, 37.76, and 30.79±0.2°.

[0099] Generally, the 2θ peak decreases with increasing Nb content (e.g., higher x / y values) because the higher Nb content slightly increases the cation-cation distance in the lattice.

[0100] Typically, all 2θ peaks of the 1:1 (x / y=1) phase are present in the higher Nb:W ratio phases. When x / y>1 (e.g., when x / y=2 or 3), corresponding to when hk0 (when h+k=odd), new peaks appear. The new peaks increase in intensity as x / y increases, with the highest intensity when x / y=3.

[0101] In some embodiments, the crystalline structure of the present invention is characterized by having a PXRD as shown in Figure 7. For example, niobium metal oxide may be Nb 18 W6O 63 The crystalline structure of the present invention may be characterized by having a PXRD as shown in Figure 7 (3:1). 16 W8O 64 The crystalline structure of the present invention may be characterized by having a PXRD as shown in Figure 7 (2:1). For example, if the niobium metal oxide is NbWO 11 If so, the crystalline structure of the present invention may be characterized by having a PXRD as shown in Figure 7 (1:1).

[0102] secondary particles The present invention provides niobium metal oxide secondary particles comprising agglomerates of the niobium metal oxide primary particles of the present invention, and having a length of 1 to 5 μm and an aspect ratio of 1 to 1.5.

[0103] Secondary particles are typically highly symmetric and have numerous symmetric features. Secondary particles may have several axes and planes of symmetry. A high degree of symmetry means that the particles can pack efficiently (e.g., have a high powder density) and have good interparticle contact between the secondary particles to support electrode reaction kinetics.

[0104] Preferably, the secondary particles have two perpendicular axes of symmetry, more preferably three perpendicular axes of symmetry. Preferably, the secondary particles have an inversion center. Preferably, the secondary particles have two perpendicular planes of symmetry, more preferably three perpendicular planes of symmetry.

[0105] The secondary particles are preferably spherical, such that the particles resemble the shape of a perfect sphere. A sphere has the greatest symmetry of any three-dimensional object, with infinite axes of rotation and infinite planes of mirror symmetry. In view of the above, increased sphericity leads to excellent packing efficiency, high bulk density, and good inter-particle contact. The more spherical the particles, the closer the packing efficiency can approach a close-packed structure (with a packing efficiency of about 74%). In view of the above, the bulk material can exhibit high density and good packing efficiency when calendered for use as an electrode for an electrochemical cell.

[0106] The secondary particles may have a sphericity of 0.95 or greater, preferably 0.96 or greater, more preferably 0.97 or greater, even more preferably 0.98 or greater, and even more preferably 0.99 or greater, which is a measure of how closely the shape of a particle resembles the shape of a perfect sphere, as described below.

[0107] Typically, the length of a secondary particle is the longest (maximum) dimension of the particle, such as the longest lateral dimension of the particle. Preferably, the secondary particles are all of similar length, so that the population of particles has a similar length distribution. Similar lengths of the population of particles further improve particle packing.

[0108] The shapes and sizes of the secondary particles can be obtained using the preparation methods described herein. In view of the above, the present invention also provides secondary particles obtained or obtainable by the inventive methods described herein.

[0109] The secondary particles comprise a plurality of primary particles, which may be integrally formed, i.e., the primary particles are typically composed of NMO, and the ions in the primary particles are joined by strong interactions, such as ionic or covalent interactions, preferably ionic interactions.

[0110] The primary particles comprise the niobium metal oxide of the present invention. Preferably, the primary particles consist essentially of the niobium metal oxide of the present invention. In some embodiments, the primary particles comprise 80% by weight or more, preferably 85% by weight or more, 90% by weight or more, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more of the niobium metal oxide of the present invention. This can be determined by any suitable method known in the art, such as elemental analysis or PXRD.

[0111] Preferably, the primary particles are substantially free of impurities.

[0112] The properties of primary particles can be measured in the same way as secondary particles, as described below: length, width, aspect ratio, and percentile values ​​can be measured by focused ion beam-scanning electron microscopy (FIB-SEM) and / or the methods described below.

[0113] Typically, the primary particles have a length of 0.1 to 2 μm, preferably 0.2 to 1.5 μm, more preferably 0.3 to 1.0 μm. The primary particles may have a width of 20 to 200 nm, preferably 40 to 150 nm, more preferably 50 to 100 nm. The primary particles may have an aspect ratio of 2 to 20, for example, 3 to 18, or 5 to 15. The primary particles may have an aspect ratio of about 10.

[0114] Generally, the shape of the primary particles is less regular than the shape of the secondary particles. Typically, the primary particles are less spherical and / or less circular than the secondary particles. Preferably, the primary particles are rod-shaped.

[0115] Secondary particles are typically formed by agglomerations of multiple primary particles. Adjacent primary particles tend to be held together by weak interactions, such as intermolecular forces. Weak interactions include long-range ionic interactions and van der Waals forces, among others.

[0116] Preferably, adjacent primary particles are connected by NMO amorphous bridges. The NMO amorphous bridges comprise NbO6 and MO6 and / or MO7 polyhedra, with covalently bonded cations and oxygen. The NMO amorphous bridges have an amorphous ionic configuration (i.e., aperiodic configuration). That is, the NMO amorphous bridges are not crystalline. This is demonstrated by fast Fourier transform (FFT) performed on HR-TEM images of the particle edges and the bridges connecting them. The FFT pattern of the primary particles shows spots due to the lack of crystallinity in the FFT of the NMO amorphous bridges. This suggests that the bridges connecting the primary particles are amorphous.

[0117] Typically, the secondary particles comprise 100 to 5000 primary particles, preferably 500 to 2000 primary particles, more preferably 700 to 1500 primary particles, even more preferably 1800 to 1200 primary particles, and even more preferably 900 to 1100 primary particles. In some embodiments, the secondary particles comprise about 1000 primary particles. The number of secondary particles can be determined by standard methods such as SEM (e.g., focused ion beam-scanning electron microscopy (FIB-SEM)), TEM, or atomic force microscopy, followed by image / data processing to determine the size of the primary and secondary particles, and the number of primary particles can be extrapolated to determine the total number of primary particles in the secondary particles.

[0118] The secondary particles comprise the niobium metal oxide of the present invention. Preferably, the secondary particles consist essentially of the niobium metal oxide of the present invention. In some embodiments, the secondary particles comprise 80% by weight or more, preferably 85% by weight or more, 90% by weight or more, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more of the niobium metal oxide of the present invention. In some embodiments, the secondary particles comprise 80% by weight or more, preferably 85% by weight or more, 90% by weight or more, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more of primary particles of the niobium metal oxide of the present invention. Preferably, the secondary particles comprise 99.9% by weight of the niobium metal oxide of the present invention.

[0119] Preferably, the secondary particles are substantially free of impurities.

[0120] The secondary particles consist of less than 10 mass% of T phase Nb2O5, Nb 16 W5O 55 , and / or Nb 14 W3O 44 Preferably, the secondary particles include T-phase Nb2O5, Nb 16 W5O 55 , and / or Nb 14 W3O 44 Does not include.

[0121] The secondary particles may contain less than 10% by weight of T-phase Nb2O5. Preferably, the secondary particles contain less than 5% by weight, e.g., less than 3%, less than 1%, less than 0.5% by weight of T-phase Nb2O5. Preferably, the secondary particles do not contain T-phase Nb2O5.

[0122] Secondary particles are less than 10% by mass of Nb 16 W5O 55 Preferably, the secondary particles contain less than 5% by weight, for example less than 3% by weight, less than 1% by weight, less than 0.5% by weight, of Nb. 16 W5O 55 Preferably, the secondary particles contain T phase Nb 16 W5O 55 Does not include.

[0123] Secondary particles are less than 10% by mass of Nb 14 W3O 44 Preferably, the secondary particles contain less than 5% by weight, for example less than 3% by weight, less than 1% by weight, less than 0.5% by weight, of Nb. 14 W3O 44 Preferably, the secondary particles contain T phase Nb 14 W3O 44 Does not include.

[0124] The secondary particles have a length of 1 to 5 μm.

[0125] Typically, the length of a secondary particle is the longest (maximum) dimension of the particle, such as the longest lateral dimension of the particle. The length of a secondary particle is generally the longitudinal dimension of the particle. The lateral dimension is the dimension observable in a plan view, such as when the particle is viewed from above by an SEM, such that the particle appears two-dimensional. The length may be the longest dimension measurable from a top-down view of the particle.

[0126] Typically, the width of a secondary particle is the shortest dimension of the particle, such as the shortest lateral dimension of the particle. The width of a secondary particle is generally the longitudinal width of the particle. The lateral dimension is the dimension observable in a plan view, such as when the particle is viewed from above by an SEM, such that the particle appears two-dimensional. The width may be the shortest dimension measurable from a top-down view of the particle.

[0127] The width of a secondary particle may be the shortest dimension perpendicular to the line defining the length dimension. The length of a secondary particle is the longest dimension of the particle, and therefore the line defining the length of the particle is the line between the particle's most distant ends. The width may be the shortest dimension of a secondary particle perpendicular to the line defining the particle's length. The shortest dimension may also be defined by the line between the particle's closest ends, which line is perpendicular to the line defining the particle's length. In other words, the shortest dimension (width) may be the narrowest section of the particle that can be connected by a line perpendicular to the line defining the particle's length.

[0128] The length and width of particles can be measured using any suitable technique. For example, a scanning electron microscope (SEM) can be used. A suitable system includes a MIRA3 SEM operating at a 6 mm working distance and a voltage of 5 kV. For EDS mapping, a suitable system includes a MIRA3 SEM operating at a 15 mm working distance and a voltage of 30 kV. The length and width of secondary particles can then be analyzed using image processing software such as MiraTC. EDS data can be collected using Aztec software from Oxford Instruments. Particle measurements can be in accordance with ISO 9276-2:2014.

[0129] The number of measurements taken for length or width is usually between 100 and 1,000. Typically, more than 100 measurements are taken. The length or width is the average of the average values ​​of the measurements taken.

[0130] The secondary particles have a length of 1 to 5 μm. Preferably, the secondary particles have a length of 1.5 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. Preferably, the secondary particles have a length of 4.5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. Preferably, the secondary particles have a length of 1.5 to 4.5 μm, more preferably 2 to 4 μm, and even more preferably 2.5 to 3.5 μm. A particularly preferred length of the secondary particles is about 3 μm.

[0131] The secondary particles have a width of 1 to 5 μm, preferably 1.5 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more. Preferably, the secondary particles have a width of 4.5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less. Preferably, the secondary particles have a width of 1.5 to 4.5 μm, more preferably 2 to 4 μm, even more preferably 2.5 to 3.5 μm. A particularly preferred width of the secondary particles is about 3 μm.

[0132] Typically, the length and / or width of a population of secondary particles (e.g., 100 to 1,000 particles measured) results in a normal particle size distribution. Preferably, the population of secondary particles has lengths and / or widths that have a unimodal particle size distribution. A unimodal distribution has only one peak in the particle size distribution. In such cases, the peak can coincide with the median average particle length or the median average particle width. Particle measurements may be in accordance with ISO 9276-2:2014.

[0133] The length percentile values ​​of the secondary particle size distribution can also be calculated, such as D100, D90, D50, and D10. These values ​​can be calculated based on the number and size distribution of particles relative to particle length.

[0134] The D100 length is the secondary particle length at which 100% of the secondary particles have a length less than or equal to the D100 particle length.

[0135] The secondary particles may have a D100 length of 10 μm or less, preferably 8 μm or less, more preferably 6 μm or less, even more preferably 5 μm or less, and even more preferably 4 μm or less.

[0136] The D90 length is the secondary particle length at which 90% of the secondary particles have a length less than or equal to the D90 particle length.

[0137] The secondary particles may have a D90 length of 9 μm or less, preferably 8 μm or less, more preferably 6 μm or less, even more preferably 5 μm or less, and even more preferably 4 μm or less.

[0138] The D50 length is the secondary particle length at which 50% of the secondary particles have a length less than or equal to the D50 particle length.

[0139] The secondary particles may have a D50 length of 5 μm or less, preferably 4 μm or less, and more preferably 3 μm or less. The secondary particles may have a D50 length of 1 to 5 μm. Preferably, the secondary particles have a D50 length of 1.5 to 4.5 μm, more preferably 2 to 4 μm, and even more preferably about 3 μm.

[0140] The D10 length is the secondary particle length at which 10% of the secondary particles have a length less than or equal to the D10 particle length.

[0141] The secondary particles may have a D10 length of 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 2.5 μm or more.

[0142] In some embodiments, the population of secondary particles has a low length standard deviation, which indicates a narrow secondary particle size distribution. In some embodiments, the length standard deviation of the population of particles is 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, even more preferably 0.75 μm or less, and even more preferably 0.5 μm or less.

[0143] The aspect ratio is the ratio between the length of a secondary particle and the width of the secondary particle. The length and width are defined and measured as above, with multiple measurements being taken for the length or width, typically between 100 and 1000. Typically, more than 100 measurements are taken. The length or width is the average of the average values ​​of the measurements taken, and the aspect ratio is calculated from the average of these average values. In view of the above, the aspect ratio may be the ratio between the longest dimension of a secondary particle and the shortest dimension of a secondary particle.

[0144] The secondary particles have an aspect ratio of 1 to 1.5. Preferably, the secondary particles have an aspect ratio of 1 to 1.4, more preferably 1 to 1.3, even more preferably 1 to 1.2, and even more preferably 1 to 1.1. The secondary particles preferably have an aspect ratio of about 1. An aspect ratio of about 1 means that the length and width of the secondary particles are the same. An aspect ratio of about 1 means that the longest dimension of the secondary particle and the shortest dimension of the secondary particle are the same. The secondary particles are highly symmetrical. This aids in efficient packing of the secondary particles.

[0145] The secondary particles may have a sphericity of 0.95 or greater, preferably 0.96 or greater, more preferably 0.97 or greater, even more preferably 0.98 or greater, and even more preferably 0.99 or greater. Sphericity is a measure of how closely the shape of a particle resembles the shape of a perfect sphere. The sphericity of a particle is the ratio of the surface area of ​​a sphere having the same volume as the particle to the surface area of ​​the particle. The sphericity of a perfect sphere is 1. Sphericity can be calculated using the equation, where V is the volume of the particle and A is the surface area of ​​the particle. Sphericity = (π 1 / 3 (6*V) 2 / 3 ) / A

[0146] The volume and surface area of ​​the particles can be calculated by any suitable method, such as using the length and width of the particles measured above. For example, a scanning electron microscope (SEM) can be used. A suitable system includes a MIRA3 EM operating at 5 kV and a working distance of 6 mm. The secondary particles can then be analyzed using image processing software such as MiraTC. EDS mapping can be performed using a MIRA3 EM operating at 30 kV and a working distance of 15 mm, and analyzed using Aztec software from Oxford Instruments.

[0147] The secondary particles may have a circularity of 0.95 or greater, preferably 0.96 or greater, more preferably 0.97 or greater, even more preferably 0.98 or greater, and even more preferably 0.99 or greater. The circularity of a three-dimensional particle can refer to the circularity of the particle when viewed from above. Circularity can be calculated using the lateral dimensions of the particle and the visible area of ​​the particle as observable, such as in a plan view, in which the particle appears two-dimensional when viewed from above. Circularity can be measured from a top-down view of the particle, such as when viewing the particle using a microscope (e.g., SEM).

[0148] Circularity is a measure of how closely the shape of a particle resembles the shape of a perfect circle. The circularity of a particle is the ratio of the perimeter of a circle that has the same visible area as the particle to the visible area of ​​the particle. It can be calculated using the following formula, where A is the visible surface area of ​​the particle and P is the perimeter of the particle: Circularity = (4π*A) / P 2

[0149] The number of measurements taken to determine sphericity or roundness is usually between 100 and 1000. Typically, more than 100 measurements are taken. The sphericity or roundness is the average of the average values ​​of the measurements taken. Particle measurements can be performed in accordance with ISO 9276-2:2014.

[0150] The secondary particles have a surface roughness R of 0.05 to 1 μm, preferably 0.08 to 0.5 μm, and more preferably 0.1 to 0.2 μm. t The secondary particles may have a surface roughness R of 1 μm or less, preferably 0.7 μm or less, more preferably 0.5 μm or less, even more preferably 0.3 μm or less, and even more preferably 0.1 μm or less. t may have

[0151] Surface roughness is a measure of the variation in the surface profile of a particle. t is the total profile height, which is the total perpendicular distance (perpendicular to the particle surface) between the maximum profile height (peak) and the minimum profile height (valley) along the profile evaluated. Surface roughness can be measured using any suitable method, such as atomic force microscopy. Surface roughness can be measured according to ISO 4287:1997.

[0152] Preparation method Generally, the present invention provides a method for preparing niobium metal oxide secondary particles, comprising the steps of: providing a precursor mixture of a Nb source and a M source; calcining the precursor mixture at a temperature of 550 to 1,100°C; wherein M is a metal other than Nb.

[0153] The precursor mixture of the Nb source and the M source can be prepared by any suitable method. The mixture is preferably highly homogeneous. In some embodiments, the precursor mixture is prepared by co-precipitation of the Nb source and the M source. The resulting niobium metal oxide secondary particles may be the secondary particles of the present invention. Preferably, the resulting niobium metal oxide secondary particles are highly regular and symmetrical. Preferably, the resulting secondary particles are spherical.

[0154] In view of the above, in a third aspect, the present invention provides a method for preparing niobium metal oxide secondary particles according to any one of claims 11 to 16, comprising: NbX a and MY bco-precipitating Nb oxide and M oxide from the solution; calcining the precipitate at a temperature of 550 to 1100°C; Including, wherein M is selected from Ti, Zr, V, Cr, W, and Mo; X and Y are independently one or more counter ions; and a and b are independently 2 to 6.

[0155] In some embodiments, the present invention provides a method for preparing the niobium metal oxide secondary particles of the present invention, comprising: NbX a and MY b in a solvent to form a solution; NbX a and MY b co-precipitating Nb oxide and M oxide from the solution; calcining the precipitate at a temperature of 550 to 1,100°C; Including, wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo; X and Y are independently one or more counter ions; and a and b are independently 2 to 6.

[0156] In some embodiments, the present invention provides a method for preparing the niobium metal oxide secondary particles of the present invention, comprising: NbX a and MY b in a solvent to form a solution; NbX a and MY b co-precipitating Nb oxide and M oxide from the solution; Separating the precipitate from the solvent; calcining the precipitate at a temperature of 550 to 1,100°C; Including, wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo; X and Y are independently one or more counter ions; and a and b are independently 2 to 6.

[0157] Yu et al. used Nb oxide and W oxide precursors to synthesize Nb 18 W 16 O 93 describes a two-step hydrothermal method for preparing NWO. The two-step method involves first precipitating Nb and then precipitating W. Because the precipitations are not simultaneous, there is insufficient mixing of the Nb and W components, and the precipitate is poorly homogeneous. As a result, the calcined NWO forms "nanobar-shaped" particles, as opposed to the secondary particles of the present invention, which are typically spherical.

[0158] Zhou et al. describe a solvothermal method for preparing NbWO using NbCl and WCl precursors. Zhou uses oxalic acid to initiate precipitation. However, the use of a precipitation reagent means that the precipitation of NbCl and WCl is not simultaneous, and the resulting precipitate is poorly homogeneous. As a result, the calcined NWO forms nanorods as opposed to the secondary particles of the present invention.

[0159] The present invention can use heating under solvothermal conditions to precipitate Nb and metal precursors, advantageously also providing highly homogeneous precursors for preparing secondary particles. The atomic-scale mixing achieved by this method means that the precipitate has high homogeneity of the two metal ions. Therefore, the need for metal ion diffusion is largely eliminated, and typically only intracrystallite metal ion diffusion is required. Calcination then results in the highly regular and symmetrical secondary particles of the present invention. The particles are preferably substantially, e.g., highly spherical.

[0160] Starting materials The method for preparing niobium metal oxide is NbX a and MY b is used as the starting material.

[0161] M is any suitable metal other than Nb, such as a transition metal. M may be a Group 3, 4, or 5 metal, preferably a Group 4 or 5 metal, more preferably a Group 5 metal. Typically, M is selected from Ti, Zr, V, Cr, W, and Mo. Preferably, M is selected from Cr, W, and Mo, more preferably W and Mo, and even more preferably W.

[0162] X and Y are independently one or more counterions. In some embodiments, X and Y are independently oxalate, C 1~3 In some embodiments, X and Y are independently selected from alkoxide, O, S, F, Cl, and Br. 1~3 In other embodiments, X and Y are independently selected from alkoxide, O, and Cl. 1~3 alkoxides, F, Cl, and Br.

[0163] In some embodiments, X is not oxygen. In some embodiments, X and Y are not oxygen.

[0164] Oxalate is C2O4 2- C 1~3 Alkoxides include methoxide (CHO - ), ethoxide (CH3CH2O - ), propoxide (CH3CH2CH2O - or (CH3)2CHO - ) is selected.

[0165] Preferably, X and Y are independently selected from oxalate, F, Cl, and Br, more preferably oxalate and Cl. In some embodiments, X and Y are both Cl. In some embodiments, X and Y are both oxalate.

[0166] Ammonium (NH4 + Additional positive counterions, such as cations of ...

[0167] The values ​​of a and b are independently 2 to 6. Preferably, a and b are 3 to 5, and more preferably, a is 5 and b is 6.

[0168] In some embodiments, X is selected from F, Cl, and Br, and a is 5. Preferably, NbX a is NbCl5.

[0169] In some embodiments, Y is selected from F, Cl, and Br, and a is 6. Preferably, MY b is WCl6.

[0170] In some embodiments, NbX a is NbCl5, MY b is WCl6.

[0171] In some embodiments, X is oxalate and a is 3. Preferably, NbX a is niobium oxalate, which is Nb(C2O4)3 - An example source of niobium oxalate is ammonium niobium oxalate, which is Nb(C2O4)3(NH4).

[0172] In some embodiments, Y is oxygen and b is 3.5. Preferably, MY b is the metatungstate, and the metatungstate is (H 1 / 6 WO 3.5 ) -0.5 This is (H2W 12 O 40 ) -6 An example source of metatungstate is ammonium metatungstate, which is sometimes known as (NH4) 0.5 (H 1 / 6 WO 3.5 ), for example (NH4)6(H2W 12 O 40 )

[0173] In some embodiments, Y is oxygen and b is 3.5. Preferably, MY b is a paratungstate, and the paratungstate is (H2W 12 O 42 ) -10 An example of a source of paratungstate is ammonium paratungstate, which is (NH4) 0.83 (H 1 / 6 WO 3.5 ), e.g. (NH4) 10 (H2W 12 O 42 )

[0174] In some embodiments, NbX a is niobium oxalate, and MY b is ammonium metatungstate or paratungstate.

[0175] Melting process The method for preparing niobium metal oxide secondary particles is NbX a and MY b This may include a step of dissolving the compound in a solvent. This may also be referred to as a dissolving step.

[0176] Dissolution typically occurs before the precipitation step described below.

[0177] The solvent is NbX a and MY b The solvent may be any suitable solvent capable of solubilizing the compound. Mixtures of solvents may be used. Aqueous solvents such as water may be used. Alcohols (e.g., C 1~6 An organic solvent such as an alkyl alcohol can be used. Preferably, the solvent is water, ethanol, or propanol, such as water, ethanol, isopropanol, or a mixture thereof. More preferably, the solvent is ethanol, water, or a mixture thereof.

[0178] Typically, NbX ais ammonium niobium oxalate, and MY b When is ammonium metatungstate or paratungstate, the solvent is water.

[0179] NbX a and MY b The NbX may be added to the solvent separately or together. The solvent may be agitated, such as by stirring or sonication, to dissolve the NbX. a and MY b It can assist in the dissolution of

[0180] Typically, the melting occurs in NbX a and MY b is complete when all of has dissolved in the solvent, which can be determined by any suitable method, such as by visually observing that the solution is clear.

[0181] Therefore, the solution typically contains NbX completely dissolved in the solvent. a and MY b It has.

[0182] Precipitation process Generally, the method for preparing niobium metal oxide secondary particles is NbX a and MY b This involves precipitating Nb oxides and M oxides from the solution of NbX. a and MY b This step is sometimes called the precipitation step.

[0183] Coprecipitation refers to the simultaneous precipitation of two components. The precipitation process is preferably instantaneous, i.e., the two components begin to precipitate together. This means that the Nb and M compounds are removed from the solution simultaneously, and the resulting precipitate is a homogeneous mixture of Nb and M compounds.

[0184] Nb and M are generally precipitated as Nb oxide and M oxide. Nb and M are typically precipitated as solvated Nb and M oxides. The solvated form refers to a form in which the metal oxide is complexed with solvent molecules. For example, when the solvent is water, Nb and M are typically precipitated as hydrated niobium oxide and hydrated M oxide (e.g., hydrated tungsten oxide).

[0185] The solution can be heated at any suitable pressure required to achieve co-precipitation. This is typically greater than 100 kPa, e.g., 500 kPa or more, 1000 kPa or more, 1500 kPa or more, or 1800 kPa or more. The pressure may be less than 5000 kPa, e.g., 4500 kPa or less, or 4000 kPa or less. The pressure may be between 1000 and 5000 kPa, preferably between 1500 and 4500 kPa, and more preferably between 1800 and 4000 kPa.

[0186] The solution can be heated to any suitable temperature needed to achieve co-precipitation, typically between 120 and 200°C. In some embodiments, the solution is heated to a temperature of 120°C or higher, preferably 140°C or higher, and more preferably 150°C or higher. In some embodiments, the solution is heated to a temperature of 170°C or lower, preferably 160°C or lower, and more preferably 150°C or lower. In some embodiments, the solution is heated to a temperature of 130 to 170°C, preferably 140 to 160°C, and more preferably about 150°C.

[0187] The solution is heated for any suitable time needed to achieve co-precipitation. a and MY b In some embodiments, the NbX may be heated for a sufficient time to achieve precipitation of at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, and even more preferably at least 90% of the NbX. a and MY bIn some embodiments, the solution is heated for 0.5 to 6 hours, preferably 1 to 3 hours, and more preferably about 2 hours. The amount of precipitate can be determined by mass spectrometry of the dried precipitate or by suitable spectroscopic analysis of the solution.

[0188] The solution can be heated by any suitable method required to achieve precipitation, such as co-precipitation. Preferably, heating is performed by microwave heating. The heating results in rapid precipitation and co-precipitation of the Nb and W sources. Microwave heating is particularly preferred because heating is rapid and consistent throughout the sample. Microwaves promote localized, instantaneous, and consistent heating throughout the sample, creating multiple nucleation sites that lead to rapid precipitation of the NMO precursor. Thermal gradients through the sample are minimized compared to traditional heating methods. As a result, the majority of the sample can undergo co-precipitation.

[0189] The solution can be heated under solvothermal conditions. Solvothermal conditions refer to heating to a temperature higher than the boiling point of the solvent at atmospheric pressure. For example, if the solvent is ethanol, which has a boiling point of 78.37°C at 1 atmosphere, solvothermal conditions refer to heating to a temperature above 78.37°C. As another example, if the solvent is isopropanol, which has a boiling point of 82.5°C at 1 atmosphere, solvothermal conditions refer to heating to a temperature above 82.5°C.

[0190] Solvothermal conditions are typically achieved by heating the solution in a sealed container. The sealed container is substantially air-impermeable. The sealed container may be an inert container, such as a ceramic or glass container. By heating in the sealed container, the pressure inside the container increases as the solvent evaporates into the headspace of the sealed container. As a result, the increased pressure increases the boiling point of the solvent as the partial pressure in the headspace increases. Under solvothermal conditions, the pressure inside the sealed container is increased to above 1 atmosphere.

[0191] Preferably, no additional reagents are used in the precipitation step, in other words, precipitation occurs spontaneously when the precipitate is heated using the conditions described above.

[0192] Calcination process The method for preparing niobium metal oxide secondary particles includes a step of calcining the precipitate at a temperature of 550 to 1,100° C. This is sometimes referred to as the calcination step.

[0193] The precipitate can be calcined at a temperature of 550 to 1,100°C, which is suitable for preparing the secondary particles of the present invention. Preferably, the precipitate is calcined at a temperature of 600°C or higher, more preferably 700°C or higher, and even more preferably 800°C or higher. Preferably, the precipitate is calcined at a temperature of 1,000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower. Preferably, the precipitate is calcined at a temperature of 600 to 1,000°C, more preferably 700 to 950°C, and even more preferably 800 to 900°C.

[0194] In general, calcination at these lower temperatures was found to reduce the surface roughness of the secondary particles, which is advantageous because the smooth and regular particle shape allows for isotropic lithium (de)intercalation and very high loading efficiency during charge and discharge.

[0195] The precipitate can be calcined by heating at a ramp rate of 1-25°C / min until the target temperature is reached.

[0196] The precipitate can be calcined at the above target temperature for 6 to 48 hours, for example, 12 to 24 hours. Preferably, the precipitate is calcined at the target temperature for 6 to 12 hours.

[0197] In some embodiments, the precipitate is calcined at 800° C. for 12 to 48 hours, for example, 12 hours.

[0198] In some embodiments, the precipitate is calcined at 850° C. for 6 to 24 hours, then at 900° C. for 0.5 to 3 hours, for example, at 850° C. for 12 hours, then at 900° C. for 1.5 hours.

[0199] In some embodiments, the precipitate is calcined for 6 to 12 hours at 500-900° C. In one such embodiment, the precipitate is calcined at 500° C. for 1.5 hours, then at 600° C. for 1.5 hours, then at 700° C. for 1.5 hours, then at 800° C. for 1.5 hours, then at 900° C. for 1.5 hours.

[0200] Calcination refers to the thermal treatment of a solid material to cause a phase transition or reaction of the material. Calcination can be carried out in the presence of air.

[0201] The precipitate is typically transferred to a heat-resistant vessel such as a ceramic crucible for calcination.

[0202] Calcination can be carried out as a batch or continuous process.

[0203] Separation process The method for preparing niobium metal oxide secondary particles may further include a step of separating the precipitate from the solvent, which may also be referred to as the separation step.

[0204] The separation step is typically carried out after the precipitation step described above and before the calcination step.

[0205] Isolation can be achieved by any suitable method, such as filtering, washing, and drying (such as spray drying or spray pyrolysis).

[0206] In some embodiments, the separating step comprises separating the precipitate from the organic solvent by filtration, which can be accomplished under vacuum, for example, using a Buchner funnel.

[0207] In some embodiments, the separating step includes washing the precipitate with an organic solvent to separate the precipitate from the organic solvent. The washing can be performed using a washing solvent that is the same as or different from the organic solvent used in the immediately preceding step. When a different washing solvent is used, the washing solvent may be one that forms an azeotrope with the organic solvent. For example, ethanol can be used as the washing solvent.

[0208] In some embodiments, the separating step includes separating the precipitate from the organic solvent by drying the precipitate. Drying refers to evaporating the organic solvent. Evaporation of the solvent can be achieved by drying the precipitate under vacuum. Alternatively, evaporation of the solvent can be achieved by heating the precipitate. For example, drying can occur as a result of heating during the calcination step. In other words, the separating step can be performed as part of the calcination step.

[0209] In some embodiments, the separating step comprises separating the precipitate from the organic solvent by spray drying, freeze drying, or spray pyrolysis. Preferably, the precipitate is separated from the organic solvent by spray drying or spray pyrolysis, more preferably by spray pyrolysis.

[0210] Spray drying typically dries a suspension of precipitate by atomizing the slurry and drying the atomized slurry with hot gas, which evaporates the solvent, leaving behind the precipitate. Spray pyrolysis typically dries by spraying the suspension or solution onto a heated substrate (e.g., surface), which aids in drying by evaporating the solvent. Spray drying and spray pyrolysis can result in precipitate particles with regular, small sizes that may be well suited for calcination.

[0211] working electrode Generally, the present invention provides a working electrode for an electrochemical cell, the working electrode comprising a niobium metal oxide. The present invention provides a working electrode for an electrochemical cell, the working electrode comprising a niobium metal oxide of the first aspect of the present invention, such as secondary particles of the niobium metal oxide of the first aspect.

[0212] In a fourth aspect, the present invention provides a working electrode for an electrochemical cell, the working electrode comprising niobium metal oxide secondary particles of the second aspect of the present invention.

[0213] The working electrode is electrically conductive and can be electrically connected to a counter electrode, for example, in an electrochemical cell.

[0214] The working electrode may be the anode or the cathode during the discharging process, for example in a lithium ion battery. Typically, the working electrode is the anode during the discharging process.

[0215] In some embodiments, the working electrode comprises the niobium metal oxide secondary particles of the present invention as the bulk electrode active material. That is, the electrode active material is the material that constitutes the main body of the working electrode. Preferably, the working electrode comprises 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and even more preferably 80% by weight or more of the niobium metal oxide secondary particles, based on the total weight of the working electrode. The working electrode can consist essentially of the niobium metal oxide secondary particles.

[0216] The working electrode optionally comprises a mixture of niobium metal oxide secondary particles and an additional active material.

[0217] The additional active material may be an additional metal oxide. For example, the working electrode may be made of lithium titanate (LiTiO; Li4TiO 12 ), titanium niobium oxide (e.g., TiNb2O7), titanium tantalum oxide (e.g., TiTa2O7), tantalum molybdenum oxide (e.g., Ta8W9O 47 ), niobium molybdenum oxide (e.g., Nb2Mo3O 14 ), and niobium tungsten oxide (e.g., Nb16 W5O 55 , Nb 18 W8O 69 , Nb2WO8, Nb 18 W 16 O 93 , or Nb 22 W 20 O 115 The niobium metal oxide secondary particles may comprise a mixture of niobium metal oxide secondary particles and an additional active material selected from the group consisting of:

[0218] The additional active material may be a carbon electrode material such as graphite. A working electrode comprising a mixture of niobium metal oxide secondary particles and graphite is cheaper to produce while maintaining the beneficial properties outlined above.

[0219] When the working electrode comprises niobium metal oxide secondary particles and an additional active material, it preferably comprises 50% by mass or more of the niobium metal oxide secondary particles, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more of the niobium metal oxide secondary particles, relative to the total mass of the active material.

[0220] In some embodiments, the working electrode comprises the niobium metal oxide secondary particles of the present invention on the surface of the electrode. That is, the surface of the working electrode is terminated with the niobium metal oxide secondary particles of the present invention. Preferably, the niobium metal oxide secondary particle surface is the surface that contacts the electrolyte in a typical electrochemical cell. In some such embodiments, the working electrode may comprise a niobium metal oxide secondary particle layer disposed on a secondary active electrode material. The secondary active electrode material is different from the surface material. The niobium metal oxide secondary particle layer may be a coating on the secondary active electrode material.

[0221] The secondary active electrode material can be selected from carbon, silicon, or metal oxides. The secondary active electrode material can be selected from graphite, reduced graphite oxide, or carbon black. The secondary active electrode material can be Ketjen black, or Super P carbon, or hard or soft amorphous carbon. The secondary active electrode material can be lithium titanate (LTO; Li4Ti5O12 ), titanium tantalum oxide (e.g., TiTa2O7), or tantalum molybdenum oxide (e.g., Ta8W9O 47 ) can be selected.

[0222] The thickness of the niobium metal oxide secondary particle layer can be known by the ratio of the secondary active electrode material to the niobium metal oxide secondary particle coating, or can be determined using standard techniques such as SEM. The niobium metal oxide secondary particle layer may have a maximum thickness of 10 μm or less, e.g., 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less. The niobium metal oxide secondary particle layer may have a minimum thickness of 0.5 μm or more, e.g., 1 μm or more, 2 μm or more, 5 μm or more, or 10 μm or more. The niobium metal oxide secondary particles may have a thickness in a range selected from the maximum and minimum amounts listed above.

[0223] The niobium metal oxide secondary particle layer can be disposed directly on the secondary active electrode material, or there can be an intermediate layer of active material between the secondary active electrode material and the niobium metal oxide secondary particle layer. The intermediate layer can be a different secondary active electrode material, a conductivity additive, a binder, or a current collector.

[0224] The working electrode may include a conductive carbon material to improve conductivity. The conductive carbon can be mixed with secondary particles, a secondary active electrode material, an intermediate layer, or a combination thereof. Preferably, the conductive carbon is mixed with the secondary particles of the present invention. The conductive carbon material may be carbon black, graphite, nanoparticle carbon powder, carbon fiber, and / or carbon nanotubes. The working electrode typically includes 2 to 20 wt %, preferably 5 to 15 wt %, more preferably 8 to 12 wt %, and even more preferably about 10 wt % of conductive carbon based on the total weight of the working electrode.

[0225] The working electrode may include a binder that improves adhesion of the electrode material to the current collecting surface. The binder can be mixed with the secondary particles, the secondary active electrode material, the intermediate layer, or a combination thereof. Preferably, the binder is mixed with the secondary particles of the present invention. Typical examples of binders are PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR, and copolymers thereof. The working electrode typically includes 2 to 20 wt %, preferably 5 to 15 wt %, more preferably 8 to 12 wt %, and even more preferably about 10 wt % of the binder, based on the total weight of the working electrode. Preferably, the binder is PVDF and / or CMC.

[0226] The working electrode can have any suitable density. High density can be achieved by the excellent packing characteristics of the niobium metal oxide secondary particles of the present invention. The area loading can indicate the density of the niobium metal oxide.

[0227] The working electrode may have any suitable area loading of niobium metal oxide secondary particles as the active material. Typically, the area loading is between 1 and 20 mg cm. -2 , preferably 2 to 10 mg cm -2 , more preferably 3 to 8 mg cm -2 , and even more preferably 5 to 7 mg cm -2 The area loading is approximately 6 mg cm -2 Alternatively, the areal loading may be lower, for example, about 2 mg cm -2 may be.

[0228] The working electrode is typically fixed to a current collector, such as a copper or aluminum collector, which may be in the form of a plate.

[0229] The inventors used Nb2W2O as the active material. 11 , Nb 18 W6O 63 , and Nb 16 W8O 64of spherical secondary particles, conductive carbon (Super P, TIMCAL), and binder (PVDF, Kynar) in a mass ratio of active material / carbon / binder of 8:1:1, with an active material loading of 2 mg cm -2 and an electrode area of ​​1.27 cm for a Li metal counter electrode in a 2032-type coin cell geometry. 2 The working electrode was evaluated using 1.0 M LiPF6 in ethylene carbonate / dimethyl carbonate (1:1 v / v) as the electrolyte.

[0230] The inventors have used Nb as the active material. 18 W6O 63 We found that a cell containing spherical secondary particles of Nb2W2O2 as the active material lost about 4% of its discharge capacity when cycled at a 10 C rate for 1,000 cycles. 11 It was found that when the above cell containing spherical secondary particles was cycled at a 10 C rate for 1000 cycles, it lost about 15% of its discharge capacity.

[0231] electrochemical cell The present invention provides an electrochemical cell comprising the working electrode of the present invention. Preferably, the electrochemical cell comprises a counter electrode, an electrolyte, and the working electrode of the present invention.

[0232] The present invention also provides a lithium-ion battery comprising one or more electrochemical cells of the present invention.

[0233] The working electrode of the present invention may be the anode or the cathode during the discharging process, for example in a lithium ion battery. Typically, the working electrode is the anode during the discharging process.

[0234] Electrochemical cells typically include a counter electrode and an electrolyte. Electrochemical cells may also include current collectors. Electrochemical cells may be electrically connected to a power source. Electrochemical cells may be electrically connected to a measuring device, such as an ammeter or voltmeter.

[0235] The electrochemical cell may be a lithium-ion cell. A lithium-ion cell typically includes a working electrode of the present invention, a lithium-containing or lithium-intercalating counter electrode, an electrolyte, and a separator. The electrolyte is suitable for solubilizing lithium ions, and the separator is permeable to lithium ions.

[0236] The counter electrode may be the anode or the cathode during the discharging process, for example in a lithium ion battery, and is typically the cathode during the discharging process.

[0237] Suitable cathode materials include lithium-containing or lithium intercalate materials, such as lithium metal oxides, where the metal is typically a transition metal such as Co, Fe, Ni, V, or Mn, or a combination thereof. Some examples of positive electrode materials include lithium cobalt oxide (LiCoO), lithium nickel manganese cobalt oxide (NMC, LiNiMnCoO, e.g., LiNi 0.6 Co 0.2 Mn 0.2 O2), lithium vanadium fluorophosphate (LiVPO4F), lithium nickel cobalt aluminum oxide (NCA, LiNiCoAlO2), lithium iron phosphate (LFP, LiFePO4), and manganese-based spinels (e.g., LiMn2O4). Preferably, the cathode electrode material is LCO, NCA, or NMC (e.g., NMC-811).

[0238] The counter electrode may include a conductive carbon material to improve conductivity, which may be carbon black, graphite, nanoparticle carbon powder, carbon fiber, and / or carbon nanotubes.

[0239] The counter electrode may include a binder to improve adhesion of the active material to the current collecting surface. Examples of binders are typically PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR, and copolymers thereof.

[0240] The counter electrode is typically fixed to a current collector, such as a copper or aluminum collector, which may be in the form of a plate.

[0241] Typically, the electrolyte in an electrochemical cell is suitable for solubilizing lithium ions. Typically, the electrolyte in a charge and discharge cell comprises lithium ions. Typically, the electrolyte comprises a lithium salt such as LiTFSI, (lithium bis(trifluoromethane)sulfonimide, LiPF, LiBF, LiClO, LiTF (lithium triflate), or lithium bis(oxalato)borate (LiBOB).

[0242] The electrolyte may be a liquid electrolyte, such as one that is liquid at room temperature, for example, 25° C. Preferred electrolytes are stable at high and low temperatures.

[0243] The electrolyte may be a non-aqueous electrolyte. The electrolyte may include a polar aprotic solvent. The electrolyte may include an organic solvent. Solvents for dissolving lithium ions are well known in the art.

[0244] Suitable solvents include carbonate solvents such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), chloroethylene carbonate, fluorocarbonate solvents (e.g., fluoroethylene carbonate and trifluoromethylpropylene carbonate), and dialkyl carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0245] Suitable solvents also include sulfone solvents, such as methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone (MiPS), propyl sulfone, butyl sulfone, tetramethylene sulfone (sulfolane), phenyl vinyl sulfone, allyl methyl sulfone, methyl vinyl sulfone, divinyl sulfone (vinyl sulfone), diphenyl sulfone (phenyl sulfone), dibenzyl sulfone (benzyl sulfone), vinylene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2-chlorophenyl methyl sulfone, methyl ... Phenyl methyl sulfone, 3,4-dichlorophenyl methyl sulfone, 4-(methylsulfonyl)toluene, 2-(methylsulfonyl)ethanol, 4-bromophenyl methyl sulfone, 2-bromophenyl methyl sulfone, 4-fluorophenyl methyl sulfone, 2-fluorophenyl methyl sulfone, 4-aminophenyl methyl sulfone, sultones (e.g., 1,3-propane sultone), and sulfone solvents containing ether groups (e.g., 2-methoxyethyl(methyl) sulfone and 2-methoxyethoxyethyl(ethyl) sulfone).

[0246] Suitable solvents also include silicon-containing solvents such as siloxanes or silanes. For example, hexamethyldisiloxane (HMDS), 1,3-divinyltetramethyldisiloxane, polysiloxanes, and polysiloxane-polyoxyalkylene derivatives. Some examples of silane solvents include methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane.

[0247] To improve performance, additives can be included in the electrolyte, such as vinylene carbonate (VC), vinyl ethylene carbonate, allyl ethyl carbonate, t-butylene carbonate, vinyl acetate, divinyl adipate, acrylic nitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, ethylene carbonate, halogenated ethylene carbonates, α-bromo-γ-butyrolactone, methyl chloroformate, 1,3-propane sultone, ethylene sulfite (ES), propylene sulfite (PS), vinyl ethylene sulfite (VES), fluoroethylene sulfite (FES), 12-crown-4 ether, carbon dioxide (CO2), sulfur dioxide (SO2), and sulfur trioxide (SO3).

[0248] The electrochemical cell may also include a solid porous membrane disposed between the cathode and the cathode. The solid porous membrane can partially or completely replace the liquid electrolyte. The solid porous membrane may comprise a polymer (e.g., polyethylene, polypropylene, or copolymers thereof) or an inorganic material, such as a transition metal oxide (e.g., titania, zirconia, yttria, hafnia, or niobia) or a typical metal oxide such as silicon oxide, which may take the form of glass fiber. The membrane is typically selectively permeable to the charge carrier ions of the cell (e.g., lithium ions). That is, the membrane is selectively porous for lithium ions.

[0249] The solid non-porous membrane may include lithium ion conductors, such as LLZO (garnet family), LSPO (LISICON family), LGPS (thio-LISICON family), LATP / LAGP (NASICON family), LLTO (perovskite family), and phosphide / sulfide glass ceramics.

[0250] The electrochemical cells may be provided in any suitable form, such as in the form of a coin cell, a pouch cell, a prismatic cell, or a cylindrical cell.

[0251] battery The present invention also provides a battery comprising one or more electrochemical cells of the present invention. The battery may be a lithium ion battery.

[0252] If multiple cells are present, they may be provided in series or in parallel.

[0253] The batteries of the present invention can be provided in road vehicles such as automobiles, mopeds, or trucks. Alternatively, the batteries of the present invention can be provided in rail vehicles such as trains or electric trains. The batteries of the present invention can also be provided in electric bicycles (e-bikes), drones, electric aircraft, and electric or hybrid boats. Similarly, the batteries of the present invention can be provided in power tools such as power drills or saws, gardening tools such as lawnmowers or grass trimmers, or household appliances such as toothbrushes or hair dryers. The batteries of the present invention can be provided in regenerative braking systems. The batteries of the present invention can be provided in portable electronic devices such as mobile phones, laptops, or tablets. The batteries of the present invention can be provided in power grid management systems, emergency backup systems, power boxes, or remote charging systems.

[0254] Charging or discharging method In another aspect, there is provided a method of charging or discharging an electrochemical cell of the sixth aspect, or a lithium ion battery comprising the electrochemical cell.

[0255] The method of charging or discharging typically involves intercalating lithium into the working electrode, which can reduce or oxidize niobium or metal, preferably niobium, during (de)intercalation.

[0256] Typically, lithium is intercalated into pentagonal and / or tetragonal channels in the NMO crystal structure, preferably into pentagonal channels adjacent to PCs filled with -Nb-O-Nb-O- strings.

[0257] definition The following common definitions are used herein as dictated by the relevant context. CS: Crystal shear NMO: Niobium metal oxide NWO: Niobium tungsten oxide PC: Pentagonal Channel TTB: Tetragonal tungsten bronze

[0258] The voltage values ​​given herein are, as is common in the art, Li + / Li.

[0259] C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. C-rate can be defined as the reciprocal of the number of hours to reach a defined maximum capacity, e.g., 10C corresponds to a 6-minute discharge or charge time. The maximum capacity can be a theoretical maximum capacity or an empirically determined maximum capacity. For example, the theoretical maximum capacity can be defined for one electron transfer per transition metal atom in the active electrode material.

[0260] High charge and discharge rates can also be described by reference to the current density relative to the mass of the electrode active material (by weight).

[0261] As used herein, "% by weight" refers to a percentage calculated on a mass basis.

[0262] As used herein, "V / V" refers to a ratio calculated on a volume basis.

[0263] Other Preferences Any compatible combination of the above embodiments is expressly disclosed herein just as if each combination were individually and explicitly set forth.

[0264] Various other aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0265] "And / or," as used herein, should be construed as a specific disclosure of each of the two specified features or components, with or without the other. For example, "A and / or B" should be construed as a specific disclosure of (i) A, (ii) B, and (iii) each of A and B, as if each were set forth individually herein.

[0266] Unless the context indicates otherwise, the feature descriptions and definitions set forth above are not limited to any particular aspect or embodiment of the present invention, but apply equally to all aspects and embodiments described.

[0267] Certain aspects and embodiments of the present invention will now be described, by way of example, and with reference to the above-mentioned figures. [Example]

[0268] The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

[0269] 1.1-Preparation of NWO phase with various Nb:W ratios Niobium metal oxide bronze phase was prepared by solvothermal synthesis.

[0270] NbCl5 (Alfa Aesar, 99%) and WCl6 (Acros Organics, 99.9+%) were added to ethanol (20 mL, Merck) and stirred to completely dissolve the NbCl5 and WCl6 in the ethanol to form a solution. The solution was stirred until clear, confirming that the NbCl5 and WCl6 were completely dissolved. The molar ratio of Nb:W was varied by adding different amounts of NbCl5 and WCl6 as shown in Table 1. The amounts shown are on a 1 g scale.

[0271] [Table 1]

[0272] The solution was transferred to an 80 ml (50 ml maximum capacity) Teflon reaction vessel (Anton Paar) made of PTFE and then placed in an alumina jacket (Anton Paar). A magnetic stir bar was added to the vessel. 20 ml of ethanol solution was added, and the vessel had approximately 60 ml of headspace when sealed.

[0273] The vessel was then sealed and heated to 150 °C for 2 h under solvothermal conditions and constant stirring in a 1500 W microwave reactor (Anton Paar, Multiwave Pro). The ramp rate was 5 °C / min. The pressure was maintained in the range of 18-40 bar (1800 kPa-4000 kPa) during heating, depending on the volume of the reaction vessel.

[0274] NbCl5 and WCl6 precipitated from the ethanol solvent. The precipitation was visually confirmed. A white precipitate formed and separated from the supernatant. The sample was allowed to cool to room temperature in the reaction vessel. The pressure was then released and the sample was separated by filtration before opening the vessel.

[0275] The solution was filtered using a Buchner funnel to remove the solvent. The precipitate was washed with ethanol (3 times). The precipitate was then dried at 65°C for 12 hours to remove any traces of solvent, leaving a dry precipitate.

[0276] The dried precipitate was then placed in an alumina crucible and calcined in an oven at 850° C. for 12 hours and then at 900° C. for 1.5 hours to obtain a niobium metal oxide bronze phase. Calcination was carried out in air at ambient pressure.

[0277] Example 1 is Nb2W2O 11 This resulted in the formation of

[0278] Example 2 is Nb 16 W8O 64 This resulted in the formation of

[0279] Example 2.5 is Nb 10 W4O 37 This resulted in the formation of

[0280] Example 3 is Nb 18 W6O 63 This resulted in the formation of

[0281] Comparative Examples 4 and 5 are Nb 18 W6O 63 and T-phase Nb2O5 mixture was formed.

[0282] Comparative Example 6 resulted in the formation of T-phase Nb2O5.

[0283] 1.2-Preparation of NWO phases - various temperatures Comparative Example 7 was prepared by solvothermal synthesis in a manner similar to Example 3 in Section 1.1 above, and has a Nb:W ratio of 3:1.

[0284] However, Comparative Example 7 was calcined in an oven at 1200° C. (vs. 900° C. for Example 3) for 12 hours.

[0285] Comparative Example 7 is Nb 16 W5O 55 , Nb 14 W3O 44 and Nb2WO8 mixture was formed.

[0286] Comparative Example 8 was prepared by solid-state synthesis according to the method described in WO 2019 / 234248. The product was prepared by grinding dry powders of NbO and WO together and then calcining the mixture at 1200 °C.

[0287] Comparative Example 8 is Nb 16 W5O 55 This resulted in the formation of

[0288] 1.3- Additional preparation of NWO phase Examples 1a, 2a, 3a, 4a, and 5b were synthesized as described above for Examples 1, 2, 3, 4, and 5, except that the examples were calcined at 800°C.

[0289] Examples 2a, 3a, 4a, and 5a were found to have similar crystal structures to Examples 2, 3, 4, and 5, despite the slightly lower calcination temperatures.

[0290] 2.1-Microscopic characterization of NWO particles Scanning electron microscopy (SEM) was performed to examine the morphology of the dried precipitate and calcined NWO phase. SEM samples were prepared by sprinkling example powders onto carbon tape placed on an SEM stub. SEM was performed using a Tescan MIRA3 at a voltage of 5 kV and a working distance of 6 mm. Images were recorded using MiraTC software.

[0291] SEM images of the precipitate of Example 3 (after filtration and drying, but before calcination) are shown in Figures 2(a-c) and 3(a-b). The precipitate is shown to be amorphous. The SEM images show a spherical morphology with primary particle diameters of 1-5 μm (see Figure 2c). The primary particles aggregate into random, irregular clusters with diameters of approximately 20 μm (see Figure 2a).

[0292] Energy dispersive X-ray spectroscopy (EDS) was also performed on the precipitate of Example 3 and overlaid on the SEM image. SEM was performed as described above, except that the operating voltage was 30 kV and the working distance was 15 mm. EDS data was collected using Aztec software from Oxford Instruments.

[0293] SEM-EDS mapping images of the precipitate of Example 3 (after filtration and drying, but before calcination) are shown in Figure 3(c-f).

[0294] The EDS images of Nb (Fig. 3c), W (Fig. 3d), and O (Fig. 3e) reveal a heterogeneous distribution of Nb, W, and O atoms within each precipitate particle, which is also explained by the uniform color of the layered images for all Nb, W, and O in Fig. 3f.

[0295] It is believed that the highly heterogeneous distribution of atoms allows for the use of lower calcination temperatures. The molecular-scale mixing achieved by this method overcomes the need for cation migration throughout the precursor crystallites. Thus, the energy barrier to atom migration and rearrangement is lower, meaning that lower temperatures can be used during calcination. All of the phases in Examples 1-3 exhibit the same morphology.

[0296] SEM images of the NWO phase prepared in Example 3 (after calcination) are shown in Figure 4(a-c). The NWO phase of the example is shown to have a spherical morphology in the form of spherical secondary particles (see Figure 4c).

[0297] The spherical secondary particles have diameters of approximately 2-3 μm and an aspect ratio of approximately unity. The sphericity of the particles is high, at approximately 0.95 or greater. The surface roughness of the particles is low because the primary particles form compact, close-packed agglomerates.

[0298] The primary particles that make up the secondary particles are much smaller and irregular in shape. They have lengths in the range of about 0.2-1 μm and widths in the range of about 50-100 nm. They are rod-shaped.

[0299] Transmission electron microscopy (TEM) images of the NWO phase prepared in Comparative Example 7 are shown in Figure 5(a-c). A JEOL ARM200F (Cs-corrected) transmission electron microscope was used in STEM mode at 200 kV to image and acquire high-resolution EDS data from the NWO oxide particles.

[0300] Calcination at a higher temperature of 1,200°C (compared to 900°C in Example 3) changes the particle morphology. TEM images show rod-like primary particles, which aggregate into irregularly shaped secondary particles.

[0301] Both the primary particles and secondary particles of Comparative Example 7 have lower sphericity and higher surface roughness than the particles of Example 3. As a result, the packing efficiency of Comparative Example 7 is reduced.

[0302] Nb prepared in Comparative Example 8 16 W5O 55 SEM images were also prepared, which show the irregular rod-like morphology of the particles (see Figure 1).

[0303] 2.2-XRD characterization of the NWO phase Energy dispersive X-ray spectroscopy (EDS) was performed on the Nb prepared in Example 3. 18 W6O 63 (See Figure 6).

[0304] Atomic-resolution STEM-EDS datasets were acquired under low-dose conditions to reduce electron beam damage to the specimen: dwell time = 0.01 ms, spot size = 6C, aperture size = 20 μm, and electron beam current = 18 pA. Given the low electron beam current and therefore the relatively low intensity of the X-rays emitted from the specimen, multiframe STEM-EDS data acquisition was used. Each dataset typically consisted of 500–1000 frames, which were then aligned and processed using HyperSpy, a Python-based multidimensional data analysis toolbox. Aligned images and spectra were then summed across the entire dataset, and principal component analysis (PCA) and nonnegative matrix factorization (NMF) were used to denoise the data and increase the signal-to-noise ratio (SNR).

[0305] The EDS maps show a novel ordering of Nb and W cations in the TTB lattice, in particular the presence of -Nb-O-Nb-O- strings in PC and -WOWO- strings in the inner and outer squares of the octahedral sites.

[0306] Powder X-ray diffraction (PXRD) was carried out on the NWO phases of Examples 1 to 6, and the diffraction patterns are shown in Figures 7, 8, and 9(a-b).

[0307] PXRD was performed using Cu-Kα radiation with a wavelength of 1.5406 Å. A nickel filter before the detector was used to filter out κβ radiation. XRPD data were obtained by exposing NMO samples to Cu-Kα X-ray radiation using a Panalytical Empyrean powder diffractometer. Variable temperature (VT) measurements were performed using an XRK900 (Anton Paar) reactor chamber attachment. Samples were tightly packed on a glass disk mounted on a rotating sample stage. Data were recorded over the 2θ range from 2 to 100° (step size: 0.008° 2θ, counting time: 457.2 s / step). Cu-Kα radiation was generated by supplying a Cu anode with a potential of 40 kV at a current of 40 mA.

[0308] The PXRD patterns of the NWOs with different Nb:W ratios prepared in Examples 1, 2, 2.5, and 3 show reflections with similar 2θ values ​​(see FIG. 7), suggesting a common crystalline structure for all of the materials.

[0309] The reflections with 2θ in the range of 5 to 30° are the PXRD patterns of the NWOs prepared in Examples 1, 2, 2.5 and 3 and are shown in Figure 8. The reflections are labeled in the PXRD patterns.

[0310] Table 2A shows the results of Example 1 (NbWO 11 The observed 2θ values ​​of the peaks are shown along with the corresponding d-spacings and hkl indices. The top 10 strongest 2θ peaks for Example 1 are shown in Table 2B.

[0311] [Table 2]

[0312] [Table 3]

[0313] Table 3A shows the results of Example 2A (Nb 16 W8O64 The observed 2θ values ​​of the peaks are shown along with the corresponding d-spacings and hkl indices. The top 10 strongest 2θ peaks for Example 2 are shown in Table 3B.

[0314] [Table 4A]

[0315] [Table 4B]

[0316] [Table 5]

[0317] Table 4A (Table 6) shows the results of Example 3 (Nb 18 W6O 63 The observed 2θ values ​​of the peaks are shown along with the corresponding d-spacings and hkl indices. The top 10 strongest 2θ peaks for Example 3 are shown in Table 4B.

[0318] [Table 6A]

[0319] [Table 6B]

[0320] [Table 7]

[0321] The PXRD patterns of the NWOs prepared in Comparative Examples 4, 5, and 6 are shown in Figures 9a and 9b, along with those of Examples 1, 2, 2.5, and 3. Figure 9b shows reflections with 2θ in the range 5-30°.

[0322] Comparative Examples 4, 5, and 6 are T-phase Nb2O5 and Nb 18 W6O 63 Additional reflections at approximately 27° and 28° are present in Examples 4-6 but absent in Examples 1, 2, 2.5, and 3. These reflections are believed to be due to the presence of T-phase Nb2O5.

[0323] The comparative NWO phases have XRD patterns that differ from the XRD peaks of the present invention. The reference XRD patterns are T-Nb2O5 (see Tamura et al.), Nb 16 W5O 55 (see Roth et al.), Nb 14 W3O 44 (see Roth et al.), and Nb2WO8 (see Lundberg).

[0324] This suggests that the excess Nb present in the solutions of Comparative Examples 4, 5, and 6 is precipitated as T-phase Nb2O5 during calcination.

[0325] PXRD was performed for Comparative Example 7 and the diffraction pattern is shown in FIG.

[0326] The PXRD of Comparative Example 7 showed that Nb 16 W5O 55 , Nb 14 W3O 44 , Nb 12 WO 33 The results show the presence of a mixture of NWO phases such as Nb2WO8 and Nb2WO8. Using the relative intensities of the 2θ values, it was found that each of the NWO phases accounted for 58.8% (Nb 16 W5O 55 ), 26.0%(Nb 14 W3O 44 ), and 15.2% (Nb2WO8).

[0327] These phases do not have the crystal structure of the present invention. 16 W5O 55 , Nb 14 W3O 44 , and Nb 12 WO 33The phases have a block structure, with block sizes of 5x4, 4x4, and 4x3, respectively (see Kocer et al.). Nb2WO8 has a bronze structure with a different arrangement of pentagonal channels than the structure of the present invention (see Lundberg et al.). Nb2WO8 also does not have the cation ordering seen in the examples of the present invention. In Nb2WO8, PCs are randomly occupied by either Nb or W, whereas in the present invention, PCs are filled only with -Nb-O-Nb-O- strings, increasing the cation ordering.

[0328] This difference in structure can be confirmed by PXRD using profile matching, e.g., a multiphase Rietveld refinement was performed using all of the phases to match the intensities of all of the peaks in the PXRD pattern.

[0329] It is believed that the higher the calcination temperature, the more thermodynamically stable these crystalline structures that are formed. However, as shown by the SEM images discussed above (see FIG. 5), the morphology of these crystals is highly irregular compared to the spherical secondary particles of Examples 1-3. The formation of large, irregularly shaped rods at such high temperatures is believed to be due to crystal growth of these more thermodynamically stable crystalline structures.

[0330] Neutron diffraction was performed on the NWO phases of Examples 1, 2, and 3, and the diffraction patterns are shown in FIG.

[0331] All phases of Examples 1, 2, and 3 show peaks at 3.94 Å corresponding to the 001 reflection, 5.63 Å for the 210 reflection, and 8.75 Å for the 020 reflection.

[0332] The phases of Examples 2 and 3 show stronger peaks at 7.83 Å and 17.57 Å, corresponding to the 210 and 010 reflections. The peak at 17.57 Å is due to the parameters of the supercell, as explained below.

[0333] 2.3-Crystallographic analysis XRD and neutron diffraction analyses of the materials of Examples 1, 2, and 3 (shown above) were performed using Rietveld refinement to characterize the crystal structure. The structures were further confirmed using HR-STEM EDS studies as described above.

[0334] Example 1 (NbWO 11 ) crystallizes in the space group P4 / mbm (a = 12.2210 Å, c = 3.9371 Å) (Figure 12).

[0335] Nb:W was used in Example 2 (Nb 16 W8O 64 By increasing the Nb content to 2:1, a new family of reflections (hk0 and h+k = odd numbers) was observed in the PXRD (Figure 8). Specifically, reflections at hkl = 120, 230, 140, 111, 021, and 050 / 340 appear in the XRD of Example 2 but are absent in the XRD of Example 1. These reflections increase in intensity as the Nb content increases.

[0336] This can be seen in the supercell only with a = 17.4054 Å, c = 3.9450 Å (space group P4), where the c parameter is retained and the a parameter is increased by a factor of √2. This is accompanied by a corresponding decrease in intensity of the hk0 family of h+k = even reflections.

[0337] The fluctuation tendency of the hk0 reflection intensity is shown by the Nb:W ratio in Example 3 (Nb 18 W6O 63 ) continues as the ratio is further increased to 3:1 as seen in Example 1. The crystal structure of Example 3 retains the supercell size, which is believed to be due to the lower W concentration (Figure 13).

[0338] Example 1 (NbWO 11 ) unit cell and Example 2 (Nb 16 W8O 64 ) and Example 3 (Nb 18 W6O 63The relationship of the unit cell to the supercell is shown in Figure 13c. The unit cell contains four PCs. The supercell contains eight PCs. The lattice parameters of the supercell coincide with the diagonal of the unit cell. Thus, if the unit cell has lattice parameters a × a, then the supercell has lattice parameters equal to √2a × √2a.

[0339] The formation of the supercell was further confirmed using neutron diffraction, where the reflections below 3.9 Å (c parameters) are similar in all three diffraction patterns (see FIG. 11). 11 (Nb:W=1:1) shows a broad peak at 12.2 Å (a parameter), which does not exist in Examples 2 and 3. 16 W8O 64 (Nb:W=2:1) ​​and Nb in Example 3 18 W6O 63 (Nb:W=3:1) instead has a peak at 17.57 Å corresponding to the a parameter.

[0340] Neutron powder diffraction measurements were performed at room temperature using the POLARIS and GEM time-of-flight powder diffractometers at the ISIS Pulsed Spallation Neutron Source in the UK. Samples were loaded into vanadium cans with a diameter of 6 mm. 11 and Nb 16 W8O 64 For Nb, 18 W6O 63 Data were collected from Polaris for . Data from banks 1 and 4 were used for the analysis due to their appropriate d-spacing ranges (approximately 1.5 to 25 Å, and approximately 1 to 3.7 Å). A combined Rietveld refinement of PXRD and neutron diffraction data using the FULLPROF suite of programs was used to determine the final structure.

[0341] Another analysis was performed using high-resolution scanning transmission electron microscopy (HAADF HR-STEM). A JEOL ARM200F (Cs-corrected) transmission electron microscope was used in STEM mode at 200 kV to image and acquire high-resolution EDS data from NbWO oxide particles. Atomic-resolution STEM-EDS datasets were acquired under low-dose conditions to reduce electron beam damage to the specimen: dwell time = 0.01 ms, spot size = 6C, aperture size = 20 μm, and electron beam current = 18 pA. Given the fairly low electron beam current and therefore the relatively low intensity of X-rays emitted from the specimen, multiframe STEM-EDS data acquisition was used. Each dataset typically consisted of 500–1000 frames, which were then aligned and processed using HyperSpy, a Python-based multidimensional data analysis toolbox. The matched images and spectra were then summed across the entire dataset, and machine learning tools such as principal component analysis (PCA) and non-negative matrix factorization (NMF) were used to denoise the data and increase the signal-to-noise ratio (SNR).

[0342] HAADF HR-STEM imaging provides evidence for the ordering of pentagonal channels (PCs) within the crystal structure, as well as the ordering of cations and empty PCs. Example 1 (NbWO 11 ), the PCs are partially and randomly occupied (Fig. 14(a)) and therefore have a smaller a parameter of 12.2 Å. 16 W8O 64 With increasing Nb / W content, as seen in Example 3 (Nb), 50% of the PCs remain completely empty and are arranged in a square pattern (Fig. 15(c)). The remaining PCs are partially occupied by cations (Fig. 11(b)). 18 With further increasing Nb / W in W6O6), the phases retain the same structure as in Example 2 (Fig. 14(c)), with 50% of the PCs remaining completely empty and arranged in a square pattern.

[0343] Example 3 (Nb 18 W6O63 A higher magnification HAADF HR-STEM image of the ordered vacant PC is shown in Figure 15(a). The cations present in and around the square pattern of ordered vacant PC are visually brighter than the other cations (Figure 15(a)). This is considered to be further evidence of the ordering of PC vacancies and the formation of a supercell (√2a). It also suggests cation ordering, where Nb and W ions occupy specific rows of atoms (along the crystallographic c-axis) within the unit cell.

[0344] The bandgap filter and threshold were set to Example 3 (Nb 18 W6O 63 ) to provide a higher-contrast HAADF-HR(S)TEM image (see Figure 16(b)). The bright spots can be more clearly identified, further confirming the existence of a supercell structure in which 50% of the PCs are filled with -MOMO- strings and 50% of the PCs are empty, forming a square of four pentagonal channels.

[0345] The bandgap filter and threshold were calculated using Example 1 (Nb2W2O 11 ) was also applied to the HAADF-HR(S)TEM image of Example 1 to enhance the contrast (see FIG. 17A(b)). The image in FIG. 17A(b) shows that all spots remain bright except for the PC, which has been brightness-modified. This confirms the partial and random occupation of the PC in the structure of Example 1.

[0346] Further characterization and modeling showed that in Example 1, the Nb and W cations were initially equally distributed among two octahedral (2c(0, 0.5, 0.5) and 8j(x, y, 0.5)) and one pentagonal (4h(x, 0.5 + x, 0.5)) cation sites (in this case, Figure 17). 0.26In addition to the existing oxygen positions in the WO3 structural model, an additional oxygen atom was placed beneath the cation in the pentagonal cation site to form a seven-coordinate pentagonal bipyramidal (PB) site. The cation positions and their occupancies were refined to investigate the preferential occupation of the octahedral and PB cation sites by Nb and W. The final refined structure (Figure 18c) shows that Nb and W ions are distributed throughout all octahedral sites, with a slight preference for W in the 2c site. The PB site showed low occupancy, with only partial (1 / 3) occupation of this site by Nb, maintaining an overall Nb / W ratio of 1.

[0347] The layer thickness of the metal oxide polyhedra in Example 1 was calculated to be approximately 3.9 Å, corresponding to the c parameter (in this case, Figure 17). Atomic-resolution HAADF-HR(S)TEM imaging of the ab plane captured the -MOMO- channel along this axis (Figure 17B(d)), and overlay with a structural model (one unit cell) shows the atomic arrangement of Nb and W. The FFT-derived lattice parameter (a approximately 13 Å) closely matches the value obtained from the PXRD data. The intensity of the atomic columns in the HAADF-HR(S)TEM image represents the sum of the intensities of -MOMO- strings throughout the sample thickness. Variations in the intensity of the atomic columns in the HAADF image can be attributed to variations in the occupancy of a single element at a lattice site and / or different elements occupying the same lattice site. Recent advances in combining aberration-corrected (S)TEM with EDS have enabled atomic-resolution elemental mapping of crystal structures. Here, it is used to confirm the preferential occupancy of Nb and W at octahedral and PB sites obtained from XRD refinement. High-resolution (S)TEM-HAADF images and corresponding EDS elemental maps of Example 1 along the c-axis are shown in Figure 18B(d-g). In the atomic-resolution EDS map, the bright spot highlighted by the cyan circle corresponds to the 2c octahedral site, which, based on XRD refinement, is preferentially occupied by W atoms. The spot indicated by the yellow circle corresponds to the octahedral site 8j, which is partially filled by W atoms, suggesting shared occupation of W and Nb atoms. The magenta circle corresponds to the PB site 4h, which appears bright in the Nb map but is absent in the W map, confirming that the site is occupied exclusively by Nb atoms. This observation is further supported by the overlaid EDS map in Figure 18B(g).

[0348] Example 3 (Nb 18 W6O 63 The atomic line intensity profile in a HAADF STEM image of ) is shown in Figure 18. The intensity profile shows a periodic and repeating pattern in all directions, suggesting that the cations are ordered throughout the lattice.

[0349] Energy dispersive X-ray spectroscopy (EDS) was performed using Example 3 (Nb 18 W6O 63 ) was also performed and overlaid on the SEM image (see Figure 19a). STEM-EDS was performed to obtain atomic resolution mapping to identify and distinguish different rows of atoms along the c crystallographic axis. The STEM-EDS image shows that W ions occupy octahedral sites within and around the square arrangement of vacant PCs, while other PCs and octahedral sites are occupied by Nb ions (Figure 19a).

[0350] Additional TEM images were prepared of the NWO phases prepared in Examples 1, 2, and 3. Fast Fourier transform (FFT) images of the same samples were also prepared, as described above.

[0351] TEM and FFT images viewed perpendicular to the crystallographic c-axis were prepared for Example 1 (see Figures 20(a-b)). The TEM and FFT images show a d-spacing of 3.9 Å, corresponding to the c-parameter of the TTB unit cell.

[0352] Example 1 (NbWO 11 TEM and FFT images of ) were prepared along the ab plane (see Figure 21(a-b)), which shows a d-spacing of 12.2 Å, corresponding to the a-parameter of the TTB unit cell.

[0353] Example 3 (Nb 18 W6O 63 TEM and FFT images of ) were also taken along the ab plane (Figure 22) and show a d-spacing of 17.2 Å, corresponding to the supercell formed by the √2a of the smaller TTB unit cell.

[0354] These images confirm the crystallographic characterization of the new NWO phase.

[0355] Example 3 (Nb 18 W6O 63A TEM image prepared by focused ion beam (FIB) of a lamella of a secondary particle of the NWO phase derived from (A) is shown in Figure 23(a) (scale bar 1 μm). Figure 7(b) shows a closer image of the secondary particle (scale bar 1 nm).

[0356] Lamellae were prepared using a focused ion beam scanning electron microscope (FIB-SEM)—FEI Helios NanoLab. TEM images and selected area electron diffraction (SAED) patterns prepared from these lamellae were acquired via a transmission electron microscope—Thermo Scientific (FEI) Talos F200X G2 operating at 200 kV. During the formation of the lamellae, focused ion beam milling tends to destroy the edges of the lamellae, and therefore the image shown in Figure 23(a) is not spherical.

[0357] The image shows a network of primary particles that make up the secondary particle. From the image, it can be estimated that the length of the primary particles that make up the secondary particle is approximately 0.2 to 1 μm. It can also be estimated that approximately 1,000 to 1,500 primary particles make up the secondary particle.

[0358] Electrochemical characterization of the 2.4-NWO phase The NWO phase was examined against Li in a half-cell configuration.

[0359] Electrodes were prepared by mixing the active material, conductive carbon (Super P, TIMCAL), and binder (PVDF, Kynar) in a mass ratio of 8:1:1. The materials were dispersed in N-methyl-2-pyrrolidone to prepare a slurry, which was mixed in a Thinky 250 mixer. Electrodes were cast from the slurry and dried overnight in an oven at 60 °C under ambient pressure. The dried electrodes were then calendered at room temperature. The active mass loading was approximately 2 mg cm. -2 and the electrode area is 1.27 cm 2 is.

[0360] Anodic working electrodes were prepared using the NWO phases of Examples 1 and 3 (prepared in Section 1.1 above) as the active material. A cathodic counter electrode was prepared using Li metal as the active material.

[0361] Electrochemical testing was performed in a 2032 stainless steel (ss) coin cell equipped with a ss conical spring, two 0.5 mm thick ss spacer disks, and a glass microfiber separator (Whatman, GE). In a glovebox, the cell was assembled with an LP30 electrolyte (Sigma-Aldrich) consisting of 1.0 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 v / v). The cell was assembled in an argon-filled glovebox.

[0362] Galvanostatic cell cycling tests were performed at various current densities. The C-rate was calculated based on the theoretical capacity of the cathode active material. The C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. The C-rate can be defined as the reciprocal of the number of hours to reach a defined theoretical capacity.

[0363] The half-cells were cycled from 1.3 to 3.0 V vs. Li.

[0364] High-rate performance was tested up to 20 C. For cells using the anode active materials of Examples 1 and 3, the discharge capacity at different discharge rates was tested and is shown in Figure 24(a). The first four cycles were performed at C / 5, followed by six cycles at 1 C, 2 C, 5 C, 10 C, 20 C, and 1 C, respectively.

[0365] Example 1 (NbWO 11 ) the initial capacity is approximately 160mA h g at C / 5. -1 This is about 138mA h g at 1C. -1 However, at higher C-rates, the capacity loss is minimal. At 10 C, the capacity is approximately 125-130 mA h g -1At 20C, the capacity is approximately 120-125mA h g -1 This indicates that the anode has excellent rate capacity retention even at high rates.

[0366] Example 3 (Nb 18 W6O 63 ) the initial capacity is approximately 200mA h g at C / 5. -1 This is about 170mA h g at 1C. -1 However, at higher C-rates, the capacity loss is minimal. At 10 C, the capacity is approximately 150-160 mA·h·g -1 At 20C, the capacity is approximately 145 to 155mA·h·g -1 This indicates that the anode has excellent rate capacity retention even at high rates.

[0367] The anode of Example 3 has a higher capacity than the anode of Example 1.

[0368] The slightly higher capacity of Example 3 is believed to be due to the higher number of PC vacancies in Example 3 compared to Example 1, allowing for increased lithium intercalation into the empty PC. Additionally, Example 3 has a lower density than Example 1, and therefore, on a weight basis, the capacity appears to be higher for Example 3.

[0369] Known NWO materials (e.g., Nb tested in WO 2019 / 234248) 16 W5O 55 ) the capacity is improved at high C-rates. 16 W5O 55 The discharge capacity of the electrode at 0.2 C is approximately 165 mA h g -1 and 125mA h g at 20C. -1 Both the initial capacity at 0.2 C and the capacity at a high discharge rate are 11 ) and Example 3 (Nb 18 W6O 63) which is believed to be due to the improved lithium ion intercalation properties brought about by the specific regularity of the structure and the enhanced cation ordering.

[0370] The long-term cycling performance was tested for 1,000 cycles. The cells using Example 1 and Example 3 as the anode active material were cycled at a discharge rate of 10 C for 1,000 cycles, and the discharge capacity is shown in Figure 24(b).

[0371] In Example 3, the initial discharge capacity was 170 mA·h·g -1 and 160 mA h g over 1,000 cycles at 10 C. -1 This represents a capacity retention of over 94% over 1000 cycles at 10C.

[0372] In Example 1, the initial discharge capacity was 130 mA·h·g -1 and 110 mA h g over 1,000 cycles at 10 C. -1 This represents a capacity retention of over 84% over 1000 cycles at 10C.

[0373] Despite the very high 10C rate and large number of cycles, the capacity retention over 1,000 cycles is excellent. For the anode of Example 3, the capacity retention is particularly high.

[0374] Known NWO materials (e.g., Nb tested in WO 2019 / 234248) 16 W5O 55 ) and improves capacity retention. 16 W5O 55 For the electrode, the discharge capacity retention over 300 cycles at 10C charge and 10C discharge rates was 120 mA h g -1 This corresponds to a capacity retention of over 80%. The capacity retention was 11 ) was less than 84%, and Example 3 (Nb 18 W6O 63) is 94%. This is believed to be due to the specific regularity of the structure and the enhanced cation ordering of the present invention, which increases the uniformity of the lattice expansion and reduces cracking during repeated cycling at high speeds.

[0375] Additional electrochemical characterization of the 2.5-NWO phase Additional electrochemical cycling tests were performed on the NWO phase against Li in the half-cell configuration as described in Section 2.4 above.

[0376] High-rate performance was tested up to 20 C. The cells using Examples 1, 2, and 3 as the anode active materials were tested for discharge capacity at different discharge rates. The results are shown in Figure 26(d). The first four cycles were performed at C / 5, followed by six cycles at 1 C, 2 C, 5 C, 10 C, 20 C, and 1 C, respectively.

[0377] Example 1 (NbWO 11 ) and Example 3 (Nb 18 W6O 63 ), the performance is similar to that tested in Section 2.4.

[0378] In Example 2 (Nb2WO8), the initial capacity is about 185 mA h g-1 at C / 5. This is about 170 mA h g-1 at 1 C. -1 However, at higher C-rates, the capacity loss is minimal. At 10 C, the capacity is approximately 145-150 mA·h·g -1 At 20C, the capacity is approximately 135-140mA h g -1 This indicates that the anode has excellent rate capacity retention even at high rates.

[0379] The anode of Example 2 has a higher capacity than the anode of Example 1 and a slightly lower capacity than the anode of Example 3.

[0380] Long-term cycling performance was tested for 1,000 cycles. Cells using Examples 1, 2, and 3 as the anode active materials were cycled at a discharge rate of 10 C for 1,000 cycles, and the discharge capacities are shown in Figure 2. The anode materials demonstrated remarkable high-rate capability, with reversible capacities of 160, 155, and 110 mAh / g at the end of 1000 cycles at high rate (10 C).

[0381] Example 1 (NbWO 11 ) and Example 3 (Nb 18 W6O 63 ), the performance is similar to that tested in Section 2.4.

[0382] In Example 2 (Nb2WO8), the initial discharge capacity was 160 mA·h·g -1 and 155mA h g over 1,000 cycles at 10 C. -1 This represents a capacity retention of over 96% over 1000 cycles at 10C.

[0383] Despite the very high 10C rate and the large number of cycles, the capacity retention over 1,000 cycles is excellent. The capacity retention is particularly high for the anodes of Examples 2 and 3.

[0384] Although both Examples 2 and 3 have a supercell TTB structure, it is believed that Example 3 demonstrated higher capacity compared to Example 2 due to the lower molar mass of Example 2 compared to Example 3. This difference in capacity can be attributed in part to the reduction in defects present in the lattice of Example 3.

[0385] The gravimetric capacities of all three bronzes reported here are higher than the 80 mAh / g reported for α-NbWO cycling at 3 A / g (rates below 10 C). This increased capacity can be attributed to the presence of interconnected vacant pentagonal channels that encounter particles, which aid in Li-ion transport and storage.

[0386] Thermal stability of the 2.6-NWO phase The thermal stability of the example phases was tested to investigate their thermodynamic stability. Examples 1, 2a, and 3a were re-calcined at 800° C. for 30 days, and their PXRD patterns are shown in FIG.

[0387] Example 1 remained unchanged during prolonged heating, demonstrating its thermodynamic stability. However, in Example 2, approximately 71.5% of the material retained its structure, while the remainder decomposed into the known bronze phase, α-Nb2WO8. Similarly, in Example 3, only 7.6% of the material retained its structure, while the majority decomposed into Nb 14 W3O 44 (33%) and α-Nb2WO8 (59.4%).

[0388] The tested samples were also subjected to microscopic characterization using SEM. The phase composition of the decomposition products again correlated with the observed morphology changes: Example 1 maintained its spherical morphology with an increase in the size of the primary particles (FIG. 28A), while Example 2 only partially retained its spherical morphology, with the remaining portion crystallizing as micron-sized rods, consistent with typical NWO bronze and block phases (FIG. 28B). Example 3 was completely converted to micron-sized particles (FIG. 28C).

[0389] The stability of Example 1 was observed up to 1000°C, and calcination at 1200°C for 12 hours resulted in the formation of Nb 12 W 11 O 63 , Nb8W9O 47 , and Nb 14 W3O 44 The decomposition was accompanied by a transformation to a rod-like structure. Spherical secondary particles were only observed at temperatures below 900 °C, and the transformation to a rod-like structure was always accompanied by decomposition.

[0390] These findings confirm that the low-temperature synthesis approach is important for the formation of the NWO phase of the present invention. The examples were shown to have sufficient thermal stability for typical battery applications, but the structure of Example 1 was also shown to have superior high-temperature stability to Examples 2 (2a) and 3 (3a).

[0391] References Several publications have been cited above to further describe and disclose the present invention and the state of the art to which it pertains. Full citations for these references are set forth below. Each of these references is incorporated herein in its entirety. (References) Chinese Patent Application Publication No. 110304658 International Publication No. 2019 / 234248 Ekstrom et al., Acta Chem. Scand. 1971, 25, No.7 Griffith et al., Nature, 559, 556-559 Hyde et al., Acta Crystallogr. Sect. A 1973, 29, 243-248. Kocer et al., J. Am. Chem. Soc. 2019, 141, 15121-15134 Krumeich, Chem. Mater. 2022, 34, 3, 911-934 Kudo et al., Journal of Solid State Chemistry, 1988, 77, 2, 412-415 Lundberg, Acta Chemica Scandinavica 26, 1972, 2932-2940 Roth et al., Acta Cryst. 1965, 19, 26 Roth, RS, Wadsley, AD, Acta Crystallogr., 1965, 19, 32 Sayagues et al., Journal of Solid State Chemistry, 1998, 143, 1, 33-40 Tamura, S. et al., Z. Anorg. Allg. Chem., 1974, 410, 313 Wadsley et al., Acta. Crystal. 1961, 14, 660 Xia et al. Journal of Power Sources 482 (2021) 228898 Yang et al., CS Nano 2017, 11, 4, 4217-4224 Yu et al., Inorganica Chimica Acta, 2020, 507, 119562 Zhou et al., Chemistry Select, 2020, 5, 3, 1209-1213

Claims

1. Optionally intercalated with lithium, Nb ｘ M ｙ O ｚ (I) wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo; x is 2 to 18; z is 2.5x+3y; and x / y is 1 to 3; the crystal structure of the niobium metal oxide is a tetragonal tungsten bronze structure having four or eight pentagonal channels per unit cell; a portion of the pentagonal channels is filled with -Nb-O-Nb-O- strings, and the remaining portion of the pentagonal channels is optionally intercalated with lithium; Niobium metal oxide.

2. 2. The niobium metal oxide of claim 1, wherein M is selected from W and Mo, preferably M is W.

3. The niobium metal oxide according to claim 1 or 2, wherein 1 / 3 to 1 / 2 of the pentagonal channels in the niobium metal oxide are filled with -Nb-O-Nb-O- strings, preferably 1 / 3 or 1 / 2 of the pentagonal channels in the niobium metal oxide are filled with -Nb-O-Nb-O- strings.

4. 4. The niobium metal oxide of claim 1, wherein the crystal structure comprises a unit cell having space group P4 / mbm or a supercell having space group P4.

5. 5. The niobium metal oxide of claim 1, wherein the crystal structure comprises a unit cell having a parameter a of 12.2 to 12.5 Å or a supercell having a parameter √2a of 17.3 to 17.5 Å, the unit cell or supercell having a parameter c of 3.8 to 4.0 Å.

6. 6. The niobium metal oxide according to any one of claims 1 to 5, wherein the crystalline structure is characterized by a powder X-ray diffraction pattern having two or more 2θ peaks, such as three or more, for example four or more peaks, selected from the group consisting of 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, and 32.60±0.2°, wherein the powder X-ray diffraction is measured at a Cu-Kα wavelength.

7. 7. The niobium metal oxide of claim 1, wherein x / y is selected from 1, 1.5, 2, 2.5, and 3, preferably 1, 2, 2.5, and 3.

8. The niobium metal oxide of any one of claims 1 to 7, wherein the ratio of x / y is 2 to 3.

9. Nb １８ M ６ O ６３ , Nb １０ M ４ O ３７ , Nb １６ M ８ O ６４ , Nb ２ M ２ O １１ or a combination thereof, preferably Nb １８ M ６ O ６３ , Nb １６ M ８ O ６４ or a combination thereof, more preferably Nb １８ M ６ O ６３ 9. The niobium metal oxide of claim 1, wherein

10. 10. The niobium metal oxide of claim 1, wherein the crystal structure comprises tetragonal channels and pentagonal channels, and a portion of the tetragonal channels and / or a portion of the pentagonal channels are intercalated with Li.

11. Niobium metal oxide secondary particles comprising agglomerates of niobium metal oxide primary particles according to any one of claims 1 to 10, wherein the niobium metal oxide secondary particles have an average mean length of 1 to 5 µm and an aspect ratio of 1 to 1.

5.

12. The niobium metal oxide secondary particles according to claim 11, having an aspect ratio of 1 to 1.3, preferably 1 to 1.2, and more preferably 1 to 1.

1.

13. The niobium metal oxide secondary particles according to claim 11 or 12, having a sphericity of 0.95 or more, for example 0.96 or more, 0.97 or more, 0.98 or more, or 0.99 or more.

14. Niobium metal oxide secondary particles according to any one of claims 11 to 13, having a D50 particle length of 1 to 5 µm and a standard deviation of particle length of 3 µm or less.

15. Niobium metal oxide secondary particles according to any one of claims 11 to 14, wherein the primary particles of niobium metal oxide have a length of 0.3 to 1 µm and an aspect ratio of 2 to 20, and are preferably rod-shaped.

16. 16. Niobium metal oxide secondary particles according to any one of claims 11 to 15, wherein the primary particles are each connected by one or more niobium metal oxide amorphous bridges.

17. A method for preparing the niobium metal oxide secondary particles according to any one of claims 11 to 16, comprising the steps of: NbX ａ and M.Y. ｂ co-precipitating Nb oxide and M oxide from the solution; calcining the precipitate at a temperature of 550 to 1100°C; Including, M is selected from Ti, Zr, V, Cr, W, and Mo; X and Y are independently one or more counter ions; a and b are independently 2 to 6; and NbX ａ and M.Y. ｂ is optionally electrically charged.

18. The coprecipitation step is ａ and M.Y. ｂ 18. The method of claim 17, comprising heating the solution of at a temperature of 120 to 200°C, preferably 130 to 170°C, more preferably 140 to 160°C.

19. The coprecipitation step is ａ and M.Y. ｂ 19. A method according to claim 17 or 18, comprising heating the solution of formula (I) at a pressure of 1000 kPa or more, preferably from 1000 kPa to 5000 kPa, more preferably from 1500 kPa to 4500 kPa, and even more preferably from 1800 kPa to 4000 kPa.

20. 20. The method of any one of claims 17 to 19, wherein the co-precipitating step comprises heating under solvothermal conditions, such as microwave heating under solvothermal conditions.

21. A method according to any one of claims 17 to 20, wherein the precipitate is calcined at a temperature of from 600 to 1000°C, preferably from 700 to 950°C, more preferably from 800 to 900°C.

22. X and Y are independently selected from oxalate, ethoxide, O, S, F, Cl, and Br, preferably oxalate, O, and Cl; and / or M is Mo or W, preferably W; 22. The method of any one of claims 17 to 21.

23. NbX ａ is niobium oxalate or niobium chloride, and / or M.Y. ｂ is metatungstate, paratungstate, or tungsten chloride; 23. The method of any one of claims 17 to 22.

24. 24. Niobium metal oxide secondary particles comprising agglomerates of niobium metal oxide primary particles, wherein the niobium metal oxide secondary particles are obtained or obtainable by the method according to any one of claims 17 to 23.

25. 25. A working electrode for an electrochemical cell, comprising the niobium metal oxide secondary particles of any one of claims 11 to 16 or 24.

26. 26. An electrochemical cell comprising the working electrode of claim 25.

Images