Niobium metal oxide

Abstract

The present invention relates to a niobium metal oxide, niobium metal oxide secondary particles and 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 has the formula (I): NbxMyOz, where M is a metal selected from the group consisting of Ti, Zr, V, Cr, W and Mo, x is 2 to 18, z is 2.5 x + 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 cell, and a portion of the pentagonal channels is filled with-Nb-O-Nb-O-chains, and the remainder of the pentagonal channel is optionally embedded with lithium.

Description

[0001] Related applications

[0002] This case claims priority to and the benefits of GB 2218984.9, filed on December 15, 2022 (15.12.2022), the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] 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 the niobium metal oxide secondary particles. Background Art

[0004] Fast-charging lithium-ion batteries are important for energy storage in a variety of technologies, from electric vehicles and grid storage to handheld devices and backup systems. Several known niobium metal oxides (NMOs), such as niobium tungsten oxide (NWO, Griffith et al.), are used as fast-charging working electrode materials. These materials exhibit good high-rate performance and capacity retention even at high charging rates.

[0005] Most known NMOs have structures that can be derived from simple ReO 3 -type structures, such as bulk structures or tetragonal tungsten bronze (TTB).

[0006] These NMO phases are typically synthesized via a solid-state process, in which solid precursor metal oxides are ground and / or mixed to form a fine powder. This method is 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 powder is then calcined at high temperatures to form NMO. The calcination step requires high temperatures, typically exceeding 1,200°C, because the powders have low homogeneity, so metal ion diffusion needs to occur between multiple crystallites within a particle (intra-particle cation diffusion) as well as between particles (inter-particle cation diffusion). The higher energy barriers for intra- and inter-particle ion diffusion necessitate higher synthesis temperatures. By using lower temperatures, a portion of the precursor remains unreacted. Early attempts by Fiegel et al. to synthesize different NWO phases at temperatures below 900°C observed the coexistence of different phases, with equilibrium not reached even after 30 days.

[0007] NMO has also been synthesized using a solution-based mixing method (e.g., Kudo et al. 1988). In this paper, solutions of metal oxide precursors are mixed before adding a precipitating agent to induce 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, which results in the hydrolysis of Nb ions first, forming Nb2O5 islands, followed by WO3 precipitation. These methods are known to result in non-concurrent precipitation, which means that the precipitation mixture also has poor homogeneity, hindering the uniform distribution of cations in the final product. For the same reasons given above, calcination requires high temperatures (e.g., above 1,200°C) to provide the desired block NMO phase.

[0008] Poor homogeneity and high-temperature synthesis lead to the production of complexes with structural variants of different 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 typically crystallize in the form of rods, often with a wide size distribution, variable aspect ratios, and irregular morphologies. For example, WO 2019 / 234248 describes the synthesis of Nb by solid-state synthesis. 16 W5O 55 The product was prepared by grinding dry powders of Nb2O5 and WO2 together and then calcining the mixture at 1200°C. 16 W5O 55 The SEM images show the irregular rod-like morphology of the particles (see Figure 1 ).

[0009] Therefore, the actual volumetric capacity and energy density of these NMO materials are limited. The poor packing density of NMO crystallites caused by irregular particle morphology leads to voids between particles. These can also lead to poor lithium ion conductivity and electrode kinetics. Poor contact between adjacent particles means that some particles will be more or less likely to intercalate lithium, so the material is unstable at fast charge / discharge rates, resulting in poor capacity retention at high rates and after many cycles.

[0010] 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 intercalation (deintercalation) during charging or discharging. Cation disorder also means that the crystal structure expands and contracts irregularly during the intercalation (deintercalation) process, so the material is more prone to cracking. During rapid charge / discharge, when expansion and contraction are fastest, cracking is particularly evident. Overall, this leads to poor electrochemical properties, such as capacity retention, especially at high charge / discharge rates.

[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. Summary of the Invention

[0012] In its most general form, the present invention provides a niobium metal oxide having a crystal structure comprising a tetragonal tungsten bronze having pentagonal channels (PC), wherein the PC is partially filled with -Nb-O-Nb-O- strings. The -Nb-O-Nb-O- strings in the PC provide cationic ordering within the structure. A portion of the PC is filled with Nb-O-Nb-O- chains, and the remainder is optionally intercalated with lithium.

[0013] The niobium metal oxide may have the formula (I)

[0014] Nb x M y O z (I)

[0015] wherein 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 having pentagonal channels, wherein a portion of the pentagonal channels are filled with -Nb-O-Nb-O- chains. When the pentagonal channels do not contain chains, they are optionally intercalated with lithium.

[0016] The NMO phases reported here function as high-rate anode materials, showing excellent electrode kinetics, rate performance, and capacity retention, especially at high rates. These specific crystalline phases exhibit highly symmetrical and regular morphologies. In addition, the cationic ordering provided by the -Nb-O-Nb-O- chains promotes uniform lithium insertion, which leads to uniform expansion and contraction of the crystal structure during battery cycling. This new NMO phase also forms spherical secondary particles, in contrast to the irregular rod-shaped particles formed by known NMO phases.

[0017] In a first aspect of the present invention, there is provided a niobium metal oxide of formula (I)

[0018] Nb x M y O z (I)

[0019] wherein the niobium metal oxide is optionally intercalated with lithium,

[0020] 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

[0021] The crystal structure of niobium metal oxide is a tetragonal tungsten bronze structure with four or eight pentagonal channels per unit cell, and

[0022] A portion of the pentagonal channels is filled with -Nb-O-Nb-O- chains, and the remaining portion of the pentagonal channels is optionally intercalated with lithium.

[0023] The cation ordering provided by the pentagonal channels filled with -Nb-O-Nb-O- chains improves lithium intercalation in the niobium metal oxide of the present invention. During lithium intercalation and deintercalation, the niobium / metal cations in the niobium metal oxide are reduced and oxidized, respectively. Based on the structure and metal composition of the niobium metal oxide, preferential redox of niobium or metal (e.g., tungsten) cations occurs during intercalation.

[0024] Because the provided structure is more ordered (e.g., due to pentagonal channels filled with -Nb-O-Nb-O- chains), preferential redox occurs for cations in the same lattice environment throughout the structure, meaning that the lattice expands and contracts uniformly during insertion. This contrasts with known structures that do not have this cation ordering, where cations undergoing redox may be in different lattice environments, resulting in less uniform expansion and compression. Uniform expansion reduces cracking and structural defects during battery cycling, thereby improving battery performance, especially at high rates.

[0025] Generally, the present invention also provides spherical niobium metal oxide secondary particles comprising agglomerations of primary particles.

[0026] In a second aspect of the present invention, there is provided niobium metal oxide secondary particles comprising aggregates of primary particles of niobium metal oxide, such as the aggregates of the niobium metal oxide particles of the first aspect, wherein the secondary particles have a length (such as a mean average length) of 1 to 5 μm and an aspect ratio of 1 to 1.5.

[0027] The highly regular particle shape of the particles, such as a length of 1 to 5 μm and an aspect ratio of 1 to 1.5, results in uniform packing of the particles. Preferably, the particles are highly symmetrical. Preferably, the particles are spherical.

[0028] Secondary particles can be formed by multiple primary particles of the niobium metal oxide of the first aspect. Secondary particles can be referred to as secondary aggregates of primary particles. It is believed that the primary particles are closely held together by NMO amorphous bridges (amorphous bridges) between the primary particles. Therefore, the interparticle distance of the primary particles is very small, making ion diffusion easy. Strong amorphous NMO bridges are also believed to help maintain the morphology of secondary particles at extremely fast charge / discharge rates and in high cycle numbers.

[0029] The highly regular particle shape and packing also allow isotropic lithium intercalation (and deintercalation) during charge and discharge. The uniform particle shape results in consistent coordination between adjacent particles (for example, the coordination number of tightly packed spheres to adjacent particles is 12), which means that lithium intercalation is consistent throughout the bulk material. This leads to excellent high-rate performance.

[0030] The secondary particles have a very high packing efficiency due to their regular particle size, narrow particle size distribution and preferably spherical shape.

[0031] Higher packing efficiency results in greater density in the host material. The packing efficiency of the spheres can be as high as that of an ideal close-packed structure of spherical particles, which has a packing efficiency of approximately 74%. The host material exhibits particularly high density and good packing efficiency when calendered for use as an electrode in an electrochemical cell.

[0032] Higher density (e.g., high rolled density) provides a greater number of lithium intercalation sites per unit volume of the electrode. Thus, the volumetric energy density of the electrode increases as more lithium intercalation sites are present per unit volume.

[0033] Cationic ordered NMO crystal structures and secondary particles are typically not obtainable by high temperature calcination. Instead, a low temperature calcination method has been found to be required.

[0034] Generally, the present invention provides a method for preparing niobium metal oxide secondary particles, the method comprising:

[0035] Providing a precursor mixture of a Nb source and a M source, and

[0036] calcining the precursor mixture at a temperature of 550 to 1,100°C,

[0037] Here, M is a metal other than Nb.

[0038] 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, the method comprising:

[0039] Make Nb oxide and M oxide from NbX a and MY b co-precipitated in solution, and

[0040] Calcination of the precipitate at a temperature of 550 to 1100°C,

[0041] wherein M is selected from Ti, Zr, V, Cr, W and Mo, X and Y are independently one or more counterions, and a and b are independently 2 to 6.

[0042] This method allows the preparation of the NMO phase of the first aspect. The relatively low temperature calcination allows the PC to be partially filled with -Nb-O-Nb-O- chains, thereby providing cationic ordering to the structure.

[0043] The method also allows the preparation of the secondary particles of the second aspect. The secondary particles have a regular, preferably spherical morphology, which is believed to be a result of calcination at a relatively low temperature in the range of 550 to 1100°C, such as in the range of 800 to 900°C. Conventional high temperature calcination (in excess of 1200°C) results in a loss of the spherical morphology.

[0044] Since excellent cation mixing is achieved by precipitation, relatively low temperature calcination is believed to be possible. Co-precipitation of the metal cations results in atomic-scale mixing of the cations in the precipitate. This is in contrast to solid-state milling or mixing methods, in which mixing occurs only at the μm or nm scale. Similarly, co-precipitation (e.g., by heating under solvothermal conditions using microwave heating in a sealed container) results in both niobium oxide and metal (e.g., tungsten) oxide species being simultaneously precipitated into a homogeneous, atomic-scale mixed precipitate. This is in contrast to known solution-based methods, in which precipitation is non-simultaneous and results in a less homogeneous precipitate.

[0045] It is believed that precipitation of NMO from the corresponding salt precursor occurs via hydrolysis. Compared to W salts, Nb salts have a relatively high hydrolysis rate. Therefore, when reacting under ambient conditions, Nb salt hydrolysis occurs more rapidly to form NbO islands, leading to heterogeneity in the reaction mixture. In contrast, using a hydrothermal synthesis method (at elevated temperature and pressure), precipitation via hydrolysis of Nb and W salts occurs simultaneously and more rapidly, improving homogeneity.

[0046] Furthermore, the use of a coprecipitation step allows for the co-preparation of various niobium-metal oxide compounds for various metals such as Ti, Zr, V, Cr, W, and Mo. The thermal coprecipitation step is more chemistry agnostic than chemical precipitation methods that use a precipitating agent to induce precipitation.

[0047] The atomic scale mixing achieved by the inventive 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 metal ion diffusion within the crystallite is required. Therefore, the energy barrier for ion rearrangement is relatively low (and much lower than known solid-state synthesis methods). This allows the use of much lower calcining temperatures, which provides 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.

[0048] The use of lower calcination temperatures offers further advantages in terms of calcination equipment and energy usage. Lower temperature calcination results in lower overall energy requirements. This reduces manufacturing costs and the environmental impact of production. Calcination equipment (e.g., calciner and heat source) can also be made less temperature resistant, thereby reducing equipment costs.

[0049] In a fourth aspect, there is provided a niobium metal oxide secondary particle comprising aggregates of niobium metal oxide primary particles obtained or obtainable by the method of the third aspect.

[0050] In a fifth aspect, a working electrode for an electrochemical cell is provided, the working electrode comprising the niobium metal oxide secondary particle of the second aspect or the fourth aspect.

[0051] In a sixth aspect, there is provided an electrochemical cell comprising the working electrode of the fifth aspect.

[0052] In a further aspect, there is provided a lithium ion battery comprising one or more electrochemical cells of the sixth aspect.

[0053] In a further aspect, there is provided a method of charging or discharging the electrochemical cell of the sixth aspect or a lithium ion battery comprising the electrochemical cell. The method of charging or discharging typically comprises inserting lithium into the working electrode.

[0054] These and other aspects and embodiments of the invention are described in further detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention is described with reference to the drawings listed below.

[0056] Figure 1 The comparative Nb with irregular rod-like morphology prepared by the solid-state synthesis method of Comparative Example 8 is shown. 16 W5O 55 SEM images of the phase.

[0057] Figure 2 SEM images of precipitated NbCl and WCl prepared by the solvothermal method of Example 3 are shown. The images were taken after filtration and drying but before calcination. The images show different levels of magnification—the scale bar in (a) is 20 μm, the scale bar in (b) is 2 μm, and the scale bar in (c) is 1 μm.

[0058] Figure 3 Additional SEM images are shown of precipitated NbCl5 and WCl6 prepared by the solvothermal method of Example 3. The scale bars in (a) and (b) are 10 μm. Figure 3 (cf) show SEM-EDS maps of precipitated NbCl5 and WCl6 prepared by the solvothermal method of Example 3. (c) shows the SEM EDS map of Nb, (d) shows the SEM EDS map of W, (e) shows the SEM EDS map of O, and (f) is a superposition of Nb, W, and O.

[0059] Figure 4 Shown are SEM images at different magnification levels of the NWO product prepared in Example 3 after calcination at 900° C. The scale bar in (a) is 20 μm, the scale bar in (b) is 2 μm, and the scale bar in (c) is 1 μm.

[0060] Figure 5 Shown are transmission electron microscopy (TEM) images at different magnification levels of the mixture of NWO phases prepared in Comparative Example 7. The scale bar in (a) is 10 μm, the scale bar in (b) is 20 μm, and the scale bar in (c) is 50 μm.

[0061] Figure 6 The Nb prepared in Example 3 is shown18 W6O 63 EDS spectrum map (spectrum map).

[0062] Figure 7 It shows that in Example 1 (Nb:W=1, Nb2W2O 11 ), Example 2 (Nb:W=2, Nb 16 W8O 64 ), Example 2.5 (Nb:W=2.5, Nb 10 W4O 37 ) and Example 3 (Nb:W=3, Nb 18 W6O 63 ), which shows a PXRD pattern of NWO prepared in the range of 5 to 80 degrees in 2θ.

[0063] Figure 8 It shows that in Example 1 (Nb:W=1, Nb2W2O 11 ), Example 2 (Nb:W=2, Nb 16 W8O 64 ), Example 2.5 (Nb:W=2.5, Nb 10 W4O 37 ) and Example 3 (Nb:W=3, Nb 18 W6O 63 ), which shows a PXRD pattern of NWO prepared in the range of 5 to 30 degrees in 2θ.

[0064] Figure 9 a shows the PXRD patterns of the NWO phases prepared in Comparative Examples 4, 5, and 6 and Examples 1, 2, 2.5, and 3, which are displayed in the 2θ range of 10 to 80 degrees. Figure 9 b shows the same NWO phase in the 2θ range of 18 to 34 degrees.

[0065] Figure 10 The PXRD of Comparative Example 7 is shown and shows a mixture of NWO phases such as Nb 16 W5O 55 、Nb 14 W3O 44 and Nb2WO8.

[0066] Figure 11 Example 1 (Nb:W=1, Nb2W2O 11 ), Example 2 (Nb:W=2, Nb 16 W8O 64 ) and Example 3 (Nb:W=3, Nb 18 W6O 63 ) is the neutron diffraction pattern of NWO prepared in .

[0067] Figure 12 shows the Nb2W2O prepared in Example 1 11 (a) Rietveld refinement (full spectrum fitting refinement) and (b) crystal structure of (Nb:W=1:1).

[0068] Figure 13 shows the Nb prepared in Example 3 18 W6O 63 (a) Rietveld refinement and (b) crystal structure of (Nb:W=3:1). (c) shows Nb2W2O 11 (Simple TTB unit cell) and Nb 18 W6O 63 The relationship between the crystal structures of the supercell, where Nb2W2O 11 The unit cell of Nb is shown in the upper left, and 18 W6O 63 The supercell is shown in the center.

[0069] Figure 14 It shows that in (a) Example 1 (Nb:W=1, Nb2W2O 11 )、(b) Example 2 (Nb:W=2,Nb 16 W8O 64 ) and (c) Example 3 (Nb:W=3, Nb 18 W6O 63 HR-STEM image of NWO prepared in ). The scale bar is 10 nm.

[0070] Figure 15 Example 3 (Nb:W=3, Nb 18 W6O 63 ) HR-STEM images of NWO prepared in (a) shows the bright spots in HR-STEM, which indicate the Nb 18 W6O 63 Cation ordering in . (b) Includes HRSTEM overlay with the crystal structure. (c) Shows a unit cell of the crystal structure.

[0071] Figure 16 Example 3 (Nb:W=3, Nb 18 W6O 63 ). (a) shows the image of NWO particles before applying a bandgap filter and setting a threshold, and (b) shows the image of NWO particles after applying a bandgap filter and setting a threshold.

[0072] Figure 17AIt is shown that by Example 1 (Nb:W=1, Nb2W2O 11 HAADF-HRSTEM images of NWO particles prepared using a bandgap filter (a) before applying a bandgap filter and setting a threshold, and (b) after applying a bandgap filter and setting a threshold. Scale bar: 5 nm.

[0073] Figure 17B Example 1 (Nb:W=1, Nb2W2O 11 ) was used to analyze the structure of the NWO prepared in FIG. Figure 17B (a) shows the Rietveld fit of 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, where the superposition of the structural model (one unit cell) shows the atomic positions of Nb and W. For clarity, Figure 17B (d) and Figure 17B (e) Nb (red), Figure 17B (f)W(green) and Figure 17B (g) The second unit cell is drawn in the corresponding EDS map of the Nb and W superposition.

[0074] Figure 18 Shows Nb 18 W6O 63 Another HAADF STEM image of (prepared by Example 3). This image has three sections (ac) marked across the atomic plane. For sections (ac), the line intensity spectra of the atoms are shown along different atomic planes in the HAADF STEM image.

[0075] Figure 19A (a) Nb prepared in Example 3 18 W6O 63 Atomic-resolution STEM-EDS images of (a) (scale bar, 5 nm). The upper left image is a STEM image. The lower left image is a STEM-EDS map of Nb, and the lower right image is a STEM-EDS map of W. The upper right image is an overlay of the EDS maps of Nb and W. (b) shows a close-up of the image in (a) (scale bar, 2 nm).

[0076] Figure 19B Shows the results from Nb 18 W6O 63 HR(S)TEM-EDS data of the particles. (a) STEM-HAADF map and corresponding STEM-EDS elemental maps of (b) Nb and (c) W; (d) overlay of the elemental maps of (b) and (c); (e) aligned and accumulated STEM images from the same sample (composed of 1024 frames); decomposed loadings corresponding to (f) Nb and (g) W obtained by NMF. The NMF-based decomposition indicates the positions of the Nb and W atomic columns in the overlay (h) constructed from (f) and (g). All scale bars are 2 nm.

[0077] Figure 20 Shows (a) Nb perpendicular to the c crystallographic axis 16 W8O 64 TEM image of a primary particle and (b) its corresponding fast Fourier transform.

[0078] Figure 21 Shows (a) Nb2W2O 11 TEM image of a primary particle along the c crystallographic axis and (b) its corresponding fast Fourier transform.

[0079] Figure 22 (a) Nb 18 W6O 63 TEM image of a primary particle along the c crystallographic axis and (b) its corresponding fast Fourier transform.

[0080] Figure 23 (a) Nb prepared by FIB (focused ion beam) 18 W6O 63 TEM image of a lamella of secondary particles (Example 3), showing the network of primary particles. Scale bar: 1 μm. Figure 23 (b) shows a close-up of the same TEM image, where the scale bar is 500 nm.

[0081] Figure 24 The capacities of (a) 1C, 2C, 5C, 10C, 20C and 1C, and (b) Example 1 (Nb:W=1, Nb2W2O 11 ) (lower line) and Example 3 (Nb:W=3, Nb 18 W6O 63 ) (Upper line) Long-term cyclability after 1000 cycles at 10C, showing that Example 1 (Nb:W=1, Nb2W2O 11) (lower line) and Example 3 (Nb:W=3, Nb 18 W6O 63 )(upper line) Electrochemical performance of NWO.

[0082] Figure 25 The structural modifications of the ReO3 type structure present in the crystal structure of the present invention are shown. Figure 25 (a) shows the crystallographic shear (CS) or bulk structure, and Figure 25 (b) shows the tetragonal tungsten bronze (TTB) structure observed in the NWO material of the present invention. The different channels are labeled T=triangular, S=square / quadrangular, and P=pentagonal.

[0083] Figure 26 Further electrochemical characterization of the NWO anode of the present invention is shown. Figure 26 (a) Figure 26 (b) and Figure 26 (c) shows the results of Example 1 (NbWO 5.5 ), Example 2 (β-Nb2WO8) and Example 3 (Nb3WO 10.5 ) Constant current discharge and charge curves under different C-rate ranges. Figure 26 (d) shows a rate summary for Examples 1, 2, and 3 based on weight capacity. Figure 26 (e) shows the high rate cycling capacity of Examples 1, 2, and 3 after 1000 cycles at 10C.

[0084] Figure 27 PXRD patterns of Examples 1-3 after calcination at 800° C. for 30 days during thermal stability testing are shown. Figure 27 (a) shows Example 1, Figure 27 (b) shows Example 2, and Figure 27 (c) shows Example 3. Figure 27 (d) shows the superposition of the Bragg positions of Example 3 and the decomposition products.

[0085] Figure 28A SEM images of Example 1 calcined at 800° C. for 30 days are shown at different magnifications.

[0086] Figure 28B The SEM images of Example 2 calcined at 800°C for 30 days at different magnifications are shown. The arrows point to the decomposition product Nb 14 W3O 44 and micron-sized particles of α-Nb2WO8.

[0087] Figure 28CSEM images of Example 2 calcined at 800° C. for 30 days are shown at different magnifications. DETAILED DESCRIPTION

[0088] The present invention generally provides a niobium metal oxide having a crystal structure comprising a tetragonal tungsten bronze having pentagonal channels (PC), wherein a portion of the PC is filled with -Nb-O-Nb-O- chains, and the remaining PC is optionally intercalated with lithium.

[0089] Niobium metal oxides typically have a cationically ordered crystal structure, in which a portion of the PCs are filled with -Nb-O-Nb-O- chains. The remaining PCs are either vacant or intercalated with lithium. PCs are typically arranged in groups of four, interconnected by corner-sharing octahedra.

[0090] In a first aspect of the present invention, there is provided a niobium metal oxide of formula (I)

[0091] Nb x M y O z (I)

[0092] wherein the niobium metal oxide is optionally intercalated with lithium,

[0093] 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

[0094] The crystal structure of niobium metal oxide is a tetragonal tungsten bronze structure with four or eight pentagonal channels per unit cell, and

[0095] A portion of the pentagonal channels is filled with -Nb-O-Nb-O- chains, and the remaining portion of the pentagonal channels is optionally intercalated with lithium.

[0096] Niobium metal oxide phases with a tetragonal tungsten bronze structure have been previously reported, for example, by Sayagués et al. However, the cation ratio and crystal structure of the niobium metal oxide claimed in the present invention have not been reported. Sayagués et al. 12 O 32 The results are described as having a tetragonal tungsten bronze (TTB)-type √2ax√2a superstructure, in which all four pentagonal tunnels surrounding the central square of the octahedron are filled with MO chains. Sayagués et al. do not describe cation ordering. In particular, they do not describe the selective filling of PC with Nb-O chains.

[0097] Sayagués et al. prepared niobium oxide by in situ gas reaction, which is in contrast to the solvothermal and low temperature calcination of the present invention. Sayagués et al. also did not test the prepared NWO as an electrode material.

[0098] 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 known Nb2WO8 phase has a Nb / W ratio of 2, but has the same Nb / W ratio as the present invention. 16 W8O 64 (also with a Nb / W ratio of 2) has a different structure. Nb2WO8 crystallizes in an orthorhombic cell (space group, Pbcm) with a distorted structure, in which the arrangement of PC is different from that of the Nb 16 W8O 64 In addition, the cation sites of Nb2WO8 are disordered, with all sites equally occupied by Nb or W, rather than the ordered cation filling observed in the present invention.

[0099] Furthermore, CN110304658A describes the synthesis of Nb by coprecipitation of Nb and W precursors from ethanol, grinding the precipitate, and calcination. 18 W 16 O 93 Irregular nanoparticles. The precipitation was not carried out under solvothermal conditions or without microwave assisted heating. 18 W 16 O 93 The particles are a mixture of "irregular nanoparticles, spindle-shaped nanospheres and nanorods". The nanoparticles have a size of about 100nm, and the nanorods have a size of 150nm. The nanospheres are secondary particles with a size of 300-400nm and are made of primary particles with a size of 50-200nm. The particles described in CN110304658A are much smaller than the spherical secondary particles of the present invention, which have a length of 1 to 5μm. In addition, the Nb described in CN110304658A is much smaller than the spherical secondary particles of the present invention, which have a length of 1 to 5μm. 18 W 16 O 93 It does not have the specific crystal structure of the present invention, so the morphology of the produced particles is different.

[0100] Xia et al. described the production of Nb by ball milling niobium oxide and tungsten oxide and calcining at 1200 °C. 18 W 16 O 93The coprecipitation and low temperature calcination used in the present invention are not described. Xia et al. showed that shorter calcination times resulted in smaller particles. However, the 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 a well-known ReO3 type structure and not the crystal structure of the present invention.

[0101] The inventors have developed a new niobium metal oxide phase with a specific cationically ordered crystal structure in which pentagonal channels are partially filled with -Nb-O-Nb-O- chains. These phases are prepared by a novel solvothermal coprecipitation and low-temperature calcination method, which facilitates obtaining these new NMO phases and highly spherical secondary particles of these NMO phases. These phases and particles are particularly suitable for use in working electrodes of electrochemical cells (e.g., lithium-ion batteries) and offer excellent volumetric capacity and volumetric energy density, as well as high rate capability and long-term cycling performance.

[0102] Niobium metal oxide

[0103] The present invention provides a niobium metal oxide of formula (I)

[0104] Nb x M y O z (I)

[0105] wherein the niobium metal oxide is optionally intercalated with lithium,

[0106] 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

[0107] The crystal structure of niobium metal oxide is a tetragonal tungsten bronze structure with four or eight pentagonal channels per unit cell, and

[0108] A portion of the pentagonal channels is filled with -Nb-O-Nb-O- chains, and the remaining portion of the pentagonal channels is optionally intercalated with lithium.

[0109] Generally, niobium metal oxide refers to a metal oxide comprising niobium, one or more other metals, and oxygen. Preferably, the niobium metal oxide is a binary metal oxide comprising niobium, one other metal, and oxygen.

[0110] Niobium metal oxide has the formula (I): Nb x M y O z .

[0111] Formula (I) may relate to an NMO phase comprising Nb2O5 and MO3, such as comprising Nb2O5 and WO3.

[0112] NMO comprises niobium and any other suitable metal ("M" in formula (I)), such as a transition metal. The metal may be a Group 3, Group 4, or Group 5 metal, preferably a Group 4 or Group 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.

[0113] The number of moles of Nb in NMO is defined by "x" in formula (I). x is 2 to 18, preferably 8 to 18, more preferably 12 to 18. X can be 2, 16 or 18, preferably 16 or 18, more preferably 18. X is typically an integer.

[0114] The number of moles of M in NMO is defined by "y" in formula (I). y may be from 1 to 18, preferably from 2 to 12, more preferably from 4 to 10, even more preferably from 6 to 8. Preferably, y is 6. Y is typically an integer.

[0115] The number of moles of O in NMO is defined by "z" in formula (I). z is 2.5x + 3y. Thus, z can be 8 to 99, preferably 11 to 70, more preferably 45 to 64, even more preferably 63 to 64. Z is typically an integer.

[0116] 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 may 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, even more preferably 2 and 3, and most preferably x / y is 3. Alternatively, x / y may be selected from 1, 2, and 3, preferably 2 and 3, and even more preferably 3.

[0117] 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 .

[0118] 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 .

[0119] Typically, the niobium metal oxides of the present invention are crystalline materials. In other words, NMOs have an ordered solid-state structure comprising a repeating pattern of ionic positions in three-dimensional space. The smallest repeating structural unit is called a unit cell. The unit cell is repeated (by translation along the major axis of the unit cell) to define the crystal structure.

[0120] The unit cell can be defined in terms of the lengths of the major axes and the angles between the major axes. The unit cell can also be defined in terms of the space group or other symmetries within the unit cell.

[0121] The niobium metal oxide of the present invention has a tetragonal tungsten bronze (TTB)-type crystal structure. TTB is a type of distorted ReO3 structure with lower symmetry than the ReO3 structure. The TTB structure is known for a variety of materials. Similar to the ReO3 crystal structure, TTB comprises corner-sharing MO6 octahedra, and the MO6 octahedra are typically oriented along the crystallographic c-axis.

[0122] 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"). The supercell may be related to the unit cell having space group P4 / mbm. The lattice parameters of the supercell correspond to the diagonals of the unit cell (see Figure 13c ). Thus, when the unit cell has lattice parameter a×a, the supercell has a lattice parameter equal to √2a×√2a. The lattice parameter c can be the same.

[0123] In some embodiments, the crystal structure comprises a unit cell having space group P4 / mbm. In some embodiments, the crystal structure comprises a unit cell having 12 to 12 The parameter a and 3.5 to c, preferably 12.2 to The parameter a and 3.7 to c, more preferably 12.2 to The parameter a and 3.8 to c, even more preferably a parameter of about 12.2 and about Specifically, the crystal structure may have a parameter a of and c is In such embodiments, x / y may be 1. Preferably, the niobium metal oxide is Nb2M2O 11 , such as Nb2W2O 11 .

[0124] In some embodiments, the crystal structure has a supercell having 17 to The parameter √2a and 3.5 to c, preferably 17.2 to The parameter √2a and 3.7 to c, more preferably 17.3 to The parameter √2a and 3.8 to c, even more preferably about The parameter √2a and about Specifically, the crystal structure can have a parameter √2a of and c is In such embodiments, x / y may be 2 or 3. Preferably, the niobium metal oxide is Nb 18 M6O 63 、Nb 10 M4O 37 or Nb 16 M8O 64 , such as Nb 18 W6O 63 、Nb 10 W4O 37 or Nb 16 W8O 64 .

[0125] The TTB structure also includes "channels" through the structure. These channels are oriented perpendicular to the ab planes. The shape of the channels is defined by the edges of the corner-sharing MO6 octahedra. Typically, TTB includes triangular, quadrilateral, and pentagonal channels. The parent ReO3 structure has only quadrilateral channels. Since TTB is a type of twisted ReO3 structure, eight of these quadrilateral channels are twisted to form eight pentagonal channels and eight triangular channels (Hyde et al.).

[0126] In the present invention, the TTB structure includes pentagonal channels (PCs) partially filled with -Nb-O-Nb-O- chains. The TTB structure may include 4 or 8 PCs per unit cell. The TTB also includes 4 or 8 triangular channels per unit cell. The triangular channels are typically unoccupied. The TTB also typically includes quadrilateral channels.

[0127] A portion of the pentagonal channels is filled with -Nb-O-Nb-O- chains. "A portion" means that only some of the pentagonal channels are occupied by -Nb-O-Nb-O- chains. The remainder is unoccupied or optionally intercalated with lithium. Except when reversibly intercalated with lithium, the pentagonal channels are typically not occupied by any metal (e.g., M) from the NMO other than Nb.

[0128] A -Nb-O-Nb-O- chain refers to a chain of -[Nb-O]- repeating units. A -Nb-O-Nb-O- chain includes at least two repeating units, such as 5, 10, 20, 50, 100, 200, or 300 repeating units. The -Nb-O-Nb-O- is located in a PC that is connected to an adjacent unit cell.

[0129] In some embodiments, -Nb-O-Nb-O- chains fill 1 / 3 or more of the PC in the niobium metal oxide. In some embodiments, -Nb-O-Nb-O- chains fill 1 / 2 or less of the PC in the niobium metal oxide. Preferably, -Nb-O-Nb-O- chains fill 1 / 3 to 1 / 2 of the PC. In some embodiments, Nb-O-Nb-O- chains fill about 1 / 3 or about 1 / 2 of the PC.

[0130] For example, in the case of x / y=1 (e.g., NMO is Nb2M2O 11 , such as Nb2W2O 11 ), about 1 / 3 of the PC in the niobium metal oxide is filled with -Nb-O-Nb-O- chains. In the case where x / y=greater than 1, about 1 / 2 of the PC in the niobium metal oxide is filled with -Nb-O-Nb-O- chains. In the case where x / y=2 (e.g., NMO is Nb 16 M8O 64 , such as Nb 16 W8O 64 ), about 1 / 2 of the PC in the niobium metal oxide is filled with -Nb-O-Nb-O- chains. 16 M8O 64 , such as Nb 16 W8O 64 ), about 1 / 2 of the PC in the niobium metal oxide is filled with -Nb-O-Nb-O- chains.

[0131] In some embodiments, when 1 / 2 of the PCs are filled with -Nb-O-Nb-O- chains, two of the four PCs surrounding the 2×2 central bulk of the MO6 octahedron remain unoccupied. Preferably, the PCs are filled with -Nb-O-Nb-O- chains in an orderly manner, such as by alternating PCs. For example, two of the four PCs on the diagonal of the 2×2 central bulk of the MO6 octahedron may be filled. It is believed that the ordering is due to a reduction in cation-cation repulsion.

[0132] Preferably, the crystal structure exhibits cationic ordering. In other words, the occupancy of PC is ordered. Filling PC with only -Nb-O-Nb-O- chains is an example of cationic ordering. Alternating packing of PC (e.g., every other PC is packed around a 2×2 central block of MO6 octahedron) is also an example of cationic ordering.

[0133] The niobium metal oxides of the present invention are capable of intercalating lithium, for example, during cycling of a lithium-ion electrochemical cell. Intercalation of lithium into the niobium metal oxide typically occurs by intercalating Li into the remaining portions of the quadrilateral channels and / or pentagonal channels. In some embodiments, other species may optionally be present in the triangular or quadrilateral channels. Typically, the triangular channels are unoccupied. Preferably, the quadrilateral channels are unoccupied or optionally intercalated with lithium.

[0134] Intercalation typically refers to the reversible insertion of lithium into the crystal structure.

[0135] During lithium insertion, the cations in the niobium metal oxide are reduced. During lithium deinsertion, the cations are oxidized. Depending on the structure and metal composition of the niobium metal oxide, there is a preferential redox of niobium or metal (e.g., tungsten) cations during the insertion process.

[0136] Due to the cation ordering of the -Nb-O-Nb-O- chains of the present invention, cation redox during the intercalation (deintercalation) process results in a more uniform expansion and compression (shrinkage) in the lattice. In other words, due to the cation ordering, redox will occur 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 cations undergoing redox can be in different lattice environments, resulting in less uniform expansion and compression. Together with the 3D tunnel structure, the uniform expansion reduces cracking or other structural defects typically observed in known crystalline shear / bulk structures without cation ordering.

[0137] The TTB structure also includes octahedral sites that form an internal square. The internal square is a square of octahedral sites located within a set of four pentagonal channels interconnected by corner-sharing octahedra (see Figure 15 (the inner square superimposed in the middle).

[0138] The inner square of the octahedral site is usually filled with -MOMO-chains and optionally some Nb defects (wherein, M is as defined in formula (I)). The inner square of the octahedral site is completely or mainly filled with a mixture of -MOMO-chains. When x / y is 3, the inner square of the octahedral site is mainly -MOMO-chains with some Nb defects. This is because when x / y is 3, Nb is slightly excessive. When x / y is 2, the inner square of the octahedral site is only -MOMO-chains.

[0139] Preferably, when M is W, the interior squares of the octahedral sites are typically filled with a mixture of -WOWO- chains and optionally some Nb defects. When x / y is 3, the interior squares of the octahedral sites are primarily -WOWO- chains with some Nb defects. When x / y is 2, the interior squares of the octahedral sites are exclusively -WOWO- chains.

[0140] The TTB structure also includes octahedral sites that form an outer square. The outer square is a square of octahedral sites that are located outside of the four pentagonal channel groups interconnected by corner-sharing octahedra (see Figure 15 outer square superimposed in the middle).

[0141] The outer squares of the octahedral sites are usually filled with -MOMO- chains. Preferably, when M is W, the outer squares of the octahedral sites are filled with -WOWO- chains.

[0142] The TTB structure includes additional octahedral sites that are not part of the inner or outer squares.

[0143] The crystal structure can be characterized using X-ray crystallography, such as powder X-ray crystallography (PXRD).The crystal structure can be characterized by having specific 2θ values ​​in the PXRD diffraction pattern.

[0144] The crystalline structure of the niobium metal oxide can be characterized by a powder x-ray diffraction pattern having two or more 2θ peaks, such as three or more, such as 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°, and wherein the powder X-ray diffraction (PXRD) is measured at a wavelength of Cu-Ka.

[0145] XRPD data can be obtained using any suitable diffractometer, such as a Panalytical Empyrean powder diffractometer. XRPD data can be obtained by exposing NMO samples to Cu-Ka X-ray radiation. Cu-Ka has an energy of 8.04 keV, which corresponds to Details of suitable XRPDs are provided in the Examples section.

[0146] Typically, the 2θ peak is within ±0.2°. Preferably, the 2θ peak is within ±0.1°, more preferably within ±0.05°.

[0147] In some embodiments, the crystal structures of the present invention are characterized by having two or more 2-theta peaks selected from the group consisting of peaks at 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, and 32.60 ± 0.2°.

[0148] In some embodiments, the crystal 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 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°.

[0149] In some embodiments, the crystal 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°.

[0150] In one embodiment, the niobium metal oxide is Nb 18 W6O 63 or Nb 16 W8O 64 , and the crystal structure of the niobium metal oxide has two or more 2θ peaks selected from the group consisting of peaks at 10.17, 22.54, 22.87, 29.96, 26.18, 32.31, 37.80, 32.60, 52.52±0.2°.

[0151] In one embodiment, the niobium metal oxide is Nb 18 W6O 63 , and the crystal structure of the niobium metal oxide has two or more 2θ peaks selected from the group consisting of 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°.

[0152] In one embodiment, the niobium metal oxide is Nb 16 W8O 64 , and the crystal structure of the niobium metal oxide has two or more 2θ peaks selected from the group consisting of 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°.

[0153] In one embodiment, the niobium metal oxide is Nb2W2O 11 , and the crystal structure of the niobium metal oxide has two or more 2θ peaks selected from the group consisting of 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°.

[0154] In general, the 2θ peak decreases with increasing Nb content (eg, higher x / y values) because higher Nb content slightly increases the cation-cation distance in the lattice.

[0155] Typically, all 2θ peaks in the 1:1 (x / y = 1) phase are present in phases with higher Nb:W ratios. When x / y > 1 (e.g., when x / y = 2 or 3), a new peak corresponding to hk0 (where h + k = an odd number) appears. The intensity of this new peak increases with increasing x / y, reaching a maximum intensity at x / y = 3.

[0156] In some embodiments, the crystal structures of the present invention are characterized by having Figure 7 For example, when the niobium metal oxide is Nb 18 W6O 63 When , the crystal structure of the present invention may be characterized by having Figure 7 Alternatively, when the niobium metal oxide is Nb 16 W8O 64 When , the crystal structure of the present invention may be characterized by having Figure 7 For example, when the niobium metal oxide is Nb2W2O 11 When , the crystal structure of the present invention may be characterized by having Figure 7 PXRD (1:1) shown in .

[0157] secondary particles

[0158] The present invention provides niobium metal oxide secondary particles comprising aggregates of primary particles of the niobium metal oxide of the present invention, wherein the secondary particles have a length of 1 to 5 μm and an aspect ratio of 1 to 1.5.

[0159] Secondary particles are typically highly symmetric, i.e., have a high number of symmetric features. Secondary particles can have multiple axes of symmetry and planes of symmetry. High symmetry means that the particles can be efficiently packed (e.g., with a high powder density) and have good interparticle contact between the secondary particles to assist electrode kinetics.

[0160] Preferably, the secondary particle has two perpendicular axes of symmetry, more preferably three perpendicular axes of symmetry. Preferably, the secondary particle has an inversion centre. Preferably, the secondary particle has two perpendicular planes of symmetry, more preferably three perpendicular planes of symmetry.

[0161] The secondary particles are preferably spherical so that the particles resemble the shape of an ideal sphere. Of any three-dimensional object, a sphere has the highest symmetry, with infinite rotation axes and infinite symmetry mirror planes. Therefore, higher sphericity provides excellent stacking efficiency, high stacking density, and good inter-particle contact. The higher the particle sphericity, the closer the stacking efficiency can be to a tightly packed structure (whose stacking efficiency is about 74%). Therefore, when it is rolled as an electrode for an electrochemical cell, the host material can exhibit high density and good stacking efficiency.

[0162] The sphericity of the secondary particles may be 0.95 or higher, preferably 0.96 or higher, more preferably 0.97 or higher, even more preferably 0.98 or higher, yet more preferably 0.99 or higher. As described below, sphericity is a measure of how similar the particle shape is to a perfect sphere.

[0163] Typically, the length of a secondary particle is the longest (largest) dimension of the particle, such as the longest lateral dimension of the particle. Preferably, the secondary particles all have similar lengths so that the length distribution in the particle population is similar. Similar lengths of the particle population further improve the packing of the particles.

[0164] The shape and size of the secondary particles may be obtained using the preparation methods described herein.Thus, the present invention also provides secondary particles obtained or obtainable by the methods of the invention described herein.

[0165] The secondary particles comprise a plurality of primary particles. The primary particles may be formed as a whole. That is, the primary particles are typically composed of NMOs, wherein the ions in the primary particles are held together by strong interactions, such as ionic or covalent interactions, preferably ionic interactions.

[0166] 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 wt.% or more of the niobium metal oxide of the present invention, preferably 85 wt.% or more, 90 wt.% or more, 95 wt.% or more, 97 wt.% or more, 98 wt.% or more, or 99 wt.% 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.

[0167] Preferably, the primary particles are substantially free of impurities.

[0168] The properties of primary particles can be measured in a manner similar to that of secondary particles, as described below. Length, width, aspect ratio, and percentile value can be measured by focused ion beam-scanning electron microscopy (FIB-SEM) and / or the methods described below.

[0169] Typically, the length of the primary particles is 0.1 to 2 μm, preferably 0.2 to 1.5 μm, more preferably 0.3 to 1.0 μm. The width of the primary particles may be 20 to 200 nm, preferably 40 to 150 nm, more preferably 50 to 100 nm. The aspect ratio of the primary particles may be 2 to 20, such as 3 to 18, or 5 to 15. The aspect ratio of the primary particles may be about 10.

[0170] Typically, the shape of the primary particles is less regular than that 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.

[0171] Secondary particles are typically formed by the aggregation of multiple primary particles. Adjacent primary particles tend to be attached by weak interactions, such as intermolecular forces. Weak interactions include long-range ionic interactions and van der Waals forces.

[0172] Preferably, adjacent primary particles are connected by NMO amorphous bridges. The NMO amorphous bridge comprises NbO6, and MO6 and / or MO7 polyhedrons, wherein the cations are covalently bonded to oxygen. The NMO amorphous bridge has an amorphous ionic arrangement (i.e., a non-periodic arrangement). In other words, the NMO amorphous bridge is not crystalline. This can be confirmed by the fast Fourier transform (FFT) performed on the HR-TEM images of the particle ends and the bridges connecting them. The FFT image of the primary particles shows spots due to crystallinity, which are not present in the FFT of the NMO amorphous bridge. This indicates that the bridge connecting the primary particles is amorphous.

[0173] 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 yet 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 graph / data processing to determine the size of the primary and secondary particles, and extrapolating the number of primary particles to determine the total number of primary particles in the secondary particles.

[0174] 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 wt.% or more of the niobium metal oxide of the present invention, preferably 85 wt.% or more, 90 wt.% or more, 95 wt.% or more, 97 wt.% or more, 98 wt.% or more, 99 wt.% or more of the niobium metal oxide of the present invention. In some embodiments, the secondary particles comprise 80 wt.% or more of primary particles of the niobium metal oxide of the present invention, preferably 85 wt.% or more, 90 wt.% or more, 95 wt.% or more, 97 wt.% or more, 98 wt.% or more, 99 wt.% or more of primary particles of the niobium metal oxide of the present invention. Preferably, the secondary particles comprise 99.9 wt.% of the niobium metal oxide of the present invention.

[0175] Preferably, the secondary particles are substantially free of impurities.

[0176] The secondary particles may contain less than 10 wt.% of T-phase Nb2O5, Nb 16 W5O 55 and / or Nb 14 W3O 44 Preferably, the secondary particles do not contain T-phase Nb2O5, Nb 16 W5O 55 and / or Nb 14 W3O 44 .

[0177] The secondary particles may contain less than 10 wt.% T-phase Nb2O5. Preferably, the secondary particles contain less than 5 wt.% T-phase Nb2O5, such as less than 3 wt.%, less than 1 wt.%, less than 0.5 wt.% T-phase Nb2O5. Preferably, the secondary particles do not contain T-phase Nb2O5.

[0178] The secondary particles may contain less than 10 wt.% Nb 16W5O 55 Preferably, the secondary particles contain less than 5 wt.% Nb 16 W5O 55 , such as less than 3 wt.%, less than 1 wt.%, less than 0.5 wt.% Nb 16 W5O 55 Preferably, the secondary particles do not contain T-phase Nb 16 W5O 55 .

[0179] The secondary particles may contain less than 10 wt.% Nb 14 W3O 44 Preferably, the secondary particles contain less than 5 wt.% Nb 14 W3O 44 , such as less than 3 wt.%, less than 1 wt.%, less than 0.5 wt.% Nb 14 W3O 44 Preferably, the secondary particles do not contain T-phase Nb 14 W3O 44 .

[0180] The length of the secondary particles is 1 to 5 μm.

[0181] Typically, the length of a secondary particle is the longest (maximum) dimension of a particle, such as the longest lateral dimension of a particle. The length of a secondary particle is typically the longitudinal length of the particle. Lateral dimension is the observable dimension when viewing the particle from above, such as by SEM, such as in a plan view where the particle appears to be two-dimensional. Length can be the longest dimension measurable from a top view of the particle.

[0182] 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 typically the longitudinal width of the particle. The lateral dimension is the dimension observable when viewing the particle from above, such as by SEM, such as in a plan view where the particle appears to be two-dimensional. The width can be the shortest dimension measurable from a top view of the particle.

[0183] The width of a secondary particle can be the shortest dimension perpendicular to a 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 farthest endpoints of the particle. Width can be the shortest dimension of a secondary particle perpendicular to a line defining the length of the particle. The shortest dimension can also be defined by a line between the nearest endpoints of the particle, where the line is perpendicular to the line defining the length of the particle. In other words, the shortest dimension (width) can be the narrowest part of the particle, which can be connected by a line perpendicular to the line defining the length of the particle.

[0184] The length and width of the 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 running at a 6mm working distance at a 5kV voltage. For EDS maps, a suitable system includes a MIRA3 SEM running at a 15mm working distance at a 30kV voltage. The length and width of the secondary particles can then be analyzed by imaging processing software such as MiraTC. EDS data can be collected using the Aztec software of Oxford instruments. Particle measurements can be performed according to ISO 9276-2:2014.

[0185] 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 measurements taken.

[0186] The secondary particles have a length of 1 to 5 μm. Preferably, the secondary particles have a length of 1.5 μm or longer, more preferably 2 μm or longer, even more preferably 3 μm or longer. Preferably, the secondary particles have a length of 4.5 μm or shorter, more preferably 4 μm or shorter, even more preferably 3 μm or shorter. Preferably, the secondary particles have a length 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 length of the secondary particles is about 3 μm.

[0187] The secondary particles have a width of 1 to 5 μm. Preferably, the secondary particles have a width of 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.

[0188] Typically, the length and / or width of a secondary particle population (e.g., 100 to 1,000 particles measured) provides a normal particle size distribution. Preferably, the secondary particle population has a length and / or width of a unimodal particle size distribution. A unimodal distribution has only one peak in the particle size distribution. In such cases, the peak can correspond to the median average particle length or median average particle width. Particle measurements can be performed according to ISO 9276-2:2014.

[0189] The length percentile values ​​of the secondary particle size distribution, such as D100, D90, D50 and D10, can also be calculated. These values ​​can be calculated based on the particle size distribution of the number of particles and the length of the particles.

[0190] The D100 length is the secondary particle length when 100% of the secondary particles have lengths less than or equal to the D100 particle length.

[0191] The secondary particles may have a D100 length of 10 μm or shorter, preferably 8 μm or shorter, more preferably 6 μm or shorter, even more preferably 5 μm or shorter, still more preferably 4 μm or shorter.

[0192] The D90 length is the secondary particle length at which 90% of the secondary particles have lengths less than or equal to the D90 particle length.

[0193] The secondary particles may have a D90 length of 9 μm or shorter, preferably 8 μm or shorter, more preferably 6 μm or shorter, even more preferably 5 μm or shorter, still more preferably 4 μm or shorter.

[0194] The D50 length is the secondary particle length at which 50% of the secondary particles have lengths less than or equal to the D50 particle length.

[0195] The secondary particles may have a D50 length of 5 μm or less, preferably 4 μm or less, 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, even more preferably about 3 μm.

[0196] The D10 length is the secondary particle length at which 10% of the secondary particles have lengths less than or equal to the D10 particle length.

[0197] The secondary particles may have a D10 length of 0.5 μm or longer, preferably 1 μm or longer, more preferably 2 μm or longer, even more preferably 2.5 μm or longer.

[0198] In some embodiments, the secondary particle population has a low length standard deviation. This indicates a narrow secondary particle size distribution. In some embodiments, the length standard deviation of the particle population 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.

[0199] The aspect ratio is the ratio of the length of a secondary particle to the width of the secondary particle. The definitions and measurements of length and width are as described above, wherein the number of measurements taken for length or width is typically between 100 and 1000. Typically, more than 100 measurements are taken. The length or width is the average of the measurements taken, and the aspect ratio is calculated based on these averages. Therefore, the aspect ratio can be the ratio between the longest dimension of a secondary particle and the shortest dimension of the secondary particle.

[0200] The aspect ratio of the secondary particles is 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 can mean that the longest dimension of the secondary particle is the same as the shortest dimension of the secondary particle. The secondary particles are highly symmetrical. This contributes to the efficient stacking of the secondary particles.

[0201] The sphericity of the secondary particles can be 0.95 or higher, preferably 0.96 or higher, more preferably 0.97 or higher, even more preferably 0.98 or higher, and even more preferably 0.99 or higher. Sphericity is a measure of how similar the shape of a particle is to the shape of an ideal sphere. The sphericity of a particle refers to the ratio of the surface area of ​​a sphere with the same volume as the particle to the surface area of ​​the particle. The sphericity of an ideal sphere is 1. Sphericity can be calculated using the following formula, where V is the volume of the particle and A is the surface area of ​​the particle:

[0202] Sphericity = (π 1 / 3 (6*V) 2 / 3 ) / A

[0203] The volume and surface area of ​​particles can be calculated by any suitable method, such as using the length and width of the particles measured as above. For example, a scanning electron microscope (SEM) can be used. Suitable systems include MIRA3 EM operated at 5kV and 6mm working distance. Then, secondary particles can be analyzed by imaging processing software, such as MiraTC. EDS mapping can use MIRA3 EM operated at 30kV and 15mm working distance, and is analyzed using the Aztec software of Oxford instruments.

[0204] Secondary particles can have a circularity of 0.95 or higher, preferably 0.96 or higher, more preferably 0.97 or higher, even more preferably 0.98 or higher, more preferably 0.99 or higher. The circularity of three-dimensional particles can refer to the circularity of particles when viewed from above. The lateral dimension of particles and the visible area of ​​particles can be used to calculate circularity, and when observing particles from above, such as when observing in a two-dimensional plan view that particles appear, these are observable. Circularity is measurable from the top view of particles, such as when observing particles using a microscope (e.g., SEM).

[0205] Circularity is a measure of how closely a particle's shape resembles a perfect circle. A particle's circularity is the ratio of the circumference of a circle with the same visible area as the particle to the particle's visible area. This can be calculated using the following formula, where A is the particle's visible surface area and P is the particle's circumference.

[0206] Circularity = (4π*A) / P 2

[0207] The number of measurements performed to determine sphericity or roundness is typically between 100 and 1000. Typically, more than 100 measurements are performed. The sphericity or roundness is the average of the measurements performed. Particle measurements can be performed according to ISO 9276-2:2014.

[0208] The secondary particles may have a surface roughness R of 0.05 to 1 μm, preferably 0.08 to 0.5 μm, 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, still more preferably 0.1 μm or less. t .

[0209] Surface roughness is a measure of the variation in the surface profile of a particle. t Is the total height of the profile, which is the total vertical distance (perpendicular to the particle surface) between the maximum profile height (peak) and the minimum profile height (valley) along the profile being 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.

[0210] Preparation method

[0211] Generally, the present invention provides a method for preparing niobium metal oxide secondary particles, the method comprising:

[0212] Providing a precursor mixture of a Nb source and a M source, and

[0213] calcining the precursor mixture at a temperature of 550 to 1,100°C,

[0214] Here, M is a metal other than Nb.

[0215] 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 can 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.

[0216] Therefore, a third aspect of the present invention provides a method for preparing the niobium metal oxide secondary particles according to any one of claims 11 to 16, the method comprising:

[0217] Make Nb oxide and M oxide from NbXa and MY b co-precipitated in solution, and

[0218] Calcination of the precipitate at a temperature of 550 to 1100°C,

[0219] wherein M is selected from Ti, Zr, V, Cr, W, and Mo, X and Y are independently one or more counterions, and a and b are independently 2 to 6.

[0220] In some embodiments, the present invention provides a method for preparing the niobium metal oxide secondary particles of the present invention, the method comprising:

[0221] NbX a and MY b dissolve in a solvent to form a solution;

[0222] Make Nb oxide and M oxide from NbX a and MY b co-precipitated in solution, and

[0223] The precipitate is calcined at a temperature of 550 to 1,100°C,

[0224] wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo, X and Y are independently one or more counterions, and a and b are independently 2 to 6.

[0225] In some embodiments, the present invention provides a method for preparing the niobium metal oxide secondary particles of the present invention, the method comprising:

[0226] NbX a and MY b dissolve in a solvent to form a solution;

[0227] Make Nb oxide and M oxide from NbX a and MY b co-precipitated in the solution,

[0228] separating the precipitate from the solvent, and

[0229] The precipitate is calcined at a temperature of 550 to 1,100°C,

[0230] wherein M is a metal selected from Ti, Zr, V, Cr, W, and Mo, X and Y are independently one or more counterions, and a and b are independently 2 to 6.

[0231] Yu et al. described the preparation of Nb using Nb-oxide and W-oxide precursors. 18 W 16 O 93The two-step hydrothermal method precipitates Nb first, followed by W. Because the precipitation occurs simultaneously, the Nb and W components are poorly mixed, and the precipitate is less uniform. Consequently, the calcined NWO forms "nanorod-shaped" particles, as opposed to the generally spherical secondary particles of the present invention.

[0232] Zhou et al. described a solvothermal method for preparing Nb2WO8 using NbCl5 and WCl6 precursors. Zhou used oxalic acid to induce precipitation. However, the use of a precipitating agent meant that the precipitation of NbCl5 and WCl6 was asynchronous, and the resulting precipitate was less uniform. Consequently, the calcined NWO formed nanorods, in contrast to the secondary particles of the present invention.

[0233] The present invention can use heating under solvent thermal conditions to cause Nb and metal precursor precipitation, and advantageously also provides a highly uniform precursor for preparing secondary particles. The atomic scale mixing achieved by the inventive method means that the two metal ions of the precipitate have a high degree of uniformity. Therefore, the need for metal ion diffusion is largely eliminated, and generally only metal ion diffusion within the crystallite is required. Then, calcination provides highly regular and symmetrical secondary particles of the present invention. The particles are preferably substantially spherical, such as highly spherical.

[0234] Starting materials

[0235] Method for preparing niobium metal oxide using NbX a and MY b As starting material.

[0236] M is any suitable metal other than Nb, such as a transition metal. M can be a Group 3, Group 4, or Group 5 metal, preferably a Group 4 or Group 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, even more preferably W.

[0237] X and Y are independently one or more counterions. In some embodiments, X and Y are independently selected from oxalate, C 1-3 In some embodiments, X and Y are independently selected from oxalate, C 1-3 In other embodiments, X and Y are independently selected from oxalate, C 1-3 Alkoxide, F, Cl and Br.

[0238] In some embodiments, X is not oxygen. In some embodiments, X and Y are not oxygen.

[0239] Oxalate is C2O4 2- . C1-3 Alcohol radical is selected from methanol radical (CH3O - ), ethoxide (CH3CH2O - ), propanol (CH3CH2CH2O- or (CH3)2CHO - ).

[0240] 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.

[0241] Additional positive counterions, such as ammonium (NH4+) or other metal ions, may also be present for charge neutralization.

[0242] The value of each of a and b is independently 2 to 6. Preferably, a and b are 3 to 5, more preferably a is 5 and b is 6.

[0243] In some embodiments, X is selected from F, Cl, and Br, and a is 5. Preferably, NbX a It is NbCl5.

[0244] In some embodiments, Y is selected from F, Cl and Br, and a is 6. Preferably, MY b It is WCl6.

[0245] In some embodiments, NbX a is NbCl5, and MY b It is WCl6.

[0246] In some embodiments, X is oxalate and a is 3. Preferably, NbX a It is niobium oxalate, wherein niobium oxalate is Nb(C2O4)3 - An example source of niobium oxalate is ammonium niobium oxalate, wherein the ammonium niobium oxalate is Nb(C2O4)3(NH4).

[0247] In some embodiments, Y is oxygen and b is 3.5. Preferably, MY b It is metatungstate, where metatungstate is (H 1 / 6 WO 3.5 ) -0.5 This can also be called (H2W 12 O 40 ) -6 An example source of metatungstate is ammonium metatungstate, where ammonium metatungstate is (NH4) 0.5 (H 1 / 6 WO 3.5 ), such as (NH4)6(H2W 12 O40 ).

[0248] In some embodiments, Y is oxygen and b is 3.5. Preferably, MY b Is a paratungstate, wherein paratungstate is (H2W 12 O 42 ) -10 The practical source of paratungstate is ammonium paratungstate, where ammonium paratungstate is (NH4) 0.83 (H 1 / 6 WO 3.5 ), such as (NH4) 10 (H2W 12 O 42 ).

[0249] In some embodiments, NbX a It is niobium oxalate and MY b It is metatungstate or ammonium paratungstate.

[0250] Dissolution step

[0251] The method for preparing niobium metal oxide secondary particles may include: a and MY b Dissolve in a solvent. This can be referred to as the dissolution step.

[0252] Dissolution typically occurs prior to the precipitation step, as described below.

[0253] The solvent can be one that dissolves NbX a and MY b Any suitable solvent can be used. A mixture of solvents can be used. Aqueous solvents such as water can be used. Organic solvents such as alcohols (e.g., C 1-6 alkyl alcohol). 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.

[0254] Typically, when NbX a It is ammonium niobium oxalate and MY b When it is ammonium metatungstate or ammonium paratungstate, the solvent is water.

[0255] NbX a and MY b can be added to the solvent individually or together. The solvent can be stirred to help NbX a and MY b dissolution, such as by stirring or by ultrasound.

[0256] Typically, when all NbX a and MY bDissolution is complete when all of the ions are dissolved in the solvent. This can be determined by any suitable method, such as by visual inspection for clarity of the solution.

[0257] Therefore, the solution usually has NbX completely dissolved in the solvent. a and MY b .

[0258] Precipitation step

[0259] Generally, the method for preparing niobium metal oxide secondary particles comprises the steps of: a and MY b This involves precipitating Nb oxide and M oxide from NbX a and MY b This can be called the precipitation step.

[0260] Coprecipitation refers to the simultaneous precipitation of the two components. The precipitation step is preferably instantaneous coprecipitation, i.e., the precipitation of the two components begins simultaneously. This means that the Nb and M compounds are removed from the solution simultaneously, and the resulting precipitate is a homogeneous mixture of the Nb and M compounds.

[0261] Nb and M are typically 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 oxides are 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).

[0262] The solution can be heated under any suitable pressure required for achieving coprecipitation. This is generally greater than 100 kPa, such as 500 kPa or greater, 1000 kPa or greater, 1500 kPa or greater, or 1800 kPa or greater. The pressure can be less than 5000 kPa, such as 4500 kPa or less, or 4000 kPa or less. The pressure can be 1000 to 5000 kPa, preferably 1500 to 4500 kPa, more preferably 1800 to 4000 kPa.

[0263] The solution can be heated to any suitable temperature required to achieve coprecipitation. This is typically 120 to 200°C. In some embodiments, the solution is heated to a temperature of 120°C or higher, preferably 140°C or higher, 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, 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, more preferably about 150°C.

[0264] The solution is heated for any suitable time required to achieve coprecipitation. The solution may be heated for a sufficient time to achieve 50% or more, preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, yet more preferably 90% or more of NbX a and MY b In some embodiments, substantially all of the NbX a and MY b In some embodiments, the solution is heated for 0.5 to 6 hours, preferably 1 to 3 hours, more preferably about 2 hours. The amount of the precipitate can be determined by mass analysis of the dried precipitate or by suitable spectroscopic analysis of the solution.

[0265] The solution can be heated by any suitable method required to achieve precipitation, such as coprecipitation. Preferably, heating is performed by microwave heating. Heating results in rapid precipitation and coprecipitation 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 and leading to rapid precipitation of the NMO precursor. Compared to traditional heating methods, thermal gradients across the sample are minimized. Therefore, the bulk of the sample can undergo coprecipitation.

[0266] The solution can be heated under solvothermal conditions. Solvothermal conditions refer to heating to a temperature above 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 exceeding 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 exceeding 82.5° C.

[0267] Solvothermal conditions are usually achieved by heating the solution in a sealed container. The sealed container is essentially airtight. The sealed container can be an inert container, such as a ceramic container or a glass container. By heating in a sealed container, as the solvent evaporates into the headspace of the sealed container, the pressure in the container rises. As the partial pressure in the headspace rises, the gradually increasing pressure further increases the boiling point of the solvent. Under solvent thermal conditions, the pressure in the sealed container rises to greater than 1 atmosphere.

[0268] Preferably, no additional reagents are used in the precipitation step. In other words, when the precipitate is heated using the conditions described above, precipitation occurs spontaneously.

[0269] Calcination steps

[0270] The method for preparing niobium metal oxide secondary particles includes calcining the precipitate at a temperature of 550 to 1,100° C. This may be referred to as a calcination step.

[0271] The precipitate may be calcined at a suitable temperature of 550 to 1,100°C to prepare 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.

[0272] In general, it has been found that calcination at these lower temperatures results in a reduction in the surface roughness of the secondary particles. This is advantageous because the smooth and regular particle shape allows for isotropic lithium intercalation (and deintercalation) and very high packing efficiency during charge and discharge.

[0273] The precipitate can be calcined by heating the precipitate at a temperature ramp rate of 1 to 25° C. / min to reach the above target temperature.

[0274] The precipitate may be calcined at the target temperature for 6 to 48 hours, such as 12 to 24 hours. Preferably, the precipitate is calcined at the target temperature for 6 to 12 hours.

[0275] In some embodiments, the precipitate is calcined at 800°C for 12 to 48 hours, such as 12 hours.

[0276] In some embodiments, the precipitate is calcined at 850°C for 6 to 24 hours and then at 900°C for 0.5 to 3 hours, such as at 850°C for 12 hours and then at 900°C for 1.5 hours.

[0277] In some embodiments, the precipitate is calcined at 500 to 900° C. for 6 to 12 hours. 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, and then at 900° C. for 1.5 hours.

[0278] Calcination refers to the heat treatment of solid materials to cause them to undergo a phase change or reaction. Calcination can occur in the presence of air.

[0279] The precipitate is typically transferred to a heat-resistant container, such as a ceramic crucible for calcination.

[0280] Calcination can occur as a batch or continuous process.

[0281] Separation steps

[0282] The method for preparing niobium metal oxide secondary particles may further include separating the precipitate from the solvent. This may be referred to as a separation step.

[0283] The separation step typically occurs after the precipitation step and before the calcination step, as described above.

[0284] Separation can be achieved by any suitable method, such as by filtration, washing, and drying (such as spray drying or spray pyrolysis), among others.

[0285] In some embodiments, the isolating step comprises separating the precipitate from the organic solvent by filtration. Filtration can be achieved under vacuum, for example using a Buchner funnel.

[0286] In some embodiments, the separation step comprises separating the precipitate from the organic solvent by washing the precipitate with an 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 previous step. When a different washing solvent is used, it can be a washing solvent that forms an azeotrope with the organic solvent. For example, ethanol can be used as the washing solvent.

[0287] In some embodiments, the separation 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 during the calcining step due to heating. In other words, the separation step can occur as part of the calcining step.

[0288] In some embodiments, the separation 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 spray pyrolysis.

[0289] Spray drying typically dries a suspension of precipitate by atomizing the slurry and drying the atomized slurry with hot gases. The hot gases evaporate the solvent, leaving behind a precipitate. Spray pyrolysis typically dries a suspension or solution by spraying onto a heated substrate (e.g., a surface), where the heated substrate aids drying by evaporating the solvent. Spray drying and spray pyrolysis can provide precipitate particles with regular and small sizes, which can be well-suited for calcination.

[0290] Working electrode

[0291] 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 the niobium metal oxide of the first aspect of the present invention, such as secondary particles of the niobium metal oxide of the first aspect.

[0292] In a fourth aspect, the present invention provides a working electrode for an electrochemical cell, the working electrode comprising the niobium metal oxide secondary particles of the second aspect of the present invention.

[0293] The working electrode is electrically conductive and can be electrically connected to a counter electrode, such as within an electrochemical cell.

[0294] During the discharge step, for example in a lithium ion battery, the working electrode can be the anode or the cathode. Typically, during the discharge step, the working electrode is the anode.

[0295] 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 bulk of the working electrode. Preferably, the working electrode comprises 50 wt.% or more of the niobium metal oxide secondary particles, more preferably 60 wt.% or more, even more preferably 70 wt.% or more, and even more preferably 80 wt.% or more of the niobium metal oxide secondary particles, based on the total weight of the working electrode. The working electrode may consist essentially of the niobium metal oxide secondary particles.

[0296] Optionally, the working electrode comprises a mixture of niobium metal oxide secondary particles and an additional active material.

[0297] The additional active material may be another metal oxide. For example, the working electrode may include a mixture of niobium metal oxide secondary particles and an additional active material selected from lithium titanate (LTO; Li4Ti5O 12 ), titanium niobium oxide (such as TiNb2O7), titanium tantalum oxide (such as TiTa2O7), tantalum molybdenum oxide (such as Ta8W9O 47 ), niobium molybdenum oxides (such as Nb2Mo3O 14 ) and niobium tungsten oxides (such as Nb 16 W5O 55 、Nb 18 W8O 69 、Nb2WO8、Nb 18 W 16 O 93 or Nb 22 W 20 O 115 ).

[0298] Another 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 manufacture while maintaining the beneficial properties described above.

[0299] When the working electrode includes niobium metal oxide secondary particles and additional active materials, the working electrode preferably includes 50 wt.% or more of niobium metal oxide secondary particles based on the total weight of the active material, more preferably 60 wt.% or more, even more preferably 70 wt.% or more, and still more preferably 80 wt.% or more of niobium metal oxide secondary particles.

[0300] In some embodiments, the working electrode comprises 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 surface of the niobium metal oxide secondary particle is the surface that contacts the electrolyte in a typical electrochemical cell. In some such embodiments, the working electrode may include a layer of niobium metal oxide secondary particles disposed on a secondary active electrode material. The secondary active electrode material is different from the surface material. The layer of niobium metal oxide secondary particles may be a coating on the secondary active electrode material.

[0301] The secondary active electrode material may be selected from carbon, silicon or metal oxides. The secondary active electrode material may be selected from graphite, reduced graphite oxide or carbon black. The secondary active electrode material may be Ketjen black or Super P carbon, or hard or soft amorphous carbon. The secondary active electrode material may be selected from lithium titanate (LTO; Li4Ti5O 12 ), titanium tantalum oxide (such as TiTa2O7) or tantalum molybdenum oxide (such as Ta8W9O 47 ).

[0302] The thickness of the niobium metal oxide secondary particle layer can be known from 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 can have a maximum thickness of 10 μm or less, for example, a maximum thickness of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less. The niobium metal oxide secondary particle layer can have a minimum thickness of 0.5 μm or greater, for example, a minimum thickness of 1 μm or greater, 2 μm or greater, 5 μm or greater, or 10 μm or greater. The thickness of the niobium metal oxide secondary particles can be within a range selected from the maximum and minimum amounts given above.

[0303] The niobium metal oxide secondary particle layer can be directly disposed on the secondary active electrode material, or an intermediate layer of active material can exist 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 conductive additive, a binder, or a current collector.

[0304] The working electrode may include a conductive carbon material to improve electrical conductivity. The conductive carbon may be mixed with secondary particles, secondary active electrode materials, 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 fibers, and / or carbon nanotubes. Based on the gross weight of the working electrode, the working electrode typically comprises 2 to 20 wt.% conductive carbon, preferably 5 to 15 wt.%, more preferably 8 to 12 wt.%, even more preferably about 10 wt.% conductive carbon.

[0305] The working electrode may include a binder to improve the adhesion of the electrode material to the current collecting surface. The binder may 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. Examples of typical binders are PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR and copolymers thereof. Based on the total weight of the working electrode, the working electrode typically contains 2 to 20 wt.% of a binder, preferably 5 to 15 wt.%, more preferably 8 to 12 wt.%, even more preferably about 10 wt.% of a binder. Preferably, the binder is PVDF and / or CMC.

[0306] The working electrode can have any suitable density. High density can be achieved by the excellent packing properties of the niobium metal oxide secondary particles of the present invention. Areal loading can indicate the density of the niobium metal oxide.

[0307] The working electrode may have any suitable areal loading of niobium metal oxide secondary particles as the active material. Typically, the areal loading is 1 to 20 mg·cm- 2 , preferably 2 to 10 mg·cm- 2 , more preferably 3 to 8 mg·cm- 2 , and more preferably 5 to 7 mg·cm- 2 The surface loading can be about 6 mg·cm- 2 Alternatively, the areal loading may be lower, such as about 2 mg·cm- 2 .

[0308] The working electrode is typically affixed to a current collector, such as a copper or aluminum current collector, which may be in the form of a plate.

[0309] The present inventors have evaluated the active material containing Nb2W2O in a mass ratio of active material / carbon / binder of 8:1:1. 11 、Nb 18 W6O 63 and Nb 16 W8O 64The working electrode is composed of spherical secondary particles, conductive carbon (super P, TIMCAL), and binder (PVDF, Kynar), and the active material loading is 2 mg·cm- 2 , the electrode area is 1.27cm 2 , with a Li metal counter electrode in a 2032-type coin cell geometry, and using 1.0 M LiPF6 in ethylene carbonate / dimethyl carbonate (1:1 v / v) as the electrolyte.

[0310] The present inventors have found that the inclusion of Nb 18 W6O 63 The present inventors have found that the battery cell containing spherical secondary particles as active material loses about 4% of discharge capacity after 1,000 cycles at 10C rate. 11 A battery cell with spherical secondary particles as active material cycling 1000 times at a 10C rate resulted in a discharge capacity loss of approximately 15%.

[0311] electrochemical cell

[0312] The present invention provides an electrochemical cell comprising a working electrode of the present invention. Preferably, the electrochemical cell comprises a counter electrode, an electrolyte and a working electrode of the present invention.

[0313] The present invention also provides a lithium-ion battery comprising one or more electrochemical cells of the present invention.

[0314] During the discharge step, for example in a lithium ion battery, the working electrode of the present invention can be the anode or the cathode. Typically, during the discharge step, the working electrode is the anode.

[0315] An electrochemical cell typically includes a counter electrode and an electrolyte. The electrochemical cell may include a current collecting plate. The electrochemical cell may be electrically connected to a power source. The electrochemical cell may be electrically connected to a measuring device, such as an ammeter or voltmeter.

[0316] The electrochemical cell may be a lithium-ion cell. A lithium-ion cell generally comprises a working electrode of the present invention, a lithium-containing counter electrode or a lithium-intercalating counter electrode, an electrolyte, and a separator. The electrolyte is suitable for dissolving lithium ions, and the separator is permeable to lithium ions.

[0317] During the discharge step, for example in a lithium ion battery, the counter electrode can be an anode or a cathode. During the discharge step, the counter electrode is typically a cathode.

[0318] Suitable cathode materials include lithium-containing or lithium-intercalating materials such as lithium metal oxides, wherein 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 (LiCoO2), lithium nickel manganese cobalt oxide (NMC, LiNiMnCoO2, such as LiNi 0.6 Co 0.2 Mn 0.2 O2), lithium vanadium fluorophosphate (LiVPO4F), lithium nickel cobalt aluminate (NCA, LiNiCoAlO2), lithium iron phosphate (LFP, LiFePO4) and manganese-based spinel (e.g., LiMn2O4). Preferably, the cathode electrode material is LCO, NCA, or NMC (e.g., NMC-811).

[0319] The counter electrode may include a conductive carbon material to improve electrical conductivity. The conductive carbon material may be carbon black, graphite, nanoparticle carbon powder, carbon fiber and / or carbon nanotube.

[0320] The counter electrode may contain a binder to improve the adhesion of the active material to the current collecting surface. Examples of typical binders are PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR and copolymers thereof.

[0321] The counter electrode is typically secured to a current collector, such as a copper or aluminum current collector, which may be in the form of a plate.

[0322] Typically, the electrolyte in an electrochemical cell is suitable for dissolving lithium ions. Typically, the electrolyte in the charge and discharge cell contains lithium ions. Typically, the electrolyte comprises a lithium salt such as LiTFSI, (lithium bis(trifluoromethane)sulfonyl imide, LiPF6, LiBF4, LiClO4, LiTF (lithium trifluoromethanesulfonate), or lithium bis(oxalato)borate (LiBOB).

[0323] The electrolyte may be a liquid electrolyte, such as a liquid at ambient temperature, for example a liquid at 25° C. Preferred electrolytes are stable at elevated and decreased temperatures.

[0324] 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.

[0325] Suitable solvents include carbonate solvents. For example, 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), methylpropyl carbonate (MPC), and ethylpropyl carbonate (EPC).

[0326] Suitable solvents also include sulfone solvents. For example, 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), vinylidene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2-chlorophenyl 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, sultone (for example, 1,3-propane sultone) and sulfone solvents containing ether groups (for example, 2-methoxyethyl (methyl) sulfone and 2-methoxyethoxyethyl (ethyl) sulfone).

[0327] Suitable solvents also include silicon-containing solvents such as siloxanes or silanes. For example, hexamethyldisiloxane (HMDS), 1,3-divinyltetramethyldisiloxane, polysiloxanes, and polysiloxane-polyoxyalkylenederivatives. Some examples of silane solvents include methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane.

[0328] The electrolyte may contain additives to improve performance, 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 carbonate, α-bromo-γ-butyrolactone, methyl chloroformate, 1,3-propane sultone, vinyl sulfite (ES), propylene sulfite (PS), vinyl vinyl sulfite (VES), fluoroethylene sulfite (FES), 12-crown-4 ether, carbon dioxide (CO2), sulfur dioxide (SO2), and sulfur trioxide (SO3).

[0329] The electrochemical cell may also include a solid porous membrane located between the negative electrode and the positive electrode. The solid porous membrane may 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., titanium dioxide, zirconium oxide, yttrium oxide, hafnium oxide, or niobium oxide) or a main group metal oxide, such as silicon oxide, which may be in the form of glass fiber. The membrane is typically selectively permeable to the charge-carrying ions (e.g., lithium ions) of the cell. That is, the membrane is a selective membrane that is selectively porous to lithium ions.

[0330] Solid non-porous membranes may comprise lithium ion conductors such as LLZO (garnet family), LSPO (Lisicon family), LGPS (sulfo-Lisicon family), LATP / LAGP (Nasicon family), LLTO (perovskite family), and phosphide / sulfide glass-ceramics.

[0331] The electrochemical cells may be provided in any suitable form, such as button cell, pouch cell, prismatic cell, or cylindrical cell form.

[0332] Battery

[0333] 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.

[0334] Where a plurality of battery cells are present, these battery cells may be arranged in series or in parallel.

[0335] The battery of the present invention may be provided in a road vehicle, such as a car, a moped or a truck. Alternatively, the battery of the present invention may be provided in a rail vehicle, such as a train or a tram. The battery of the present invention may also be provided in an electric bicycle (electric vehicle), an unmanned aerial vehicle, an electric aircraft and an electric or hybrid boat. Similarly, the battery of the present invention may be provided in an electric tool such as an electric drill or saw, a garden tool such as a lawn mower or a lawn trimmer, or a household appliance such as a toothbrush or a hair dryer. The battery of the present invention may be provided in a regenerative braking system. The battery of the present invention may be provided in a portable electronic device, such as a mobile phone, a laptop or a tablet computer. The battery of the present invention may be provided in a power grid management system, an emergency backup system, a power pack or a remote charging system.

[0336] Charging or discharging process

[0337] In a further aspect, there is provided a method of charging or discharging the electrochemical cell of the sixth aspect or a lithium ion battery comprising the electrochemical cell.

[0338] The charging or discharging process generally involves inserting lithium into the working electrode. The lithium can reduce or oxidize niobium or a metal, preferably niobium, during the (or de)insertion process.

[0339] Typically, lithium is intercalated into pentagonal channels and / or quadrilateral channels in the NMO crystal structure. Preferably, lithium is intercalated into pentagonal channels adjacent to PC filled with -Nb-O-Nb-O- chains.

[0340] definition

[0341] The following common definitions are used in this article, as determined by the relevant context.

[0342] CS: Crystallographic Shear

[0343] NMO: Niobium Metal Oxide

[0344] NWO: Niobium Tungsten Oxide

[0345] PC: Pentagonal Channel

[0346] TTB: Tetragonal Tungsten Bronze

[0347] As is common in the art, reference is made to Li + / Li to obtain the voltage values ​​described in this article.

[0348] 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 maximum capacity, for example, 10 C corresponds to a discharge or charge time of 6 minutes. The maximum capacity can be a theoretical maximum capacity or an empirically determined maximum capacity. For example, the theoretical maximum capacity can be defined relative to one electron transferred per transition metal atom in the active electrode material.

[0349] High charge and discharge rates may also be described by reference to the (gravimetric) current density relative to the weight of the electrode active material.

[0350] As used herein, "wt. %" refers to % calculated on a weight basis.

[0351] As used herein, "V / V" refers to a ratio calculated on a volume basis.

[0352] Other preferences

[0353] Every compatible combination of the embodiments described above is expressly disclosed herein, as if each combination were individually and explicitly listed.

[0354] Various other aspects and embodiments of the present invention will be apparent to those skilled in the art upon reference to this disclosure.

[0355] As used herein, "and / or" will be taken as specific disclosure of each of the two specified features or components, with or without the other. For example, "A and / or B" will be taken as specific disclosure of each of (i) A, (ii) B, and (iii) A and B, as if each instance were individually set forth herein.

[0356] Unless the context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments described.

[0357] Certain aspects and embodiments of the present invention will now be described by way of example and with reference to the above-mentioned figures.

[0358] Example

[0359] The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the present invention.

[0360] 1.1 Preparation of NWO Phase – Changing the Nb:W Ratio

[0361] Niobium metal oxide bronze phase was prepared by solvothermal synthesis.

[0362] 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 to confirm complete dissolution of the NbCl₅ and WCl₆. As shown in Table 1, the Nb:W molar ratio was varied by adding varying amounts of NbCl₅ and WCl₆. The amounts shown are for a 1 g scale.

[0363] Table 1 - Nb:W ratio and amount

[0364] Example Nb:W ratio <![CDATA[Mass (g) of NbCl5]]> <![CDATA[Mass (g) of WCl6]]> Example 1 1:1 0.74071 1.087217 Example 2 2:1 1.085783 0.796858 Example 2.5 2.5:1 1.197344 0.702986 Example 3 3:1 1.28539 0.6289 Comparative Example 4 4:1 1.415501 0.519419 Comparative Example 5 5:1 1.507028 0.442404 Comparative Example 6 1:0 2.032798 0

[0365] The solution was transferred to an 80 ml (maximum capacity 50 ml) Teflon reaction vessel made of PTFE (Anton Paar) and then placed in an alumina jacket (Anton Paar). A magnetic stir bar was added to the vessel. 20 ml of ethanol solution was used, and when sealed, the vessel had approximately 60 ml of headspace.

[0366] The vessel was then sealed and heated at 150° C. in a 1500 W microwave reactor (Anton Paar, MultiwavePro) under solvothermal conditions with constant stirring for 2 hours. The heating rate was 5° C. / min. Due to the volume of the reaction vessel, the pressure was maintained in the range of 18 to 40 bar (1800 kPa to 4000 kPa) during heating.

[0367] Precipitate NbCl5 and WCl6 from the ethanol solvent. Visually confirm precipitation—a white precipitate forms and separates from the supernatant. Allow the sample to cool to room temperature in the reaction vessel. Then, release the pressure before opening the vessel and separate the sample by filtration.

[0368] The solution was filtered using a Buchner funnel to remove the solvent. The precipitate was washed in ethanol (3 times). The precipitate was then kept dry at 65°C for 12 hours to remove any traces of solvent, leaving a dry precipitate.

[0369] The dried precipitate was then added to an alumina crucible and calcined in an oven at 850° C. for 12 hours and then at 900° C. for 1.5 hours to provide a niobium metal oxide bronze phase. The calcinations were performed in air at ambient pressure.

[0370] Example 1 results in the formation of Nb2W2O 11 .

[0371] Example 2 leads to the formation of Nb 16 W8O 64 .

[0372] Example 2.5 leads to the formation of Nb 10 W4O 37 .

[0373] Example 3 leads to the formation of Nb 18 W6O 63 .

[0374] Comparative Examples 4 and 5 resulted in the formation of Nb 18 W6O 63 and a mixture of T-phase Nb2O5.

[0375] Comparative Example 6 resulted in the formation of T-phase Nb2O5.

[0376] 1.2-Preparation of NWO phase – changing temperature

[0377] Comparative Example 7 was prepared by solvothermal synthesis in the same manner as Example 3 in Section 1.1 above. Comparative Example 7 had a Nb:W ratio of 3:1.

[0378] However, Comparative Example 7 was calcined in an oven at 1200°C for 12 hours (as opposed to 900°C for Example 3).

[0379] Comparative Example 7 resulted in the formation of Nb 16 W5O 55 、Nb 14 W3O 44 and a mixture of Nb2WO8.

[0380] 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 Nb2O5 and WO2 together and then calcining the mixture at 1200°C.

[0381] Comparative Example 8 resulted in the formation of Nb 16 W5O 55 .

[0382] 1.3-Alternative preparation of NWO phase

[0383] Examples 1a, 2a, 3a, 4a and 5b were synthesized as above for Examples 1, 2, 3, 4 and 5, except that Examples 1a, 2a, 3a, 4a and 5b were calcined at 800°C.

[0384] Examples 2a, 3a, 4a and 5a were found to have similar crystal structures as Examples 2, 3, 4 and 5, despite the slightly lower calcination temperature.

[0385] 2.1-Microscopic characterization of NWO particles

[0386] Scanning electron microscopy (SEM) was used to examine the morphology of the dried precipitate and the calcined NWO phase. SEM samples were prepared by sprinkling the powders of the examples onto carbon tape placed on a SEM stub. SEM was performed using a Tescan MIRA3 at a voltage of 5 kV and an operating distance of 6 mm. Images were recorded using MiraTC software.

[0387] The SEM image of the precipitate of Example 3 (after filtration and drying, but before calcination) is as follows: Figure 2 (ac) and Figure 3 (ab) The precipitate is amorphous. The SEM images show a spherical morphology, where the primary particle diameter is 1-5 μm (see Figure 2 c). Primary particles aggregate in random, irregular clusters with a diameter of approximately 20 μm (see Figure 2 a).

[0388] Energy dispersive X-ray spectroscopy (EDS) was also performed on the precipitate of Example 3 and superimposed 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 were collected using Aztec software from Oxford Instruments.

[0389] The SEM-EDS mapping of the precipitate of Example 3 (after filtration and drying, but before calcination) is shown in FIG. Figure 3 (cf).

[0390] Nb( Figure 3 c) W( Figure 3 d) and O( Figure 3 The EDS image in e) shows the homogeneous distribution of Nb, W, and O atoms within each precipitate particle. Figure 3 This is also evidenced by the uniform colors of all Nb, W, and O layer diagrams in f.

[0391] It is believed that the highly homogeneous 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 through the precursor crystallites. Consequently, the energy barrier for atomic migration and rearrangement is lower, meaning that lower temperatures can be used during calcination. All phases of Examples 1-3 exhibit identical morphologies.

[0392] The SEM image of the NWO phase (after calcination) prepared in Example 3 is as follows: Figure 4 (ac) The NWO phase of the embodiment shows a spherical morphology in the form of spherical secondary particles (see Figure 4 c).

[0393] The spherical secondary particles have a diameter of approximately 2-3 μm and have an aspect ratio close to unity. The particles have a high sphericity of approximately 0.95 or higher. The surface roughness of the particles appears low because the primary particles form compacted, tightly packed aggregates.

[0394] The primary particles that make up the secondary particles are much smaller and more irregular in shape. The length of the primary particles is in the range of about 0.2 to 1 μm, and the width is in the range of about 50 to 100 nm. The primary particles are rod-shaped.

[0395] The transmission electron microscope (TEM) image of the NWO phase prepared in Comparative Example 7 is as follows: Figure 5 High-resolution EDS data were acquired from NWO oxide particles using a JEOL ARM200F (Cs-corrected) transmission electron microscope in STEM mode at 200 kV.

[0396] Calcination at a higher temperature of 1,200°C (compared to 900°C in Example 3) resulted in a change in particle morphology. TEM images showed rod-shaped primary particles that aggregated into irregularly shaped secondary particles.

[0397] Both the primary particles and the secondary particles of Comparative Example 7 had low sphericity and high surface roughness compared to the particles of Example 3. Therefore, the stacking efficiency of Comparative Example 7 was reduced.

[0398] The Nb prepared in Comparative Example 8 was also prepared. 16 W5O 55 The SEM image shows the irregular rod-like morphology of the particles (see Figure 1 ).

[0399] 2.2-XRD characterization of NWO phase

[0400] The Nb prepared in Example 3 18 W6O 63 Energy dispersive X-ray spectroscopy (EDS) was performed (see Figure 6 ).

[0401] Atomic-resolution STEM-EDS datasets were acquired under low-dose conditions to minimize electron beam damage to the specimen: dwell time = 0.01 ms, spot size = 6°C, aperture size = 20 μm, and beam current = 18 pA. Given the low beam current and the resulting relatively low intensity of X-rays emitted from the specimen, multiple frames of STEM-EDS data were acquired. Each dataset typically consisted of 500–1000 frames, which were then aligned and processed using HyperSpy, a Python-based multidimensional data analysis toolbox. The aligned maps and spectra were then summed over the entire dataset, and principal component analysis (PCA) and nonnegative matrix factorization (NMF) were used to reduce data noise and improve the signal-to-noise ratio (SNR).

[0402] The EDS patterns reveal a novel order of Nb and W cations in the TTB lattice, especially the presence of -Nb-O-Nb-O- chains in PC and -WOWO- chains in the inner and outer squares of the octahedral sites.

[0403] Powder X-ray diffraction (PXRD) was performed on the NWO phases of Examples 1-6, and the diffraction patterns were as follows: Figure 7 、 Figure 8 and Figure 9 (ab) shown.

[0404] The wavelength used is PXRD was performed using Cu K-α light. Kβ radiation was filtered using a nickel filter placed before the detector. XRPD data were obtained using a Panalytical Empyrean powder diffractometer by exposing the NMO samples to Cu-Kα X-ray radiation. Variable temperature (VT) measurements were performed using an XRK900 (Anton Paar) reactor chamber as an accessory. The samples were tightly packed on a glass plate placed on a rotating sample stage. Data were recorded in the range of 2-100° 2θ (step size of 0.008° 2θ, counting time of 457.2s step- 1 ). Cu-Kα radiation was generated by applying a 40 kV potential to the Cu anode at a current of 40 mA.

[0405] The PXRD patterns of NWO prepared in Examples 1, 2, 2.5 and 3 with different Nb:W ratios showed reflections with similar 2θ values ​​(see Figure 7 ). This indicates that all materials have a common crystal structure.

[0406] In the PXRD patterns of NWO prepared in Examples 1, 2, 2.5 and 3, the reflections in the 2θ range of 5 to 30 degrees are as follows: Figure 8 The reflections are marked on the PXRD pattern.

[0407] For Example 1 (Nb2W2O 11 The observed 2θ values ​​and the corresponding d spacings and hkl indices are shown in Table 2A. The top 10 most intense 2θ peaks for Example 1 are shown in Table 2B.

[0408] Table 2A - Example 1 (Nb2W2O 11 )

[0409]

[0410]

[0411] Table 2B - Example 1 (Nb2W2O 11 )

[0412]

[0413] The observed 16 W8O 64 The 2θ values ​​of Example 2 and the corresponding d spacings and hkl indices are shown in Table 3A. The top 10 strongest 2θ peaks of Example 2 are shown in Table 3B.

[0414] Table 3A - Example 2 (Nb 16 W8O 64 )

[0415]

[0416]

[0417]

[0418] Table 3B - Example 2 (Nb 16 W8O 64 )

[0419]

[0420] The observed 18 W6O 63 The 2θ values ​​of Example 3 and the corresponding d spacings and hkl indices are shown in Table 4A. The top 10 strongest 2θ peaks of Example 3 are shown in Table 4B.

[0421] Table 4A - Example 3 (Nb 18 W6O 63 )

[0422]

[0423]

[0424]

[0425] Table 4B - Example 3 (Nb 18 W6O 63 )

[0426]

[0427]

[0428] The PXRD patterns of NWO prepared in Comparative Examples 4, 5 and 6 and Examples 1, 2, 2.5 and 3 are shown in FIG. Figure 9 a and Figure 9 As shown in b. Figure 9 b shows reflections ranging from 5 to 30 degrees in 2θ.

[0429] Comparative Examples 4, 5 and 6 show T-phase Nb2O5 and Nb 18 W6O 63 Additional reflections around 27° and 28° appeared in Examples 4-6, but not in Examples 1, 2, 2.5, and 3. These reflections are believed to be due to the presence of T-phase Nb2O5.

[0430] The comparative NWO phase has an XRD pattern with different XRD peaks from the present invention. 16 W5O 55 (See Roth et al.), Nb 14 W3O 44 Reference XRD patterns of Nb2WO8 (see Roth et al.) and Nb2WO8 (see Lundberg).

[0431] This indicates that the excess Nb present in the solutions of Comparative Examples 4, 5 and 6 precipitated as T-phase Nb2O5 during the calcination process.

[0432] The PXRD of Comparative Example 7 was performed, and the diffraction pattern was as follows: Figure 10 shown.

[0433] The PXRD of Comparative Example 7 showed the presence of a mixture of NWO phases, such as Nb 16 W5O 55 、Nb 14 W3O 44 、Nb 12 WO 33 and Nb2WO8. The relative intensity of the 2θ values ​​was used to calculate the relative intensity of each NWO phase with 58.8% (Nb 16 W5O 55 )、26.0%(Nb 14 W3O 44 ) and 15.2% (Nb2WO8) are present.

[0434] These phases do not have the crystal structure of the present invention. 16 W5O 55 、Nb 14 W3O 44 and Nb 12 WO 33 The phase has a block structure, where the block sizes are 5×4, 4×4, and 4×3 (see 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 lacks the cation ordering observed in the examples of the present invention. In Nb2WO8, PC is randomly occupied by Nb or W, whereas in the present invention, PC is populated exclusively with -Nb-O-Nb-O- chains to provide greater cation ordering.

[0435] Such structural differences can be confirmed by PXRD using pattern matching, for example, by performing a multiphase Rietveld refinement on all phases to fit the intensities of all peaks in the PXRD patterns.

[0436] It is believed that higher temperature calcinations lead to the formation of these more thermodynamically stable crystal structures. However, as shown in the SEM images discussed above (see Figure 5 ), the morphology of these crystals is highly irregular compared to the spherical secondary particles of Examples 1 to 3. It is believed that the formation of large irregularly shaped rods at such high temperatures is due to the crystal growth of these more thermodynamically stable crystal structures.

[0437] Neutron diffraction of the NWO phases of Examples 1, 2 and 3 was performed, and the diffraction patterns were as follows: Figure 11 shown.

[0438] The phases of Examples 1, 2 and 3 are all The peak corresponding to the 001 reflection is shown at The peak corresponding to the 210 reflection is shown at A peak corresponding to the 210 reflection is shown at .

[0439] The phases of Examples 2 and 3 are at the reflections corresponding to 210 and 010. and A stronger peak is shown. The peak at is attributed to the a-parameter of the supercell, as explained below.

[0440] 2.3-Crystallographic analysis

[0441] The XRD and neutron diffraction patterns of the materials of Examples 1, 2 and 3 (shown above) were analyzed using Rietveld refinement and the crystal structures were characterized. The structures were further confirmed using HR-STEM EDS studies as described above.

[0442] Example 1 (Nb2W2O 11 ) in space group Medium crystallization (Figure 12).

[0443] By the same method as in Example 2 (Nb 16 W8O 64 ), the Nb:W ratio was increased to 2:1, and a new reflection family hk0 was observed in PXRD, where h+k=odd number ( 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. The intensities of these reflections increase with increasing Nb content.

[0444] This can only be done with The supercell of the space group P4 is connected, where the c parameter is preserved and the a parameter is increased by a factor of √ 2. This is accompanied by a corresponding decrease in the intensity of the hk0 reflection family for h + k = even.

[0445] As in Example 3 (Nb 18 W6O 63 ), when the Nb:W ratio is further increased to 3:1, the change trend of hk0 reflection intensity continues. The crystal structure of Example 3 retains the supercell size, which is believed to be caused by the lower W concentration (Figure 13).

[0446] Example 1 (Nb2W2O 11 ) unit cell and Example 2 (Nb 16 W8O 64 ) and Example 3 (Nb 18 W6O 63 ) of the supercells is as follows Figure 13c As shown. The unit cell consists of four PCs. The supercell consists of eight PCs. The lattice parameters of the supercell correspond to the diagonals of the unit cell. Therefore, when the unit cell has lattice parameters a×a, the supercell has a lattice parameter equal to √2a×√2a.

[0447] Neutron diffraction further confirmed the formation of the supercell, where The reflections of (c parameter) are similar in all three diffraction patterns (see Figure 11 ). Nb2W2O of Example 1 11 (Nb:W=1:1) (a parameter) shows a broad peak, which is absent in Examples 2 and 3. 16 W8O 64 (Nb:W=2:1) ​​and Nb of Example 3 18 W6O 63 (Nb:W=3:1) has the corresponding The peak with a parameter at .

[0448] Neutron powder diffraction measurements were performed at room temperature on time-of-flight powder diffractometers POLARIS and GEM at the ISIS pulsed spallation neutron source in the UK. The samples were packed into 6 mm diameter vanadium cans. For Nb2W2O 11 and Nb 16 W8O 64 , data were collected from GEM diffraction libraries 1-5, for Nb 18 W6O 63 , data were collected from Polaris. Due to its suitable d-spacing range ( and ˜1-3.7), analyzed using data from libraries 1 and 4. The final structure was determined using combined Rietveld refinement of PXRD and neutron diffraction data using the FULLPROF suite of programs.

[0449] Further analysis was performed using a high-resolution scanning transmission electron microscope (HAADF HR-STEM). Imaging was performed using a JEOL ARM200F (Cs-corrected) transmission electron microscope in STEM mode at 200 kV and high-resolution EDS data were acquired from NbWO oxide particles. Atomic resolution STEM-EDS datasets were acquired under these low-dose conditions to reduce damage to the sample by the electron beam: dwell time = 0.01 ms, spot size = 6C, aperture size = 20 μm, and beam current = 18 pA. Given the low beam current and the relatively low intensity of the X-rays emitted from the sample, multi-frame STEM-EDS data were acquired. Each dataset typically consisted of 500-1000 frames, which were then aligned and processed using HyperSpy, a Python-based multidimensional data analysis toolbox. The aligned graphs and spectra were then summed over the entire dataset, and machine learning tools such as principal component analysis (PCA) and non-negative matrix decomposition (NMF) were used to denoise the data and improve the signal-to-noise ratio (SNR).

[0450] HAADF HR-STEM imaging provides evidence for the ordering of pentagonal channels (PC) within the crystal structure as well as the ordering of cations and unoccupied PC. 11 ), PCs are partially and randomly occupied ( Figure 14 (a)), and thus have a smaller Parameter a. As in Example 2 (Nb 16 W8O 64 ), by increasing the Nb / W content, 50% of the PC remains completely unoccupied and arranged in a square pattern ( Figure 15 (c)). The remaining PC is occupied by cations ( Figure 11 (b)). For Example 3 (Nb 18 W6O6), by further increasing Nb / W, the phase retains the same structure as Example 2 ( Figure 14 (c)), where 50% of the PCs remain completely unoccupied and arranged in a square pattern.

[0451] Example 3 (Nb 18 W6O 63 ) is a higher magnification HAADF HR-STEM image as shown in Figure 15 (a) shows that the cations present in and around the ordered unoccupied PC square pattern are significantly brighter than other cations ( Figure 15(a) This is considered further evidence of PC vacancy ordering and supercell formation (√2a). It also suggests cationic ordering, in which Nb and W ions occupy specific atomic rows within the unit cell (along the crystallographic c-axis).

[0452] Applying the bandgap filter and threshold 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 distinguished and further confirm the existence of the supercell structure, where 50% of the PC is filled with -MOMO- chains and 50% of the PC is unoccupied, and the PC forms a square with four pentagonal channels.

[0453] The bandgap filter and threshold were also applied to Example 1 (Nb2W2O 11 ) to improve the contrast (see Figure 17A (b)). Figure 17A The graph in (b) shows that all spots remain bright except for the PCs which have different brightness. This supports the partial and random occupation of the PCs in the structure of Example 1.

[0454] Additional characterization and modeling indicate that in Example 1, the Nb and W cations are initially evenly distributed between 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 (now Figure 17). 0.26 In addition to the existing oxygen positions in the WO3 structural model, additional oxygen atoms are placed below the cations in the pentagonal cation positions to form 7-coordinated pentagonal bipyramidal (PB) sites. The cation positions and their occupancy are refined to investigate any preferential occupation of the octahedral and PB cation sites by Nb and W. The final refined structure ( Figure 18 c) shows that the Nb and W ions are distributed throughout the octahedral sites, with a slight preference for W at the 2c position. The PB site shows low occupancy, which can only be occupied by a portion (1 / 3) of the Nb ions at this site to maintain an overall Nb / W ratio of 1.

[0455] The layer thickness of the metal oxide polyhedron in Example 1 was calculated to be approximately which corresponds to the c parameter (now Figure 17). Atomic resolution HAADF-HR(S)TEM imaging of the ab plane captures the -MOMO- channel along this axis ( Figure 17B(d)) and the superposition with the structural model (one unit cell) shows the atomic positions of Nb and W. Lattice parameters from FFT Closely matches the value obtained from the PXRD data. The intensity of the atomic column in the HAADF-HR(S)TEM image represents the sum of the intensities of the -MOMO- chains throughout the thickness of the sample. The different intensities of the atomic columns in the HAADF image can be attributed to changes in the lattice position of a single element and / or the occupation of different elements occupying the same lattice position. Recent advances in aberration-corrected (S)TEM combined with EDS enable atomic resolution elemental mapping of crystal structures, and we use this method in this article to confirm the preferential occupation of Nb and W in the octahedral and PB sites obtained from XRD refinement. Example 1 High-resolution (S)TEM-HAADF image along the c-axis and the corresponding EDS elemental map are shown in Figure 1. Figure 18 Figure 3 (d-g) shows the atomic-resolution EDS images. The bright spot, highlighted by the cyan circle, corresponds to the 2c octahedral site, which is preferentially occupied by W atoms based on XRD refinement. The spot, indicated by the yellow circle, corresponds to the octahedral site 8j, which is partially filled with W atoms, indicating co-occupancy of W and Nb atoms. The magenta circle corresponds to the PB site 4h, which appears bright in the Nb map but missing in the W map, confirming that this site is exclusively occupied by Nb atoms. Figure 18 The superimposed EDS patterns in B(g) further support this observation.

[0456] Figure 18 The images of Example 3 (Nb) taken along three different directions (a, b and c in the ab plane) are shown. 18 W6O 63 ). The intensity spectrum shows periodic and repeating patterns in all directions, indicating that the cations are ordered throughout the lattice.

[0457] Also for Example 3 (Nb 18 W6O 63 ) was subjected to energy dispersive X-ray spectroscopy (EDS) and superimposed on the STEM image (see Figure 19a). STEM-EDS was performed to obtain atomic resolution mapping to identify and distinguish atoms in different rows along the c crystallographic axis. The STEM-EDS image shows that W ions occupy octahedral sites within and around the unoccupied PC square arrangement, and other PC and octahedral sites are occupied by Nb ions (Figure 19a).

[0458] Further TEM images of the NWO phases prepared in Examples 1, 2 and 3. Fast Fourier Transform (FFT) images of the same samples were also prepared. These were prepared as described above.

[0459] TEM and FFT images observed perpendicular to the crystal c-axis were prepared for Example 1 (see Figure 20 (ab)). TEM and FFT images show the c-parameters corresponding to the TTB unit cell. d-spacing.

[0460] Preparation of Example 1 (Nb2WO) along the ab plane 11 ) TEM and FFT diagram (see Figure 21 (ab)). This shows the a-parameter corresponding to the TTB unit cell. d-spacing.

[0461] Example 3 (Nb 18 W6O 63 )'s TEM and FFT images were also taken along the ab plane ( Figure 22 ), which shows the supercell formed by the √2a of the smaller TTB unit cell. d-spacing.

[0462] These images support the crystallographic characterization of the new NWO phase.

[0463] The NbO2 from Example 3 was prepared by focused ion beam (FIB). 18 W6O 63 ) of the secondary particles of the NWO phase are shown in the TEM image of Figure 23 As shown in (a) (scale bar 1 μm). Figure 7 (b) shows a close-up view of the secondary particles (scale bar 1 nm).

[0464] The flakes were prepared using a focused ion beam scanning electron microscope (FIB-SEM) - FEI Helios NanoLab. TEM images and selected area electron diffraction (SAED) patterns from these flakes were obtained using a transmission electron microscope - Thermo Scientific (FEI) Talos F200X G2 operating at 200 kV. During the flake formation process, focused ion beam milling tends to damage the edges of the flakes, so Figure 23 The graph shown in (a) is not spherical.

[0465] This figure shows the network of primary particles that make up the secondary particles. Based on this figure, it can be estimated that the length of the primary particles that form the secondary particles is approximately 0.2 to 1 μm. It can also be estimated that the secondary particles consist of approximately 1,000 to 1,500 primary particles.

[0466] Electrochemical characterization of 2.4-NWO phase

[0467] The NWO phase was tested on Li in a half-cell configuration.

[0468] The 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 provide a slurry, which was mixed using a Thinky mixer 250. Electrodes were cast from the slurry and dried in an oven at 60°C under ambient atmosphere overnight. The dry electrodes were then rolled at room temperature. The active mass loading was ~2 mg cm- 2 , the electrode area is 1.27cm 2 .

[0469] Anode working electrodes were prepared using the NWO phases of Examples 1 and 3 (prepared in Section 1.1 above) as active materials. Cathodic counter electrodes were prepared using Li metal as active material.

[0470] Electrochemical testing was performed in 2032 stainless steel (SS) coin cell batteries equipped with an SS conical spring, two 0.5 mm thick SS spacer disks, and a glass microfiber separator (Whatman, GE). The battery cells were assembled in a glove box using LP30 electrolyte (Sigma-Aldrich), consisting of 1.0 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 v / v). The battery cells were assembled in an argon-filled glove box.

[0471] Constant current battery 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 discharges relative to its maximum capacity. The C-rate can be defined as the inverse of the number of hours required to reach a defined theoretical capacity.

[0472] The half-cells were cycled between 1.3 and 3.0 V vs. Li.

[0473] The high rate performance was tested at up to 20 C. For the battery cells using Example 1 and Example 3 as the anode active materials, the discharge capacity at different discharge rates was tested, such as Figure 24 The first four cycles were performed at C / 5, followed by six cycles at 1C, 2C, 5C, 10C, 20C, and 1C, respectively.

[0474] For Example 1 (Nb2W2O 11 ), at C / 5, the initial capacity is about 160mA·h·g- 1 At 1C, it decreases slightly to about 138mA·h·g- 1 However, at higher C rates, the capacity decrease is minimal. At 10C, the capacity is about 125-130 mA·h·g- 1, while at 20C, the capacity is about 120-125mA·h·g- 1 This indicates that the anode has excellent rate capacity retention even at high rates.

[0475] For Example 3 (Nb 18 W6O 63 ), at C / 5, the initial capacity is about 200mA·h·g- 1 At 1C it decreases slightly to about 170mA·h·g- 1 However, at higher C rates, the capacity decrease is minimal. At 10C, the capacity is about 150-160 mA·h·g- 1 , while at 20C, the capacity is about 145-155mA·h·g- 1 This indicates that the anode has excellent rate capacity retention even at high rates.

[0476] The anode of Example 3 has a higher capacity than the anode of Example 1.

[0477] It is believed that the slightly higher capacity of Example 3 is due to the higher number of PC vacancies in Example 3 compared to Example 1, which allows more lithium to be inserted into the unoccupied PC. In addition, the density of Example 3 is lower than that of Example 1, so the capacity of Example 3 appears to be higher on a weight basis.

[0478] Compared with known NWO materials (e.g., Nb 16 W5O 55 ) compared to Nb 16 W5O 55 The discharge capacity of the electrode at 0.2C is about 165mA·h·g- 1 , which drops to 125mA·h·g- at 20C 1 The initial capacity at 0.2C and the capacity at high discharge rate are both smaller than those in Example 1 (Nb2W2O 11 ) and Example 3 (Nb 18 W6O 63 This is believed to be due to the improved lithium ion intercalation properties provided by the enhanced regularity of the structure and the improved cation ordering.

[0479] The long-term cycle performance was tested for 1,000 cycles. The battery cells using Examples 1 and 3 as anode active materials were cycled 1,000 times at a discharge rate of 10C, and the discharge capacity was as shown in FIG. Figure 24 (b) shown.

[0480] For Example 3, the initial discharge capacity is 170 mA·h·g- 1 , which dropped to only 160 mA·h·g- after 1,000 cycles at 10C 1 This represents a capacity retention of over 94% after 1000 cycles at 10C.

[0481] For Example 1, the initial discharge capacity is 130 mA·h·g- 1 , which decreased to 110 mA·h·g- after 1,000 cycles at 10C. 1 This represents a capacity retention of over 84% after 1000 cycles at 10C.

[0482] Despite the very high 10C rate and many cycles, the capacity retention over 1,000 cycles is very excellent. The capacity retention of the anode of Example 3 is particularly high.

[0483] Compared with known NWO materials (e.g., Nb 16 W5O 55 ) compared to the Nb 16 W5O 55 The discharge capacity of the electrode is maintained at 120 mA·h·g- after 300 cycles at a 10C charge and 10C discharge rate. 1 , corresponding to a capacity retention rate of more than 80%. After 1000 cycles, the capacity retention rate is less than that of Example 1 (Nb2W2O 11 ) and Example 3 (Nb 18 W6O 63 This is believed to be due to the specific regularity of the structure of the present invention and the improvement of cationic ordering, which improves the uniformity of lattice expansion and reduces cracking during repeated cycling at high rates.

[0484] Additional electrochemical characterization of the 2.5-NWO phase

[0485] Additional electrochemical cycling tests were performed on the NWO phase against Li in a half-cell configuration. The testing method was as described above in Section 2.4.

[0486] High rate performance was tested up to 20 C. For the battery cells using Examples 1, 2 and 3 as the anode active material, the discharge capacity at different discharge rates was tested. Figure 26 (d) shows the results. The first 4 cycles were performed at C / 5, followed by 6 cycles at 1C, 2C, 5C, 10C, 20C and 1C, respectively.

[0487] For Example 1 (Nb2W2O11 ) and Example 3 (Nb 18 W6O 63 ), the performance is similar to that tested in Section 2.4.

[0488] For Example 2 (Nb2WO8), at C / 5, the initial capacity is about 185 mA·h·g- 1 At 1C it decreases slightly to about 170mA·h·g- 1 However, at higher C rates, the capacity decrease is minimal. At 10C, the capacity is about 145-150 mA·h·g- 1 , while at 20C, the capacity is about 135-140mA·h·g- 1 This indicates that the anode has excellent rate capacity retention even at high rates.

[0489] 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.

[0490] The long-term cycle performance was tested for 1,000 cycles. The battery cells using Examples 1, 2, and 3 as anode active materials were cycled 1,000 times at a discharge rate of 10C, and the discharge capacity was as shown in the figure. Figure 2 The anode materials exhibit remarkable high-rate performance, with reversible capacities of 160, 155, and 110 mAh / g at the end of 1000 cycles at a high rate (10C).

[0491] For Example 1 (Nb2W2O 11 ) and Example 3 (Nb 18 W6O 63 ), the performance is similar to that tested in Section 2.4.

[0492] For Example 2 (Nb2WO8), the initial discharge capacity is 160 mA·h·g- 1 , which decreased to only 155 mA·h·g- after 1,000 cycles at 10C 1 This represents a capacity retention of over 96% after 1000 cycles at 10C.

[0493] Despite the very high 10C rate and multiple cycles, the capacity retention over 1,000 cycles is very excellent. The capacity retention of the anodes of Examples 2 and 3 is particularly high.

[0494] Although both Examples 2 and 3 have a supercell TTB structure, it is believed that Example 3 exhibits a higher capacity than Example 2 due to its lower molar mass. This difference in capacity can be attributed in part to fewer defects in the crystal lattice of Example 3.

[0495] The gravimetric capacities reported here for all three bronzes are higher than the 80 mAh / g reported for α-Nb2WO8 cycled at 3 A / g (a rate lower than 10 C). This capacity improvement can be attributed to the presence of interconnected, unoccupied pentagonal channels that run through the particle, thereby facilitating lithium ion transport and storage.

[0496] Thermal stability of 2.6-NWO phase

[0497] The thermal stability of the example phases was tested to investigate the thermodynamic stability. Examples 1, 2a, and 3a were calcined at 800°C for 30 days, and their PXRD patterns were as follows: Figure 27 shown.

[0498] Example 1 remained unchanged during the extended heating process, indicating its thermodynamic stability. However, for Example 2, ~71.5% of the material retained its structure, while the remainder decomposed into the known bronze phase α-Nb2WO8. Similarly, for 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%).

[0499] The test samples were also microscopically characterized using SEM. The phase composition of the decomposition products also correlated with the observed morphological changes: Example 1 maintained its spherical morphology, while the primary particle size increased ( Figure 28A ), while Example 2 only partially retains its spherical morphology, and the remaining part is crystallized into micron-sized rods, which is consistent with typical NWO bronze and bulk ( Figure 28B Example 3 is completely converted into micron-sized particles ( Figure 28C ).

[0500] The stability of Example 1 was observed up to 1000°C. After calcination at 1200°C for 12 h, it decomposed into Nb 12 W 11 O 63 、Nb8W9O 47 and Nb 14 W3O 44 Phase. Decomposition is accompanied by a transition to a rod-like structure. Spherical secondary particles are only observed at temperatures below 900°C, and the transition to a rod-like structure is always accompanied by decomposition.

[0501] These findings demonstrate the importance of low temperature synthesis methods for producing the NWO phases of the present invention. The examples show sufficient thermal stability for typical battery applications, and the structure of Example 1 also shows superior high temperature stability compared to Examples 2 (2a) and 3 (3a).

[0502] References

[0503] In order to more fully describe and disclose the present invention and the prior art in the field to which the present invention belongs, a number of publications are cited above. The full citations of these references are provided below. The entire contents of each of these references are incorporated herein.

[0504] CN110304658A

[0505] WO 2019 / 234248

[0506] Ekstrom et al., Acta Chem.Scand.1971,25,No.7

[0507] Griffith et al.,Nature,559,556-559

[0508] Hyde et al.,Acta Crystallogr.Sect.A 1973,29,243-248.

[0509] et al.,J.Am.Chem.Soc.2019,141,15121-15134

[0510] Krumeich,Chem.Mater.2022,34,3,911-934

[0511] Kudo et al.,Journal of Solid State Chemistry,1988,77,2,412-415

[0512] Lundberg,Acta Chemica Scandinavica 26,1972,2932-2940

[0513] Roth et al., Acta Cryst.1965,19,26

[0514] Roth,RS,Wadsley,AD,Acta Crystallogr.,1965,19,32

[0515] Sayagués et al.,Journal of Solid State Chemistry,1998,143,1,33-40

[0516] Tamura,S.et al.,Z.Anorg.Allg.Chem.,1974,410,313

[0517] Wadsley et al., Acta.Cryst.1961,14,660

[0518] Xia et al. Journal of Power Sources 482(2021)228898

[0519] Yang et al.,CS Nano 2017,11,4,4217-4224

[0520] Yu et al.,Inorganica Chimica Acta,2020,507,119562

[0521] Zhou et al.,Chemistry Select,2020,5,3,1209-1213。

Claims

1. A niobium metal oxide of formula (I) Nb x M y O z (I) in, The niobium metal oxide is optionally intercalated with lithium, 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, and A portion of the pentagonal channels is filled with -Nb-O-Nb-O- chains, and the remaining portion of the pentagonal channels is optionally intercalated with lithium.

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

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

4. The niobium metal oxide according to any preceding claim, wherein The crystal structure comprises a unit cell having a space group P4 / mbm or a supercell having a space group P4.

5. The niobium metal oxide according to any preceding claim, wherein The crystal structure comprises The unit cell of parameter a has a value of 17.3 to The supercell has a parameter √2a, and the unit cell or the supercell has a parameter √2a of 3.8 to Parameter c.

6. The niobium metal oxide according to any preceding claim, wherein The crystal structure is characterized in that the powder X-ray diffraction pattern has two or more 2θ peaks, such as three or more 2θ peaks, such as four or more 2θ peaks, wherein the 2θ peaks are 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°, and wherein the powder X-ray diffraction is measured at a wavelength of Cu-Kα.

7. The niobium metal oxide according to any preceding claim, wherein x / y is selected from the group consisting of 1, 1.5, 2, 2.5 and 3, preferably selected from the group consisting of 1, 2, 2.5 and 3.

8. The niobium metal oxide according to any preceding claim, wherein The ratio of x / y is 2 to 3.

9. The niobium metal oxide according to any preceding claim, wherein The niobium metal oxide is Nb 18 M6O 63 、Nb 10 M4O 37 、Nb 16 M8O 64 、Nb2M2O 11 or a combination thereof, preferably Nb 18 M6O 63 、Nb 16 M8O 64 or a combination thereof, more preferably Nb 18 M6O 63 .

10. The niobium metal oxide according to any preceding claim, wherein The crystal structure includes quadrilateral channels and pentagonal channels, wherein a portion of the quadrilateral channels and / or a portion of the pentagonal channels are embedded with Li.

11. A niobium metal oxide secondary particle comprising an aggregate of primary particles of the niobium metal oxide according to any preceding claim, wherein: The secondary particles have an average length of 1 to 5 μm and an aspect ratio of 1 to 1.

5.

12. The niobium metal oxide secondary particle according to claim 11, wherein The aspect ratio is 1 to 1.3, preferably 1 to 1.2, more preferably 1 to 1.

1.

13. The niobium metal oxide secondary particle according to claim 11 or 12, wherein The secondary particles have a sphericity of 0.95 or greater, such as 0.96 or greater, 0.97 or greater, 0.98 or greater, or 0.99 or greater.

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

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

16. The niobium metal oxide secondary particle 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, the method comprising: Make Nb oxide and M oxide from NbX a and MY b co-precipitated in solution, and Calcination of the precipitate at a temperature of 550 to 1100°C, wherein M is selected from Ti, Zr, V, Cr, W and Mo, X and Y are independently one or more counterions, and a and b are independently 2 to 6, wherein NbX a and MY b Optionally charged.

18. The method according to claim 17, wherein: The co-precipitation comprises heating the NbX at a temperature of 120 to 200°C, preferably 130 to 170°C, more preferably 140 to 160°C. a and MY b of solution.

19. The method according to claim 17 or 18, wherein The co-precipitation comprises heating the NbX at a pressure of 1000 kPa or higher, preferably at a pressure of 1000 kPa to 5000 kPa, more preferably at a pressure of 1500 kPa to 4500 kPa, and even more preferably at a pressure of 1800 kPa to 4000 kPa. a and MY b of solution.

20. The method according to any one of claims 17 to 19, wherein Co-precipitation includes heating under solvothermal conditions, such as microwave heating under solvothermal conditions.

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

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

23. The method according to any one of claims 17 to 22, wherein NbX a is niobium oxalate or niobium chloride, and / or MY b It is metatungstate, paratungstate or tungsten chloride.

24. A niobium metal oxide secondary particle comprising aggregates of niobium metal oxide primary particles, obtained or obtainable by the method of any one of claims 17 to 23.

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

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

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