Active electrode material

Abstract

The present invention relates to electrodes comprising mixed niobium oxides as active electrode material. The electrodes can be used in metal ion batteries, such as lithium ion batteries. The mixed niobium oxides can have the formula M I x‑u M y (x / (5‑y)) M V z Nb 100‑(x / (5‑y))‑z O 250‑u / 2 wherein: M I is a cation having an oxidation state of 1; M y is a cation having an average oxidation state of y; M V is a cation having an average oxidation state of 5; 1 < y < 4; 0.5 < x < 6; 0 < z < 10; 0 < u < 5; x > u.

Description

TECHNICAL FIELD

[0001] The present invention relates to active electrode materials, methods for manufacturing active electrode materials, and electrodes comprising active electrode materials. Such materials are of interest as active electrode materials in metal-ion batteries, such as lithium-ion or sodium-ion batteries, for example as anode materials. BACKGROUND

[0002] Lithium-ion (Li-ion) batteries are a commonly used type of rechargeable battery, with the global market projected to grow to $200 billion by 2030. Li-ion batteries are the technology of choice for electric vehicles with multiple demands in terms of technical performance to environmental impact, thus offering a viable pathway for the green car industry.

[0003] A typical lithium-ion battery is composed of multiple cells connected in series or parallel. Each individual cell is usually composed of an anode (negative electrode) and a cathode (positive electrode) separated by a porous electrically insulating membrane called a separator, immersed in a liquid capable of transporting lithium ions called electrolyte.

[0004] In most systems, the electrodes are composed of active electrode materials - meaning that it is able to chemically react with lithium ions, thus storing and releasing said lithium ions in a controlled manner reversibly - mixed with conductive additives such as carbon and polymeric binders, if necessary. A slurry of these components is coated in the form of a thin film on a current collector, usually a thin foil of copper or aluminum, thus forming an electrode after drying.

[0005] In known Li-ion battery technology, the safety limitations of graphite anodes when the battery is charged severely hinder their application in high-power electronics, automotive, and industrial. Among the wide range of potential alternatives recently proposed, lithium titanate (LTO) and mixed niobium oxides are the main contenders to replace graphite as the preferred active material for high-power fast-charging applications.

[0006] Graphite anode dependent batteries are fundamentally limited in terms of charge rate. Under nominal conditions, lithium ions intercalate into the anode active material upon charging. As the charge rate is increased, the typical graphite voltage profile is such that there is a high risk that the overpotential causes the potential at sites on the anode to become < 0 V vs. Li / Li+, which leads to a phenomenon called lithium dendrite plating, whereby lithium ions are instead deposited in the form of lithium metal on the surface of the graphite electrode. This leads to an irreversible loss of active lithium and thus a rapid decay in cell capacity. In some cases, such dendritic deposits can grow to such a size that they pierce the battery separator and cause a cell short. This triggers a catastrophic failure of the cell, leading to a fire or explosion. As a result, the fastest charging batteries with graphite anodes are limited to charge rates of 5-7 C, but often lower.

[0007] Lithium titanate (LTO) anodes do not suffer from dendrite plating at high charge rates due to their high potential (1.6 V vs. Li / Li+) and have excellent cycle life because they do not suffer from significant volume expansion of the active material upon Li ion intercalation due to their accommodating 3D crystal structure. For these two reasons, LTO cells are generally considered to be high safety cells. However, LTO is a relatively poor electronic and ionic conductor, which leads to limited capacity retention and resulting power performance at high rates, unless the material is nano-sized to increase the specific surface area and carbon coated to increase the electronic conductivity. This particle size material engineering increases the porosity and specific surface area of the active material and leads to a significant reduction in the achievable packing density in the electrode. This is important because it leads to a low density electrode and a high fraction of electrochemically inactive materials (e.g., binder, carbon additives), resulting in much lower gravimetric and volumetric energy densities.

[0008] A key measure of anode performance is the electrode volumetric capacity (mAh / cm 3 ), i.e., the amount of charge (i.e., lithium ions) that can be stored per unit volume of anode. This is an important factor in determining the total battery energy density (Wh / L) on a volumetric basis when combined with the cathode and appropriate cell design parameters. The electrode volumetric capacity can be approximated as the product of the electrode density (g / cm 3 ), the active material specific capacity (mAh / g), and the fraction of active material in the electrode. LTO anodes typically have a relatively low specific capacity (c. 165 mAh / g, to be compared to c. 330 mAh / g for graphite), combined with the low electrode density (typically < 2.0 g / cm 3 ) and low active material fraction (< 90%) discussed above, results in a very low volumetric capacity (< 300 mAh / cm 3), and thus result in low battery energy density and high $ / kWh cost in various applications. As a result, LTO batteries / cells are generally limited to specific niche applications, despite their long cycle life, fast charging capability, and high safety.

[0009] Mixed niobium oxides have been known in the academic literature for some time. Recently, the use of some mixed niobium oxides in lithium ion cells has attracted interest. For example, Zhu et al., J. Mater. Chem. A, 2019, 7, 25537 and Zhu et al., Chem. Commun., 2020, 56, 7321-7324 disclose Zn2Nb 34 O 87 and Cu2Nb 34 O 87 These papers rely on complex particle level engineering to achieve purportedly good properties, for example attempting to control particle porosity and morphology. WO2021 / 074593 and WO2021 / 074594 disclose various substituted and / or oxygen-deficient mixed niobium oxides which are found to have good properties for use as active electrode materials. However, there remains a need to identify further mixed niobium oxides having good properties for use as active electrode materials, in particular having good properties for use in lithium ion cells intended for high power / fast charging applications. For example, identifying such materials which do not require extensive particle level engineering and / or do not require a coating is an important step towards low cost battery materials entering the mass market. SUMMARY

[0010] In a first aspect, the present application provides an electrode comprising a mixed niobium oxide as an active electrode material, wherein the mixed niobium oxide has the formula M I x-u M y (x / (5-y)) M V z Nb 100-(x / (5-y))-z O 250-u / 2 .

[0011] The mixed niobium oxide can also have the formula B a M v z Nb 100-a-z O 250-a .

[0012] The mixed niobium oxide can also have the formula M b Nb 100-b O 250-2.5b+bc .

[0013] The inventors have found that electrodes according to the first aspect retain surprisingly high capacity when delithiated at high rates, for example 5C and 10C, as shown in the examples of the present invention. These are important results demonstrating the advantages of the mixed niobium oxides of the present invention for the design of high power batteries for fast charging / discharging.

[0014] In a second aspect, the present invention provides a metal-ion battery comprising a mixed niobium oxide as an active electrode material, wherein the mixed niobium oxide is as defined in the first aspect. Optionally, the metal-ion battery is a lithium-ion battery or a sodium-ion battery, preferably a lithium-ion battery.

[0015] In a third aspect, the present invention provides the use of a mixed niobium oxide as defined in the first aspect as an active electrode material in a metal-ion battery. Optionally, the metal-ion battery is a lithium-ion battery or a sodium-ion battery, preferably a lithium-ion battery.

[0016] In a fourth aspect, the present invention provides a method of manufacturing an electrode comprising providing a mixed niobium oxide as defined in the first aspect; and depositing the mixed niobium oxide onto a current collector, thereby forming an electrode. BRIEF DESCRIPTION OF DRAWINGS

[0017] The principles of the present invention will now be discussed with reference to the accompanying drawings.

[0018] Figure 1 XRD pattern of selected synthetic Wadsley-Roth 4x4 octahedral block structure.

[0019] Figure 2 TEM micrograph and selected area electron diffraction of sample 11 obtained using a Thermo Scientific (FEI) Talos F200X G2 TEM. Left: high magnification image showing highly crystalline structure. Right: selected area electron diffraction where the (110) plane spacing matches that determined by XRD.

[0020] Figure 3 XRD pattern of sample 18 collected using a Cu Ka X-ray source.

[0021] Figure 4 Voltage vs. state of charge plot for the 2nd cycle formation of samples 3 and 18 in half cell units when cycled at a C rate of C / 10 using 3.0 to 1.1 V. DETAILED DESCRIPTION

[0022] The term "mixed niobium oxide" refers to an oxide comprising niobium and at least one other cation. Mixed niobium oxides have a high redox voltage > 0.8 V vs. lithium, enabling safe and long-life operation, which is critical for battery cells of fast-charging batteries. Furthermore, each atom of the niobium cation can have two redox reactions, resulting in a higher theoretical capacity than, for example, LTO.

[0023] The mixed niobium oxide can have the formula M I x-u M y (x / (5-y)) M V z Nb 100-(x / (5-y))-z O 250-u / 2 wherein:

[0024] M I is a cation having an oxidation state of 1 ;

[0025] M y is a cation having an average oxidation state of y;

[0026] M V is a cation having an average oxidation state of 5;

[0027] 1 < y < 4;

[0028] 0.5 < x < 6;

[0029] 0 < z < 10;

[0030] 0 < u < 5;

[0031] x > u.

[0032] The mixed niobium oxide can also have the formula B a M v z Nb 100-a-z O 250-a wherein

[0033] M V is a cation having an average oxidation state of 5;

[0034] 0 < z < 10;

[0035] 0 < a < 8.

[0036] The mixed niobium oxide can also have the formula M b Nb 100-b O 250-25b+bc wherein

[0037] M is a cation selected from P, B, W, Mo, V, Ti, Si, and mixtures thereof;

[0038] c is half the average oxidation state of M;

[0039] 1.5 ≤ c ≤ 3; and

[0040] 0.5 <b≤6。

[0041] Mixed niobium oxides with the formulas defined herein are uniform because they can adopt crystal structures considered to contribute to their advantageous properties as active electrode materials. In particular, mixed niobium oxides can adopt crystal structures having a Wadsley-Roth crystal structure comprising 4×4 octahedral blocks. The Wadsley-Roth crystal structure is considered a crystallographically nonstoichiometric MO3(ReO3) crystal structure containing crystallographic shear, simplified to MO3(ReO3). 3-x Therefore, these structures typically contain [MO6] octahedral subunits in their crystal structure. In a 4×4 octahedral block structure, each block is connected only by octahedra sharing edges. This structure was reported in 1967 as having a monoclinic unit cell ( β=120.80°, space group=C2 / m). This structure and related structures have been reported in historical academic literature, but no data on electrochemical lithiation or delithiation have been provided (Andersson, Zeitschrift für anorganische undallgemeine Chemie, Vol. 351, No. 1-2, April 1967, pp. 106-112; Pekhtereva, Yu.A., & Shukaev, IL (1999), Zhurnnal Neorganicheskoj Khimii, 44(2), 290-294; Cava et al. 1983 J. Electrochem. Soc. 130 2345; Villafuerte-Castrejón, Journal of Solid State Chemistry, Vol. 71, No. 1, November 1987, No. 103-108; Norin and Bertil, Acta Chemica Scandinavica, Vol. 25 (1971), pp. 741-743; Reisman and Holtzberg, J. Am. Chem. Soc. 1958, 80, 24, 6503-6507. It is believed that this large bulk size, compared to other Wadsley-Roth structures with smaller octahedral bulk sizes, facilitates rapid lithium insertion and removal, and potentially offers higher stability compared to Wadsley-Roth structures with even larger octahedral bulk sizes.

[0042] The polymorph of niobium oxide N-Nb2O5adopts a Wadsley-Roth crystal structure comprising 4x4 octahedral blocks. Thus, the crystal structure of the mixed niobium oxide as determined by X-ray diffraction preferably corresponds to that of N-Nb2O5. The crystal structure of N-Nb2O5may be found in Andersson 1967, Zeitschrift fur anorganische und allgemeine Chemie, Volume 351, Issues 1-2, April 1967.

[0043] The mixed niobium oxide according to the application has a modified ratio of cations to anions compared to the empirical formula of N-Nb2O5. In the formula M I x-u M y (x / (5-y)) M V z Nb 100-(x / (5-y))-z O 250-u / 2 In some of the Nb is substituted by M I and M y both, increasing the ratio of cations to anions. In the formula B a M v z Nb 100-a-z O 250-a In some of the Nb has been substituted by B, resulting in a loss of oxygen in the crystal structure to maintain charge neutrality, also increasing the ratio of cations to anions; the crystal structure of materials having this formula can contain some tetrahedral boron cations between the 4x4 octahedral blocks. This modification is believed to contribute to the advantageous properties of the mixed niobium oxide for use as an active electrode material. For example, the modified ratio of cations to anions is believed to stabilise the crystal structure.

[0044] The crystal structure of the material can be determined by analysis of the X-ray diffraction (XRD) pattern, typically obtained from a Cu K source, as is well known. For example, the XRD pattern obtained from a given material can be compared to known XRD patterns to confirm the crystal structure, for example via a public database such as the ICDD Crystallography Database. Rietveld analysis and Pawley analysis can also be used to determine the crystal structure of a material, particularly for the unit cell parameters. Thus, the mixed niobium oxide can have a Wadsley-Roth crystal structure comprising 4x4 octahedral blocks as determined by X-ray diffraction.

[0045] Here, the term 'corresponds' is intended to reflect that the peaks in the X-ray diffraction pattern can be offset by no more than 0.5 degrees (preferably no more than 0.25 degrees, more preferably no more than 0.1 degrees) from the corresponding peaks in the X-ray diffraction pattern of the material listed above.

[0046] The mixed niobium oxide can adopt a monoclinic crystal structure, for example with unit cell parameters a = 90°, β = 112.6-137.6°, γ = 90°. The unit cell parameters can be determined by X-ray diffraction.

[0047] M I is a cation with an oxidation state of 1. M I may be selected from Li, Na, K and mixtures thereof. Preferably, M I is selected from Li, Na and mixtures thereof.

[0048] x is the atomic weight of M I , which ranges from 0.5 < x < 6. x can be an integer, for example x = 1, 2, 3, 4, 5 or 6. Optionally, 2 < x < 5, such as x = 2, 3, 4 or 5. Preferably, x = 4.

[0049] The formula can be defective in terms of M I , for example, due to its generally low atomic weight, some 1+ cations are lost via volatilisation. Therefore, the atomic weight of x can be modified by the variable 0 < u < 5, where x > u, for example x > u + 1. Optionally, 0 < u < 3 or 0.01 < u < 2. Alternatively, u = 0.

[0050] M y is a cation with an average oxidation state of y. The term "average oxidation state" means that when there is more than one cation, the oxidation state refers to M y as a whole. For example, if 1 / 3 of M y is W 6+ and 2 / 3 of M y is Fe 3+ , then y is 4 (1 / 3 x 6 (contribution of W) + 2 / 3 x 3 (contribution of Fe)). However, M y , M II , M III , M IV and M V may consist of a single cation, in which case the oxidation state is the oxidation state of that cation.

[0051] M ymay be selected from Li, Na, K, Cu, Zn, Mg, Ca, Ni, Fe, Mn, Co, Cr, V, Al, B, Ga, Sc, Y, In, La, Yb, Ce, Zr, Ti, Sn, Ge, Si, P, Ta, W, Mo and mixtures thereof; or Li, Na, K, Cu, Zn, Mg, Ni, Fe, Mn, Co, Cr, V, Al, B, Ga, Zr, Ti, Si, P, Ta and mixtures thereof; or Li, Na, Cu, Zn, Mg, Ni, Fe, Mn, Co, Cr, Al, B, Ga, Zr, Ti and mixtures thereof. Optionally, M y does not comprise Li.

[0052] y is in the range 1 < y < 4, optionally 2 < y < 4. y can be an integer, for example y = 1, 2, 3 or 4; preferably 2, 3 and 4. When y is an integer, optionally, all cations of M y have the same oxidation state.

[0053] When y is 1, 2, 3 or 4, M y may be selected from Li, Na, Cu, Zn, Mg, Ca, Ni, Fe, Mn, Co, Cr, Al, B, Ga, Sc, Y, In, La, Yb, Ce, Zr, Ti, Sn, Ge and mixtures thereof.

[0054] When y is 2, 3 or 4, M y may be selected from Cu, Zn, Mg, Ca, Ni, Fe, Mn, Co, Mn, Cr, Al, B, Ga, Sc, Y, In, La, Yb, Ce, Zr, Ti, Sn, Ge and mixtures thereof.

[0055] M y has an atomic weight of z, which is in the range 0 < z < 10. Optionally, 0 < z < 5. z can be > 0, for example > 0.01. Alternatively, z = 0, in which case M I is not present. y has an oxidation state of 5.

[0056] M V is an optional cation having an average oxidation state of 5. Optionally, M V is a cation having an oxidation state of 5, wherein all cations of M V have the same oxidation state 5.

[0057] M V has an atomic weight of z, which is in the range 0 < z < 10. Optionally, 0 < z < 5. z can be > 0, for example > 0.01. Alternatively, z = 0, in which case M V is not present.

[0058] M Vmay be selected from the group consisting of Mn, Fe, Al, Ga, Y, In, La, Yb, Cu, Zn, Mg, Ni, Co, Ca, Ce, Zr, Ti, Sn, Ge, Si, V, P, Ta, W, Mo, Cr and mixtures thereof; or Ce, Zr, Ti, Sn, Ge, Si, V, P, Ta, W, Mo, Cr V, P, Ta and compounds thereof; or V, P, Ta and mixtures thereof. Optionally, all of the cations forming M V have an oxidation state of 5.

[0059] When y = 1, the mixed niobium oxide can have the formula M I x-u N I x / 4 M V z Nb 100-x / 4-z O 250-u / 2 where N I is a cation having an oxidation state of 1. N I may be selected from the group consisting of Li, Na, K and mixtures thereof; preferably Li, Na and mixtures thereof.

[0060] When y = 2, the mixed niobium oxide can have the formula M I x-u M II x / 3 M V z Nb 100-x / 3-z O 250-u / 2 where M II is a cation having an average oxidation state of 2. M II may be selected from the group consisting of Cu, Zn, Mg, Ni, Fe, Mn, Co, Ca and mixtures thereof; or Cu, Zn, Mg, Ni and mixtures thereof; or Zn, Mg, Ni and mixtures thereof. Optionally, all of the cations forming M II have an oxidation state of 2.

[0061] When y = 3, the mixed niobium oxide can have the formula M I x-u M III x / 2 M V z Nb 100-x / 2-z O 250-u / 2 where M III is a cation having an average oxidation state of 3. M III may be selected from the group consisting of Mn, Cr, V, Fe, Al, B, Ga, Y, In, La, Yb, Ce and mixtures thereof; or Mn, Cr, Fe, Al, B, Ga, Y and mixtures thereof; or Cr, Al, Fe and mixtures thereof. Optionally, all of the cations forming M III have an oxidation state of 3.

[0062] When y = 4, the mixed niobium oxide can have the formula M I x-u M IV x M V z Nb 100-x-z O 250-u / 2 , where M IV is a cation with an average oxidation state of 4. M IV can be selected from Zr, Ti, Mn, Ce, Sn, Ge, V, Si and mixtures thereof; or Zr, Ti, Sn, Ge, V and mixtures thereof; or Ti, V and mixtures thereof. Optionally, all cations forming M V have an oxidation state of 4.

[0063] B a M v z Nb 100-a-z O 250-a The atomic weight of B in M

[0064] is a, and its range is 0 < a ≤ 8, for example 0.01 < a ≤ 8. Optionally, 1 ≤ a ≤ 5 or 1.5 ≤ a ≤ 3. a can be an integer. Preferably, a = 2. Up to 10 atomic% of the cations can be partially replaced by at least one cation selected from: P, K, Fe, Ti, Zr, Sn, Ge, Zn, Mg, Al, Ga, Y, W, Mo, Cr, V, Si, Ni, Mn, Ta, Li, Na and mixtures thereof; or Ti, W, Mo, Cr, Zn, Al, Fe, P and mixtures thereof. b Nb 100-b O 250-2.5b+bc In M

[0065] as described above, M is a cation selected from P, B, W, Mo, V, Ti, Si and mixtures thereof. M can be selected from P, W, B, Ti and mixtures thereof; or P, W and mixtures thereof. Preferably, M contains P and / or W. Up to 10 atomic% of the cations can be partially replaced by at least one cation selected from: K, Fe, Zr, Sn, Ge, Zn, Mg, Al, Ga, Y, Cr, Ni, Mn, Ta, Li, Na and mixtures thereof; or Cr, Zn, Al, Fe and mixtures thereof. b is 0.5 < b ≤ 6, or 1 ≤ b ≤ 5.75, or 1.5 ≤ b ≤ 5.5. c is half of the average oxidation state of M and is 1.5 ≤ c ≤ 3, or 2 ≤ c ≤ 2.75, or 2.5. b Nb 100-b O 250-2.5b+bcThe most intense peak between 18.15-18.65° 2Θ in the X-ray diffraction pattern of the sample can have a full width half maximum of >0.2; optionally >0.4, >0.6 and / or <0.9 (e.g., >0.2 to <0.9). Figure 3 XRD patterns of samples having this peak are shown. It is believed that samples having this peak include some connected tetrahedral cations between 4x4 octahedral sheets within a Wadsley-Roth crystal structure. Materials having this crystal structure are found to have particularly high capacities.

[0066] It should be understood that the discussion of variables (e.g., M, M I , x, u, M y , y, M v , z, a, b, c) of the formula is intended to be read in combination. For example, a mixed niobium oxide can have the formula M I x-u M y (x / (5-y)) M V z Nb 100-(x / (5-y))-z O 250-u / 2 wherein:

[0067] M I is Li, Na, and mixtures thereof;

[0068] M y is a cation having an average oxidation state of y selected from the group consisting of Li, Na, Cu, Zn, Mg, Ca, Ni, Fe, Mn, Co, Cr, Al, B, Ga, Sc, Y, In, La, Yb, Ce, Zr, Ti, Sn, Ge, and mixtures thereof;

[0069] M V is a cation having an average oxidation state of 5 selected from the group consisting of V, P, Ta, and mixtures thereof;

[0070] 1 < y < 4;

[0071] 2 < x < 6;

[0072] 0 < z < 10;

[0073] 0 < u < 3;

[0074] x > u + 1.

[0075] For example, a mixed niobium oxide can have the formula M I x M y (x / (5-y)) Nb 100-(x / (5-y)) O 250 wherein:

[0076] M I is Li, Na and mixtures thereof;

[0077] M y is a cation in oxidation state y selected from Li, Na, Cu, Zn, Mg, Ca, Ni, Fe, Mn, Co, Cr, Al, B, Ga, Sc, Y, In, La, Yb, Ce, Zr, Ti, Sn, Ge and mixtures thereof, wherein M y all cations forming M

[0078] y = 1, 2, 3 or 4;

[0079] x = 3, 4 or 5.

[0080] M y , M I , N I , M II , M III , M IV and M can also be selected from each of the specific elements used in the examples.

[0081] Optionally, if further cations are present in addition to Li and Nb, the mixed niobium oxide contains only Li. One example of such a material is Li4Cr2Nb 98 O 250 where Cr is a cation in addition to Li and Nb. Furthermore, the mixed niobium oxide can contain no Li. It will be appreciated that mixed niobium oxides, including those containing no Li, can reversibly intercalate Li in situ when functioning as an active electrode material in a lithium-ion battery.

[0082] The cations in the mixed niobium oxide can be partially substituted by further cations in different oxidation states, for example up to 20 atomic %, 10 atomic % or 5 atomic % of the cations can be substituted. Substitution of cations in different oxidation states forms a charge imbalanced material. The charge imbalance can be compensated by oxygen deficiency (substitution by a lower oxidation state cation) or excess (substitution by a higher oxidation state cation). Alternatively or additionally, the charge imbalance can be compensated by oxidation or reduction of the cations.

[0083] The oxygen anions can be partially substituted by substitutable electronegative anions such as F, CI, Br, S, Se, N and mixtures thereof. Optionally, up to 10 atomic % or 5 atomic % of the oxygen anions can be substituted by substitutable electronegative anions.

[0084] The mixed niobium oxide is preferably in particulate form. The mixed niobium oxide can have a D 50Particle size. These particle sizes are advantageous because they are easy to handle and make into electrodes. In addition, these particle sizes avoid the need to use complex and / or expensive methods to provide nano-sized particles. Nano-sized particles (e.g., having a D 50 Particles of nano-sized dimensions are generally more complex to synthesize and require additional safety considerations.

[0085] The mixed niobium oxide can have a D 10 Particle size. By maintaining the D 10 By maintaining the D

[0086] The mixed niobium oxide can have a D 90 Particle size. By maintaining the D 90 By maintaining the D

[0087] The term "particle size" refers to the equivalent spherical diameter (esd), i.e. the diameter of a sphere having the same volume as the given particle, wherein the volume of the particle is to be understood as including the volume of any internal pores of the particle. The terms "D n " and "D n Particle size" refer to the diameter below which there is a population of n% by volume of the particles, i.e. the terms "D 50 " and "D 50 Particle size" refer to the median particle size by volume below which there is a population of 50% by volume of the particles. In the case of materials comprising primary crystallites agglomerated into secondary particles, it is to be understood that the particle size refers to the diameter of the secondary particles. The particle size can be determined by laser diffraction. The particle size can be determined according to ISO 13320:2009, e.g. using the Mie theory.

[0088] The mixed niobium oxide can have a specific surface area in the range of 0.1-100 m 2 / g, or 0.2-50 m 2 / g, or 0.5-20 m 2The BET surface area is generally in the range of 0.1 to 10 m2 / g. Generally, a low BET surface area is preferred in order to minimize the reaction of the mixed niobium oxide with the electrolyte, for example, to minimize the formation of a solid electrolyte interphase (SEI) layer during the first charge-discharge cycle of an electrode comprising the material. However, a too low BET surface area can result in unacceptably low charge rates and capacities because the bulk of the mixed niobium oxide has little access to metal ions in the surrounding electrolyte.

[0089] The term "BET surface area" refers to the surface area per unit mass calculated using the Brunauer-Emmett-Teller theory by measuring the physical adsorption of gas molecules on the surface of a solid. For example, the BET surface area can be determined according to ISO 9277:2010.

[0090] The mixed niobium oxide can be coated with carbon, for example, to improve its surface electronic conductivity and / or to prevent reaction with the electrolyte.

[0091] The mixed niobium oxide can have a protective coating; optionally, the protective coating comprises niobium oxide, aluminum oxide, zirconium oxide, organic or inorganic fluorides, organic or inorganic phosphates, titanium oxide, lithiated versions thereof, and mixtures thereof.

[0092] In a first aspect, the mixed niobium oxide forms the active electrode material of an electrode, preferably the active electrode material of a lithium-ion battery anode. However, any of the mixed niobium oxides defined herein can be provided as an active electrode material suitable for incorporation into an electrode. For example, the mixed niobium oxides disclosed herein can be provided as a raw material rather than as part of an electrode, for example, for sale to an electrode manufacturer.

[0093] The electrode is typically in the form of an electrode composition in electrical contact with a current collector, wherein the electrode composition comprises the mixed niobium oxide. The current collector is typically a metal foil, for example, a copper or aluminum foil.

[0094] Optionally, the mixed niobium oxide forms at least 5 wt.%, 10 wt.% or 50 wt.% of the total active electrode material in the electrode. The mixed niobium oxide can form the only active electrode material in the electrode.

[0095] The electrode composition can further comprise at least one further component selected from the group consisting of a binder, a conductive additive, a different active electrode material (for example, a further mixed niobium oxide as defined herein), and mixtures thereof. For example, one electrode composition comprises about 92 wt.% of the mixed niobium oxide, about 5 wt.% of a conductive additive (for example, carbon black), and about 3 wt.% of a binder (for example, poly(vinylidene fluoride)) based on the total dry weight of the electrode composition.

[0096] Examples of suitable binders include polyvinylidene fluoride and copolymers thereof (PVDF), polytetrafluoroethylene (PTFE) and copolymers thereof, polyacrylonitrile (PAN), poly(meth)acrylic acid ester or poly(butyl)acrylic acid ester, polyvinyl chloride (PVC), polyvinyl formal, polyether amide, poly(meth)acrylic acid, polyacrylamide, polyitaconic acid, polystyrene sulfonic acid, polyacrylic acid (PAA) and alkali metal salts thereof, modified polyacrylic acid (mPAA) and alkali metal salts thereof, cellulose-based polymers, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginate and alkali metal salts thereof, butadiene acrylonitrile rubber (NBR), hydrogenated form of NBR (HNBR), styrene butadiene rubber (SBR), and polyimide. The binder can be present in the electrode composition in an amount of 0-30 wt.%, or 0.1-10 wt.%, or 0.1-5 wt.%, based on the total dry weight of the electrode composition.

[0097] The conductive additive is preferably a non-active material which is included to improve the electrical conductivity between the active electrode material and between the active electrode material and the current collector. The conductive additive can suitably be selected from graphite, carbon black, carbon fibres, vapour grown carbon fibres (VGCF), carbon nanotubes, graphene, acetylene black, ketjen black, metal fibres, metal powders and conductive metal oxides. Preferred conductive additives include carbon black and carbon nanotubes. The conductive additive can be present in the electrode composition in an amount of 0-20 wt.%, 0.1-10 wt.% or 0.1-5 wt.%, based on the total dry weight of the electrode composition.

[0098] The active electrode material can be present in the electrode composition in an amount of 100-50 wt.%, 99.8-80 wt.% or 99.8-90 wt.%, based on the total dry weight of the electrode composition. When the active electrode material is present in an amount of 100 wt.% of the electrode composition, the active electrode material can be used in a solid state electrode.

[0099] When a different active electrode material is present in addition to the mixed niobium oxide, the active electrode material can be selected from lithium titanium oxide, titanium niobium oxide, a different mixed niobium oxide, graphite, hard carbon, soft carbon, silicon, doped versions thereof, and mixtures thereof.

[0100] The mixed niobium oxide can be combined with lithium titanium oxide to form the active electrode material.

[0101] The lithium titanium oxide preferably has a spinel or orthorhombic crystal structure, for example as determined by X-ray diffraction. An example of a lithium titanium oxide having a spinel crystal structure is Li4Ti5O12. 12An example of lithium titanium oxides with an orthorhombic manganese oxide crystal structure is Li₂Ti₃O₇. These materials have been shown to have good properties for use as active electrode materials. Therefore, lithium titanium oxides can have the same structure as determined by X-ray diffraction as Li₄Ti₅O₇. 12 And / or the crystal structure of Li₂Ti₃O₇. Lithium titanium oxide may be selected from Li₄Ti₅O₇. 12 Li2Ti3O7 and its mixtures.

[0102] Lithium titanium oxides may be doped with additional cations or anions. Lithium titanium oxides may be oxygen-deficient. Lithium titanium oxides may form coatings, optionally wherein the coating is selected from carbon, polymers, metals, metal oxides, metalloids, phosphates, and fluorides.

[0103] Lithium titanium oxides can be synthesized using conventional ceramic techniques, such as solid-state synthesis or sol-gel synthesis. Alternatively, lithium titanium oxides can be obtained from commercial suppliers.

[0104] Lithium titanium oxide is preferably in particulate form. The lithium titanium oxide may have a density (D) in the range of 0.1-50 μm, or 0.25-20 μm, or 0.5-15 μm. 50 Particle size. Lithium titanium oxide may have a D particle size of at least 0.01 μm, or at least 0.1 μm, or at least 0.5 μm. 10 Particle size. Lithium titanium oxides may have a D particle size not exceeding 100 μm, 50 μm, or 25 μm. 90 Particle size. By using D 90 Maintaining the particle size within this range improves the packing of lithium titanium oxide particles in a mixture with mixed niobium oxide particles.

[0105] Due to the low electronic conductivity of the material, lithium titanium oxide is typically used in battery anodes with small particle sizes. Conversely, mixed niobium oxide, as defined herein, can be used with larger particle sizes because it typically has a higher lithium-ion diffusion coefficient than lithium titanium oxide. Advantageously, in the composition, lithium titanium oxide can have a smaller particle size than mixed niobium oxide, for example, making the Dx of the lithium titanium oxide... 50 Particle size and D of mixed niobium oxide 50 The particle size ratio is in the range of 0.01:1 to 0.9:1, or 0.1:1 to 0.7:1. In this way, smaller lithium titanium oxide particles can be accommodated in the voids between larger mixed niobium oxide particles, thereby improving the filling efficiency of the composition.

[0106] Lithium titanium oxide can have a range of 0.1-100 μm. 2 / g, or 1-50m 2 / g, or 3-30m 2 BET surface area within the range of / g.

[0107] The ratio by mass of lithium titanium oxide to mixed niobium oxide can be in the range of 0.5:99.5 to 99.5:0.5, preferably in the range of 2:98 to 98:2. In one embodiment, the active electrode material comprises a higher proportion of lithium titanium oxide than mixed niobium oxide, for example a ratio by mass of at least 2:1, at least 5:1, or at least 8:1. Advantageously, this allows mixed niobium oxide to be incrementally introduced into existing electrodes based on lithium titanium oxide without requiring major changes to manufacturing techniques, thereby providing an effective way to improve the properties of existing electrodes. In another embodiment, the active electrode material has a higher proportion of mixed niobium oxide than lithium titanium oxide, for example such that the ratio by mass of lithium titanium oxide to mixed niobium oxide is less than 1 :2, or less than 1 :5, or less than 1 :8. Advantageously, this allows the cost of the active electrode material to be reduced by replacing some of the mixed niobium oxide with lithium titanium oxide.

[0108] Mixed niobium oxide can be combined with niobium oxide to form the active electrode material. The niobium oxide can be selected from the group consisting of Nb 12 O 29 , NbO2, NbO and Nb2Os. Preferably, the niobium oxide is Nb2Os.

[0109] The niobium oxide can be doped with additional cations or anions, for example assuming that the crystal structure of the niobium oxide corresponds to that of an oxide consisting of Nb and O (for example, Nb 12 O 29 , NbO2, NbO and Nb2Os). The niobium oxide can be oxygen-deficient. The niobium oxide can constitute a coating, optionally wherein the coating is selected from the group consisting of carbon, a polymer, a metal, a metal oxide, a metalloid, a phosphate and a fluoride.

[0110] The niobium oxide can have the crystal structure of Nb 12 O 29 , NbO2, NbO or Nb2Os as determined by X-ray diffraction. For example, the niobium oxide can have the crystal structure of orthorhombic Nb2Os or the crystal structure of monoclinic Nb2Os. Preferably, the niobium oxide has the crystal structure of monoclinic Nb2Os, most preferably the crystal structure of H-Nb2Os. Further information on the crystal structure of Nb2Os can be found in Griffith et al., J. Am. Chem. Soc. 2016, 138, 28, 8888-8899.

[0111] The niobium oxide can be synthesised by conventional ceramic techniques, for example solid state synthesis or sol-gel synthesis. Alternatively, the niobium oxide can be obtained from a commercial supplier.

[0112] The niobium oxide is preferably in particulate form. The niobium oxide can have a D 50 particle size. The niobium oxide can have a D 10 particle size. The niobium oxide can have a D 90 particle size. By maintaining the D 90 particle size within this range, the packing of the niobium oxide particles in the mixture with which they are mixed is improved.

[0113] The niobium oxide can have a BET surface area in the range 0.1-100 m 2 / g, or 1-50 m 2 / g, or 1-20 m 2 / g.

[0114] The ratio by mass of niobium oxide to mixed niobium oxide can be in the range 0.5:99.5 to 99.5:0.5, or in the range 2:98 to 98:2, or preferably in the range 15:85 to 35:55.

[0115] The present application also provides the use of a mixed niobium oxide as defined herein in an anode of a metal-ion battery, optionally wherein the metal-ion battery is a lithium-ion or sodium-ion battery, preferably a lithium-ion battery. Lithium-ion batteries include liquid-based batteries, polymer-based batteries, semi-solid based batteries and all-solid-state based batteries.

[0116] A further embodiment of the present application is an electrochemical device comprising an anode, a cathode and an electrolyte disposed between the anode and the cathode, wherein the anode comprises an active electrode material according to the first aspect of the present application; optionally wherein the electrochemical device is a metal-ion battery, such as a lithium-ion battery or a sodium-ion battery. For example, the anode can be an electrode according to the first aspect of the present application. Preferably, the electrochemical device is a lithium-ion battery having a reversible anode active material specific capacity of greater than 180 mAh / g at 20 mA / g, wherein the battery is capable of charging and discharging at a current density of 200 mA / g or greater, or 1000 mA / g or greater, or 2000 mA / g or greater, or 4000 mA / g or greater, relative to the anode active material, while retaining greater than 70% of the initial cell capacity at 20 mA / g. It has been found that the use of an active electrode material according to the first aspect of the present application can enable the production of a lithium-ion battery having this combination of properties, which represents a lithium-ion battery particularly suitable for applications where high charging and discharging current densities are desired. Notably, examples have shown that the active electrode material according to the first aspect of the present application has an excellent capacity retention at high C-rates.

[0117] Electrochemical devices preferably have an N / P ratio >1, where N / P is defined as:

[0118]

[0119] in:

[0120] Area loading (mg / cm-) 2 () is the dry loading of the electrode composition, without considering the current collector;

[0121] The active fraction (wt%) is the percentage of the dry electrode composition used as the active material;

[0122] First lithiation / delithiation capacity (mAhg) -1 ) is the specific capacity at C / 10 at 25°C, measured on an equivalent half-cell cell with a lithium metal counter electrode, during the first lithiation cycle of the anode or the first delithiation cycle of the cathode.

[0123] The first lithiation / delithiation capacity was measured on an equivalent half-cell cell. An equivalent half-cell cell can be understood as utilizing the same electrode composition deposited with the same areal loading and activity fraction as a full-cell cell. For the anode, the first constant current C / 10 lithiation (discharge, negative current) capacity (relative to Li / Li+) was measured at 25°C. For the cathode, the first constant current C / 10 delithiation (charge, positive current) capacity (relative to Li / Li+) was measured at 25°C.

[0124] N / P is preferably greater than 1, for example, ≥1.01. N / P can be in the range of >1-2, or 1.01-1.5, or most preferably 1.05-1.3.

[0125] The cathode comprises an active cathode material, which may be selected from LiNi. 1-x M x O2-based nickel-based oxides (where M = Co, Mn, Al), such as NMC (lithium nickel manganese cobalt oxide), NCA (lithium cobalt aluminum oxide), and LCO (lithium cobalt oxide); and LNMO (lithium nickel manganese oxide) (e.g., LiNi). 0.5 Mn 1.5 O4). For example, the active cathode material can be lithium nickel manganese cobalt oxide. Active cathode materials are widely available from commercial suppliers. Active cathode materials may be doped with additional cations and / or anions.

[0126] The choice of active electrode material can affect the appropriate voltage range, including for determining the first lithiation / delithiation capacity. For example, the appropriate voltage range can be LNMO: 5.2-3V, upper cutoff at 5.2V; NCA, NMC, and LCO: 4.5-2.7V, upper cutoff at 4.5V; mixed niobium oxide: 3-0V, lower cutoff at 0V. A narrower range can be LNMO: 5-3V, upper cutoff at 5V; NCA, NMC, and LCO: 4.3-2.7V, upper cutoff at 4.3V; mixed niobium oxide: 3V-1.0V, lower cutoff at 1.0V.

[0127] The appropriate voltage range can be determined empirically. For example, the voltage profile is related to the change in energy state of the anode and cathode materials, which is associated with the removal or insertion of electrons and ions. The cutoff voltage of the battery cell can be chosen to fall before a particular inflection point in the voltage profile, which corresponds to the energy state of one or both electrodes rising above a critical level that causes the crystal structure to decay to a lower energy structure at a rate that is significantly detrimental to the performance of the battery cell. The absolute voltage at which this occurs is a function of the electrode potential of both electrodes, but can be calculated by using a common reference electrode, and does not need to be determined experimentally for well-behaved families of materials with reliable standard electrochemical behavior.

[0128] The cathode active material is preferably in particulate form, for example having a D50 in the range 0.1-100 pm or 0.5-50 pm or 1-20 pm. 50 Particle size.

[0129] The electrolyte can include any material suitable for metal ion battery operation, preferably lithium ion battery operation. For example, the electrolyte can be a non-aqueous solution (e.g., an organic electrolytic solution). The electrolyte can include one or more non-aqueous solvents and a salt at least partially dissolved in the solvent. For example, the solvent can include an organic solvent such as, for example, ethylene carbonate (EC) and / or other carbonate-based solvents, or butyrate, or acetate, or mixtures thereof. The solvent can include 1M LiPF6 dissolved in a mixture of aprotic solvents such as, for example, a 1:1 mixture by weight of ethylene carbonate and other carbonate-based solvents or butyrate or acetate.

[0130] Suitable salts for use in the present application include LiPF6, LiSbF6, LiBF4, LiTFSI, LiFSI, LiAlCl4, LiAsF6, LiClO4, LiGaCl4, LiC(SO2CF3)3, LiN(CF3SO2)2, Li(CF3SO3), LiB(C6H4O2)2, LiBOB (lithium bis(oxalato)borate), and LiDFOB (lithium difluoro(oxalato)borate). Suitable low viscosity solvents (e.g., organic solvents) for use in the electrolyte can include, but are not limited to, ethyl methyl carbonate (EMC), dioxolane (DOL), ethyl acetate (EA); propyl acrylate (PA); butyl acetate (BA); methyl butanoate (MB); ethyl butanoate (EB); dimethyl carbonate (DMC); diethyl carbonate (DEC); 1,2-dimethoxyethane (DME); tetrahydrofuran (THF); methyl acetate (MA); diethylene glycol dimethyl ether (DGL); triethylene glycol dimethyl ether; tetraethylene glycol dimethyl ether; cyclic carbonates; cyclic esters; cyclic amides; propylene carbonate (PC); methyl propylene carbonate (MPC); acetonitrile; dimethyl sulfoxide (DMS); dimethylformamide; dimethylacetamide; gamma-butyrolactone (GBL); and N-methyl pyrrolidone (NMP); and various mixtures or combinations thereof.

[0131] The mixed niobium oxide can be synthesized by conventional ceramic techniques. For example, it can be made by one or more of solid state synthesis or sol-gel synthesis. The mixed niobium oxide can additionally be synthesized by one or more of commonly used alternative techniques such as hydrothermal or microwave hydrothermal synthesis, solvothermal or microwave solvothermal synthesis, co-precipitation synthesis, spark or microwave plasma synthesis, combustion synthesis, electrospinning, spray pyrolysis, chemical vapor deposition, atomic layer deposition, and mechanical alloying.

[0132] The mixed niobium oxide can be provided by a method comprising the steps of: providing one or more precursor materials; mixing the precursor materials to form a precursor material mixture; and heat treating the precursor material mixture at a temperature in the range of 400-1350 or 800-1250, thereby providing the mixed niobium oxide.

[0133] To provide the mixed niobium oxide comprising additional electronegative anions other than oxygen, the method can further comprise the steps of: mixing the mixed niobium oxide with a precursor comprising the additional electronegative anion to provide a further precursor material mixture; and optionally heat treating the further precursor material mixture at a temperature in the range of 300-1200 or 800-1100 under reducing conditions, thereby providing the mixed niobium oxide comprising the additional electronegative anion.

[0134] For example, to provide mixed niobium oxide comprising N, the method can further comprise the steps of mixing the mixed niobium oxide with a precursor comprising N (e.g. melamine or urea) to provide a further precursor material mixture; and heat treating the further precursor material mixture under reducing conditions (e.g. under N2) at a temperature in the range 300-1200, thereby to provide mixed niobium oxide comprising N.

[0135] For example, to provide mixed niobium oxide comprising F, the method can further comprise the steps of mixing the mixed niobium oxide with a precursor comprising F (e.g. polyvinylidene fluoride or NH4F) to provide a further precursor material mixture; and heat treating the further precursor material mixture under oxidising conditions (e.g. in air) at a temperature in the range 300-1200, thereby to provide mixed niobium oxide comprising F.

[0136] The method can comprise a further step of heat treating the mixed niobium oxide under reducing conditions at a temperature in the range 400-1350 or 800-1250, thereby to induce further oxygen vacancies in the mixed niobium oxide.

[0137] The precursor material for making the mixed niobium oxide can comprise one or more metal oxides, metal hydroxides, metal salts or ammonium salts. For example, the precursor material can comprise one or more metal oxides or metal salts of different oxidation states and / or different crystal structures. Examples of suitable precursor materials include, but are not limited to: Nb2O5, Nb(OH)5, niobic acid, NbO, ammonium niobate oxalate, NH4H2PO4, (NH4)2PO4, (NH4)3PO4, P2O5, H3PO3, Ta2O5, WO3, ZrO2, TiO2, MoO3, V2O5, ZrO2, CuO, ZnO, Al2O3, K2O, KOH, CaO, GeO2, Ga2O3, SnO2, CoO, Co2O3, Fe2O3, Fe3O4, MnO, MnO2, NiO, Ni2O3, H3BO3, ZnO, Li2CO3, Na2CO3, H3BO3, NiO, Mg5(CO3)4(OH)2.5H2O and MgO. The precursor material can not comprise a metal oxide, or can comprise a source of ions other than an oxide. For example, the precursor material can comprise a metal salt (e.g. NO3 - , SO3 -) or other compounds (e.g., oxalate, carbonate). For substitution of the oxide anion with other electronegative anions, the precursor can include one or more organic compounds, polymers, inorganic salts, organic salts, gases, or ammonium salts; examples include, but are not limited to: melamine, NH4HCO3, NH3, NH4F, PVDF, PTFE, NH4CI, NH4Br, NH4I, Br2, CI2, I2, ammonium oxychloride amide, and hexamethylenetetramine.

[0138] When it is desired to make a mixed niobium oxide comprising cations of a particular oxidation state, a precursor comprising cations in that oxidation state can be selected. For example, when it is desired to make a mixed niobium oxide comprising Mn 2+ , MnO can be used as a precursor. When it is desired to make a mixed niobium oxide comprising Mn 4+ , MnO2 can be used as a precursor.

[0139] Some or all of the precursor materials can be particulate materials. Where they are particulate materials, preferably they have a D 50 particle size of less than 20 pm (e.g., 10 nm to 20 pm). Providing particulate materials having such a particle size can help to facilitate more intimate mixing of the precursor materials, resulting in more efficient solid state reactions during the heat treatment step. However, it is not essential that the precursor materials have an initial particle size of <20 pm, as the particle size of one or more of the precursor materials can be mechanically reduced during the step of mixing the precursor materials to form the precursor material mixture.

[0140] The step of mixing the precursor materials to form the precursor material mixture and / or further precursor material mixtures can be carried out by a process selected from dry or wet / solvated planetary ball milling, rolling ball milling, high energy ball milling, bead milling, pin milling, fractionation steps, high shear milling, air jet milling, steam jet milling, planetary mixing, powder packing, and / or impact milling. The force used for mixing / milling can depend on the morphology of the precursor materials. For example, where some or all of the precursor materials have a larger particle size (e.g., a D 50 particle size of greater than 20 pm), the milling force can be selected to reduce the particle size of the precursor materials such that the particle size of the precursor material mixture is reduced to 20 pm or less in diameter. Where the particle size of the particles in the precursor material mixture is 20 pm or less, this can facilitate more efficient solid state reactions of the precursor materials in the precursor material mixture during the heat treatment step. Solid state synthesis can also be carried out in pellets formed from the precursor powders under high pressure (>10 MPa).

[0141] The step of heat treating the precursor material mixture and / or the further precursor material mixture can be performed for a period of 1 hour to 24 hours, more preferably 3 hours to 18 hours. For example, the heat treating step can be performed for 1 hour or more, 2 hours or more, 3 hours or more, 6 hours or more, or 12 hours or more. The heat treating step can be performed for 24 hours or less, 18 hours or less, 16 hours or less, or 12 hours or less.

[0142] The step of heat treating the precursor material mixture can be performed in a gaseous atmosphere, preferably air. Suitable gaseous atmospheres include: air, N2, Ar, He, CO2, CO, O2, H2, NH3, and mixtures thereof. The gaseous atmosphere can be a reducing atmosphere. Where it is desired to produce an oxygen-deficient material, preferably the step of heat treating the precursor material mixture is performed in an inert or reducing atmosphere.

[0143] The step of heat treating the further precursor material mixture can be performed under reducing conditions. Reducing conditions include under an inert gas, such as nitrogen, helium, argon; or under a mixture of an inert gas and hydrogen; or under vacuum. Preferably, the step of heat treating the further precursor material mixture comprises heating under an inert gas.

[0144] The further step of heat treating the mixed niobium oxide and / or the mixed niobium oxide comprising additional electronegative anions, optionally under reducing conditions, can be performed for a period of 0.5 hours to 24 hours, more preferably 2 hours to 18 hours. For example, the heat treating step can be performed for 0.5 hours or more, 1 hour or more, 3 hours or more, 6 hours or more, or 12 hours or more. The further step of heat treating can be performed for 24 hours or less, 18 hours or less, 16 hours or less, or 12 hours or less. Reducing conditions include under an inert gas, such as nitrogen, helium, argon; or under a mixture of an inert gas and hydrogen; or under vacuum. Preferably, heating under reducing conditions comprises heating under an inert gas.

[0145] In some methods, it can be advantageous to perform a two-step heat treatment. For example, the precursor material mixture and / or the further precursor material mixture can be heated at a first temperature for a first length of time, and subsequently heated at a second temperature for a second length of time. Preferably, the second temperature is higher than the first temperature. Performing such a two-step heat treatment can aid the solid state reaction to form the desired crystal structure. This can be performed sequentially, or can be performed with an intermediate regrinding step.

[0146] The method can comprise one or more post-processing steps after formation of the mixed niobium oxide. In some cases, the method can comprise a post-processing step of heat treating the mixed niobium oxide, sometimes referred to as 'annealing'. Such a post-processing heat treatment step can be performed in a different gas atmosphere to the step of heat treating the precursor material mixture to form the mixed niobium oxide. The post-processing heat treatment step can be performed in an inert or reducing gas atmosphere. Such a post-processing heat treatment step can be performed at a temperature higher than 500°C, for example at about 900°C. Incorporating a post-processing heat treatment step can be beneficial, for example, to form vacancies or defects in the mixed niobium oxide, for example to induce oxygen deficiency; or to perform anion exchange on the formed mixed niobium oxide, for example to exchange O anions with N.

[0147] The method can comprise the step of milling and / or classifying (e.g. impact milling, jet milling, steam jet milling, high energy milling, high shear milling, pin milling, air classification, wheel classification, sieving, cyclone separation, bead milling) the mixed niobium oxide to provide material having any of the particle size parameters given above.

[0148] The present application provides a method of making an electrode, the method comprising providing a mixed niobium oxide as defined herein; and depositing the mixed niobium oxide onto a current collector, thereby forming an electrode. Providing the mixed niobium oxide can comprise synthesising the mixed niobium oxide by a method provided herein. The step of depositing can comprise forming a slurry of the mixed niobium oxide and a solvent. The slurry can comprise at least one further component selected from a binder, a conductive additive, a different active electrode material, and mixtures thereof. The slurry can be deposited onto a current collector and the solvent removed, thereby forming an electrode layer on the current collector. Further steps can be implemented as appropriate, such as a heat treatment for curing any binder and / or calendering of the electrode layer. For example, the solvent can be removed by drying, for example at a temperature of 30-100. The electrode can be calendered to a density of 2-3.5 or 2.6-2.9 g cm -3 The electrode layer can have a thickness in the range of 5 pm to 2 mm, preferably 5 pm to 1 mm, preferably 5 pm to 500 pm, preferably 5 pm to 200 pm, preferably 5 pm to 100 pm, preferably 5 pm to 50 pm.

[0149] Alternatively, the slurry can be shaped into a self-supporting film or mat comprising the mixed niobium oxide, for example by casting the slurry onto a suitable casting template, removing the solvent, and then removing the casting template. The resulting film or mat is in the form of a cohesive self-supporting mass, which can then be bonded to a current collector by known methods.

[0150] Example

[0151] Mixed niobium oxides are synthesized via a solid state route. For example, an appropriate amount of Nb2O5and precursor materials are mixed and ground using a pestle and mortar or an impact mill to form a homogeneous precursor mixture. The resulting mixture is heat treated to high temperature (> 800 °C) using a heating rate of between 5-10 °C / min in an alumina crucible for 6-12 h. The process is repeated until the desired single phase (4x4 Wadsley-Roth block structure) is observed in the X-ray diffraction pattern. Specifically, stoichiometric amounts of precursor materials (Nb2O5, Li2CO3, Na2CO3, H3BO3, TiO2, Al2O3, Fe2O3, Cr2O3, NiO and Mg5(CO3)4(OH)2.5H2O) are mixed and hand ground in a pestle and mortar for 15 minutes (about 5 g) or using an impact mill at 20,000 rpm for 4 minutes (about 50 g). The resulting powder is placed in an alumina crucible and heat treated in a muffle furnace in air at T1= 875-1150 °C, optionally 900-1150 °C for 6-12 h. All heating steps use a heating rate of 5 °C / min. Optionally, an additional grinding and heat treatment step T2 is performed to improve phase purity. After this, a final grinding step is performed using a pestle and mortar or an impact mill to perform de-agglomeration. The composition and synthesis parameters are summarized in Table 1.

[0152]

[0153]

[0154]

[0155] Table 1: Summary of synthesized materials

[0156] Material Characterization

[0157] The phase purity of the samples is analyzed using a Rigaku Miniflex powder X-ray diffractometer in the 2 theta range (10-70°) with a scan rate of 1 ° / min or a Bruker D8 powder diffractometer in the 2 theta range 10-50° or 10-60° (step size 0.0189°, time per step 0.42 s).

[0158] Figure 1 Figure 3 The measured XRD diffractograms of selected samples are shown. Figure 2 The TEM micrographs showing the obtained highly crystalline structure are shown. Table 2 provides the unit cell parameters obtained from Pawley refinement based on the N-Nb2O5structure.

[0159]

[0160] ​​

[0161] Table 2: Summary of cell parameters of samples calculated from Pawley refinement in Topas software.

[0162] Electrochemical Characterization

[0163] Li-ion battery cell charge rates are typically expressed as "C-rates". A 1C charge rate means the charging current at which the battery cell is fully charged in 1 hour, a 10C charge means the battery is fully charged in 1 / 10th of an hour (6 minutes). The C-rate here is defined in terms of the reversible capacity of the anode observed within the voltage limit applied in the second cycle delithiation of the anode, i.e. for an anode showing 1.0 mAh cm -2 of active material within the 1.1-3.0V voltage limit, the 1C rate corresponds to a current density of 1.0 mA cm -2 of active material applied. In typical materials as described herein, this corresponds to about 185 mA / g active material.

[0164] Electrochemical tests were performed in half coin cells (CR2032 size) for analysis. In half coin testing, active material was tested in electrodes versus Li metal electrodes to assess its fundamental performance. In the following examples, the active material composition to be tested was combined with N-methyl pyrrolidone (NMP), carbon black (Super P) acting as a conductive additive, and poly(vinylidene fluoride) (PVDF) binder, and mixed using a laboratory scale centrifugal planetary mixer to form a slurry. The non-NMP composition of the slurry was 92 wt% active material, 5 wt% conductive additive, 3 wt% binder. The slurry was coated on an Al foil current collector by doctor blade coating to a desired loading of 50-100 g m -2 of active material, and dried by heating. The electrodes were then calendered to a density of 2.6-2.9 g cm -3 to achieve a target porosity of 35-47%. The electrodes were punched to the desired size and combined with a separator (Celgard porous PP / PE), Li metal, and electrolyte (1.3 M LiPF6 in EC / DEC) within a steel coin cell housing and sealed under pressure. The cells were then cycled between 1.1-3.0V at low current rate (C / 10) at 25°C to achieve 2 full lithiation and delithiation cycles. Following this, the cells were tested for performance at increasing current density. During these tests, the cells were subjected to asymmetric cycling at 25°C, with slow lithiation first (C / 5), followed by increasing delithiation rates (e.g. 1C, 5C, 10C) to provide capacity retention.

[0165] Data for 3 to 5 cells prepared from the same electrode coating were averaged, and the error is represented by the standard deviation. Thus, these data represent a robust study showing the improvement achieved with the material according to the invention compared to the previous materials. These data are shown in Tables 3 and 4. The curves of voltage versus state of charge for samples 1 and 18 are shown in Figure 4

[0166] For homogenous, smooth coatings on Cu and Al current collector foils, coatings without visible defects or agglomerates were also prepared with a centrifugal planetary mixer up to 94 wt% active material, 4 wt% conductive additive, 2 wt% binder composition as for these samples above. These were prepared with PVDF (i.e. NMP based) and CMC:SBR (i.e. water based) binder systems. The coatings could be calendered to 35% to 40% porosity at 80°C for PVDF and 50°C for CMC:SBR at 1.0 to 5.0 mAh cm -2 This is important to demonstrate the feasibility of these materials in high energy and high power applications with high active material content.

[0167]

[0168]

[0169] Table 3: Performance of electrodes at C / 10 over 2 full lithiation and delithiation cycles between 1.1-3.0V

[0170]

[0171] Table 4: Performance of electrodes at increasing current density

[0172] Discussion

[0173] The mixed niobium oxides according to the invention were found to exhibit remarkable properties at high delithiation rates, for example 5C and 10C. In particular, in some cases, the specific capacity at lower rates was largely maintained at high rates, for example the capacity at 10C was 97.7% or more of the capacity at 0.5C; this is an extremely high capacity retention. These are important results demonstrating the advantages of the mixed niobium oxides of the invention for the design of high power batteries for fast charge / discharge.​

Claims

1. An electrode comprising a mixed niobium oxide as active electrode material, wherein the electrode is in the form of an electrode composition in electrical contact with a current collector, wherein the electrode composition comprises a mixed niobium oxide, wherein the mixed niobium oxide has a Wadsley-Roth block structure comprising 4x4 octahedral blocks, wherein the mixed niobium oxide has the formula M I x-u M y (x / (5-y)) M V z Nb 100-(x / (5-y))-z O 250-u / 2 wherein: M I is a cation with oxidation state 1, wherein M I is selected from Li, Na, K and mixtures thereof; M y It is a cation with an average oxidation state of y, where M y Selected from Li, Na, K, Cu, Zn, Mg, Ca, Ni, Fe, Mn, Co, Cr, V, Al, B, Ga, Sc, Y, In, La, Yb, Ce, Zr, Ti, Sn, Ge, Si, P, Ta, W, Mo and mixtures thereof; M V It is a cation with an average oxidation state of 5, wherein M V Selected from Mn, Fe, Al, Ga, Y, In, La, Yb, Cu, Zn, Mg, Ni, Co, Ca, Ce, Zr, Ti, Sn, Ge, Si, V, P, Ta, W, Mo, Cr and mixtures thereof; 1 ≤ y ≤ 4； 0.5 ≤ x ≤ 6； 0 ≤ z ≤ 10； 0 ≤ u ≤ 5； x > u.

2. The electrode according to claim 1, wherein (i) M y Selected from Li, Na, K, Cu, Zn, Mg, Ni, Fe, Mn, Co, Cr, V, Al, B, Ga, Zr, Ti, Si, P, Ta and mixtures thereof; or (ii) M y Selected from Li, Na, Cu, Zn, Mg, Ni, Fe, Mn, Co, Cr, Al, B, Ga, Zr, Ti and their mixtures.

3. The electrode according to claim 1, wherein: (i) y is 1, 2, 3, or 4; or (ii) y is 2 ≤ y ≤ 4; or (iii) y is 2, 3 or 4.

4. The electrode according to claim 1, wherein M is formed y All cations have the same oxidation state.

5. The electrode according to claim 1, wherein: M I Selected from Li, Na, and mixtures thereof.

6. The electrode according to claim 1, wherein the mixed niobium oxide has the formula M I x-u N I x / 4 M V z Nb 100-x / 4- z O 250-u / 2 ,in: N I It is a cation with an oxidation state of 1.

7. The electrode according to claim 6, wherein: (i) N I Selected from Li, Na, K and mixtures thereof; or (ii) N I Selected from Li, Na, and mixtures thereof.

8. The electrode according to claim 1, wherein the mixed niobium oxide has the formula M I x-u M II x / 3 M V z Nb 100-x / 3- z O 250-u / 2 ,in: M II It is a cation with an average oxidation state of 2.

9. The electrode according to claim 8, wherein M is formed II All of the cations have an oxidation state of 2.

10. The electrode according to claim 8, wherein: (i) M II Selected from Cu, Zn, Mg, Ni, Fe, Mn, Co, Ca and mixtures thereof; or (ii) M II Selected from Cu, Zn, Mg, Ni and mixtures thereof; or (iii) M II Selected from Zn, Mg, Ni and their mixtures.

11. The electrode according to claim 1, wherein the mixed niobium oxide has the formula M I x-u M III x / 2 M V z Nb 100-x / 2- z O 250-u / 2 ,in: M III It is a cation with an average oxidation state of 3.

12. The electrode of claim 11, wherein M is formed III All of the cations have an oxidation state of 3.

13. The electrode according to claim 11, wherein: (i) M III Selected from Mn, Cr, V, Fe, Al, B, Ga, Y, In, La, Yb, Ce and mixtures thereof; or (ii) M III Selected from Mn, Cr, Fe, Al, B, Ga, Y and mixtures thereof; or (iii) M III Selected from Cr, Al, Fe and their mixtures.

14. The electrode according to claim 1, wherein the mixed niobium oxide has the formula M I x-u M IV x M V z Nb 100-x-z O 250-u / 2 ,in: M IV It is a cation with an average oxidation state of 4.

15. The electrode of claim 14, wherein M is formed IV All of the cations have an oxidation state of 4.

16. The electrode according to claim 14 or 15, wherein: (i) M IV Selected from Zr, Ti, Mn, Ce, Sn, Ge, V, Si and mixtures thereof; or (ii) M IV Selected from Zr, Ti, Sn, Ge, V and mixtures thereof; or (iii) M IV It consists of Ti, V, and mixtures thereof.

17. The electrode according to claim 1, wherein: (i) x is 1, 2, 3, 4, 5, or 6; or (ii) x is 2 ≤ x ≤ 5; or (iii) x = 4.

18. The electrode according to claim 1, wherein: (i) 0 ≤ u ≤ 3; or (ii) 0.01 ≤ u ≤ 2; or (ii) u = 0.

19. The electrode according to claim 1, wherein x ≥ u + 1.

20. The electrode of claim 1, wherein the mixed niobium oxide contains only Li if there are further cations other than Li and Nb.

21. The electrode according to claim 1, wherein M y It does not contain Li, or the mixed niobium oxide described therein does not contain Li.

22. The electrode according to claim 1, wherein: (i) M V Selected from Ce, Zr, Ti, Sn, Ge, Si, V, P, Ta, W, Mo, Cr and mixtures thereof; or (ii) M V Selected from V, P, Ta and their mixtures.

23. The electrode according to claim 1, wherein M is formed V All of the cations have an oxidation state of 5.

24. The electrode according to claim 1, wherein: (i) 0 ≤ z ≤ 5; and / or (ii) z > 0; or (iii) z = 0.

25. The electrode of claim 1, wherein the cation is partially replaced by cations of different oxidation states; optionally, up to 20 atomic percent of the cation is replaced by cations of different oxidation states.

26. The electrode of claim 1, wherein the oxygen anions are partially replaced by electronegative anions such as F, Cl, Br, S, Se, N and mixtures thereof; optionally, up to 10 atomic percent of the oxygen anions have been partially replaced by electronegative anions.

27. The electrode according to claim 1, wherein the mixed niobium oxide has a D in the range of 0.1-100 μm, or 0.5-50 μm, or 1-20 µm. 50 Particle size.

28. The electrode according to claim 1, wherein the mixed niobium oxide has a content of 0.1-100 μm. 2 / g, or 0.2-50m 2 / g, or 0.5-20 m 2 BET surface area within the range of / g.

29. The electrode of claim 1, wherein the mixed niobium oxide is coated with carbon.

30. The electrode of claim 1, wherein the mixed niobium oxide has a protective coating; optionally, wherein the protective coating comprises niobium oxide, aluminum oxide, zirconium oxide, organic and inorganic fluorides, organic and inorganic phosphates, titanium oxide, its lithiated form, and mixtures thereof.

31. The electrode according to claim 1, wherein the mixed niobium oxide has a monoclinic crystal structure; optionally, wherein the mixed niobium oxide has cell parameters a = 25.7-31.4 Å, b = 3.4-4.2 Å, c = 15.8-19.3 Å, α = 90°, β = 112.6-137.6°, γ = 90°.

32. The electrode according to claim 1, wherein the crystal structure of the mixed niobium oxide corresponds to the crystal structure of N-Nb2O5.

33. The electrode according to claim 1, wherein the mixed niobium oxide forms at least 5%, 10%, or 50% by weight of the total active electrode material in the electrode; or wherein the mixed niobium oxide is the only active electrode material in the electrode.

34. The electrode according to claim 1, further comprising at least one other component selected from binders, conductive additives, different active electrode materials and mixtures thereof.

35. The electrode of claim 34, wherein the different active electrode materials are selected from lithium titanium oxide, titanium niobium oxide, different mixed niobium oxides, graphite, hard carbon, soft carbon, silicon, their doped and / or carbon-coated forms, and mixtures thereof.

36. A metal-ion battery comprising an electrode according to any one of claims 1 to 35, optionally wherein the metal-ion battery is a lithium-ion battery, and said electrode forms an anode.

37. The metal-ion battery of claim 36, wherein the metal-ion battery is a lithium-ion battery having a reversible anode active material specific capacity of greater than 180 mAh / g at 20 mA / g, wherein the battery is capable of charging and discharging at a current density of 200 mA / g or greater, or 1000 mA / g or greater, or 2000 mA / g or greater, or 4000 mA / g or greater relative to the anode active material, while retaining greater than 70% of the initial cell capacity at 20 mA / g.

38. An electrochemical device comprising an anode, a cathode, and an electrolyte disposed between the anode and the cathode, wherein the anode comprises a mixed niobium oxide as the active anode material according to any one of claims 1 to 32, wherein the device has an N / P ratio >1, wherein N / P is defined as: in: Area loading (mg / cm-) 2 () is the dry loading of the electrode composition, without considering the current collector; The active fraction (wt%) is the percentage of the dry electrode composition that serves as the active material; First lithiation / delithiation capacity (mAhg) -1 ) is the specific capacity at C / 10 at 25°C, measured on an equivalent half-cell cell with a lithium metal counter electrode, during the first lithiation cycle of the anode or the first delithiation cycle of the cathode.

39. The use of the mixed niobium oxide according to any one of claims 1 to 32 in a metal-ion battery; optionally as an active electrode material in the anode of a lithium-ion battery.

40. A method for manufacturing an electrode, the method comprising: Provides a mixed niobium oxide as claimed in any one of claims 1 to 32; as well as The mixed niobium oxide is deposited onto the current collector to form the electrode.

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