Active electrode material

Abstract

The invention relates to a method of making niobium-containing metal oxide granules for the manufacture of a niobium-containing active electrode material. The method comprises: providing at least one precursor material comprising niobium; and compacting the at least one precursor material to form niobium-containing metal oxide granules, wherein the ratio of the tapped density of the niobium-containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55.

Description

[0001] Active electrode material

[0002] Field of the Invention

[0003] The present invention relates to active electrode materials, methods for the manufacture of 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.

[0004] Background

[0005] Lithium-ion (Li-ion) batteries are a commonly used type of rechargeable battery with a global market predicted to grow to $200bn by 2030. Li-ion batteries are the technology of choice for electric vehicles that have multiple demands across technical performance to environmental impact, providing a viable pathway for a green automotive industry.

[0006] A typical lithium-ion battery is composed of multiple cells connected in series or in parallel. Each individual cell is usually composed of an anode (negative polarity electrode) and a cathode (positive polarity electrode), separated by a porous, electrically insulating membrane (called a separator), immersed into a liquid (called an electrolyte) enabling lithium ions transport.

[0007] In most systems, the electrodes are composed of an active electrode material - meaning that it is able to chemically react with lithium ions to store and release them reversibly in a controlled manner - mixed if necessary with an electrically conductive additive (such as carbon) and a polymeric binder. A slurry of these components is coated as a thin film on a current collector (typically a thin foil of copper or aluminium), thus forming the electrode upon drying.

[0008] In the known Li-ion battery technology, the safety limitations of graphite anodes upon battery charging is a serious impediment to its application in high-power electronics, automotive and industry. Among a wide range of potential alternatives proposed recently, lithium titanate (LTO) and mixed niobium oxides are the main contenders to replace graphite as the active material of choice for high power, fast-charge applications.

[0009] Batteries relying on a graphitic anode are fundamentally limited in terms of charging rate. Under nominal conditions, lithium ions are inserted into the anode active material upon charging. When charging rate increases, typical graphite voltage profiles are such that there is a high risk that overpotentials lead to the potential of sites on the anode to become < 0 V vs. Li / Li+, which leads to a phenomenon called lithium dendrite electroplating, whereby lithium ions instead deposit at the surface of the graphite electrode as lithium metal. This leads to irreversible loss of active lithium and hence rapid capacity fade of the cell. In some cases, these dendritic deposits can grow to such large sizes that they pierce the battery separator and lead to a short-circuit of the cell. This can trigger a catastrophic failure of the cell leading to a fire or an explosion. Accordingly, the fastest-charging batteries having graphitic anodes are limited to charging rates of 5-7 C, but often much less.

[0010] Lithium titanate (LTO) anodes do not suffer from dendrite electroplating at high charging rate thanks to their high potential (1 .6 V vs. LI / LI+) , and have excellent cycle life as they do not suffer from significant volume expansion of the active material upon intercalation of Li ions due to their accommodating 3D crystal structure. LTO cells are typically regarded as high safety cells for these two reasons. However, LTO is a relatively poor electronic and ionic conductor, which leads to limited capacity retention at high rate and resultant power performance, unless the material is nanosized to increase specific surface area, and carbon-coated to increase electronic conductivity. This particle-level material engineering increases the porosity and specific surface area of the active material, and results in a significantly lower achievable packing density in an electrode. This is significant because it leads to low density electrodes and a higher fraction of electrochemically inactive material (e.g. binder, carbon additive), resulting in much lower gravimetric and volumetric energy densities.

[0011] A key measure of anode performance is the electrode volumetric capacity (mAh / cm3), that is, the amount of electric charges (that is lithium ions) that can be stored per unit volume of the anode. This is an important factor to determine the overall battery energy density on a volumetric basis (Wh / L) when combined with the cathode and appropriate cell design parameters. Electrode volumetric capacity can be approximated as the product of electrode density (g / cm3), active material specific capacity (mAh / g), and fraction of active material in the electrode. LTO anodes typically have relatively low specific capacities (c. 165 mAh / g, to be compared with c. 330 mAh / g for graphite) which, combined with their low electrode densities (typically <2.0 g / cm3) and low active material fractions (<90%) discussed above, lead to very low volumetric capacities (<300 mAh / cm3) and therefore 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.

[0012] However, there remains a need to identify further active electrode materials, in particular with good properties for use in Li-ion cells intended for high-power / fast-charging applications. Identifying such materials e.g. without the need for extensive particle-level engineering and / or without coatings is an important step to low-cost battery materials for mass market uptakes. Niobium-based electrode active materials have been identified as key candidates to address these issues with LTO and graphite materials, however their manufacturing process requires further improvements.

[0013] Herein, we describe a method to reduce the typically long and high temperature conditions required to manufacture niobium-based electrode active materials through improving powder flowability before heat treatment. Summary of the Invention

[0014] In a first aspect, the invention provides a method of making niobium-containing metal oxide granules, the method comprising: providing at least one precursor material comprising niobium; and compacting the at least one precursor material to form niobium-containing metal oxide granules, wherein the ratio of the tapped density of the niobium-containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55.

[0015] The inventors have found that niobium-containing metal oxide granules according to the first aspect have improved processability and enable significant improvements in the manufacturing of materials for use in high-power batteries suitable for fast charge / discharge, as shown by the examples presented herein.

[0016] In a second aspect, the invention provides niobium-containing metal oxide granules wherein the ratio of the tapped density of the niobium-containing metal oxide granules to the bulk density of the niobium- containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55, preferably wherein said granules are obtained or obtainable by the method of the first aspect.

[0017] In a third aspect, the invention provides niobium-containing metal oxide granules obtained or obtainable by the method of the first aspect.

[0018] In a fourth aspect, the invention provides a process for the manufacture of a niobium-containing active electrode material comprising the steps of:

[0019] (i) heating the niobium-containing metal oxide granules of the second or third aspects, preferably at a temperature in the range of from 600 to 1300 °C, preferably for a time in the range of from 0.1 to 6 hours; and

[0020] (ii) optionally, modifying the particle size distribution of the niobium-containing material obtained from step (i), preferably when said modifying step is or comprises deagglomeration.

[0021] In a fifth aspect, the invention provides a niobium-containing active electrode material obtained or obtainable from said niobium-containing metal oxide granules of the second or third aspects, preferably wherein said niobium-containing active electrode material is obtained or obtainable by the process of the fourth aspect.

[0022] In a sixth aspect, the invention provides the use of the niobium-containing metal oxide granules of the second or third aspects in the manufacture of a niobium-containing active electrode material.

[0023] In a seventh aspect, the invention provides a composition comprising the niobium-containing active electrode material of the fifth aspect, and further comprising at least one other component; preferably wherein the at least one other component is selected from a binder, a solvent, a conductive additive, a different active electrode material, and mixtures thereof. This composition is also referred to herein as an electrode composition. In an eighth aspect, the invention provides an electrode comprising the niobium-containing active electrode material as defined in the fifth aspect, or a composition as defined in the seventh aspect, as an active electrode material.

[0024] In a ninth aspect, the invention provides a metal-ion battery comprising the electrode of the eighth aspect, preferably wherein the metal-ion battery is a lithium-ion battery and the electrode forms the anode.

[0025] In a tenth aspect, the invention provides the use of the niobium-containing active electrode material as defined in the fifth aspect, or a composition as defined in the seventh aspect, as an active electrode material in a metal-ion battery; preferably in an anode of a lithium-ion battery.

[0026] In an eleventh aspect, the invention provides a method of making an electrode, the method comprising: providing the niobium-containing active electrode material of the fifth aspect, or a composition as defined in the seventh aspect; and depositing said niobium-containing active electrode material or said composition onto a current collector, thereby forming the electrode.

[0027] It will be appreciated that the generic and specific features and the preferences described hereinbelow are equally applicable to all aspects of the invention.

[0028] Detailed Description of the Invention

[0029] The method of the invention produces niobium-containing metal oxide granules having a Hausner ratio (H) in the range of from 1 .00 to 1 .55.

[0030] As used herein, the term “Hausner ratio” has the same meaning as that commonly used in the art, and in this invention it refers to the ratio of the tapped density of the niobium-containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules. It is generally understood that the Hausner ratio is a proxy measurement for flowability, where a lower Hausner ratio correlates to higher flowability.

[0031] The niobium-containing metal oxide granules are made from a precursor material by the method of the invention. The precursor material comprises niobium (Nb), and may be an oxide comprising Nb.

[0032] The precursor material may comprise one or more metal oxides, metal hydroxides or metal salts and combinations thereof. Suitable salts include nitrate, sulphite, sulphate, halide (preferably fluoride, chloride or bromide), carbonate, borate or salts of organic acids (such as oxalate). In particular, the precursor material preferably comprises metal oxides and / or metal hydroxides, preferably metal oxides, optionally in combination with one or more metal salts with anions other than oxide, preferably halide (preferably fluoride, chloride or bromide). It will be appreciated that the reference in this paragraph to metal oxides, metal hydroxides and metal salts is to such materials which comprise niobium. The niobium may be, and preferably is, present in said precursor material with other metals. Other metals useful in the provision of an active electrode material may also be present, as described hereinbelow. The precursor material may also comprise an ammonium salt. Other cationic species suitable for cation substitution in the niobium- containing metal oxide are described hereinbelow.

[0033] The niobium in the precursor material may be in any of its oxidation states, and is preferably in oxidation state +2, +4 or +5, and more preferably in oxidation state +5.

[0034] Examples of suitable precursor materials comprising niobium include Nb2Os, Nb(OH)s, niobic acid, NbO, ammonium niobate oxalate, NbO2, NbO2F, NbsO F, niobium chloride, niobium fluoride, niobium bromide. Preferably the niobium-containing precursor material comprises, and preferably is, a niobium oxide.

[0035] The precursor material comprising niobium may contain further precursors other than the precursor material comprising niobium. For substitution of the base material (i.e. the niobium-containing metal oxide) by other cations, the precursor material may contain one or more metal oxides, metal hydroxides and / or metal salts wherein the metal is other than niobium, and / or other cation-providing species. Non- metals and metalloids, such as boron, phosphorus, silicon and / or germanium (and particularly boron, phosphorus and / or silicon), may also be used for substitution of the base material. Examples of such cation substitution precursor materials include but are not limited to: NH4H2PO4, (NH4)2HPO4, (NF ^PC P2O5, H3PO3, Ta2O6, WO3, ZrO2, TiO2, M0O3, V2O5, ZrO2, CuO, Cr2O3, ZnO, AI2O3, K2O, KOH, CaO, GeO2, Ga2Os, SnO2, CoO, C02O3, Fe20s, FesO4, MnO, MnO2, NiO, Ni2Os, H3BO3, IJ2CO3, Na2CO3, Mgs(CO3)4(OH)2.5H2O, and MgO. Additionally, or alternatively, the oxygen anion of the niobium- containing metal oxide may be substituted. Forthe substitution of the oxygen anion with other electronegative anions the precursor material may include one or more organic compounds, polymers, inorganic salts, organic salts, gases, or ammonium salts; examples include melamine, NH4HCO3, NH3, NH4F PVDF, PTFE, NH4CI, NH4Br, NH4I, Br2, CI2, I2, ammonium oxychloride amide, and hexamethylenetetramine.

[0036] The precursor material comprising niobium may further comprise one or more of Ti, W, Zn, Cr, Al, P, Zr, Mo, Li, B, Fe, Mg, Si, Hf, V, Ta, K, Cu, Sn, Na, In, Ga or Ca , preferably Ti, W, Zn, Cr, Al, P, Zr, Mo, Li, B, Fe, Mg, Si, Hf, V, Ta, K, Cu, Sn, Na, or Ca. The precursor material comprising niobium may further comprise one or more of Mn, Co, or Ni, but preferably does not comprise Mn, Co, or Ni.

[0037] The precursor material comprising niobium preferably further comprises one or more of Ti, W, Zn, Cr, Al, P, Mo, Li, B, Fe, Si, V, K, Cu, or Na, and more preferably further comprises one or more of Ti, W, Zn, Cr, Al, P, Li, B, Fe or Na, and more preferably comprises one or more of Ti, Zn, Cr or P.

[0038] When it is desired to make niobium-containing metal oxide granules comprising a cation of a specific oxidation state, a precursor material comprising that cation at that oxidation state may be selected. For example, when making niobium-containing metal oxide granules comprising Mn2+, MnO may be used as the precursor. When making niobium-containing metal oxide granules comprising Mn4+, MnO2 may be used as the precursor. The precursor material may be at least 0.5, preferably at least 10.0, or most preferably at least 12.0 wt% titanium precursor, and optionally no more than 25.0 wt% titanium precursor, based on the total weight of all precursor materials. The titanium is preferably in oxidation state +4. Most preferably, the titanium precursor is titanium oxide.

[0039] The precursor material may be no more than 96.0, preferably no more than 93.0, or most preferably no more than 91 .0 wt% niobium precursor, and optionally at least 75.0 wt% niobium precursor, based on the total weight of all precursor materials.

[0040] The niobium-containing metal oxide granules, in particular for use as an active electrode material, may further comprise Li and / or Na, which may reversibly intercalate in situ when the metal oxide granules or active electrode material is in a metal-ion battery.

[0041] Some or all of the precursor materials may be particulate materials.

[0042] The method of the invention comprises compacting said at least one precursor material to form niobium- containing metal oxide granules. As used herein, the term “compacting” means the application of a compaction step, where a pressure force is applied to a solid material in order to compress it. The solid material may be a powder or particulate material. The pressure force may be applied by any suitable means, such as but not limited to a press, a pelletiser, or rollers.

[0043] The compaction step increases the bulk density of the solid material. This bulk density increase may be accomplished by the removal of air voids in the material, or by agglomeration of the particles of the solid material. The relative importance of these mechanisms in contributing to the compaction step varies between solid materials, and depends on factors such as the plasticity of the primary particles of the solid material and the relative volume of gases (e.g. air) that are present in the bulk of the solid material.

[0044] The compaction step typically also increases the tapped density of the solid material.

[0045] In the methods of the invention, the compacting of the at least one precursor material suitably comprises wet compacting, dry compacting, or both wet compacting and dry compacting. Dry compacting is preferred.

[0046] One example of wet compacting is wet granulation, whereby a solid material and a granulating liquid are mixed in a mixing vessel and agitated to form granules of the solid material.

[0047] One example of dry compacting is pelletisation, whereby a solid material is compressed such that relatively fine primary particles are agglomerated to form relatively large secondary particles (i.e. pellets) by collision of the primary particles in, for example, a pellet press, a rotary drum, or using a disc pelletiser. A further example of dry compacting is roller compaction, whereby a solid material is fed into a compacting zone formed by two (or more) counter- rotating rollers, and compressed by the action of the counter-rotating rollers to form a compacted material. A compaction process may involve the addition of one or more excipients to the solid material or, in the case ofwet granulation, the granulating liquid. The one or more excipients may comprise a lubricant, a binder, and / or any other processing aid. In preferred methods of the invention, no binder is used in the compaction process, such that the method is a binder-free process. In preferred methods of the invention, no excipients are used in the compacting step.

[0048] The method of the invention forms niobium-containing metal oxide granules which exhibit a Hausner ratio) in the range of from 1 .00 to 1 .55, preferably from 1 .00 to 1 .50, more preferably from 1 .00 to 1 .40, or from 1 .00 to 1 .35, or from 1 .00 to 1 .30, or from 1 .00 to 1 .25.

[0049] In the method of the invention, the difference between the Hausner ratio of the niobium-containing metal oxide granules and the Hausner ratio of the unprocessed starting material (i.e. said at least one precursor material prior to compaction) is in the range of from 0.20 to 0.70, and preferably from 0.30 to 0.60, such as about 0.30, about 0.35, about 0.40, about 0.45, about 0.50, about 0.55, about 0.60, or about 0.65. The difference is such that the Hausner ratio of the niobium-containing metal oxide granules is lower than that of said at least one precursor material prior to compaction.

[0050] As noted above, the compacting step has the effect of increasing the bulk density of the material, such that the bulk density of the niobium-containing metal oxide granules is higher than that of the starting material (i.e. said at least one precursor material comprising niobium prior to compaction). Typically, the compacting step also increases the tapped density of the material, such that the tapped density of the niobium-containing metal oxide granules is higher than that of the starting material (i.e. said at least one precursor material comprising niobium prior to compaction).

[0051] After the compaction step, particularly wherein wet compaction (such as wet granulation) has been used, a subsequent drying step may be performed on the granules, and where the compaction step is a wet compaction step (such as wet granulation) a subsequent drying step is preferably performed on the granules.

[0052] After the compacting step has been performed, the niobium-containing metal oxide granules may be further processed, such as by one or more of heating or comminution, e.g. crushing, milling, grinding, or cutting.

[0053] In particular, the niobium-containing metal oxide granules may be heated, which is of particular utility to form a niobium-containing active electrode material according to the fifth aspect of the invention. The heating step is preferably conducted at a temperature in the range of from 600 to 1300 °C, preferably from 750 to 1200 °C, and preferably for a time in the range of from 0.1 to 6 hours, preferably from 0.1 to 3 hours, more preferably from 0.1 to 1 hour.

[0054] The heating may be conducted in at least one static powder bed. Alternatively, or additionally, the heating may be conducted in dynamic powder flow. Preferably the heating is conducted in dynamic powder flow, such as in a rotary furnace. Preferably the heating is conducted in a rotary furnace. Preferably the heating step is rotary calcination.

[0055] One advantage of the invention is that the niobium-containing metal oxide granules produced by the method described herein have improved flowability, when compared to the unprocessed starting material (i.e. said at least one precursor material comprising niobium). As a consequence of the improved material properties imparted by the method of the invention, alternative heating methods and apparatus, such as heating in a rotary furnace (for instance by rotary calcination using a rotary calciner) may advantageously be employed, that are not possible to be used with the unprocessed precursor material. Such alternative heating methods have surprisingly been found to be advantageous when used to heat the niobium- containing metal oxide granules to form a niobium-containing active electrode material. The advantages of using such alternative heating methods include shorter reaction times and / or improved yields and / or improved efficiency and / or economy, compared to the use of conventional or static heating methods.

[0056] By conducting the heating in dynamic powder flow (e.g. in a rotary furnace), it has surprisingly been found that the reaction time for the formation of a niobium-containing active electrode material from the niobium- containing metal oxide granules is significantly reduced. The reaction time is preferably reduced by 10% or more, such as by 20%, 30%, 40%, 50%, 60%, or more. The reaction time is preferably reduced by a factor of about 1 .5 or more, such as about 1 .5, about 2.0, about 2.5, or about 3.0.

[0057] Optionally, the process further comprises a step of modifying the particle size distribution of the niobium- containing active electrode material, preferably when said modifying step is or comprises a deagglomeration process. It will be appreciated that such a step is suitably conducted after the heating step described hereinabove.

[0058] In a preferred embodiment, the niobium-containing active electrode material resulting from the process described hereinabove exhibits a Wadsley-Roth or Tetragonal Tungsten Bronze crystal structure. The crystal structure of a material may be determined by analysis of X-ray diffraction (XRD) patterns (particularly those obtained using Cu K-a radiation), as is widely known. For instance, XRD patterns obtained from a given material can be compared to known XRD patterns to confirm the crystal structure, e.g. via public databases such as the ICDD crystallography database. Rietveld analysis can also be used to determine the crystal structure of materials, in particular for the unit cell parameters.

[0059] Ti2Nbio029 and TiNb2O? are materials having a Wadsley-Roth structure. Preferably, the niobium- containing active electrode material has the crystal structure of TiNb2O?. The crystal structure of TiNbzO? can be described as having a 3x3x°° crystallographic block structure composed of [MOe] octahedra, where M is Ti or Nb. The crystal structure is typically monoclinic. The crystal structure of TiNb2O? may be found at PDF card 00-039-1407. The unit cell parameters a, b, and c may be where a is 17.66-17.74 A preferably 17.68-17.72 A, b is 3.77-3.84 A preferably 3.79-3.82 A, and c is 11 .86-11 .94 A preferably 11 .88-11 .92 A. The crystal structure of the first phase may have unit cell parameters a and y each being about 90°, preferably wherein a = y = 90°; whereas p may be 95.30-95.37° preferably 95.32-95.36°. The niobium-containing active electrode material resulting from the process described hereinabove is preferably in particulate form, preferably having a Dso particle diameter in the range of 0.1-100 pm, or 0.5- 50 pm, or 1-20 pm.

[0060] The niobium-containing active electrode material resulting from the process described hereinabove, preferably exhibits a crystallite size of greater than 180 nm, or greater than 200 nm, or greater than 225 nm, or greater than 250 nm.

[0061] The niobium-containing active electrode material resulting from the process described hereinabove, preferably exhibits a BET surface area in the range of 0.1-100 m2 / g, or 0.25-50 m2 / g, or 0.40-20 m2 / g. In general, a low BET surface area is preferred in order to minimise the reaction of the active electrode material with the electrolyte, e.g. minimising the formation of solid electrolyte interphase (SEI) layers during the first charge-discharge cycle of an electrode comprising the material. However, a BET surface area which is too low results in unacceptably low charging rate and capacity due to the inaccessibility of the bulk of the active electrode material to metal ions in the surrounding electrolyte.

[0062] As noted hereinabove, the present invention also provides a composition comprising the niobium- containing active electrode material described hereinabove. The composition may comprise at least one other component, preferably selected from a binder, a solvent, a conductive additive, an active electrode material which is different from said niobium-containing active electrode material, and mixtures thereof. Said composition is also referred to herein as an “electrode composition”.

[0063] Examples of suitable binders include polyvinylidene fluoride and its copolymers (PVDF), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)methacrylate or poly(butyl)methacrylate, polyvinyl chloride (PVC), polyvinyl fomal, polyetheramide, polymethacrylic 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, carboxymethylcellulose (CMC), modified carboxymethylcellulose (mCMC), sodium carboxymethylcellulose (Na-CMC), polyvinylalcohol (PVA), alginates and alkali metal salts thereof, butadieneacrylonitrile rubber (NBR), hydrogenated form of NBR (HNBR), styrene-butadiene rubber (SBR) and polyimide. The binder may be present in the composition at 0-30 wt%, or 0.1-10 wt%, or 0.1-5 wt%, based on the total dry weight of the composition.

[0064] Suitable solvents include water and N-methyl-2-pyrrolidone (NMP) and carbonate-based solvents (such as ethylene carbonate, propylene carbonate, dimethyl carbonate, etc). Typically, the solvents are selected from water and NMP. The optional solvent may be present in the composition at 0-70 wt%, or 0.1-70 wt%, or 0.1-50 wt%, based on the total weight of the composition. The solvent facilitates the preparation of the slurry which is then used to form the electrode, as discussed hereinbelow. During the process of electrode formation, the solvent is evaporated. Where the solvent is present in the electrode composition, it is typically present in an amount of no more than 70 wt%, preferably no more than 50 wt%, typically in the range of 5-70 wt%, more typically in the range of 30-70%, preferably in the range of 30-50 wt%, based on the total weight of the composition. Advantageously, the solvent is used in the minimum amount required to form a slurry suitable for electrode formation.

[0065] Conductive additives are preferably non-active materials which are included in order to improve electrical conductivity between the active electrode material and the current collector. The conductive additives may suitably be selected from graphite, carbon black, carbon fibers, vapor-grown carbon fibres (VGCF), carbon nanotubes, graphene, acetylene black, ketjen black, metal fibers, metal powders and conductive metal oxides. Preferred conductive additives include carbon black and carbon nanotubes. Conductive additives may be present in the composition at 0-20 wt%, 0.05-10 wt%, or 0.05-5 wt%, based on the total dry weight of the composition.

[0066] When a different active electrode material is present in addition to said niobium-containing active electrode material, it may be selected from lithium titanium oxide, titanium niobium oxide, a mixed-phase oxide, graphite, hard carbon, soft carbon, silicon, doped and / or carbon-coated versions thereof, and mixtures thereof.

[0067] The present invention also provides an electrode comprising said niobium-containing active electrode material or said electrode composition as an active electrode material.

[0068] The present invention also provides a method of making said electrode, said method comprising providing the electrode composition defined herein; and depositing said composition onto a current collector, thereby forming the electrode. The depositing step may include forming a slurry of the electrode composition wherein a solvent is present in combination with one or more of the other components described hereinabove for said composition. The slurry is suitably deposited onto a current collector and the solvent removed, thereby forming an electrode layer on the current collector. Further steps, such as heat treatment to cure any binders and / or calendering of the electrode layer may be carried out as appropriate. For example, the solvent may be removed by drying e.g. at temperatures of 30-200°C. The electrode may be calendared to a density of 2-3.5 or 2.5-2.9 g cm-3. The electrode layer may have a thickness in the range of from 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. Alternatively, the slurry may be formed into a freestanding film or mat, for instance 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, freestanding mass which may then be bonded to a current collector by conventional methods known in the art.

[0069] Preferably, the niobium-containing active electrode material forms at least 25 wt.%, preferably at least 50 wt.%, or at least 75 wt% of the total active electrode material in the electrode; or wherein said niobium- containing active electrode material is the sole active electrode material in the electrode.

[0070] The invention also provides a metal-ion battery comprising the electrode defined hereinabove. The metalion battery is preferably a lithium-ion or sodium-ion battery, preferably a lithium-ion battery, and the electrode forms the anode. Lithium-ion batteries include liquid-based batteries, polymer-based batteries, semi-solid-based batteries and full solid-state-based batteries.

[0071] Preferably, said metal-ion battery has a reversible anode active material specific capacity of greater than 200 mAh / g at 20 mA / g, wherein the battery can be charged and discharged at current densities relative to the anode active material of 200 mA / g or more, or 1000 mA / g or more, or 2000 mA / g or more, or 4000 mA / g or more whilst retaining greater than 70% of the initial cell capacity at 20 mA / g. It has been found that use of the active electrode materials of the invention can enable the production of a metal-ion battery with this combination of properties, representing a metal-ion battery that is particularly suitable for use in applications where high charge and discharge current densities are desired.

[0072] Measurement Methods

[0073] (i) Bulk Density

[0074] Bulk density was measured according to the standard DIN ISO 697. Typically, the sample was filled in a 500 ml stainless steel measuring jar through a funnel, excess material is scraped, and the weight is measured.

[0075] (ii) Tapped Density

[0076] Tapped density of each sample was determined according to DIN ISO Norm 787-11 , typically using widely available laboratory equipment such as JEL-Stampfvolumeter STAV 2003. The tap density is calculated by dividing the weight of the material by its volume after 1250 taps.

[0077] (Hi) Hausner Ratio

[0078] The measurements for bulk and tapped density were used to calculate the Hausner ratio for each material, which is a commonly used method of determining flowability of powdered or granulated material. Thus, the Hausner ratio (H) = tapped density / bulk density. Lower Hausner ratios are correlated with improved flowability.

[0079] (iv) Particle diameter

[0080] The term “particle diameter’’ refers to the equivalent spherical diameter (esd), i.e. the diameter of a sphere having the same volume as a given particle, where the particle volume is understood to include the volume of any intra-particle pores. The terms “Dn” and “Dnparticle diameter” refer to the diameter below which n% by volume of the particle population is found, e.g. the terms “Deo” and “Deo particle diameter” refer to the volume-based median particle diameter below which 50% by volume of the particle population is found. Where a material comprises primary crystallites agglomerated into secondary particles, it will be understood that the particle diameter refers to the diameter of the secondary particles. Particle diameters are suitably determined by laser diffraction. Particle diameters are suitably determined in accordance with ISO 13320:2009, for example using Mie theory. Preferably the particle size parameters are measured by laser diffraction using a Horiba Partica LA960V2, in particular on the basis of a dry dispersion with an injection pressure of 0.3 MPa, a refractive index of 1 .9 and an absorption index of 0.5.

[0081] (v) Crystallite size

[0082] Crystallite size is calculated from a powder X-ray diffraction pattern using the Scherrer equation utilising the peak with the highest signal to noise ratio. X-ray diffraction analysis was conducted using Rigaku Smartlab powder diffractometer using Cu Ka radiation.

[0083] (vi) BET surface area

[0084] The term “BET surface area” refers to the surface area per unit mass calculated from a measurement of the physical adsorption of gas molecules on a solid surface, using the Brunauer-Emmett-Teller theory. BET surface areas can be determined in accordance with ISO 9277:2010.

[0085] Unless otherwise indicated, the standard measurement methods used are preferably those which were current on 9 February 2024.

[0086] The invention is illustrated by the following non-limiting examples.

[0087] Examples

[0088] A precursor material comprising niobium was synthesised according to the procedure described in WO- 2023 / 214181 -A, the contents ofwhich are incorporated herein in their entirety.

[0089] Wet granulation example

[0090] A 1 kg batch of the precursor material comprising niobium was mixed in a multifunctional mixing system (Eirich EL1 at 30° tilt). When the mixing procedure was complete, 500 g of the powder mixture was removed, and 65-80 mL of water was added by pouring in a continuous thin stream from a beaker to the remaining 500 g of precursor through the open top port of the mixer during active mixing. A moderate mixing speed of 7.5 m / s in counter-rotation mode was used. The wet granulation process resulted in the formation of niobium-containing metal oxide granules.

[0091] The granules were dried at 60°C for 12 h before use in a high temperature calcination step to remove the water but could equally be used directly in a high temperature calcination process, or 2-step heat treatment process in the same furnace.

[0092] Dry compaction examples

[0093] Pelletisation

[0094] 50 g of a precursor material comprising niobium was pressed in an 18 mm diameter pellet press at 5 MPa for 30-60 seconds, producing 10 x 5 g pellets. The pellet density was 2.8 g / cm3. Roller compaction

[0095] Dry compaction of a precursor material comprising niobium was conducted on a roller compactor. The roller compactor comprised a feed hopper, a feed screw, smooth rollers, and a granulation stage. The granulation stage comprised, sequentially, a flake crusher, a pre-granulator, and a fine granulator.

[0096] The precursor material was deposited into the feed hopper, and the compaction process was carried out at 230 bar. The resulting niobium-containing metal oxide granules had a bulk density of 1.46 kg / dm3. Before this dry compaction, the precursor material had a bulk density of 1 .02 kg / dm3. A further increase in the bulk density of the niobium-containing metal oxide granules was achieved by a recompaction on the same roller compactor apparatus under the same conditions, producing the niobium-containing metal oxide granules having a bulk density of 1 .67 kg / dm3.

[0097] The dry compaction process advantageously resulted in granules without the water content in the granules produced by the wet process, thereby providing a more energy-efficient process, as well as granules advantageously having a higher density and greater resilience (less friable). The granules were also more easily handled and removed from the apparatus, thereby minimising material losses and operational inefficiencies, and facilitating scale-up.

[0098] Results

[0099] Example 1

[0100] To determine the flowability of the niobium-containing metal oxide granules compared to unprocessed (i.e. ungranulated) precursor material comprising niobium, the bulk density of a sample of each material followed by the tapped density were measured, as described hereinabove. The results are shown in Table 1 .

[0101] Table 1: Bulk density, tapped density and Hausner ratio of unprocessed vs wet granulated and dry compacted product forms.

[0102] ‘roller compaction method It can be seen from Table 1 that the materials that were processed by wet granulation and dry compaction both had lower Hausner ratios, and therefore improved flowability, relative to the unprocessed precursor material. In addition, the niobium-containing metal oxides granules that were produced by dry compaction (in this case, roller compaction) were a further improvement over those produced by wet granulation, relative to the unprocessed precursor material.

[0103] In addition, there was no requirement for any binder to aid with material compaction.

[0104] Further Examples:

[0105] Samples were made by same methods for dry roller compaction and wet granulation as described above, except that about 30% more water than for Example 1 was added during wet granulation. The composition of these samples was as follows:

[0106] Example 2: 76.7 weight % niobium oxide, 23.3 weight % titanium oxide

[0107] Example 3: 89.2 weight % niobium oxide, 10.8 weight % titanium oxide

[0108] Example 4: 96.5 weight % niobium oxide, 3.5 weight % zinc oxide

[0109] Example 5: 91.6 weight % niobium oxide, 8.1 weight % ammonium hydrogen phosphate, 0.3 weight % chromium oxide

[0110] Table 2 below reports the measurements of bulk density (BD in g / cm3), tapped density (TD in g / cm3) and the Hausner ratio (H) of these samples.

[0111] Table 2: Bulk density (BP), tapped density (TD) and Hausner ratio (H) of unprocessed vs dry compacted and wet granulated product forms.

[0112] ‘roller compaction method

[0113] 5 “reference example

[0114] Calcination examples

[0115] 50 g of a niobium-containing metal oxide prepared according to the pelletisation example above was heated in a box furnace at a rate of 5 °C per minute to 1100 °C, dwelled for 1 hour, then cooled to room temperature.

[0116] 50 g of a powder of precursor material comprising niobium (i.e. the same material, but unprocessed / not compacted) was heated alongside the compacted material. This heating process produces a niobium- containing active electrode material.

[0117] Powder XRD patterns for each of the resultant materials were measured on a Rigaku Smartlab powder diffractometer using Cu Ka radiation and compared. It could be seen from this comparison that XRD peaks associated with the starting material (i.e. the pelletised or unprocessed materials) had lower intensity in the pelletised sample than in the unprocessed sample. The height of the highest diffraction peak from the precursor phase (relating to niobium oxide in this case) as a fraction of the height of the highest peak in the target phase pattern was used as an indicator of reaction progress after 1 hour. The results are presented in Table 3. This indicates that the formation of a niobium-containing active electrode material was proceeding at a higher rate in the pelletised (i.e. compacted) sample than in the unprocessed sample.

[0118] Table 3: Comparison of relative diffraction pattern peak intensities in processed and unprocessed partially reacted material.

[0119] This experiment was repeated on a larger scale, using 100 g of the niobium-containing metal oxide granules prepared according to the roller compaction example above, and 100 g of a powder of precursor material comprising niobium (i.e. the same material, but unprocessed / not compacted).

[0120] Samples of 100 g of roller compacted granules and unprocessed powder were subjected to identical heat treatment periods of 45 minutes, 90 minutes, 3 hours, 6 hours, and 12 hours at 1100 °C, and then examined by powder XRD. Rietveld refinement was used to calculate the mass fraction of unreacted material / impurity in the sample to quantitatively probe the progress of the reaction. The results are presented in Table 4. The results showed that, similarly to the small-scale calcination using pelletised niobium-containing metal oxide, the formation of a niobium-containing active electrode material was proceeding at a higher rate in the roller compacted sample than in the unprocessed sample. Table 4: The impurity fraction remaining at progressive time points in the reaction process for roller compacted material and unprocessed powder

[0121] The XRD reaction monitoring showed that the conversion of the niobium-containing metal oxide granules prepared according to the roller compaction example above into a niobium-containing active electrode material was complete in about 6 hours. In comparison, the conversion of the powder of precursor material comprising niobium into a niobium-containing active electrode material required about 12 hours to proceed to completion.

[0122] Thus, compaction leads to improvements in the calcination process used in the synthesis of active electrode material, in particular by enabling a reduction in the duration and potentially also the temperature of the process.

[0123] Rotary calcination example

[0124] 2500 g of the niobium-containing metal oxide granules prepared according to the roller compaction example above were subjected to heating in a three-zone lab scale rotary calciner (Nabertherm RSRC 120-750 / 13, dimensions 110 x 95 x 1790 mm). The conversion of this granulated material into a niobium-containing active electrode material proceeded to completion in about 3 hours in the hot zone of the calciner. This is a significant reduction in reaction time compared to the same reaction conducted above in a static powder bed (i.e. a box furnace), which took about 6 hours. This is due to the higher heat transfer and powder mobility.

[0125] Attempts to use the precursor material comprising niobium in uncompacted powder form (i.e. unprocessed according to the method of the present invention) in the rotary calciner was problematic, due to the poor flowability of the uncompacted powder material impeding the feeding of the material into the reaction chamber. The unprocessed material was therefore deemed to be unsuitable for use in the rotary calciner. As such, the improved reaction times associated with the use of a rotary calciner are only achievable when niobium-containing metal oxide granules are used, rather than unprocessed (i.e. uncompacted) precursor material comprising niobium. In other words, a more flowable granulated metal oxide that reacts faster, is advantageous in a rotary calcination process (i.e. dynamic powder flow). Post-processing of calcined materials

[0126] The calcined materials that may be sintered into large particles (> 1 mm diameter) can then be postprocessed into a fine powder for use in battery electrodes. This is typically done through de-agglomeration or milling processes, specifically in this study by impaction milling with a benchtop IKA Multidrive at 20K RPM for 2 minutes, then using a Retsch ZM200 centrifugal mill at 18K RPM.

[0127] The particle size distribution analysis in Table 5 below shows that the granulated sample comprises a wider range of particle sizes under these milling conditions, but with the same mode and median and more volume on the extreme high and low ends of the range.

[0128] Table 5: Size thresholds of the active material made from the compacted granule vs powder material after fine milling

[0129] Electrochemical testing

[0130] A set of coatings was prepared by adding 3 x 5 mm alumina beads to the mixing vessel containing the active material described above for slurry mixing at 2000 rpm by a centrifugal planetary mixer. The coatings appeared smooth and homogeneous.

[0131] Electrochemical tests were carried out in half-coin cells (CR2032 size) for analysis. In half-coin tests, the active material is tested in an electrode versus a Li metal electrode to assess its fundamental performance. In the below examples, the active material composition to be tested was combined with N-Methyl Pyrrolidone (NMP), carbon black acting as a conductive additive, and poly(vinyldifluoride) (PVDF) binder and mixed to form a slurry using a lab-scale centrifugal planetary mixer. The non-NMP composition of the slurries was 92 wt% active material, 5 wt% conductive additive, 3 wt% binder. The slurry was coated on an Al foil current collector to the desired loading of 70 g nr2by doctor blade coating and dried. The electrodes were then calendered to a density of 2.6 - 3.2 g cm-3at 80°C to achieve targeted porosities of 35-40%. Electrodes were punched out at the desired size and combined with a separator (Celgard porous PP / PE), Li metal, and electrolyte (1.3 M LiPFs in EC / DEC) inside a steel coin cell casing and sealed under pressure. Cycling was then carried out at 25°C at low current rates (C / 10) for 2 full cycles of lithiation and de-lithiation between 1.1 - 3.0 V. Afterwards, the cells were tested for their performance at increasing current densities. During rate tests, the cells were cycled asymmetric at 25°C, with a slow charge (lithiation, C / 5) followed by increasing discharge rates (de-lithiation, e.g. 1 C, then 2C, then 5C, then 10C, then 20C) for dis-chargeability tests (e.g. measuring capacity retention).

[0132] The results of electrochemical testing to compare the battery active material made from the granulated and the unprocessed material are shown in Table 6.

[0133] Table 6: Electrochemical testing of the active material made from either granulated or unprocessed material. Li 1 is the 1stlithiation specific capacity at 0. 1 C. Deli 1, Deli 2 are the 1stand 2nddelithiation specific capacities. CE1 is the 1stcycle Coulombic Efficiency.

[0134] Active material made from Active material made from granulated material uncompacted powder

[0135] Value Standard deviation Value Standard deviation

[0136] Li 1 [mAh / g] 215.87 2.13 213.80 2.90

[0137] Deli 1 [mAh / g] 210.97 1.82 210.70 4.30

[0138] Deli 2 [mAh / g] 212.59 1.71 209.70 3.70

[0139] CE1 [%] 97.72% 0.15% 98.50% 0.80%

[0140] 0.5C [mAh / g] 204.71 0.73 202.20 3.70

[0141] 1C [mAh / g] 203.71 0.56 201.70 3.80

[0142] 2C [mAh / g] 201.80 0.70 201.10 4.10

[0143] 5C [mAh / g] 198.84 0.91 199.80 4.80

[0144] 0.5C [mAh / g] 207.03 0.71 207.20 4.20

[0145] It can be seen from Table 6 that the electrochemical performance of the granulated material is similar to that of the uncompacted powder and is therefore suitable for use as an electrode active material, with the improved processing properties described hereinabove.

[0146] Further calcination examples

[0147] Examples 2 to 5 were calcined under identical reaction conditions to investigate the effect that varied chemical stoichiometry in the precursor mixture has on the effect of granulation on the reaction process. The example samples were heated from room temperature to 1100°C at 5°C / minute, dwelling for 1 hour at 1100°C, then cooled to room temperature at a spontaneous rate. The calcined samples were then finely ground, X-ray diffraction patterns were measured, and Rietveld refinement analysis was used to quantify the phase composition of the samples. The mass percentage of unreacted material which had not yet converted into the target crystal phase was calculated and used to compare the rates at which the conversion reaction proceeds in the granulated and ungranulated samples. Table 7 Calcination experiments with a range of chemical compositions

[0148] “reference example The results show that granulation of the precursors causes the synthesis reaction to be more advanced after 1 hour than when unprocessed powdered precursors are used, and that there is a correlation between the amounts of different species in the precursor mixture and the improvement effect achieved from granulation. Moreover, the precursors must be granulated to have a Hausner ratio of less than 1 .55 to show this improvement in reaction rate.

[0149] Numbered embodiments

[0150] 1 . A method of making niobium-containing metal oxide granules, the method comprising: providing at least one precursor material comprising niobium; and compacting the at least one precursor material to form niobium-containing metal oxide granules, wherein the ratio of the tapped density of the niobium-containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55.

[0151] 2. The method of embodiment 1 , wherein the precursor material further comprises one or more of Ti, W, Zn, Cr, Al, P, Zr, Mo, Li, B, Fe, Mg, Si, Hf, V, Ta, K, Cu, Sn, Na, or Ca, preferably wherein the precursor material further comprises Ti, W, Zn, Cr, Al, P, Mo, Li, B, Fe, Si, V, K, Cu, or Na.

[0152] 3. The method of embodiment 1 or embodiment 2, wherein the precursor material further comprises one or more of Ti, Zn, P, Cr, W, Al, B, Fe, Li, or Na, preferably wherein the precursor material further comprises one or more of Ti, Zn, P, or Cr.

[0153] 4. The method of any one of embodiments 1 to 3, wherein the compacting of the at least one precursor material comprises wet granulation or dry compaction or a combination thereof.

[0154] 5. The method of embodiment 4, wherein the dry compaction is a roll compaction process.

[0155] 6. The method of embodiment 4 or embodiment 5, wherein the dry compaction is a binder-free process.

[0156] 7. Niobium-containing metal oxide granules wherein the ratio of the tapped density of the niobium- containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55.

[0157] 8. Niobium-containing metal oxide granules obtained or obtainable by the method of any of embodiments 1-6.

[0158] 9. A process for the manufacture of a niobium-containing active electrode material comprising the step of heating the niobium-containing metal oxide granules as defined in embodiment 7 or 8 to form a niobium-containing active electrode material.

[0159] 10. The process of embodiment 9, wherein the heating is conducted at a temperature in the range of from 600 to 1300 °C, preferably from 750 to 1200 °C.

[0160] 11 . The process of embodiment 9 or 10, wherein the heating is conducted for a time period in the range of from 0.1 to 6 hours, preferably from 0.1 to 3 hours, more preferably from 0.1 to 1 hour.

[0161] 12. The process of any of embodiments 9-11 , wherein the heating is conducted in at least one static powder bed.

[0162] 13. The process of any of embodiments 9-11 , wherein the heating is conducted in dynamic powder flow.

[0163] 14. The process of any of embodiments 9-11 or 13, wherein the heating is conducted in a rotary furnace and / or wherein said heating is rotary calcination.

[0164] 15. The process of any of embodiments 9-14, further comprising a step of modifying the particle size distribution of the niobium-containing active electrode material.

[0165] 16. The process of embodiment 15, wherein the step of modifying the particle size distribution comprises a deagglomeration process. 17. A niobium-containing active electrode material obtained or obtainable by the process of any of embodiments 9-16.

[0166] 18. The active electrode material of embodiment 17 which has a Wadsley-Roth or Tetragonal Tungsten Bronze crystal structure.

[0167] 19. The active electrode material of embodiment 17 or 18, which is in particulate form, preferably having a Dso particle diameter in the range of 0.1-100 pm, or 0.5-50 pm, or 1-20 pm.

[0168] 20. The active electrode material of any of embodiments 17-19, which has a BET surface area in the range of 0.1-100 m2 / g, or 0.25-50 m2 / g, or 0.40-20 m2 / g.

[0169] 21. The active electrode material of any of embodiments 17-20, which has a crystallite size of greater than 180 nm, or greater than 200 nm, or greater than 225 nm, or greater than 250 nm.

[0170] 22. A composition comprising the niobium-containing active electrode material as defined in any of embodiments 17-21 , and further comprising at least one other component; preferably wherein said at least one other component is selected from a binder, a solvent, a conductive additive, a different active electrode material, and mixtures thereof.

[0171] 23. An electrode comprising the niobium-containing active electrode material of any of embodiments 17-21 or the composition of embodiment 22 as an active electrode material.

[0172] 24. The electrode of embodiment 23, wherein the metal oxide forms at least 25 wt.%, at least 50 wt.%, or at least 75 wt% of the total active electrode material in the electrode; or wherein the metal oxide is the sole active electrode material in the electrode.

[0173] 25. The electrode of embodiment 23 or 24, further comprising at least one other component selected from a binder, a conductive additive, a different active electrode material, and mixtures thereof.

[0174] 26. The electrode of any of embodiments 23-25, or the composition of embodiment 22, wherein the different active electrode material is selected from lithium titanium oxide, titanium niobium oxide, a mixed-phase oxide, graphite, hard carbon, soft carbon, silicon, doped and / or carbon-coated versions thereof, and mixtures thereof.

[0175] 27. A metal-ion battery comprising the electrode of any of embodiments 23-26, preferably wherein the metal-ion battery is a lithium-ion battery and the electrode forms the anode.

[0176] 28. The metal-ion battery according to embodiment 27, which is a lithium-ion battery having a reversible anode active material specific capacity of greater than 200 mAh / g at 20 mA / g, wherein the battery can be charged and discharged at current densities relative to the anode active material of 200 mA / g or more, or 1000 mA / g or more, or 2000 mA / g or more, or 4000 mA / g or more whilst retaining greater than 70% of the initial cell capacity at 20 mA / g.

[0177] 29. Use of the niobium-containing active electrode material as defined in any of embodiments 17-21 or the composition as defined in embodiment 22 or 26, as an active electrode material in a metalion battery; preferably in an anode of a lithium-ion battery.

[0178] 30. A method of making an electrode, the method comprising: providing a niobium-containing active electrode material as defined in any of embodiments 17-21 or a composition as defined in embodiment 22 or 26; and depositing said niobium-containing active electrode material or said composition onto a current collector, thereby forming the electrode.

Claims

Claims1. A method of making niobium-containing metal oxide granules, the method comprising: providing at least one precursor material comprising niobium; and compacting the at least one precursor material to form niobium-containing metal oxide granules, wherein the ratio of the tapped density of the niobium-containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55.

2. The method of claim 1 , wherein the precursor material further comprises one or more of Ti, W, Zn, Cr, Al, P, Zr, Mo, Li, B, Fe, Mg, Si, Hf, V, Ta, K, Cu, Sn, Na, or Ca, preferably wherein the precursor material further comprises Ti, W, Zn, Cr, Al, P, Mo, Li, B, Fe, Si, V, K, Cu, or Na.

3. The method of claim 1 or claim 2, wherein the precursor material further comprises one or more of Ti, Zn, P, Cr, W, Al, B, Fe, Li, or Na, preferably wherein the precursor material further comprises one or more of Ti, Zn, P, or Cr.

4. The method of any one of claims 1 to 3, wherein the at least one precursor material comprises at least 0.5, at least 10.0, or 12.0 wt% titanium precursor, and optionally no more than 25.0 wt% titanium precursor, based on the total weight of all precursor materials.

5. The method of claim 4, wherein the oxidation state of Ti in the titanium precursor is +4.

6. The method of claim 5, wherein the titanium precursor is titanium oxide.

7. The method of any one of claims 1-6, wherein the at least one precursor material comprises no more than 96.0, no more than 93.0, or no more than 91 .0 wt% niobium precursor, and optionally at least 75.0 wt% niobium precursor, based on the total weight of all precursor materials.

8. The method of claim 7, wherein the oxidation state of Nb in the niobium precursor is +5.

9. The method of claim 8, wherein the niobium precursor is NbzOs.

10. The method of any one of claims 1 to 9, wherein the compacting of the at least one precursor material comprises wet granulation or dry compaction or a combination thereof.11 . The method of claim 10, wherein the dry compaction is a roll compaction process.

12. The method of claim 10 or claim 11 , wherein the dry compaction is a binder-free process.

13. Niobium-containing metal oxide granules wherein the ratio of the tapped density of the niobium- containing metal oxide granules to the bulk density of the niobium-containing metal oxide granules (Hausner ratio) is in the range of from 1.00 to 1.55.

14. Niobium-containing metal oxide granules obtained or obtainable by the method of any of claims 1-12.

15. A process for the manufacture of a niobium-containing active electrode material comprising (a) following the method of any one of claims 1-12, and the step of heating the niobium-containing metal oxide granules to form a niobium-containing active electrode material; or (b) the step of heating the niobium-containing metal oxide granules as defined in any one of claims 13-14 to form a niobium-containing active electrode material.

16. The process of claim 15, wherein the heating is conducted at a temperature in the range of from 600 to 1300 °C, preferably from 750 to 1200 °C.

17. The process of claim 15 or 16, wherein the heating is conducted for a time period in the range of from 0.1 to 6 hours, preferably from 0.1 to 3 hours, more preferably from 0.1 to 1 hour.

18. The process of any of claims 15-17, wherein the heating is conducted in at least one static powder bed.

19. The process of any of claims 15-17, wherein the heating is conducted in dynamic powder flow.

20. The process of any of claims 15-17 or 19, wherein the heating is conducted in a rotary furnace and / or wherein said heating is rotary calcination.21 . The process of any of claims 15-20, further comprising a step of modifying the particle size distribution of the niobium-containing active electrode material.

22. The process of claim 21 , wherein the step of modifying the particle size distribution comprises a deagglomeration process.

23. The process of any of claims 15-22, wherein the niobium-containing active electrode material has a Wadsley-Roth or Tetragonal Tungsten Bronze crystal structure.

24. The process of any of claims 15-23, wherein the niobium-containing active electrode material has the crystal structure of TiNb2O? or Ti2NbwO29; or has the crystal structure of TiNb2O?.

25. The process of any of claims 15-24, wherein the niobium-containing active electrode material is in particulate form, preferably having a Deo particle diameter in the range of 0.1-100 pm, or 0.5-50 pm, or 1-20 pm.

26. The process of any of claims 15-25, wherein the niobium-containing active electrode material has a BET surface area in the range of 0.1-100 m2 / g, or 0.25-50 m2 / g, or 0.40-20 m2 / g.

27. The process of any of claims 15-26, wherein the niobium-containing active electrode material has a crystallite size of greater than 180 nm, or greater than 200 nm, or greater than 225 nm, or greater than 250 nm.

28. A niobium-containing active electrode material obtained or obtainable by the process of any of claims 15-27.

29. An electrode comprising the niobium-containing active electrode material of claim 28 as an active electrode material.

30. A metal-ion battery comprising the electrode of claim 30, preferably wherein the metal-ion battery is a lithium-ion battery and the electrode forms the anode.31 . The metal-ion battery according to claim 30, which is a lithium-ion battery having a reversible anode active material specific capacity of greater than 200 mAh / g at 20 mA / g, wherein the battery can be charged and discharged at current densities relative to the anode active material of 200 mA / g or more, or 1000 mA / g or more, or 2000 mA / g or more, or 4000 mA / g or more whilst retaining greater than 70% of the initial cell capacity at 20 mA / g.

32. Use of the niobium-containing active electrode material as defined in claim 28, as an active electrode material in a metal-ion battery; preferably in an anode of a lithium-ion battery.

33. A method of making an electrode, the method comprising:(a) following the process of any one of claims 15-27, and depositing the niobium-containing active electrode material onto a current collector, thereby forming the electrode; or(b) providing a niobium-containing active electrode material as defined in claim 28; and depositing said niobium-containing active electrode material onto a current collector, thereby forming the electrode.