Active electrode material

Abstract

The present invention relates to a mixed-phase oxide used as an active electrode material, for example, in a lithium-ion or sodium-ion battery. The mixed-phase oxide contains Nb and Ti, and also contains M(III) and / or M(II); wherein M(III) is selected from Cr, Al, Ga, and mixtures thereof; M(II) is selected from Zn, Cu, Mg, and mixtures thereof; wherein the mixed-phase oxide contains an interpenetrating mixture of a first phase and a second phase; wherein the first phase has a crystal structure of TiNb2O7, and the second phase has a crystal structure of Zn2Nb 34 O 87 of.

Description

Technical Field

[0001] The present invention relates to active electrode materials, methods for manufacturing active electrode materials, and electrodes comprising the active electrode materials. Such materials are of interest as active electrode materials (e.g., as anode materials) in metal ion batteries such as lithium ion or sodium ion batteries. Background Art

[0002] Lithium ion (Li-ion) batteries are a commonly used type of rechargeable battery, and their global market is expected to grow to $200 billion by 2030. Li-ion batteries are the preferred technology for electric vehicles with diverse requirements in terms of technical performance to environmental impact, thus providing a viable path for the green automotive industry.

[0003] A typical lithium ion battery consists of multiple cells connected in series or in parallel. Each individual cell generally consists of an anode (negative polarity electrode) and a cathode (positive polarity electrode), which are separated by a porous electrical insulating membrane (referred to as a separator) and immersed in a liquid (referred to as an electrolyte) capable of transporting lithium ions.

[0004] In most systems, the electrodes are composed of an active electrode material - meaning it is capable of undergoing a chemical reaction with lithium ions to reversibly store and release the lithium ions in a controlled manner - optionally mixed with a conductive additive (such as carbon) and a polymeric binder. 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), thereby forming an electrode after drying.

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

[0006] Batteries relying on graphite anodes are fundamentally limited in terms of the charging rate. Under nominal conditions, lithium ions are inserted into the anode active material during charging. When the charging rate increases, the typical graphite voltage profile results in a high risk that the overpotential causes the potential at sites on the anode to become <0V relative to Li / Li+, which leads to a phenomenon called lithium dendrite plating, whereby lithium ions are instead deposited on the surface of the graphite electrode in the form of lithium metal. This results in an irreversible loss of active lithium and thus leads to a rapid decay of the cell capacity. In some cases, such dendritic deposits can grow to such large sizes that they pierce the battery separator and cause the cell to short-circuit. This can trigger a catastrophic failure of the cell, leading to fire or explosion. Therefore, the fastest-charging batteries with graphite anodes are limited to a charging rate of 5 - 7C, but are typically lower.

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

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

[0009] Titanium niobium oxides have been proposed as active electrode materials. US2012 / 0052401A1 discloses oxides of the general formula Li x M 1- y Nb y Nb2O7, where 0 ≤ x ≤ 3, 0 ≤ y ≤ 1, and M represents Ti or Zr. US2015 / 0086872A1 discloses TiNb2O7-based oxides with a carbon coating in a specific form. US2019 / 0296343A1 and US2014 / 0120404A1 disclose mixtures of TiNb2O7 phase with Ti2Nb 10 O 29 、Nb 14 TiO 37 、TiNb 24 O 64 and / or TiO2 phases. US202I / 0376307A1 discloses Nb-Ti oxides where the molar ratio of Nb to Ti > 2 and containing 100 - 2,000 ppm of K, Fe, and / or P. EP3667805A1 discloses Ti-containing oxides with a coating layer containing Zn, In, Sn, Pb, Hg, Cu, Cd, Ag, and / or Bi. US2015 / 0125753A1 discloses Nb composite oxides with a P compound on their surface.

[0010] However, there is still a need to identify further active electrode materials, especially those with good properties for lithium-ion battery cells intended for high-power / fast-charging applications. For example, determining such materials without the need for extensive particle-level engineering and / or without coatings is an important step for low-cost battery materials to enter the mass market. SUMMARY OF THE INVENTION

[0011] In a first aspect, the present invention provides a mixed-phase oxide for use as an active electrode material;

[0012] wherein the mixed-phase oxide contains Nb and Ti and also contains M(III) and / or M(II);

[0013] where M(III) is selected from Cr, Al, Ga, and mixtures thereof;

[0014] M(II) is selected from Zn, Cu, Mg, and mixtures thereof;

[0015] wherein the mixed-phase oxide comprises an interpenetrating mixture of a first phase and a second phase;

[0016] wherein the first phase has a crystal structure of TiNb2O7, and the second phase has a crystal structure of Zn2Nb 34 O 87 of.

[0017] The inventors have found that, as shown in this example, the mixed-phase oxide according to the first aspect has excellent properties for designing high-power batteries for fast charging / discharging, such as maintaining a high capacity at high rates of 5C and 10C.

[0018] In a second aspect, the present invention provides an electrode comprising the mixed-phase oxide according to the first aspect as an active electrode material.

[0019] In a third aspect, the present invention provides a metal ion battery comprising the electrode according to the second aspect. Optionally, the metal ion battery is a lithium ion battery or a sodium ion battery, preferably a lithium ion battery. Preferably, the electrode forms the anode of the metal ion battery.

[0020] In a fourth aspect, the present invention provides the use of the mixed-phase oxide defined in the first aspect in a metal ion battery, optionally as an active electrode material in the anode. Optionally, the metal ion battery is a lithium ion battery or a sodium ion battery, preferably a lithium ion battery.

[0021] In a fifth aspect, the present invention provides a method of manufacturing an electrode, which comprises providing a mixed-phase oxide as described in the first aspect; and depositing the mixed-phase oxide on a current collector to thereby form an electrode. Description of the Drawings

[0022] Figure 1 : XRD of Samples 1-8 Detailed Description

[0023] The mixed-phase oxide comprises Nb, Ti, M(III) and M(II). Oxides containing Nb and at least one other cation can have a high redox voltage of >0.8V relative to lithium, enabling safe and long-life operation, which is crucial for battery cells of fast-charging batteries. In addition, each atom of the Nb cation can have two redox reactions, resulting in a higher theoretical capacity than, for example, LTO.

[0024] The mixed-phase oxide comprises an interpenetrating mixture of a first phase and a second phase. It should be understood that the interpenetrating mixture renders the first phase and the second phase inseparable without destroying the mixed-phase oxide.

[0025] The first phase has a crystal structure of TiNb2O7, and the second phase has a crystal structure of Zn2Nb34 O 87 The crystal structures. It is believed that the interpenetrating mixtures of these phases, together with the presence of M(III) and / or M(II), result in the modification of each of the two "base" oxides that define the crystal structure (i.e., TiNb2O7 and pure Zn2Nb 34 O 87 ), such that each is simultaneously modified by the substituting element. For example, the first phase contains M(III) and / or M(II) in addition to Ti and Nb, and the second phase contains M(III) and / or Ti in addition to M(II) and Nb. The inventors have found that this simultaneous substitution method improves the properties of each of the "base" oxides, and that the "base" oxides, in combination with the interpenetrating mixture of the two phases, provide a synergistic benefit compared to the first and second phases separately. For example, the mixed-phase oxides of the present invention provide surprisingly improved performance at high rates of 5C and above. In addition, the addition of M(II) and / or M(III) cations increases the entropy of the system and favors the formation of the desired crystal structure.

[0026] The first phase has the crystal structure of TiNb2O7, which can be considered to have a ReO3-derived MO3-x crystal structure known as the Wadsley-Roth crystal structure. The Wadsley-Roth crystal structure is considered to be a crystallographically non-stoichiometric MO3 (ReO3) crystal structure containing crystallographic shear, with the simplified formula MO 3-x . Thus, these structures typically contain [MO6] octahedral subunits in their crystal structures. Phases having these structures are considered to have advantageous properties for use as active electrode materials (e.g., in lithium-ion batteries).

[0027] The open tunnel-like MO3 crystal structures provide ideal candidates for high Li-ion storage capacity and high-rate insertion / extraction. The crystallographic non-stoichiometry present in the crystal structure gives rise to the Wadsley-R o th crystallographic superstructure. These superstructures, in combination with other properties such as the Jahn-Teller effect and crystallographic disorder enhanced by the use of multiple mixed cations, stabilize the crystal and keep the tunnels open and stable during insertion, resulting in extremely high rate performance due to the high Li-ion diffusion rate (reported to be about 10 -13 cm 2 s -1 ).

[0028] The crystal structure of TiNb2O7 can be described as having a 3x3x∞ crystalline block structure composed of [MO6] octahedra, where M is Ti or Nb. The crystal structure is typically monoclinic. The crystal structure of TiNb2O7 can be found in PDF card 00-039-1407. The unit cell parameters a, b, and c can be such that a is Preferably b is Preferably and c is Preferably The crystal structure of the first phase may have unit cell parameters α and γ each of approximately 90°, preferably where α = γ = 90°; and β may be 95.30 - 95.37°, preferably 95.32 - 95.36°.

[0029] Without wishing to be bound by theory, the inventors believe that adding a larger cation (e.g., Zn 2+ ) to the Wadsley - Roth crystal structure will change the lattice parameters of the structure and thus enable better diffusion of lithium ions. In addition, doping with such non - redox - active cations can avoid octahedral tilting during charging and discharging, thereby conferring structural stability.

[0030] The second phase has a crystal structure of Zn2Nb 34 O 87 which can also be considered to have a ReO3 - derived MO 3-x Wadsley - Roth crystal structure. The crystal structure of Zn2Nb 34 O 87 can be described as having a 3x4x∞ crystalline block structure composed of [MO6] octahedra, where M is Zn or Nb. When M(II) is absent, the crystal structure Zn2Nb 34 O 87 is obtained by using Zn sites with M(III) or Ti. It is believed that compared to other Wadsley - Roth structures with smaller octahedral block sizes, the large block size is beneficial for rapid insertion and removal of lithium and may have potentially higher stability with respect to the unit cells of those structures with larger octahedral block sizes. The Zn octahedra can be randomly distributed in the structure or can preferentially occupy specific sites, such as at the edges or corners of the blocks. This corresponds to 2 / 3 of a zinc cation / block.

[0031] The crystal structure of the second phase can be monoclinic or orthorhombic, or can be considered a mixture of monoclinic and orthorhombic. The crystal structure of monoclinic Zn2Nb 34 O 87 can be found in ICDD crystallographic database entry PDF card 00 - 013 - 0317. The crystal structure of orthorhombic Zn2Nb 34 O 87 can be found in PDF card 04 - 021 - 7859.

[0032] When refined to a monoclinic crystal structure, the unit cell parameters a, b, and c can be such that a is Preferably b is Preferably and c is Preferably The unit cell parameters α and γ are each approximately 90°, preferably where α = γ = 90°; β can be 113.00 - 113.75°, preferably 113.06 - 113.69°.

[0033] As is well known, the crystal structure of a phase can be determined by analyzing an X - ray diffraction (XRD) pattern obtained using Cu K - α radiation. For example, the XRD pattern obtained from a given material can be compared with a known XRD pattern to confirm the crystal structure, such as 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 with respect to unit cell parameters. Thus, the crystal structures of the first and second phases can be determined by XRD.

[0034] The XRD pattern of the mixed - phase oxide preferably exhibits a peak A attributable to the first phase at 2θ = 26.0 ± 0.1°. The XRD pattern of the mixed - phase oxide preferably exhibits a peak B attributable to the second phase at 2θ = 24.9 ± 0.1°. The intensity I of peak B B and the intensity I of peak A A The ratio can be 0 < I B / I A ≤ 0.4, or 0.01 ≤ I B / I A ≤ 0.25, or preferably 0.05 ≤ I B / I A ≤ 0.22. In a particular embodiment, the ratio is 0.07 ≤ I B / I A ≤ 0.16. The peak intensity ratio can be conveniently calculated using the normalized heights of peaks A and B.

[0035] The weight ratio of the first phase to the second phase can be 199:1 - 1:1, or 99:1 - 3:1, or 50:1 - 8:1. The weight ratio of each phase in the mixed - phase oxide can be determined by refining the XRD pattern of the mixed - phase oxide. The target weight ratio can be obtained by controlling the relative amounts of the elemental precursors used in the synthesis.

[0036] Other phases may be present in the mixed-phase oxide. For example, the first phase and the second phase may form at least 80 wt%, at least 90 wt%, or at least 95 wt% of the mixed-phase oxide. The first phase and the second phase may form substantially all of the mixed-phase oxide, such as having less than 1 wt% of other phases. Preferably, the first phase forms at least 85 wt%, or at least 90 wt%, or at least 92 wt% of the mixed-phase oxide.

[0037] Nb is preferably the major cation present in the mixed-phase oxide. For example, relative to all cations, the mixed-phase oxide may contain 66 - 80 atomic%, or 66.5 - 75 atomic%, or 66.9 - 69.9 atomic% of Nb.

[0038] Relative to all cations, the mixed-phase oxide may contain 33 - 17 atomic%, or 33.1 - 24 atomic%, or 33.2 - 30 atomic% of Ti.

[0039] Relative to all cations, the mixed-phase oxide may contain >0 - 1 atomic%, or 0.01 - 0.4 atomic%, or 0.01 - 0.2 atomic% of M(III).

[0040] Relative to all cations, the mixed-phase oxide may contain >0 - 2 atomic%, or 0.01 - 1 atomic%, or 0.02 - 0.5 atomic% of M(II).

[0041] Relative to the amount of Nb, the combined amount of M(III) and M(II) may be ≥0.05 atomic%, ≥0.5 atomic%, or ≥0.6 atomic%.

[0042] The atomic ratio of Ti:Nb may be at least 0.3:1, or at least 0.4:1, or 0.42:1 - 0.5:1.

[0043] It should be understood that the amounts of Nb, Ti, M(III), and / or M(II) may be combined to further define the mixed-phase oxide.

[0044] M(III) represents cations that typically adopt a 3+ oxidation state in oxides. M(III) is selected from Cr, Al, Ga, and mixtures thereof; or Cr, Al, and mixtures thereof. Preferably, M(III) is Cr.

[0045] M(II) represents cations that typically adopt a 2+ oxidation state in oxides. M(II) is selected from Zn, Cu, Mg, and mixtures thereof; or Zn, Cu, and mixtures thereof. Preferably, M(II) is Zn.

[0046] Preferably, the mixed-phase oxide contains M(III), most preferably M(III) and M(II), especially when M(III) is Cr and M(II) is Zn.

[0047] The mixed-phase oxide may optionally further contain at least one additional element; optionally, wherein the additional element is selected from Zr, Hf, V, Fe, Ta, Mo, W, Mn, Co, Ni, Cd, B, Si, Sn, P, and mixtures thereof; or Zr, V, Fe, Mo, W, Mn, Co, Ni, Cd, B, Si, P, and mixtures thereof; or preferably Zr, V, Fe, Mo, W, Cu, P, and mixtures thereof. The at least one additional element may be present in an amount of ≤1.5 atomic % or 0.01-1.0 atomic % relative to all cations. The at least one additional element may be present in an amount of ≤5 atomic % or ≤1 atomic % or a total amount of 0.01-0.5 atomic % relative to the amount of Nb.

[0048] When M(III) and / or M(II) is limited to preferred elements, the optional additional element may include elements that substitute for M(III) and / or M(II). For example, when M(III) is Cr and M(II) is Zn, the at least one additional element may further be selected from Al, Ga, Cu, Mg, and mixtures thereof.

[0049] Alternatively, the cations in the mixed-phase oxide may consist of Nb, Ti, M(III), and / or M(II); or consist of Nb, Ti, M(III), and M(II).

[0050] It should be understood that the mixed-phase oxide may also contain Li and / or Na, and when the oxide serves as an active electrode material in a metal-ion battery, Li and / or Na can be reversibly inserted in-situ.

[0051] Advantageously, it has been found that the mixed-phase oxide can be formed by a simple solid-state synthesis method, as shown in this example. In addition, improved properties provided by an interpenetrating mixture of a first phase and a second phase are provided without the need for particle-level engineering, such as the need to form a core / shell structure that typically requires complex synthesis. Therefore, it is preferred that the interpenetrating mixture of the first phase and the second phase does not form a core / shell structure. For example, the interpenetrating mixture of the first phase and the second phase does not form a structure in which the first phase forms a shell portion and the second phase forms a core portion surrounded by the shell portion.

[0052] The mixed-phase oxide is preferably in particulate form. The mixed-phase oxide may have a D in the range of 0.1-100 μm, or 0.5-50 μm, or 1-20 μm 50Particle size. These particle sizes are advantageous because they are easy to handle and fabricate into electrodes. In addition, these particle sizes obviate the need to use complex and / or expensive methods to provide nanoparticles. Nanoparticles (e.g., particles having a D 50 particle size of 100 nm or less) are generally more complex to synthesize and require additional safety considerations.

[0053] The mixed-phase oxide may have a D 10 particle size of at least 0.05 μm, or at least 0.1 μm, or at least 0.5 μm, or at least 1 μm. By maintaining the D 10 particle size within these ranges, the likelihood of parasitic reactions in the Li-ion battery cell is reduced due to the reduced surface area, and it is easier to handle in the electrode slurry with less binder.

[0054] The mixed-phase oxide may have a D 90 particle size of no more than 200 μm, no more than 100 μm, no more than 50 μm, or no more than 20 μm. By maintaining the D 90 particle size within these ranges, the proportion of the particle size distribution with large particle sizes is minimized, making it easier to fabricate the material into a homogeneous electrode.

[0055] The term "particle size" 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 should be understood to include the volume of any internal pores of the particle. The terms "D n " and "D n particle size" refer to such a diameter below which there is an n% volume of the particle population, i.e., the terms "D 50 " and "D 50 particle size" refer to the volume-based median particle size below which there is 50% volume of the particle population. In the case where the material contains primary microcrystals agglomerated into secondary particles, it should 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, for example using Mie theory.

[0056] The mixed-phase oxide may have a surface area in the range of 0.1 - 100 m 2 / g, or 0.25 - 50 m 2 / g, or 0.5 - 20 m 2The BET surface area is within the range of / g. Generally, a low BET surface area is preferred to minimize the reaction of the mixed-phase oxide with the electrolyte, for example, to minimize the formation of the solid electrolyte interphase (SEI) layer during the first charge-discharge cycle of an electrode containing the material. However, an overly low BET surface area results in unacceptable low charge rates and capacities because it is difficult for the bulk of the mixed-phase oxide to access metal ions in the surrounding electrolyte.

[0057] The term "BET surface area" refers to the surface area per unit mass calculated by measuring the physical adsorption of gas molecules on the solid surface using the Brunauer-Emmett-Teller theory. For example, the BET surface area can be determined according to ISO 9277:2010.

[0058] The mixed-phase oxide can have a crystallite size greater than 180 nm, or greater than 200 nm, or greater than 225 nm, or preferably greater than 250 nm. The crystallite size can be in the range of 180 nm - 20 μm, or 200 nm - 10 μm, or 225 nm - 5 μm, or 250 nm - 3 μm. Compared with materials having smaller crystallites, these crystallite size ranges are considered to improve ion transport because there are fewer grain boundaries in the material and thus lower interfacial resistance. Denser particles and electrodes with higher density can also be produced with larger crystallite sizes. The crystallite size can be conveniently measured by the Scherrer method using crushed Si crystals as a standard.

[0059] In a powder X-ray diffraction pattern, the shape of the diffraction peak is determined by the convolution of the line profile generated by the diffractometer optical system (instrument contribution) and the line profile generated by the sample (sample-related peak broadening). The finite size of the diffracting crystallites in the sample contributes to the width of the diffraction peak. The instrument contribution can be considered, and then by using the Scherrer equation, the volume-weighted average crystallite diameter can be determined using the diffraction peak width. The Scherrer equation relates the width of the diffraction peak at a given Bragg angle to the minimum crystallite diameter.

[0060]

[0061] where K is the Scherrer constant, which has a value of 0.9 in this case. λ is the wavelength of the X-ray, β is the corrected peak width calculated according to β 样品 β 标准 calculated from the full width at half maximum of the selected diffraction peaks from the sample under study and the standard sample respectively, and θ is the Bragg angle of the sample peak under study.

[0062] Preferably, the Scherrer method is used to determine the volume-weighted average crystallite size of the sample, where the instrument contribution can be determined from the measurement of a standard sample. The standard sample should be a crystalline material with a large crystallite size, e.g., an average crystallite size > 1 μm, and ideally having a Bragg peak at the same angle as the peak selected for analysis in the test sample. Typically, LaB6 (e.g., NIST SRM 660C) or crushed Si crystals (e.g., NIST SRM 640C) are used. The sample peak selected for analysis should be a single Bragg reflection peak and preferably the peak with the highest scattering intensity. The full width at half maximum (FWHM) of the peak is measured by finding the points in the diffraction peak where the scattering intensity is between the background intensity and the peak maximum intensity and measuring the difference in the 2θ Bragg angle values of the peak at these scattering intensity values.

[0063] Preferably, the standard sample and the test sample should be measured on the same instrument under the same conditions. The scan speed and step size of the diffraction measurement should be such that the peak intended for study contains at least 8 data point measurements above the half-maximum point, and the maximum intensity point in the peak is at least 10 times the background intensity.

[0064] Transmission electron microscopy (TEM) examination can be additionally used to confirm the crystallite size determined by the Scherrer method. The overall size measured in the particle size distribution by selected area electron diffraction (SAED) examination is close to D 50 particles with a diameter to study the degree of crystallite domains in the particles. When the zone axis has been aligned and a clear diffraction pattern has been obtained, a spatial map can be generated by measuring the diffraction pattern at spatial intervals until a grain boundary is encountered.

[0065] The mixed-phase oxide can be coated with carbon, e.g., to improve its surface electron conductivity and / or prevent reaction with the electrolyte.

[0066] The mixed-phase oxide can have a protective coating; optionally, the protective coating includes niobium oxide, aluminum oxide, zirconium oxide, organic or inorganic fluorides, organic or inorganic phosphates, titanium oxide, its lithiated form, and mixtures thereof.

[0067] The electrode of the second aspect is typically in the form of an electrode composition in electrical contact with a current collector, where the electrode composition contains the mixed-phase oxide. The current collector is typically a metal foil, e.g., copper or aluminum foil.

[0068] Optionally, the mixed-phase oxide forms at least 25 wt%, 50 wt%, or 75 wt% of the total active electrode material in the electrode. The mixed-phase oxide can form the sole active electrode material in the electrode.

[0069] The electrode composition may further comprise at least one other component selected from binders, conductive additives, different active electrode materials (such as additional mixed-phase oxides as defined herein), and mixtures thereof. For example, based on the total dry weight of the electrode composition, an electrode composition comprises about 92 wt% of a mixed-phase oxide, about 5 wt% of a conductive additive (such as carbon black), and about 3 wt% of a binder (such as poly(vinylidene fluoride)).

[0070] 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 formal, polyether amide, polymethacrylic acid, polyacrylamide, itaconic acid, polystyrene sulfonic acid, polyacrylic acid (PAA) and its alkali metal salts, modified polyacrylic acid (mPAA) and its alkali metal salts, cellulose-based polymers, carboxymethyl cellulose (CMC), modified carboxymethyl cellulose (mCMC), sodium carboxymethyl cellulose (Na-CMC), polyvinyl alcohol (PVA), alginates and their alkali metal salts, nitrile butadiene rubber (NBR), the hydrogenated form of NBR (HNBR), styrene butadiene rubber (SBR), and polyimide. The binder may 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.

[0071] The conductive additive is preferably an inactive material, which is included to improve the conductivity between the active electrode materials and between the active electrode materials and the current collector. The conductive additive may be suitably selected from graphite, carbon black, carbon fiber, vapor-grown carbon fiber (VGCF), carbon nanotube, graphene, acetylene black, ketjen black, metal fiber, metal powder, and conductive metal oxide. Preferred conductive additives include carbon black and carbon nanotubes. Based on the total dry weight of the electrode composition, the conductive additive may be present in the electrode composition in an amount of 0-20 wt%, 0.1-10 wt%, or 0.1-5 wt%.

[0072] Based on the total dry weight of the electrode composition, the mixed-phase oxide may be present in the electrode composition in an amount of 100-50 wt%, 99.8-80 wt%, or 99.8-90 wt%. When the active electrode material is present at 100 wt% of the electrode composition, it can be used as a solid-state electrode.

[0073] When different active electrode materials are present in addition to the mixed-phase oxide, they may be selected from lithium titanium oxide, titanium niobium oxide, different mixed-phase oxides, graphite, hard carbon, soft carbon, silicon, their doped forms, and mixtures thereof.

[0074] The mixed-phase oxide may be combined with lithium titanium oxide to form an active electrode material.

[0075] The lithium titanium oxide preferably has a spinel or orthorhombic manganese oxide crystal structure, for example, as determined by X-ray diffraction. An example of a lithium titanium oxide having a spinel crystal structure is Li4Ti5O 12 . An example of a lithium titanium oxide having an orthorhombic manganese oxide crystal structure is Li2Ti3O7. These materials have been shown to have good properties for use as active electrode materials. Thus, the lithium titanium oxide can have a crystal structure corresponding to Li4Ti5O 12 and / or Li2Ti3O7 as determined by X-ray diffraction. The lithium titanium oxide can be selected from Li4Ti5O 12 , Li2Ti3O7, and mixtures thereof.

[0076] The lithium titanium oxide can be doped with additional cations or anions. The lithium titanium oxide can be oxygen-deficient. The lithium titanium oxide can form a coating, optionally where the coating is selected from carbon, polymers, metals, metal oxides, metalloids, phosphates, and fluorides.

[0077] The lithium titanium oxide can be synthesized by conventional ceramic techniques (e.g., solid-state synthesis or sol-gel synthesis). Alternatively, the lithium titanium oxide can be obtained from commercial suppliers.

[0078] The lithium titanium oxide is preferably in particulate form. The lithium titanium oxide can have a D 50 particle size in the range of 0.1 - 50 μm, or 0.25 - 20 μm, or 0.5 - 15 μm. The lithium titanium oxide can have a D 10 particle size of at least 0.01 μm, or at least 0.1 μm, or at least 0.5 μm. The lithium titanium oxide can have a D 90 particle size not exceeding 100 μm, not exceeding 50 μm, or not exceeding 25 μm. By maintaining the D 90 particle size within this range, the packing of the lithium titanium oxide particles in a mixture with the mixed-phase oxide particles is improved.

[0079] Due to the low electronic conductivity of the material, the lithium titanium oxide is typically used in small particle sizes for battery anodes. In contrast, the mixed-phase oxide as defined herein can be used in larger particle sizes because it generally has a higher lithium ion diffusion coefficient than the lithium titanium oxide. Advantageously, in the composition, the lithium titanium oxide can have a smaller particle size than the mixed-phase oxide, for example such that the ratio of the D 50 particle size of the lithium titanium oxide to the D 50 particle size of the mixed-phase oxide is in the range of 0.01:1 to 0.9:1, or 0.1:1 to 0.7:1. In this way, the smaller lithium titanium oxide particles can be accommodated in the voids between the larger mixed-phase oxide particles, thereby improving the packing efficiency of the composition.

[0080] The lithium titanium oxide may have a BET surface area in the range of 0.1 - 100 m 2 / g, or 1 - 50 m 2 / g, or 3 - 30 m 2 / g.

[0081] The mass ratio of the lithium titanium oxide to the mixed - phase oxide may 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 implementation, the active electrode material contains a higher proportion of lithium titanium oxide than the mixed - phase oxide, such as a mass ratio of at least 2∶1, at least 5∶1, or at least 8∶1. Advantageously, this allows the incremental introduction of the mixed - phase oxide into an existing lithium - titanium - oxide - based electrode without major changes to the manufacturing technology, thus providing an effective way to improve the properties of the existing electrode. In another implementation, the active electrode material has a higher proportion of the mixed - phase oxide than the lithium titanium oxide, such as a mass ratio of the lithium titanium oxide to the mixed - phase oxide 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 - phase oxide with lithium titanium oxide.

[0082] The mixed - phase oxide may be combined with niobium oxide to form the active electrode material. The niobium oxide may be selected from Nb 12 O 29 、NbO2, NbO and Nb2O5. Preferably, the niobium oxide is Nb2O5.

[0083] The niobium oxide may be doped with additional cations or anions, assuming, for example, that the crystal structure of the niobium oxide corresponds to the crystal structure of an oxide composed of Nb and O (e.g., Nb 12 O 29 、NbO2, NbO and Nb2O5). The niobium oxide may be oxygen - deficient. The niobium oxide may form a coating, optionally where the coating is selected from carbon, polymer, metal, metal oxide, metalloid, phosphate and fluoride.

[0084] The niobium oxide may have a crystal structure of Nb12O 29 、NbO2, NbO or Nb2O5, as determined by X - ray diffraction. For example, the niobium oxide may have an orthorhombic Nb2O5 crystal structure or a monoclinic Nb2O5 crystal structure. Preferably, the niobium oxide has a monoclinic Nb2O5 crystal structure, most preferably the H - Nb2O5 crystal structure. Further information on the crystal structure of Nb2O5 can be found in Griffith et al., J. Am. Chem. Soc. 2016, 138, 28, 8888 - 8899. The niobium oxide can be synthesized by conventional ceramic techniques (e.g., solid - state synthesis or sol - gel synthesis). Alternatively, the niobium oxide can be obtained from commercial suppliers.

[0085] The niobium oxide is preferably in particulate form. The niobium oxide may have a D 50 particle size in the range of 0.1 - 100 μm, or 0.5 - 50 μm, or 1 - 20 μm. 10 The niobium oxide may have a D 90 particle size of at least 0.05 μm, or at least 0.5 μm, or at least 1 μm. 90 By maintaining the D

[0086] particle size within this range, the packing of the niobium oxide particles in a mixture with the mixed - phase oxide particles is improved. 2 The niobium oxide may have a BET surface area in the range of 0.1 - 100 m 2 / g, or 1 - 50 m 2 / g, or 1 - 20 m

[0087] The mass ratio of the niobium oxide to the mixed - phase oxide may be in the range of 0.5∶99.5 to 99.5∶0.5, or in the range of 2∶98 to 98∶2, or preferably in the range of 15∶85 to 35∶55.

[0088] The present invention also provides the use of the mixed - phase oxide as defined herein in the 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. The lithium - ion battery includes a liquid - based battery, a polymer - based battery, a semi - solid - based battery, and an all - solid - state - based battery.

[0089] Another implementation of the present invention is an electrochemical device that includes an anode, a cathode, and an electrolyte disposed between the anode and the cathode, wherein the anode comprises the mixed - phase oxide according to the first aspect of the present invention; optionally wherein the electrochemical device is a metal - ion battery, such as a lithium - ion battery or a sodium - ion battery. Preferably, the electrochemical device is a lithium - ion battery having a reversible anode active material specific capacity of greater than 230 mAh / g at 23 mA / g, wherein the battery can be charged and discharged 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 with respect to the anode active material, while maintaining an initial battery capacity of greater than 70% at 23 mA / g. It has been found that using the active electrode material of the first aspect of the present invention can produce a lithium - ion battery having such a combination of properties, which represents a lithium - ion battery particularly suitable for applications requiring high charge and discharge current densities. Notably, the examples have shown that the active electrode material according to the first aspect of the present invention has excellent capacity at high C - rates.

[0090] The mixed-phase oxide can be synthesized by conventional ceramic techniques. For example, it can be prepared by one or more of solid-state synthesis or sol-gel synthesis, preferably using solid-state synthesis of particulate precursors as shown in the examples. In addition, the mixed-phase oxide can be synthesized by one or more of common 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.

[0091] The mixed-phase 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 in a temperature range of 800 °C - 1350 °C or 1000 °C - 1300 °C to provide the mixed-phase oxide.

[0092] The mixed-phase oxide can be modified to contain at least one electronegative element, replacing the oxygen anions with anionic moieties selected from F, Cl, Br, I, N, S, Se, and mixtures thereof; or F, Cl, N, S, and mixtures thereof; or preferably F, N, and mixtures thereof. The total amount of at least one electronegative element can be present in an amount of ≤5 atomic % or ≤1 atomic % relative to the amount of O. The electronegative element can be introduced by mixing the mixed-phase oxide with a precursor containing the electronegative element to provide another precursor material mixture; and optionally heat-treating the additional precursor material mixture in a temperature range of 300 - 1200 °C or 800 - 1100 °C under reducing conditions to provide a mixed-phase oxide containing the additional electronegative element.

[0093] For example, to provide a mixed-phase oxide containing N, the method can further comprise the steps of: mixing the mixed-phase oxide with a precursor containing N (e.g., melamine or urea) to provide another precursor material mixture; and heat-treating the additional precursor material mixture in a temperature range of 300 °C - 1200 °C under reducing conditions (e.g., under N2) to provide a mixed-phase oxide containing N.

[0094] For example, to provide a mixed-phase oxide containing F, the method can further comprise the steps of: mixing the mixed-phase oxide with a precursor containing F (e.g., polyvinylidene fluoride or NH4F) to provide another precursor material mixture; and heat-treating the additional precursor material mixture in a temperature range of 300 °C - 1200 °C under oxidizing conditions (e.g., in air) to provide a mixed-phase oxide containing F.

[0095] The method may include an additional step of heat-treating the mixed-phase oxide in a temperature range of 400 - 1350 °C or 800 - 1250 °C under reducing conditions to induce oxygen vacancies in the mixed-phase oxide.

[0096] The precursor material for preparing the mixed-phase oxide may include one or more metal oxides, metal hydroxides, metal salts, or ammonium salts. For example, the precursor material may include one or more metal oxides or metal salts with 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, NbO2, ammonium oxalate niobate, 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, Cr2O3, MnO, MnO2, NiO, Ni2O3, H3BO3, ZnO, Li2CO3, Na2CO3, H3BO3, NiO, Mg5(CO3)4(OH)2·5H2O, and MgO. The precursor material may not contain metal oxides, or may contain an ion source other than oxides. For example, the precursor material may contain metal salts (e.g., NO3 - , SO3 - ) or other compounds (e.g., oxalates, carbonates). For substituting oxygen anions with other electronegative anions, the precursor may 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, NH4Cl, NH4Br, NH4I, Br2, Cl2, I2, ammonium oxychloride amide, and hexamethylenetetramine.

[0097] Some or all of the precursor materials may be particulate materials. In the case where they are particulate materials, preferably, they have a D 50 particle size less than 20 μm (e.g., 250 nm to 20 μm). Providing particulate materials with such a particle size can help promote closer mixing of the precursor materials, thereby producing a more efficient solid-state reaction during the heat-treatment step. However, it is not necessary for the precursor materials to have an initial particle size < 20 μm, since the particle size of one or more precursor materials can be mechanically reduced during the step of mixing the precursor materials to form a precursor material mixture.

[0098] The step of mixing precursor materials to form a precursor material mixture and / or an additional precursor material mixture can be carried out by a method selected from the following: dry or wet / solvent planetary ball milling, rolling ball milling, high-energy ball milling, bead milling, needle milling, classification steps, high-shear grinding, air jet milling, steam jet milling, planetary mixing, high-shear mixing, impact mixing, powder blending, and / or impact grinding. The force used for mixing / grinding can depend on the morphology of the precursor materials. For example, in the case where some or all of the precursor materials have a relatively large particle size (e.g., a D 50 particle size greater than 20 μm), the grinding 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 a diameter of 20 μm or less. When the particle size of the particles in the precursor material mixture is 20 μm or less, this can facilitate a more efficient solid-state reaction of the precursor materials in the precursor material mixture during the heat treatment step. The solid-state synthesis can also be carried out in pellets formed from the precursor powder under high pressure (>10 MPa).

[0099] The step of heat-treating the precursor material mixture and / or the further precursor material mixture can be carried out for a time of 1 hour to 24 hours, more preferably 3 hours to 18 hours. For example, the heat treatment step can be carried out for 1 hour or longer, 2 hours or longer, 3 hours or longer, 6 hours or longer, or 12 hours or longer. The heat treatment step can be carried out for 24 hours or shorter, 18 hours or shorter, 16 hours or shorter, or 12 hours or shorter.

[0100] The step of heat-treating the precursor material mixture can be carried out in a gas atmosphere, preferably air. Suitable gas atmospheres include: air, N2, Ar, He, CO2, CO, O2, H2, NH3, and mixtures thereof. The gas atmosphere can be a reducing atmosphere. In the case where an oxygen-deficient material is desired to be prepared, preferably, the step of heat-treating the precursor material mixture is carried out in an inert atmosphere or a reducing atmosphere.

[0101] The step of heat-treating the further precursor material mixture can be carried out 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 additional precursor material mixture includes heating under an inert gas.

[0102] Optionally, an additional step of heat treating the mixed-phase oxide and / or the mixed-phase oxide containing additional electronegative anions under reducing conditions may be carried out for a time of from 0.5 hours to 24 hours, more preferably from 2 hours to 18 hours. For example, the heat treatment step may be carried out for 0.5 hours or longer, 1 hour or longer, 3 hours or longer, 6 hours or longer or 12 hours or longer. A further step of heat treatment may be carried out for 24 hours or shorter, 18 hours or shorter, 16 hours or shorter or 12 hours or shorter. 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 includes heating under an inert gas.

[0103] In some methods, it may be advantageous to carry out a two-step heat treatment. For example, the precursor material mixture and / or an additional precursor material mixture may be heated at a first temperature for a first time length and subsequently heated at a second temperature for a second time length. Preferably, the second temperature is higher than the first temperature. Carrying out such a two-step heat treatment can assist solid-state reactions to form the desired crystal structure. This may be carried out sequentially or may be carried out in the presence of an intermediate regrinding step.

[0104] The method may include one or more post-treatment steps after forming the mixed-phase oxide. In some cases, the method may include a post-treatment step of heat treating the mixed-phase oxide, which is sometimes referred to as "annealing". Such a post-treatment heat treatment step may be carried out in a gas atmosphere different from the step of heat treating the precursor material mixture to form the mixed-phase oxide. The post-treatment heat treatment step may be carried out in an inert or reducing gas atmosphere. Such a post-treatment heat treatment step may be carried out at a temperature above 500 °C, for example at about 900 °C. Including the post-treatment heat treatment step may be beneficial for, for example, forming vacancies or defects in the mixed-phase oxide, such as inducing oxygen deficiency; or for anion exchange on the formed mixed-phase oxide, such as exchanging O anions with N.

[0105] The method may include the steps of grinding and / or classifying the mixed-phase oxide (e.g., impact grinding, jet grinding, steam jet grinding, high-energy grinding, ball milling, high-shear grinding, needle milling, air classification, wheel classification, screening, cyclone separation, bead milling) to provide a material having any of the particle size parameters given above.

[0106] The present invention provides a method of manufacturing an electrode, the method comprising providing a mixed-phase oxide as defined herein; and depositing the mixed-phase oxide on a current collector so as to form an electrode. Providing the mixed-phase oxide may comprise synthesizing the mixed-phase oxide by the method provided herein. The depositing step may comprise forming a slurry of the mixed-phase oxide and a solvent. The slurry may comprise at least one other component selected from binders, conductive additives, different active electrode materials, and mixtures thereof. The slurry may be deposited onto the current collector and the solvent removed so as to form an electrode layer on the current collector. Further steps may optionally be carried out, such as heat treatment for curing any binder and / or calendering of the electrode layer. For example, the solvent may be removed by drying, for example, at a temperature of 30-100 °C. The electrode may be calendered to a density of 2-3.5 or 2.6-2.9 g cm -3 The electrode layer may have a thickness in the range of 5 μm to 2 mm, preferably 5 μm to 1 mm, preferably 5 μm to 500 μm, preferably 5 μm to 200 μm, preferably 5 μm to 100 μm, preferably 5 μm to 50 μm.

[0107] Alternatively, the slurry may be formed into a self-supporting film or mat comprising the mixed-phase 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 sticky, free-standing mass and may then be bonded to the current collector by known methods.

[0108] Examples

[0109] The mixed-phase oxide was synthesized by a solid-state route. In the first step, the precursor materials (Nb2O5, TiO2, ZnO, Cr2O3, CuO, MgO, Al2O3, and Ga2O3) were ground to a D 50 particle size below 20 μm. Subsequently, appropriate amounts of the precursors were combined and mixed in an impact mill at 20,000 rpm to obtain a homogeneous powder mixture (50 g in total). Depending on the desired Wadsley-Roth phase, the resulting powder was heat-treated in an alumina crucible in a muffle furnace at between 1100-1200 °C for 1-24 hours. Samples 3-12 were removed from the furnace, impact milled at 20,000 rpm, and heated a second time using the same conditions. A heating rate of 5 °C / minute was used for all heat treatment conditions. Finally, a defragmentation step was utilized by impact milling at 20,000 for at least 2 minutes to adjust the desired particle size distribution if necessary. The particle size distribution of the dry powder was obtained by a Horiba laser diffraction particle analyzer. The air pressure was maintained at 0.3 MPa. The results are listed in Table 1.

[0110] Table 1: Summary of the synthesized materials. The particle size distribution of the dry powder was obtained using a Horiba laser diffraction particle analyzer at an air pressure of 0.3 MPa.

[0111]

[0112]

[0113] *Reference sample

[0114] Nomenclature (e.g., 95TiNb2O7:5Cr 0.6 Zn 1.6 Nb 33.8 O 87 ) refers to a mixed-phase oxide made from precursors that are weighed to provide 95 parts by weight of TiNb2O7 and 5 parts by weight of Cr 0.6 Zn 1.6 Nb 33.8 O 87 The elemental ratio of the mixture. Compared to the "base" oxide, the first and second phases in the synthesized mixed-phase oxide will contain additional substituted elements. Specifically:

[0115] In Samples 3-5, the first phase has the crystal structure of TiNb2O7 but also contains Cr and / or Zn, and the second phase has the crystal structure of Zn2Nb 34 O 87 but also contains Cr and / or Ti;

[0116] In Sample 6, the first phase has the crystal structure of TiNb2O7 but also contains Al and / or Zn, and the second phase has the crystal structure of Zn2Nb 34 O 87 but also contains Al and / or Ti;

[0117] In Sample 7, the first phase has the crystal structure of TiNb2O7 but also contains Cr, and the second phase has the crystal structure of Zn2Nb 34 O 87 but contains Cr and / or Ti;

[0118] In Sample 8, the first phase has the crystal structure of TiNb2O7 but also contains Cr and / or Al, and the second phase has the crystal structure of Zn2Nb 34 O 87 but contains Cr, Al, and / or Ti;

[0119] In Sample 9, the first phase has the crystal structure of TiNb2O7 but also contains Ga and / or Al, and the second phase has the crystal structure of Zn2Nb 34 O 87 but contains Ga, Al, and / or Ti;

[0120] In sample 10, the first phase has the crystal structure of TiNb2O7 but also contains Cu and / or Ga, and the second phase has the crystal structure of Zn2Nb 34 O 87 but contains Cu, Ga, and / or Ti;

[0121] In sample 11, the first phase has the crystal structure of TiNb2O7 but also contains Zn, and the second phase has the crystal structure of Zn2Nb 34 O 87 but also contains Ti;

[0122] In sample 12, the first phase has the crystal structure of TiNb2O7 but also contains Mg and / or Cr, and the second phase has the crystal structure of Zn2Nb 34 O 87 but contains Mg, Cr, and / or Ti.

[0123] Table 2: Comparison of anatase peak intensities of samples measured by in-situ PXRD during the synthesis process. The anatase TiO2(101) peak was measured at 25.2° 2θ.

[0124]

[0125] *Reference sample

[0126] Relative to the reference systems TiNb2O7 and 95TiNb2O7:5Ti2Nb 10 O 29 , the synthetic advantages of the examples herein have been shown. These data were collected from a Rigaku SmartLab SE powder X-ray diffractometer using a variable temperature heating stage, where the unreacted samples were heated at a rate of 6 °C / minute and XRD scans were performed every 2 minutes to provide the results in Table 2. The syntheses of samples 3 and 5 were completed at temperatures below 1200 °C, as indicated by the absence of anatase peaks, but the syntheses of samples 1* and 13* were not completed. After heat-treating samples 1* and 13* at 1200 °C for 12 hours, the synthesis of sample 13* was completed, but the synthesis of sample 1* was not completed. This was demonstrated by the presence of the rutile TiO2(110) peak in the XRD pattern of sample 1*. These data indicate an improvement in the synthesis efficiency of the samples according to the present invention, which is beneficial for more cost-effective manufacturing.

[0127] Material Characterization

[0128] The phase purity of the samples was analyzed using a Rigaku Miniflex powder X-ray diffractometer in the 2θ range (10° - 70°) at a scan rate of 1° / min. Figure 1Shows the measured XRD diffraction patterns of Samples 1 - 8. Table 3 shows the crystal structure parameters obtained from the refinement of the XRD patterns of each sample. The first phase with the crystal structure of TiNb2O7 was found to have peaks at the same positions matching the ICDD entry 00 - 039 - 1407 (space group I12 / ml) (with some displacements due to crystal modifications, up to about 0.2°). The second phase with the crystal structure of Zn2Nb 34 O 87 was found to have peaks at the same positions matching the ICDD database entry 00 - 013 - 0317 (space group A12 / ml) (with some displacements due to crystal modifications, up to about 0.2°). The crystal structure of Sample 2 was refined using a combination of monoclinic (A12 / m1) and orthorhombic (Amma - PDF card 04 - 021 - 7859) crystal structures. The second phase of the mixed - phase oxide was refined only using the monoclinic crystal structure. Compared with the reference database entries of the "base" crystal structure, the peak displacements reflect the incorporation of substituting elements with different ionic radii (e.g., TiNb2O7 substituted with Cr and / or Zn and Zn2Nb 34 O 87 ) substituted with Cr and / or Ti). The mass ratio of the first phase to the second phase obtained from the refinement was found to be in very good agreement with the expected ratio based on the precursor amounts, and the small differences again reflect the expected substituting elements.

[0129] Sample 3 was subjected to TEM - EDX analysis. The analysis showed that the cations were uniformly distributed throughout the observed particles and the cations were not confined to specific domains. This supports the existence of an interpenetrating mixture of the first and second phases and the simultaneous substitution of the "base" phase.

[0130] Table 3: Summary table of the unit - cell parameters of each sample calculated by Rietveld refinement of their powder XRD spectra using the software TOPAS. RWP represents the goodness - of - fit and accuracy of the Rietveld refinement. I B / I A was calculated based on the ratio of the normalized peak heights of the characteristic peaks.

[0131]

[0132]

[0133]

[0134] Table 4: Summary table of the microcrystalline sizes of Samples 3, 4, 8, and 12 calculated using the Scherrer equation with crushed Si crystals as the standard.

[0135]

[0136] Electrochemical Characterization

[0137] The charging rate of a Li-ion battery cell is usually expressed as “C-rate”. A 1C charging rate means the charging current at which the cell is fully charged in 1 hour, and a 10C charge means the cell is fully charged in 1 / 10 (6 minutes) of 1 hour. Here, the C-rate is defined based on the observed reversible capacity of the anode within the voltage limit applied during its second cycle of de-lithiation, i.e., within the voltage limit of 1.1 - 3.0V, the anode exhibits a capacity of 1.0 mAh cm -2 capacity, and a 1C rate corresponds to a current density of 1.0 mA cm -2 applied. In typical materials as described herein, this corresponds to approximately 250 mA / g of active material.

[0138] Electrochemical tests were conducted in a half-button cell (CR2032 size) for analysis. In the half-button test, the active material was tested in an electrode relative to a Li metal electrode to evaluate its basic properties. In the following examples, the active material composition to be tested was combined with N-methylpyrrolidone (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, and 3 wt% binder. The slurry was coated onto an Al foil current collector by doctor blading until the desired loading of 69 - 75 g m -2 was achieved, and dried by heating. Then the electrode was calendared to a density of 2.6 - 2.9 g cm -3 at 80 °C to achieve a target porosity of 30 - 35%. The electrode was punched into the desired size and the electrode was combined with a separator (Celgard porous PP / PE), Li metal, and an electrolyte (1.3 M LiPF6 in EC / DEC) within a steel button cell housing and sealed under pressure. Then cycling was carried out at 25 °C at a low current rate (C / 10) between 1.1 - 3.0V to achieve 2 complete lithiation and de-lithiation cycles. After this, the performance of the cell was tested at increasing current densities. During these tests, the cell was cycled asymmetrically at 25 °C, slowly lithiated (C / 5), followed by an increased de-lithiation rate (e.g., 5C, 10C) to provide capacity. The data of 3 - 5 cells prepared from the same electrode coating were averaged, and the error was represented by the standard deviation. Thus, these data represent a reliable study, which shows that the materials according to the present invention achieve an improvement compared to previous materials. These data are shown in Table 5.

[0139] Table 5: Summary of the electrochemical test results of the Li ion half button cell units.

[0140]

[0141] Discussion

[0142] It was found that the interpenetrating mixture of the first and second phases and the simultaneous substitution of the "base" phase provided a surprising improvement in the properties of the mixed-phase oxides compared to either single phase. Specifically, at high rates of 5C and above, it was found that the delithiation specific capacities of Samples 3 - 5 (mixed-phase oxides containing Nb, Ti, Cr, and Zn) were higher than those of Sample 1* (TiNb2O7) and Sample 2* (Cr 0.6 Zn 1.6 Nb 33.8 O 87 ), thus exhibiting a synergistic improvement. Similarly, each of Samples 6 (mixed-phase oxide containing Nb, Ti, Al, and Zn), Sample 7 (mixed-phase oxide containing Nb, Ti, and Cr), Sample 8 (mixed-phase oxide containing Nb, Ti, Cr, and Al), Sample 9 (mixed-phase oxide containing Nb, Ti, Ga, and Al), Sample 10 (mixed-phase oxide containing Nb, Ti, Cu, and Ga), Sample 11 (mixed-phase oxide containing Nb, Ti, and Zn), and Sample 12 (mixed-phase oxide containing Nb, Ti, Mg, and Cr) had a delithiation specific capacity higher than both Sample 1* and Sample 2* at 5C and above.

[0143] It can be expected that a similar advantage will be shown for the ranges of the described elements M(III) and M(II).

Claims

1. A mixed-phase oxide used as an active electrode material; wherein the mixed-phase oxide contains Nb and Ti and also contains M(III) and / or M(II); wherein M(III) is selected from Cr, Al, Ga, and mixtures thereof; M(II) is selected from Zn, Cu, Mg, and mixtures thereof; wherein the mixed-phase oxide contains an interpenetrating mixture of a first phase and a second phase such that the first phase and the second phase cannot be separated without destroying the mixed-phase oxide; wherein the first phase has a crystal structure of TiNb2O7, and the second phase has a crystal structure of Zn2Nb 34 O 87 .

2. The mixed-phase oxide according to claim 1, wherein the XRD pattern of the mixed-phase oxide exhibits a peak A attributable to the first phase at 2θ = 26.0 ± 0.1°.

3. The mixed-phase oxide according to claim 1 or 2, wherein the XRD pattern of the mixed-phase oxide exhibits a peak B attributable to the second phase at 2θ = 24.9 ± 0.1°.

4. The mixed-phase oxide according to claim 3, wherein the intensity I of peak B B and the intensity I of peak A A have a ratio of 0 < I B / I A ≤ 0.4, or 0.01 ≤ I B / I A ≤ 0.25, or 0.05 ≤ I B / I A ≤ 0.22, or 0.07 ≤ I B / I A ≤ 0.

16.

5. The mixed-phase oxide according to claim 1, wherein the weight ratio of the first phase to the second phase is 199:1 - 1:1, or 99:1 - 3:1, or 50:1 - 8:

1.

6. The mixed-phase oxide according to claim 1, wherein the first phase forms at least 85 wt%, or at least 90 wt%, or at least 92 wt% of the mixed-phase oxide.

7. The mixed-phase oxide according to claim 1, wherein the first phase and the second phase form at least 80 wt%, at least 90 wt%, or at least 95 wt% of the mixed-phase oxide.

8. The mixed-phase oxide according to claim 1, which contains 66 - 80 atomic% of Nb, 33 - 17 atomic% of Ti, and, relative to all cations, also contains >0 - 1 atomic% of M(III) and / or >0 - 2 atomic% of M(II).

9. The mixed-phase oxide according to claim 1, wherein the combined amount of M(III) and M(II) is ≥0.05 atomic%, or ≥0.5 atomic%, or ≥0.6 atomic% relative to the amount of Nb.

10. The mixed-phase oxide according to claim 1, wherein the atomic ratio of Ti:Nb is at least 0.3:1, or at least 0.4:1, or 0.42:1 to 0.5:

1.

11. The mixed-phase oxide according to claim 1, which contains M(III), or contains M(III) and M(II).

12. The mixed-phase oxide according to claim 1, wherein M(III) is Cr, Al, and mixtures thereof, and M(II) is Zn.

13. The mixed-phase oxide according to claim 1, wherein M(III) is Cr, Al, and mixtures thereof; or wherein M(III) is Cr.

14. The mixed-phase oxide according to claim 1, wherein M(II) is Zn, Cu, and mixtures thereof; or wherein M(II) is Zn.

15. The mixed-phase oxide according to claim 1, which contains M(III) and M(II), wherein M(III) is Cr and M(II) is Zn.

16. The mixed-phase oxide according to claim 1, wherein the mixed-phase oxide is in particulate form, optionally wherein the mixed-phase oxide has a D within the range of 0.1 - 100 μm, or 0.5 - 50 μm, or 1 - 20 µm 50 particle size.

17. The mixed-phase oxide according to claim 1, wherein the mixed-phase oxide has a BET surface area in the range of 0.1 - 100 m 2 / g, or 0.25 - 50 m 2 / g, or 0.5 - 20 m 2 / g.

18. The mixed-phase oxide according to claim 1, wherein the mixed-phase oxide has a crystallite size greater than 180 nm, or greater than 200 nm, or greater than 225 nm, or greater than 250 nm.

19. The mixed-phase oxide according to claim 1, which further comprises at least one additional element; optionally, wherein the additional element is selected from: (i) Zr, Hf, V, Fe, Ta, Mo, W, Mn, Co, Ni, Cd, B, Si, Sn, P, and mixtures thereof; or (ii) Zr, V, Fe, Mo, W, Mn, Co, Ni, Cd, B, Si, P, and mixtures thereof; or (iii) Zr, V, Fe, Mo, W, P, and mixtures thereof.

20. The mixed-phase oxide according to claim 19, wherein the total amount of the at least one additional element is present in an amount of ≤5 at%, or ≤1 at%, or ≤0.5 at% relative to the amount of Nb.

21. The mixed-phase oxide according to claim 1, which further comprises at least one electronegative element selected from: (i) F, Cl, Br, I, N, S, Se, and mixtures thereof; or (ii) F, Cl, N, S, and mixtures thereof; or (ii) F, N, and mixtures thereof.

22. The mixed-phase oxide according to claim 21, wherein the total amount of the at least one electronegative element is present in an amount of ≤5 at% or ≤1 at% relative to the amount of O.

23. The mixed-phase oxide according to claim 1, wherein the interpenetrating mixture of the first phase and the second phase does not form a core / shell structure.

24. The mixed-phase oxide according to claim 1, wherein the mixed-phase oxide is coated with carbon.

25. A composition comprising the mixed-phase oxide according to any one of claims 1 to 24 and at least one other component, wherein the at least one other component is selected from binders, solvents, conductive additives, different active electrode materials, and mixtures thereof.

26. An electrode comprising the mixed-phase oxide according to any one of claims 1 to 24 as an active electrode material.

27. The electrode according to claim 26, wherein the mixed-phase 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 mixed-phase oxide is the sole active electrode material in the electrode.

28. The electrode according to claim 26 or 27, which further comprises at least one other component selected from binders, conductive additives, different active electrode materials, and mixtures thereof.

29. The electrode according to claim 28, wherein the different active electrode materials are selected from lithium titanium oxides, titanium niobium oxides, different mixed-phase oxides, graphite, hard carbon, soft carbon, silicon, their doped and / or carbon-coated forms, and mixtures thereof.

30. A metal ion battery, comprising an electrode as claimed in any one of claims 26 to 29, optionally wherein the metal ion battery is a lithium ion battery and the electrode forms an anode.

31. The metal ion battery as claimed in claim 30, wherein the metal ion battery is a lithium ion battery having a reversible anode active material specific capacity of greater than 230 mAh / g at 23 mA / g, wherein the battery is capable of charging and discharging at a current density of 230 mA / g or greater, or 1000 mA / g or greater, or 2000 mA / g or greater, or 4000 mA / g or greater with respect to the anode active material, while maintaining greater than 70% of the initial cell capacity at 23 mA / g.

32. Use of a mixed phase oxide as claimed in any one of claims 1 to 24 in a metal ion battery; optionally as an active electrode material in the anode of a lithium ion battery.

33. A method of manufacturing an electrode, the method comprising: providing a mixed phase oxide as claimed in any one of claims 1 to 24; and depositing the mixed phase oxide on a current collector to form the electrode.

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