LI/NA-ION BATTERY ANODE MATERIALS

Abstract

The invention relates to active electrode materials and to methods for the manufacture of active electrode materials. Such materials are of interest as active electrode materials in lithium-ion or sodium-ion batteries. The invention provides an active electrode material expressed by the general formula [M][Nb].sub.y[O].sub.z; wherein the active electrode material is oxygen deficient; wherein M consists of one of Mg, Cr, W, Mo, Cu, Ga, Ge, Ca, K, Ni, Co, Al, Sn, Mn, Ce, Sb, Y, La, Hf, Ta, Zn, In, or Cd; y satisfies 0.5≤y≤49; and z satisfies 4≤z≤124.

Claims

1. An active electrode material expressed by the general formula [M][Nb].sub.y[O].sub.z; wherein the active electrode material is oxygen deficient; wherein M consists of one of Mg, Cr, W, Mo, Cu, Ga, Ge, Ca, K, Ni, Co, Al, Sn, Mn, Ce, Sb, Y, La, Hf, Ta, Zn, In, or Cd; y satisfies 0.5≤y≤49; and z satisfies 4≤z≤124.

2. The active electrode material according to claim 1, wherein z is defined as z=(z′−z′α) wherein α satisfies 0<α<0.05.

3. The active electrode material according to any preceding claim, wherein (i) M consists of one of Mo, W, Al, Zn, Ga, Ge, Ta, Cr, Cu, K, Mg, Ni, or Hf; or (ii) M consists of one of Mo, W, Al, Zn, Ga, or Ge; or (iii) M consists of one of Mo, W, Al, or Zn.

4. The active electrode material according to any preceding claim, expressed by the general formula [M].sub.x[Nb].sub.y[O].sub.(z′−z′α), selected from the group consisting of: MoNb.sub.12O.sub.(33-33 α) WNb.sub.12O.sub.(33-33 α) W.sub.7Nb.sub.4O.sub.(31-31 α) W.sub.9Nb.sub.8O.sub.(47-47 α) Zn.sub.12Nb.sub.34O.sub.(87-87 α) Cu.sub.2Nb.sub.34O.sub.(87-87 α) AlNb.sub.11O.sub.(29-29 α) GaNb.sub.11O.sub.(29-29 α) GeNb.sub.18O.sub.(4-47 α) W.sub.16Nb.sub.18O.sub.(93-93 α) W.sub.5Nb.sub.16O.sub.(55-55 α) AlNb.sub.49O.sub.(124-124 α) GaNb.sub.49O.sub.(124-124 α) wherein a satisfies 0<α<0.05.

5. The active electrode material according to any preceding claim, expressed by the general formula [M].sub.x[Nb].sub.y[O].sub.(z′−z′α), selected from the group consisting of: MoNb.sub.12O.sub.(33-33 α) WNb.sub.12O.sub.(33-33 α) W.sub.7Nb.sub.4O.sub.(31-31 α) W.sub.9Nb.sub.8O.sub.(47-47 α) Zn.sub.2Nb.sub.34O.sub.(87-87 α) AlNb.sub.11O.sub.(29-29 α) GeNb.sub.18O.sub.(47-47 α) wherein α satisfies 0≤α≤0.05.

6. The active electrode material according to any preceding claim, expressed by the general formula [M]x[Nb].sub.y[O].sub.(z′−z′α), selected from the group consisting of: MoNb.sub.12O.sub.(33-33 α) WNb.sub.12O.sub.(33-33 α) W.sub.7Nb.sub.4O.sub.(31-31 α) W.sub.9Nb.sub.8O.sub.(47-47 α) wherein α satisfies 0≤α≤0.05.

7. The active electrode material according to claim 1, wherein the active electrode material has the formula MoNb.sub.12O.sub.(33-33 α) wherein a satisfies 0<α<0.05.

8. The active electrode material according to claim 1, wherein the active electrode material has the formula WNb.sub.12O.sub.(33-33 α) wherein a satisfies 0<α<0.05.

9. The active electrode material according to claim 1, wherein the active electrode material has the formula W.sub.5Nb.sub.6O.sub.(55-55 α) wherein a satisfies 0<α<0.05.

10. The active electrode material according to claim 1, wherein the active electrode material has the formula W.sub.7Nb.sub.4O.sub.(31-31 α) wherein a satisfies 0<α<0.05.

11. The active electrode material according to claim 1, wherein the active electrode material has the formula Zn.sub.2Nb.sub.34O.sub.(87-87 α) wherein a satisfies 0<α<0.05.

12. The active electrode material according to claim 1, wherein the active electrode material has the formula AlNb.sub.11O.sub.(29-29 α) wherein a satisfies 0<α<0.05.

13. The active electrode material according to claim 1, wherein the active electrode material is expressed by the general formula [W][Nb].sub.y[O].sub.z; optionally wherein the active electrode material is selected from WNb.sub.12O.sub.(33-33 α), W.sub.7Nb.sub.4O.sub.(31-31 α), W.sub.9Nb.sub.8O.sub.(47-47 α), W.sub.16Nb.sub.18O.sub.(93-93 α), and W.sub.5Nb.sub.16O.sub.(55-55 α) wherein a satisfies 0<α<0.05.

14. The active electrode material according to any preceding claim, wherein the crystal structure of the active electrode material as determined by X-ray diffraction corresponds to the crystal structure of the unmodified form of the active electrode material, wherein the unmodified form is expressed by the general formula [M][Nb].sub.y[O].sub.z wherein the unmodified form is not oxygen deficient, wherein the unmodified form is selected from M2.sup.INb.sub.5O.sub.13, M2.sup.I.sub.6Nb.sub.10.8O.sub.30, M2.sup.IINb.sub.2O.sub.6, M2.sup.II.sub.2Nb.sub.34O.sub.87, M2.sup.IIINb.sub.11O.sub.29, M2.sup.IIINb.sub.49O.sub.124, M2.sup.IVNb.sub.24O.sub.62, M2.sup.IVNb.sub.2O.sub.7, M2.sup.IV.sub.2Nb.sub.10O.sub.29, M2.sup.IV.sub.2Nb.sub.14O.sub.39, M2.sup.IVNb.sub.14O.sub.37, M2.sup.IVNb.sub.6O.sub.17, M2.sup.IVNb.sub.18O.sub.47, M2.sup.VNb.sub.9O.sub.25, M2.sup.V.sub.4Nb.sub.18O.sub.55, M2.sup.V.sub.3Nb.sub.17O.sub.50, M2.sup.VINb.sub.12O.sub.33, M2.sup.VI.sub.4Nb.sub.26O.sub.77, M2.sup.VI.sub.3Nb.sub.14O.sub.44, M2.sup.VI.sub.5Nb.sub.16O.sub.55, M2.sup.VI.sub.8Nb.sub.18O.sub.69, M2.sup.VINb.sub.2O.sub.8, M2.sup.VI.sub.16Nb.sub.18O.sub.93, M2.sup.VI.sub.20Nb.sub.22O.sub.115, M2.sup.VI.sub.9Nb.sub.8O.sub.47, M2.sup.VI.sub.82Nb.sub.54O.sub.381, M2.sup.VI.sub.31Nb.sub.20O.sub.143, M2.sup.VI.sub.7Nb.sub.4O.sub.31, M2.sup.VI.sub.15Nb.sub.2O.sub.50, M2.sup.VI.sub.3Nb.sub.2O.sub.14, and M2.sup.VI.sub.11Nb.sub.12O.sub.63, wherein the numerals I, II, III, IV, V, and VI represent the oxidation state of M.

15. The active electrode material according to any one of the preceding claims wherein at least some of the material has a Wadsley-Roth crystal structure and/or a tetragonal tungsten bronze crystal structure, or wherein substantially all of the active electrode material has a Wadsley-Roth crystal structure and/or a tetragonal tungsten bronze crystal structure.

16. The active electrode material according to any one of the preceding claims wherein the active electrode material comprises a plurality of primary crystallites, some or all of the primary crystallites optionally being agglomerated into secondary particles.

17. The active electrode material according to claim 16, wherein the average diameter of the primary crystallites is from 10 nm to 10 μm.

18. The active electrode material according to claim 16 or claim 17, wherein some or all of the primary crystallites are agglomerated into secondary particles, and the average diameter of the secondary particles is from 1 μm to 30 μm.

19. The active electrode material according to any of claims 16-18 wherein the active electrode material comprises a carbon coating formed on the surface of the primary crystallites and/or secondary particles.

20. The active electrode material according to claim 19 wherein the carbon coating is present in an amount of up to 5 w/w%, based on the total weight of the active electrode material.

21. The active electrode material according to any preceding claim, wherein the active electrode material has a BET surface area in the range of 0.1-100 m.sup.2/g, or 0.5-50 m.sup.2/g, or 1-20 m.sup.2/g.

22. An active electrode material according to any one of the preceding claims wherein the crystal structure of the active electrode material, as determined by X-ray diffraction analysis, corresponds to the crystal structure of one or more of: (i) MoNb.sub.12O.sub.33 WNb.sub.12O.sub.33 W.sub.7Nb.sub.4O.sub.31 W.sub.9Nb.sub.8O.sub.47 Zn.sub.2Nb.sub.34O.sub.87 CU.sub.2Nb.sub.34O.sub.87 AlNb.sub.11O.sub.29 GaNb.sub.11O.sub.29 GeNb.sub.18O.sub.47 W.sub.16Nb.sub.18O.sub.93 W.sub.5Nb.sub.16O.sub.55 AlNb.sub.49O.sub.124 GaNb.sub.49O.sub.124; or (ii) MoNb.sub.12O.sub.33 WNb.sub.12O.sub.33 W.sub.4Nb.sub.7O.sub.31 W.sub.9Nb.sub.8O.sub.47 Zn.sub.2Nb.sub.34O.sub.87 AlNb.sub.11O.sub.29 GeNb.sub.18O.sub.47; or (iii) MoNb.sub.12O.sub.33 WNb.sub.12O.sub.33 W.sub.7Nb.sub.4O.sub.31 W.sub.9Nb.sub.8O.sub.47

23. An active electrode material according to any one of the preceding claims, further comprising Li and/or Na.

24. An electrochemical device comprising an anode, a cathode and an electrolyte disposed between the anode and the cathode, wherein the anode comprises an electrode active material according to any one of claims 1 to 23.

25. A use of an electrode active material according to any one of claims 1 to 23 as an anode active material, or a component of an anode active material, in an anode in conjunction with a cathode and an electrolyte in: (i) a lithium ion battery for charging and discharging of the lithium ion battery; or (ii) a sodium ion battery for charging and discharging of the sodium ion battery.

26. A method for processing an electrode active material according to any one of claims 1 to 23 as or in an anode active material for: (i) a lithium ion battery, wherein the method includes diffusing lithium ions into the anode active material; or for (ii) a sodium ion battery, wherein the method includes diffusing sodium ions into the anode active material.

27. A method of making an active electrode material according to any one of claims 1 to 23, the method comprising steps of: providing one or more precursor materials; mixing said precursor materials to form a precursor material mixture; and heat treating the precursor material mixture in a temperature range from 400° C.-1350° C. to form the active electrode material.

28. The method of making an active electrode material according to claim 27 wherein the one or more precursor materials includes a source of M and a source of Nb.

29. The method of making an active electrode material according to claim 27 or claim 28 wherein the precursor materials include one or more metal oxides, metal hydroxides, metal salts or oxalates.

30. The method according to any one of claims 27 to 29 wherein the one or more precursor materials are particulate materials, optionally having an average particle size of <20 μm in diameter.

31. The method according to any one of claims 27 to 30 wherein the step of mixing said precursor materials to form a precursor material mixture is performed by a process selected from dry or wet planetary ball milling, rolling ball milling, high shear milling, air jet milling, and/or impact milling.

32. The method according to any one of claims 27 to 31 wherein the step of heat treating the precursor material mixture is performed for a time of from 1 to 14 h.

33. The method according to any one of claims 27 to 32 wherein the step of heat treating the precursor material mixture is performed in a gaseous atmosphere, the gas being selected from air, N.sub.2, Ar, He, CO.sub.2, CO, O.sub.2, H.sub.2, and mixtures thereof.

34. The method according to any one of claims 27 to 33 wherein the method includes one or more post-processing steps selected from: (i) heat treating the active electrode material; (ii) mixing the active electrode material with a carbon source, and, optionally, further heating the mixture, thereby forming a carbon coating on the active electrode material; (iii) spray-drying the active electrode material; and/or (iv) milling the active electrode material to modify the active electrode material particle size.

35. The method according to any one of claims 27 to 34 wherein the method includes a post-processing step of heat treating the active electrode material in an inert or reducing gaseous atmosphere at temperatures of above 500° C. to form oxygen deficiencies in the active electrode material.

Description

SUMMARY OF THE FIGURES

[0199] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0200] FIG. 1 shows XRD diffraction patterns of samples 1, 4, 14, 2, 5, 15, 16, 18 and 22;

[0201] FIG. 2 shows XRD diffraction patterns of samples 8 and 9;

[0202] FIG. 3 shows XRD diffraction patterns of samples 6, 7, 17, 19 and 20;

[0203] FIG. 4 shows XRD diffraction patterns of samples 10, 11 and 21;

[0204] FIG. 5 shows XRD diffraction patterns of samples 12 and 13;

[0205] FIG. 6 shows TGA characterisation in air of sample 3;

[0206] FIG. 7 shows the particle size distribution of samples 1, 2, 15, and 16;

[0207] FIG. 8 shows the particle size distribution of sample 3;

[0208] FIG. 9 is an SEM image of sample 3 before pyrolysis and coated with conductive Au for imaging;

[0209] FIG. 10 is an SEM image of sample 3 after pyrolysis (no conductive coating);

[0210] FIGS. 11 are SEM images of samples 1 and 2;

[0211] FIG. 12 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.05C rate for samples 1 and 16;

[0212] FIG. 13 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.05C rate for samples 6 and 7;

[0213] FIG. 14 shows lithiation and delithiation capacity obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, at current densities of 0.5C, 10, 2C, 5C (seen as step-changes in the data) for samples 1, 4, and 16;

[0214] FIG. 15 shows Lithiation capacity obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window at current densities of 0.5C, 10, 2C, 5C, 0.5C (seen as step changes in the data) for samples 6, 7, and 17;

[0215] FIGS. 16(a) and (b) show EIS measurements of samples 1, 7, and 16 at different axes scales.

[0216] FIG. 17 shows the particle size distributions of sample 16 before and after post-processing;

[0217] FIG. 18 is an SEM image of the surface of an electrode made from sample 22, focused on the surface of an active material particle;

[0218] FIG. 19 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.05C rate for samples 12 and 13;

[0219] FIG. E1 shows XRD diffraction patterns of samples E1, E2.

[0220] FIG. E2 shows XRD diffraction patterns of samples E3, E4, E5.

[0221] FIG. E3 shows XRD diffraction patterns of samples E6, E7, E8.

[0222] FIG. E4 shows XRD diffraction patterns of samples E9, E10.

[0223] FIG. E5 shows the particle size distributions of samples E2, E4, E7, E10.

[0224] FIG. E6 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.1C rate for samples E1 and E2.

[0225] FIG. E7 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.1C rate for samples E3 and E5.

[0226] FIG. E8 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.1C rate for samples E6 and E7.

[0227] FIG. E9 shows representative lithiation and delithiation voltage profiles obtained by galvanostatic cycling in half cell configuration, 1.1-3.0 V voltage window, first 2 cycles at 0.1C rate for samples E9 and E10. The x axis is in terms of state-of-charge (SOC), to be able to normalise the curves to their maximum capacities and evaluate the curve shape.

[0228] FIG. E10 shows XRD diffraction patterns of E11-E14.

DETAILED DESCRIPTION OF THE INVENTION

[0229] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0230] A number of different materials were prepared and characterised, as summarised in Table 1, below. Broadly, these samples can be split into a number of groups:

[0231] Samples 1, 2, 3, 4, 5, 14, 15, 16, 18, and 22 belong to the same family of Wadsley-Roth phases based on MoNb.sub.12O.sub.33(M.sup.6+Nb.sub.12O.sub.33, 3×4 block of octahedra with a tetrahedron at each block corner). The blocks link to each other by edge sharing between NbO.sub.6 octahedra, as well as corner sharing between M.sup.6+O.sub.4 tetrahedra and NbO.sub.6 octahedra. Sample 1 is the base crystal structure, which is modified to a mixed metal cation structure by exchanging one or multiple cations in samples 2 to 4, and/or in a mixed crystal configuration (blending with isostructural WNb.sub.12O.sub.33) in samples 14, 15, 16, 18, and 22. Oxygen deficiencies are created in the base crystal in sample 5 and in the mixed metal cation structure 18.

[0232] Sample 3 is a spray-dried and carbon-coated version of the crystal made in sample 2, and sample 22 is a spray-dried and carbon-coated version of the crystal made in sample 16.

[0233] Samples 6, 7, 17, 19, 20 belong to the same family of Wadsley-Roth phases based on ZrNb.sub.24O.sub.62 (M.sup.4+Nb.sub.24O.sub.62, 3×4 block of octahedra with half a tetrahedron at each block corner).

[0234] Samples 8, 9 and El 1 belong to the same family of Wadsley-Roth phases based on WNb.sub.12O.sub.33 (M.sup.6+Nb.sub.12O.sub.33, a 3×4 NbO.sub.6 octahedra block with a tetrahedron at each block corner).

[0235] Samples 10, 11 and 21 belong to the same family of Wadsley-Roth phases based on VNb.sub.9O.sub.25 (M.sup.6+Nb.sub.9O.sub.25, a 3×3 NbOsoctahedra block with a tetrahedron at each block corner).

[0236] Samples 12, 13 and E14 belong to the same family of tungsten tetragonal bronzes (TTB) based on W.sub.7Nb.sub.4O.sub.31(M.sup.6+.sub.7Nb.sub.4O.sub.31). This is a tetragonal tungsten bronze structure, where MO.sub.6(M=0.4 Nb+0.6 W) octahedra are exclusively corner-sharing, with 3, 4, and 5 -sided tunnels. Some of these tunnels are filled with —O-M-O— chains whereas others are open for lithium ion transport and storage.

[0237] Samples E1, E2, E13 belong to the same family of Wadsley-Roth phases based on Zn.sub.2Nb.sub.34O.sub.87 (M.sup.2+.sub.2Nb.sub.34O.sub.87). This orthorhombic phase consists out of 3×4 blocks of MO.sub.6 octahedra (M═Zn.sup.+2/Nb+.sup.5), where the blocks are connected exclusively by edge-sharing and have no tetrahedra.

[0238] Samples E3, E4, E5, E12 belong to the same family of Wadsley-Roth phases based on AlNb.sub.11O.sub.29 (M.sup.3+Nb.sub.34O.sub.87). The structure belongs to monoclinic shear structure with 3×4 octahedra blocks connected through exclusively edge-sharing and have no tetrahedra.

[0239] Samples E6, E7, E8 belong to the same family of Wadsley-Roth phases based on GeNb.sub.18O.sub.47 (M.sup.4+Nb.sub.18O.sub.47). The structure is similar to sample 10 with 3×3 NbO.sub.6 octahedra blocks and one tetrahedron connecting blocks at corners. However, the structure contains intrinsic defects due to Ge.sup.+4 instead of V.sup.5+.

[0240] Samples E9, E10 belong to the same family of Wadsley-Roth phases based on W.sub.5Nb.sub.16O.sub.55 (M.sup.6+.sub.5Nb.sub.16O.sub.55). The structure is made of 4x5 blocks connected at the sides by edge-sharing (W,Nb)O.sub.6 and connected at the corners by Wat tetrahedra. This structure is similar to Sample 8 and 9 but with a larger block size.

TABLE-US-00001 TABLE 1 A summary of different compositions synthesized. Sample Material No. Composition Synthesis  1 * MoNb.sub.12O.sub.33 Solid state  2 Ti.sub.0.05Mo.sub.0.95Nb.sub.12O.sub.33 Solid state  3 Ti.sub.0.05Mo.sub.0.95Nb.sub.12O.sub.33 + C Solid state, spray dry, carbon pyrolysis  4 Zr.sub.0.05Mo.sub.0.95Nb.sub.12O.sub.33 Solid state  5 MoNb.sub.12O.sub.<33 Solid state  6 * ZrNb.sub.24O.sub.62 Solid state  7 V.sub.0.05Zr.sub.0.95Nb.sub.24O.sub.62 Solid state  8 * WNb.sub.12O.sub.33 Solid state  9 Ti.sub.0.05W.sub.0.95Nb.sub.12O.sub.33 Solid state 10 * VNb.sub.9O.sub.25 Solid state 11 Ti.sub.0.05V.sub.0.95Nb.sub.9O.sub.25 Solid state 12 * W.sub.7Nb.sub.4O.sub.31 (WNb.sub.0.57O.sub.4.43) Solid state 13 Ti.sub.0.05W.sub.0.95Nb.sub.0.57O.sub.4.43 (Ti.sub.0.35W.sub.6.65Nb.sub.4O.sub.31) Solid state 14 W.sub.0.25Mo.sub.0.75Nb.sub.12O.sub.33 Solid state 15 Ti.sub.0.05W.sub.0.25Mo.sub.0.70Nb.sub.12O.sub.33 Solid state 16 Ti.sub.0.05Zr.sub.0.05W.sub.0.25Mo.sub.0.65Nb.sub.12O.sub.33 Solid state 17 Ti.sub.0.05Zr.sub.0.95Nb.sub.24O.sub.62 Solid state 18 Ti.sub.0.05Zr.sub.0.05W.sub.0.25Mo.sub.0.65Nb.sub.12O.sub.<33 Solid state 19 Mo.sub.0.05Zr.sub.0.95Nb.sub.24O.sub.62 Solid state 20 Mo.sub.0.05V.sub.0.05Zr.sub.0.95Nb.sub.24O.sub.62 Solid state 21 Mo.sub.0.05V.sub.0.95Nb.sub.9O.sub.25 Solid state 22 Ti.sub.0.05Zr.sub.0.05W.sub.0.25Mo.sub.0.65Nb.sub.12O.sub.33 + C Solid state, spray dry, carbon pyrolysis E1* Zn.sub.2Nb.sub.34O.sub.87 Solid state E2 Ge.sub.0.1Zn.sub.1.9Nb.sub.34O.sub.87 Solid state E3* AlNb.sub.11O.sub.29 Solid state E4 Fe.sub.0.05Al.sub.0.95Nb.sub.11O.sub.29 Solid state E5 Ga.sub.0.05Al.sub.0.95Nb.sub.11O.sub.29 Solid state E6* GeNb.sub.18O.sub.47 Solid state E7 K.sub.0.02Co.sub.0.02Ge.sub.0.96Nb.sub.18O.sub.47 Solid state E8 K.sub.0.02Co.sub.0.02Ge.sub.0.96Nb.sub.18O.sub.47-α Solid state E9* W.sub.5Nb.sub.16O.sub.55 Solid state E10 W.sub.5Nb.sub.16O.sub.55-α Solid state E11 WNb.sub.12O.sub.33-α Solid state E12 AlNb.sub.11O.sub.29-α Solid state E13 Zn.sub.2Nb.sub.34O.sub.87-α Solid state E14 W.sub.7Nb.sub.4O.sub.31-α Solid state Samples indicated with * are comparative samples.

[0241] Material Synthesis

[0242] Samples listed in Table 1 were synthesised using a solid-state route. In a first step, metal oxide precursor commercial powders (Nb.sub.2O.sub.5, NbO.sub.2, MoO.sub.3, ZrO.sub.2, TiO.sub.2, W03, V205, ZrO.sub.2, K2O, CoO, Fe2O.sub.3, GeO.sub.2, Ga2O.sub.3, Al.sub.2O.sub.3, ZnO and/or MgO) were mixed in stochiometric proportions and planetary ball-milled at 550 rpm for 3h in a zirconia jar and milling media with a ball to powder ratio of 10:1. The resulting powders were then heated in a static muffle furnace in air in order to form the desired crystal phase. Samples 1 to 5 and 12 to 16, 18 and 22 were heat-treated at 900° C. for 12h; samples 6 to 9, 17, 19, and 20 were heat-treated at 1200° C. for 12h, with samples 6, 7, 17, 19 and 20 undergoing a further heat treatment step at 1350° C. for an additional 4h; samples 10, 11 and 21 were heat-treated at 1000° C. for 12h. Sample 3 and 22 were further mixed with a carbohydrate precursor (such as sucrose, maltodextrin or other water-soluble carbohydrates), dispersed in an aqueous slurry at concentrations of 5, 10, 15, or 20 w/w% with ionic surfactant, and spray-dried in a lab-scale spray-drier (inlet temperature 220° C., outlet temperature 95° C., 500 mL/h sample introduction rate). The resulting powder was pyrolyzed at 600° C. for 5h in nitrogen. Sample 5 and 18 were further annealed in nitrogen at 900° C. for 4 hours.

[0243] Samples E1, E2, E6, E7, E8, E9, E10 were prepared by ball milling as above, and impact milling at 20,000 rpm as needed to a particle size distribution with D90<20 μm, then heat-treated as in a muffle furnace in air at 1200° C. for 12 h; samples E8, E10, E11, E12, E13 were further annealed in nitrogen at 1000° C. for 4 h; E14 was annealed in nitrogen at 900° C. for 5 h. Samples E3, E4, E5 were heat-treated at 1300° C. for 12 h. Samples E1-E10 were de-agglomerated after synthesis by impact milling or jet milling to the desired particle size ranges.

[0244] Elemental Analysis of Samples

[0245] Elemental analysis was carried out by Inductively-Coupled Plasma-Optical Emission Spectroscopy (ICP-MS/OES). The measurements were carried out on a Thermo Scientific ICP-OES Duo iCAP 7000 series. The samples were digested using 5 ml Nitric acid and 1 ml HF acid and an internal standard was used to account for any instrumental variation. In this process the plasma is used to vaporise the material into its atomic/ionic state of elements. The atoms are in excited state due to high temperature and the decay to normal state through energy transitions. The characteristic radiation emitted by each excited ion is measured for analysis. The results are set out in Table 2, below.

TABLE-US-00002 TABLE 2 Summary of ICP-OES elemental analysis results for samples 1, 2, 4, 14, 3, 16, 9, 11, and 17 Sample Composition Elemental ratio Expected Measured  1* MoNb.sub.12O.sub.33 Nb/Mo 12 12  2 Ti.sub.0.05Mo.sub.0.95Nb.sub.12O.sub.33 Mo/Ti 19 18  4 Zr.sub.0.05Mo.sub.0.95Nb.sub.12O.sub.33 Mo/Zr 19 18 14 W.sub.0.25Mo.sub.0.75Nb.sub.12O.sub.33 Mo/W  3   3.1  3 Ti.sub.0.05Mo.sub.0.95Nb.sub.12O.sub.33 + C Mo/Ti 19 18 16 Ti.sub.0.05Zr.sub.0.05W.sub.0.25Mo.sub.0.65Nb.sub.12O.sub.33 Mo/Zr; Mo/Ti 13; 13 11.4; 13.5  9 Ti.sub.0.05W.sub.0.95Nb.sub.12O.sub.33 W/Ti 19 18 11 Ti.sub.0.05V.sub.0.95Nb.sub.9O.sub.25 V/Ti 19 19 17 Ti.sub.0.05Zr.sub.0.95Nb.sub.24O.sub.62 Zr/Ti 19 19

[0246] This table of elemental analysis demonstrates that substantially the expected cation ratio has been achieved for each composition tested.

[0247] XRD Characterisation of Samples

[0248] The phase purity of some samples was analysed using Rigaku Miniflex powder X-ray diffractometer in 2 θ range (10-70°) at 1°/min scan rate.

[0249] FIG. 1 shows the measured XRD diffraction patterns for samples 1, 4, 14, 2, 5, 15, 16, 18, 22 which are relevant to Comparative Study A. All diffraction patterns have peaks at the same locations (within instrument error, that is 0.1°), and match JCPDS crystallography database entry JCPDS 73-1322, which corresponds to MoNb.sub.12O.sub.33. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size ˜200 nm according to the Scherrer equation and crystal structure matching MoNb.sub.12O.sub.33.

[0250] FIG. 2 shows the measured XRD diffraction patterns for samples 8 and 9. FIG. E10 shows the XRD pattern for sample E11. All diffraction patterns have peaks at the same locations (within instrument error, that is 0.1°), and match JCPDS crystallography database entry JCPDS 73-1322, which corresponds to WNb.sub.12O.sub.33. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size ˜200 nm according to the Scherrer equation and crystal structure matching WNb.sub.12O.sub.33.

[0251] FIG. 3 shows the measured XRD diffraction patterns for samples 6, 7, 17, 19, 20 which are relevant to Comparative Study B. All diffraction patterns have peaks at the same locations (within instrument error, that is 0.1°), and match JCPDS crystallography database entry JCPDS 01-072-1655, which corresponds to ZrNb.sub.24O.sub.62. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size ˜200 nm according to the Scherrer equation and crystal structure matching ZrNb.sub.24O.sub.62.

[0252] FIG. 4 shows the measured XRD diffraction patterns for samples 10, 11, 21. All diffraction patterns have peaks at the same locations (within instrument error, that is 0.1°), and match JCPDS crystallography database entry JCPDS 00-049-0289, which corresponds to VNb.sub.9O.sub.25. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size ˜200 nm according to the Scherrer equation and crystal structure matching VNb.sub.9O.sub.25.

[0253] FIG. 5 shows the measured XRD diffraction patterns for samples 12 and 13. FIG. E10 shows the XRD pattern for sample E14. All diffraction patterns have peaks at the same locations (within instrument error, that is 0.1°), and match JCPDS crystallography database entry JCPDS 00-020-1320, which corresponds to W.sub.7Nb.sub.4O.sub.31. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size ˜200 nm according to the Scherrer equation and crystal structure matching W.sub.7Nb.sub.4O.sub.31.

[0254] FIG. E1 shows the measured XRD diffraction patterns for samples E1, E2. FIG. E10 shows the XRD pattern for sample E13. All diffraction patterns have peaks at the same locations (within)0.1-0.2°, and match JCPDS crystallography database entry JCPDS 22-353. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size 52±12 nm according to the Scherrer equation and crystal structure matching Zn.sub.2Nb.sub.34O.sub.87.

[0255] FIG. E2 shows the measured XRD diffraction patterns for samples E3, E4, E5. FIG. E10 shows the XRD pattern for sample E12. All diffraction patterns have peaks at the same locations (within)0.1-0.2°, and match JCPDS crystallography database entry JCPDS 72-159 (isostructural Ti.sub.2Nb.sub.10O.sub.29). There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size 53±16 nm according to the Scherrer equation and crystal structure matching AlNb.sub.11O.sub.29.

[0256] FIG. E3 shows the measured XRD diffraction patterns for samples E6, E7, E8. All diffraction patterns have peaks at the same locations (within)0.1-0.2° , and match ICSD crystallography database entry 72683 (isostructural PNb.sub.9O.sub.25). There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size 53±3 nm according to the Scherrer equation and crystal structure matching GeNb.sub.18O.sub.47.

[0257] FIG. E4 shows the measured XRD diffraction patterns for samples E9, E10. All diffraction patterns have peaks at the same locations (within)0.1-0.2°, and match JCPDS crystallography database entry JCPDS 44-0467. There is no amorphous background noise and the peaks are sharp and intense. This means that all samples are phase-pure and crystalline, with crystallite size 37±11 nm according to the Scherrer equation and crystal structure matching W5Nbi6O.sub.55.

[0258] TGA Characterisation of Samples

[0259] Thermogravimetric Analysis (TGA) was performed on some samples using a Perkin Elmer Pyris 1 system in a synthetic air atmosphere. Samples were first held for 15 min at 30° C., then heated from 30° C. to 950° C. at 5° C./min, and finally held for 30 min at 950° C. TGA was performed on sample 3 to quantify carbon content, and on sample 5 to show mass increase as oxygen vacancies are filled.

[0260] FIG. 6 shows TGA characterisation in air of sample 3. The sharp drop in mass between ˜400° C. and 500° C. is attributed to the decomposition of the carbon coating. The decomposition temperature corresponds to a mixture of amorphous and graphitic carbon. The amount of mass loss indicates that sample 3 includes 1.1 w. % of carbon coating, which is in line with the amount expected from the stoichiometry of the precursors.

[0261] Qualitative Assessment of Oxygen Deficiency

[0262] As discussed above, sample 5 and 18 were heat-treated at 900° C. for 12 h to form the active electrode material, and was then further annealed in nitrogen (a reducing atmosphere) at 900° C., in a post-processing heat treatment step. A colour change from white to dark purple was observed after the post-processing heat treatment in nitrogen, indicating change in oxidation states and band structure of the material, as a result of oxygen deficiency of the sample.

[0263] Samples E8, E10, E11, E12, E13 were further annealed in nitrogen at 1000° C. for 4 h, sample E14 was annealed in nitrogen at 900° C. for 5 h. Sample E7 transitions from a white colour to a deep yellow colour upon introduction of induced oxygen deficiencies in sample E8; sample E9 transitions from an off-white colour to a blue-grey colour upon introduction of induced oxygen deficiencies in sample E10; sample 8 transitions from off-white to light blue in E11; sample E3 transitions from white to grey/black in E12; sample E1 transitions from white to grey/black in E3; sample 12 transitions from light yellow to dark blue in E14.

[0264] Particle Size Distribution Analysis of Samples

[0265] Particle Size Distributions were obtained with a Horiba laser diffraction particle analyser for dry powder.

[0266] Air pressure was kept at 0.3 MPa. The results are set out in Table 3, below.

TABLE-US-00003 TABLE 3 Summary of particle size distribution statistics for samples 1, 2, 15, 16, 18, 3 before pyrolysis, 3 after pyrolysis, 16 and 18 after post-processing, and samples E1-E14. D.sub.10 D.sub.50 D.sub.90 Sample [μm] [μm] [μm]  1* 3.8 11.2 50.0  2 2.6 10.9 87.4 15 3.6 21.2 55.3 16 4.7 31.2 82.9 18 5.1 57.7 176 3 before pyrolysis 4.2 8.2 16.3 3 after pyrolysis 6.7 12.7 51.1 16 after impaction 1.0 2.6 4.8 milling 18 after impaction 1.4 4.4 9.6 milling E1* 3.7 5.9 9.3 E2 5.1 9.2 16.5 E3* 3.6 6.6 12.0 E4 4.3 7.7 13.9 E5 3.7 7.0 15.5 E6* 4.3 8.1 16.5 E7 4.3 9.7 20.4 E8 5.3 10.8 21.3 E9* 3.1 5.5 9.3 E10 2.7 5.1 9.3 E11 3.3 5.5 8.7 E12 4.2 7.8 18.4 E13 4.2 6.8 10.8 E14 1.2 4.5 10.1

[0267] FIG. 7 shows particle size distributions (measured particle size being secondary particle size, not crystal or crystallite size) for samples 1, 2, 15, and 16, as a representative example of particle size distributions obtained by solid state routes in this study without further processing or size optimisation. The particle size distributions are typically bi-modal, with a first mode ˜10 μm, and a second mode ˜90 μm. Sample 3 presents significant differences in terms of particle size distribution, as shown in FIG. 8 due to the spray-drying and pyrolysis post-processing step.

[0268] All particle size distributions can also be refined with further processing steps, for example spray drying, ball milling, high shear milling, jet milling or impact milling to reduce the particle size distribution to the desired range (e.g. d90 <20 μm, <10 μm or <5 μm) as shown in FIG. 17 and Table 3. Typically the particle size distributions are tuned by optimising the phase formation process (i.e. solid state synthesis route) and post-processing steps for the target application. For example, for a Li ion electrode with high power, one would typically target lower average particle sizes, amongst other considerations.

[0269] FIG. E5 shows the particle size distributions for samples E2, E4, E7, E10 in their final form, which are then processed into electrode slurries and inks.

[0270] SEM Characterisation of Samples

[0271] The morphology of some samples was analysed by Scanning Electron Microscopy (SEM).

[0272] FIGS. 9 and 10 show SEM images of sample 3 before and after pyrolysis. A porous microsphere morphology with carbon coating is observed, with primary crystallites organised into secondary particles. It can be seen that the material has with homogeneous porous particles that can pack efficiently to form a high-density electrode. Qualitatively the conductivity is vastly improved as a conductive coating does not need to be applied for SEM imaging to be carried out, implying an order of magnitude improvement in material surface conductivity. FIG. 18 is an SEM image of the surface of a particle in an electrode of sample 22, where conductive carbon black particles contained in the electrode can also be seen in the right side of the image. This visibly shows evidence of a conformal carbon coating around the MNO material.

[0273] FIG. 11 shows SEM images of samples 1 and 2, and corroborates XRD and PSD data, showing compact secondary particle micron-size particles composed of ˜200 nm primary crystallites.

[0274] Electrochemical Testing of Samples

[0275] Electrochemical tests were carried out in half-coin cells (CR2032 size) for initial analysis. In half-coin tests, the 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 (although it is also possible to form aqueous slurries by using water rather than NMP). The non-NMP composition of the slurries was 80 w. % active material, 10 w. % conductive additive, 10 w. % binder. The slurry was then coated on an Al foil current collector to the desired loading of 1 mg/cm.sup.2 by doctor blade coating and dried in a vacuum oven for 12 hours. Electrodes were punched out at the desired size and combined with a separator (Celgard porous PP/PE), Li metal, and electrolyte (1 M LiPF.sub.6 in EC/DEC) inside a steel coin cell casing and sealed under pressure. Formation cycling was then carried out at low current rates (C/20) for 2 full charge and discharge cycles. After formation, further cycling can be carried out at a fixed or varied current density as required. These tests have been termed “half-cell galvanostatic cycling” for future reference. For samples E1-E10, the electrolyte was altered to 1.3 M LiPF6 in 3:7 EC/DEC, and the formation cycling was carried out at C/10 for 2 charge/discharge cycles in the limits 1.1-3.0 V. The values shown for these samples is an average of 3 measurements, with the error being the standard deviation.

[0276] Homogeneous, smooth coatings on current collector foil, the coatings being free of visible defects were also prepared as above with a centrifugal planetary mixer to a composition of 94 w. % active material, 4 w. % conductive additive, 2 w. % binder. The coatings were calendared at 80° C. to a density of up to 3.0 g/cm.sup.3 at loadings of 1.3-1.7 mAh/cm.sup.2 in order to demonstrate possible volumetric capacities >700 mAh/cm.sup.3 in the voltage range 0.7-3.0 V at C/20, and >640 mAh/cm.sup.3 in the voltage range 1.1-3.0 V at C/5. This is an important demonstration of these materials being viable in a commercially focussed electrode power cell formulation, where retaining performance after calendaring to a high electrode density allows for high volumetric capacities. Loadings of up to and including 1.0, 1.5, 2.0, 2.5, or 3.0 mAh/cm.sup.2 may be useful for Li-ion cells focussed on power performance; loadings greater than 3.0, 4.0, or 5.0 mAh/cm.sup.2 are useful for energy-focussed performance in Li ion cells. Calendaring of these materials was demonstrated down to electrode porosity values of 35%, and typically in the range 35-40%; defined as measured electrode density divided by the average of the true densities of each electrode component adjusted to their w/w%.

[0277] Electrical conductivity of electrodes made with the samples listed in Table 1 was measured using a 4-point probe thin film resistance measurement apparatus. Slurries were formulated according to the procedure described above and coated on a dielectric mylar film at a loading of 1 mg/cm.sup.2. Electrode-sized discs where then punched out and resistance of the coated-film was measured using a 4-point probe. Bulk resistivity can be calculated from measured resistance using the following equation:

Bulk resistivity (ρ)=2πs(V/I); R=V/I; s=0.1 cm =2λx0.1xR (Ω)   (3)

[0278] The results of this test are shown in Table 4, below:

TABLE-US-00004 TABLE 4 Summary of 4-point probe resistivity measurement results for samples 1, 2, 4, 5, 6, 7, 13 to 20, and 22. Resistance Bulk resistivity Sample [kΩ] [kΩ .Math. cm]  1* 8.5 5.3  2 1.7 1.1  4 3.2 2.0  5 0.52 0.33  6* 0.37 0.23  7 0.52 0.33 13 0.45 0.28 14 2.7 1.7 15 1.2 0.75 16 1.3 0.82 17 0.34 0.21 18 0.89 0.56 19 0.18 0.11 20 0.20 0.13 22 0.33 0.21

[0279] Samples E1-E14 also had their 4-point probe resistance measured to quantify their electrical resistivity. This was carried out with a different Ossila instrument (T2001A3-UK) at 23° C. for coatings on mylar films at loadings of 1.0 mg/cm.sup.2. The results for sheet resistance (Ω/square) are outlined in Table 4a, with error based on the standard deviation of 3 measurements.

TABLE-US-00005 TABLE 4a Summary of 4-point probe resistivity measurement results for samples E1 to E14. Sample Sheet Resistivity [Ω/square] E1* .sup. 1242 ±156 E2  1041 ± 103 E3* 1396 ± 74 E4 1215 ± 52 E5 1057 ± 35 E6* 1092 ± 52 E7 1009 ± 89 E8  965 ± 83 E9* 1135 ± 92 E10 1113 ± 99 E12  891 ± 61 E13 1027 ± 13 12*  853 ± 51 E14  846 ± 57  6*  880 ± 29

[0280] The direct current internal resistance (DCIR) and the resultant area specific impedance (ASI) is a key measurement of internal resistance in the electrode in a Li-ion cell. In a typical measurement, a cell that has already undergone formation will be cycled at C/2 for 3 cycles. With the electrode in its delithiated state a C/2 discharge current is applied for 1 h to achieve ˜50% lithiation. The cell is rested for 30 mins to equilibrate at its OCV (open circuit voltage), and then a 5C current pulse is applied for 10 s, followed by a 30 mins rest to reach the OCV. During the 10 s pulse the voltage response is sampled at a higher frequency to determine the average internal resistance accurately. The resistance is then calculated from V=IR, using the difference between the OCV (the linear average between the initial OCV before the pulse and afterwards) and the measured voltage. The resistance is then multiplied by the area of the electrode to result in the ASI.

[0281] The results of this test are shown in Table 5, below:

TABLE-US-00006 TABLE 5 Summary of DCIR/ASI measurement results for samples 1, 2, 4, 7, 14, 16, and 17. Sample ASI/Ω .Math. cm.sup.2  1* 141  2 125  4 120  6* 126  7 162 13 67 14 99 16 74 17 162 18 75 19 164 22 121

[0282] The reversible specific capacity 0/20, initial coulombic efficiency, nominal lithiation voltage vs Li/Li+ at C/20, 5C/0.5C capacity retention, and 100/0.50 capacity retention for a number of samples were also tested, the results being set out in Table 6, below. Nominal lithiation voltage vs Li/Li+ has been calculated from the integral of the V/Q curve divided by the total capacity on the 2.sup.nd cycle 0/20 lithiation. Capacity retention at 10C and 5C has been calculated by taking the specific capacity at 10C or 5C, and dividing it by the specific capacity at 0.5C. It should be noted that the capacity retention was tested with symmetric cycling tests, with equivalent C-rate on lithiation and de-lithiation. Upon testing with an asymmetric cycling program, 100/0.50 capacity retention greater than 89% is routinely observed.

[0283] Samples E1-E10 were tested with minor differences in Table 6a, the reversible specific capacity shown is the 2.sup.nd cycle delithiation capacity at 0/10, the nominal lithiation voltage vs Li/Li+ is at C/10 in the 2.sup.nd cycle, the rate tests were carried out with an asymmetric cycling program with no constant voltage steps (i.e. constant current), with lithiation at C/5 and delithiation at increasing C-rates.

TABLE-US-00007 TABLE 6 Summary of electrochemical testing results from Li-ion half coin cells using a number of samples. In general (although not exclusively) it is beneficial to have a higher capacity, a higher ICE, a lower nominal voltage, and higher capacity retentions. Reversible Nominal specific Initial lithiation 5 C/0.5 C 10 C/0.5 C capacity coulombic voltage vs capacity capacity C/20 efficiency Li/Li.sup.+ retention retention Sample [mAh/g] [%] [V] [%] [%]  1* 214 87.8 1.61 62 35  2 240 90.9 1.61 64 45  3 203 84.9 1.58 79 68  4 286 90.7 1.59 68 54  5 253 86.0 1.60 63 43  6* 224 93.5 1.57 61 38  7 263 93.6 1.58 74 67  8* 192 82.0 1.60 54 36  9 188 86.8 1.61 64 54 10* 172 74.3 1.55 64 54 11 176 71.6 1.59 56 45 12* 164 93.9 1.77 86 81 13 184 95.4 1.75 86 80 14 278 91.0 1.59 15 228 89.2 1.59 16 281 90.8 1.58 72 58 17 203 94.6 1.58 18 228 90.1 1.59 84 68 19 193 87.0 1.56 63 44 21 169 70.9 1.59 67 56 22 267 86.9 1.57 71 62

TABLE-US-00008 TABLE 6a Summary of electrochemical testing results from Li-ion half coin cells using a number of samples. Nominal Specific Initial lithiation 5 C/0.5 C 10 C/0.5 C capacity C/10 coulombic voltage C/10 ASI capacity capacity Sample [mAh/g] efficiency [%] [V] [Ω .Math. cm.sup.2] retention [%] retention [%] E1* 222 ± 7  98.23 ± 0.51 1.543 ± 0.001 169 ± 10 96.5 ± 0.1 95.9 ± 0.1 E2 273 ± 17 98.52 ± 0.45 1.550 ± 0.001 106 ± 18 97.3 ± 0.4 96.2 ± 0.7 E3* 244 ± 26 96.75 ± 0.31 1.549 ± 0.002 166 ± 17 96.1 ± 0.6 95.2 ± 0.8 E4 252 ± 9  98.80 ± 0.86 1.549 ± 0.001 109 ± 9  98.4 ± 0.0 97.4 ± 0.1 E5 272 ± 21 99.69 ± 1.56 1.549 ± 0.001 122 ± 3  96.3 ± 0.3 94.8 ± 0.4 E6* 134 ± 14 80.97 ± 1.55 1.539 ± 0.007 485 ± 75 72.8 ± 5.7 64.1 ± 7.2 E7 150 ± 8  82.15 ± 0.12 1.531 ± 0.000 390 ± 32 67.0 ± 0.4 56.8 ± 0.5 E8 144 ± 2  81.64 ± 1.35 1.530 ± 0.001 400 ± 42 72.9 ± 1.2 63.3 ± 1.5 E9* 211 ± 5  94.53 ± 0.18 1.630 ± 0.001 129 ± 13 96.2 ± 0.4 95.1 ± 0.5 E10 201 ± 7  98.42 ± 1.12 1.626 ± 0.000 118 ± 16 96.2 ± 0.1 94.9 ± 0.2 E12 198 ± 13 97.71 ± 0.25 1.544 ± 0.001 208 ± 8  95.2 ± 0.8 92.9 ± 1.0 E13 203 ± 15 98.22 ± 0.12 1.546 ± 0.001 199 ± 10 97.7 ± 0.0 97.7 ± 0.5

[0284] The modification of mixed niobium oxide-based Wadsley-Roth and Bronze structures as outlined in the claims demonstrate the applicability of the present invention to improve active material performance in Li-ion cells. By substituting the non-Nb cation to form a mixed cation structure as described, the entropy (cf disorder) can increase in the crystal structure, reducing potential energy barriers to Li ion diffusion through minor defect introduction (e.g. samples E7, 16). Modification by creating mixed cation structures that retain the same overall oxidation state demonstrate the potential improvements by altering ionic radii, for example replacement of an Mo.sup.6+ cation with W.sup.6+ in sample 14 or Fe.sup.3+ or Ga.sup.3+ for Al.sup.3+ in samples E4 and E5, which can cause minor changes in crystal parameters and Li-ion cavities (e.g. tuning the reversibility of Type VI cavities in Wadsley-Roth structures) that can improve specific capacity, Li-ion diffusion, and increase Coulombic efficiencies of cycling by reducing Li ion trapping. Modification by creating mixed cation structures that result in increased oxidation state (e.g. Ge.sup.4+ to replace Zn.sup.2+ in sample E2, or Mo.sup.6+ for Zr.sup.4+ in sample 19) demonstrate similar potential advantages with altered ionic radii relating to capacity and efficiency, compounded by introduction of additional electron holes in the structure to aid in electrical conductivity. Modification by creating mixed cation structures that result in decreased oxidation state (e.g. K+ and Co.sup.3+ to replace Ge.sup.4+ in sample E7, or Ti.sup.4+ to replace Mo.sup.6+ in sample 2) demonstrate similar potential advantages with altered ionic radii relating to capacity and efficiency, compounded by introduction of oxygen vacancies and additional electrons in the structure to aid in electrical conductivity. Modification by inducing oxygen deficiency from high temperature treatment in inert or reducing conditions demonstrate the loss of a small proportion of oxygen from the structure, providing a reduced structure of much improved electrical conductivity (e.g. sample 5, E10 and E12-14) and improved electrochemical properties such as capacity retention at high C-rates (e.g. sample 5, E13). Combination of mixed cation structures and induced oxygen deficiency allows multiple beneficial effects (e.g. increased specific capacity, reduced electrical resistance) to be compounded (e.g. samples 18, E8).

[0285] FIGS. 12, 13, and 19 show representative lithiation/delithiation curves for unmodified and modified MoNb.sub.12O.sub.33 (FIG. 12—samples 1 and 6) ZrNb.sub.24O.sub.62 (FIG. 13—samples 6 and 7), and W.sub.7Nb.sub.4O.sub.31 (FIG. 19—samples 12 and 13) in their first two formation cycles at C/20 rate. In FIG. 12, approximately 90% of the specific capacity for sample 16 demonstrated is shown to be in a narrow voltage range of ca. 1.2—2.0 V, and in FIG. 13 approximately 90% of the capacity for sample 7 demonstrated is shown to be in a narrow range of ca. 1.25-1.75 V; these data highlight the attractive voltage profiles achievable with MNO crystals based upon Wadsley-Roth crystal structures. In FIG. 19, approximately 90% of the specific capacity for sample 13 is shown to be in a narrow range of ca. 1.2-2.2 V; this demonstrates that attractive voltage profiles are achieved with MNO crystals based upon a tetragonal bronze crystal structure. Secondly, the complex metal oxide samples 7, 16, and 13 demonstrate improved specific capacity as compared to their unmodified crystals samples 1, 6 and 12. This is due to the cations that are included in the complex structures increasing the number of sites in the crystal that Li ions can accommodate due to their differing ionic radii and oxidation states, thus increasing capacity. An increase in ICE was observed between samples 1 and 16, and samples 12 and 13, which further demonstrates that Li ions intercalated in the modified crystal structure can be more efficiently delithiated as the Li ion sites are modified to enable their de-intercalation.

[0286] FIG. E5 demonstrates the particle size distribution of samples E2, E4, E8, E11 containing primarily a single peak that has a narrow distribution, i.e. D.sub.10 and D.sub.90 are similar in value to D.sub.50. This is advantageous for processing the material in electrode slurries for efficient packing of the material, and to maintain a homogeneous electrochemical performance (e.g. a smaller particle will be fully lithiated in advance of a larger particle due to shorter diffusion distances).

[0287] FIG. E6 shows the advantage in modifying sample E1, particularly with regard to improving the observed specific capacity through substituting Zn.sup.2+ cations with Ge.sup.4+ cations of higher valency. FIG. E7 demonstrates the improved specific capacity observed on modifying sample E6 by substituting Ge4+ with K and Co cations, i.e. with cations of reduced valency. FIG. E9 demonstrates the improvement in ICE, and reduction in nominal lithiation voltage possible by introduction of induced oxygen vacancies that reduces polarisation effects through improving conductivity, and through improving the reversibility of lithiation/delithiation processes.

[0288] Across all materials tested, each material according to the invention demonstrates an improvement versus the unmodified ‘base’ crystal structure. This is inferred from measurements of resistivity/impedance by two different methods, and also electrochemical tests carried out in Li-ion half coin cells, particularly the capacity retention at increased current densities (cf. rates, Table 6, FIGS. 14 and 15). Without wishing to be bound by theory, the inventors suggest that this is a result of increased ionic and electronic conductivity of the materials as defects are introduced, or by alterations to the crystal lattice by varying ionic radii; also evidenced by DCIR/ASI (Table 5) and EIS (FIG. 16) measurements to show decreased resistance or impedance upon material modification. Li-ion diffusion rates likely also increase in materials according to the invention, as compared with the unmodified ‘base’ materials. Specific capacities themselves may also increase in some cases as shown in Table 6, as doping/exchange with metal ions of different sizes can expand or contract the crystal lattice and allow for more intercalation or more reversibility of intercalation of Li-ions than possible in the unmodified structure.

[0289] The data in Table 4 show a large reduction in the resistivity between sample 1 (comparative) and samples 2, 4, 5, 14, 15, 16, 18, 22, demonstrating the effect of embodiments of the present invention on improving electrical conductivity of the crystal structures through both cation exchange, oxygen deficiencies, and carbon coating. Samples 17, 19, and 20 also show a similarly low resistivity versus sample 6. The resistivity slightly increased upon incorporation of 0.05 equivalents of V species in the base crystal in sample 7, however an improvement in specific capacity was observed due to the changes in available Li-ion sites in the crystal lattice likely as a result of the differing ionic radius of V over Zr (see Table 6).

[0290] The data in Table 5 shows a large reduction in the DCIR/ASI from sample 1 (comparative) to samples 2, 4, 14, 16, 18 and 22, reflecting the trends shown in Table 4. Samples 7, 17, and 19 demonstrate a higher than these by DCIR, however these relate to a different base crystal structure. Without wishing to be bound by theory, the inventors hypothesise that samples 7, 17, and 19 demonstrate an increase in DCIR/ASI as compared with the comparative material of sample 6 (ZrNb.sub.24O.sub.62) due to the changes in the crystal lattice with the introduced cations of different ionic radii. However, it remains beneficial in terms of conductivity for these structures for samples 17 and 19 as the electrical resistivity is decreased as shown in Table 4, thereby minimising joule heating and enabling a more uniform current distribution across the material, which in turn can enable improved safety and lifetime of a Li ion system. For sample 7, whilst there is no demonstrated improvement utilising V to exchange with Zr, there is an increase in specific capacity, as discussed above.

[0291] In Table 6, across most samples there is a trend for improved specific capacities, initial Coulombic efficiencies (ICE), nominal lithiation voltage vs Li/Li+, and importantly capacity retention at 5C and 10C vs 0.5C for materials according to the invention versus the comparative ‘base’ materials (e.g. samples 1, 6, 8, 10, 12). For example samples 2, 3, 4, 5, 14, 15, 16, 18, 22 all demonstrate improvements in one or more of these parameters vs sample 1. This is also the case for samples 7, 17, 19 versus sample 6 across multiple parameters; sample 11 and 21 versus 10 where an improvement in specific capacity or capacity retention is observed; sample 9 versus 8 where ICE and capacity retention are improved; and sample 13 versus 12* where there are improvements in all parameters.

[0292] FIGS. 14 and 15 demonstrate improved capacity retention at higher cycling rates for materials according to the invention (samples 4, 16, 7, 17) versus the comparative materials (samples 1 and 6).

[0293] Electrochemical impedance spectroscopy (EIS) measurements were also carried out to gain a further understanding on the impedance present in the electrode in a Li-ion cell. In a typical measurement, the cell is prepared as for DCIR measurements to ˜50% lithiation and then the frequency of alternating charge/discharge current pulses is varied whilst measuring the impedance. By plotting the real and imaginary components as the axes, and varying the AC frequency, a Nyquist plot is generated. From this plot for a Li-ion cell different types of impedance in the cell can be identified, however it is typically complex to interpret. For example, Ohmic resistance can be partially separated from electrochemical double layer effects and also separated from diffusion effects.

[0294] FIG. 16(a) and (b) show EIS spectra for (comparative) sample 1 and samples 16 and 7 (samples according to the invention).

[0295] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0296] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0297] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0298] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0299] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0300] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example +/−10%.

[0301] Numbered Embodiments

[0302] The following numbered embodiments form part of the description. [0303] 1. An active electrode material expressed by the general formula [M1].sub.x[M2].sub.(1-x) [Nb].sub.y[O].sub.z, wherein: [0304] M1 and M2 are different; [0305] M1 represents one or more of Ti, Mg, V, Cr, W, Zr, Nb, Mo, Cu, Fe, Ga, Ge, Ca, K, Ni, Co, Al, Sn, Mn, Ce, Te, Se, Si, Sb, Y, La, Hf, Ta, Re, Zn, In, or Cd; [0306] M2 represents one or more of Mg, V, Cr, W, Zr, Nb, Mo, Cu, Fe, Ga, Ge, Ca, K, Ni, Co, Al, Sn, Mn, Ce, Te, Se, Si, Sb, Y, La, Hf, Ta, Re, Zn, In, or Cd; and wherein [0307] x satisfies 0<x<0.5; [0308] y satisfies 0.5≤y≤49 [0309] z satisfies 4≤z≤124 [0310] 2. The active electrode material according to embodiment 1, wherein M2 is selected from one or more of Mo, W, V, or Zr. [0311] 3. The active electrode material according to embodiment 2 wherein the [M1].sub.x[M2].sub.(1-x)[Nb].sub.y[O].sub.z is a material selected from the group consisting of: [0312] M1.sub.xMo.sub.(1-x)Nb.sub.12O.sub.(33-33 α) [0313] M1.sub.xW.sub.(1-x)Nb.sub.12O.sub.(33-33α) [0314] M1.sub.xV.sub.(1-x)Nb.sub.9O.sub.(25-25 α) [0315] M1.sub.xZr.sub.(1-x)Nb.sub.24O.sub.(62-62 α) [0316] M1.sub.xW.sub.(1-x)Nb.sub.0.57O.sub.(4.43-4.43 α) [0317] M1.sub.xW.sub.(1-x)Nb.sub.0.89O.sub.(5.22-5.22 α) [0318] where M1 represents one or more of Ti, Mg, V, Cr, W, Zr, Nb, Mo, Cu, Fe, Ga, Ge, Ca, K, Ni, Co, Al, Sn, Mn, Ce, Te, Se, Si, Sb, Y, La, Hf, Ta, Re, Zn, In, or Cd; and wherein [0319] x satisfies 0<x<0.5; and [0320] α satisfies 0≤≤≤0.05. [0321] 4. The active electrode material according to any one of the preceding embodiments wherein the active electrode material is oxygen deficient. [0322] 5. An active electrode material expressed by the general formula [M].sub.x[Nb].sub.y[O].sub.(z′-z′α), selected from the group consisting of: [0323] MoNb.sub.12O.sub.(33-33 α) [0324] WNb.sub.12O.sub.(33-33 α) [0325] VNb.sub.9O.sub.(25-25 α) [0326] ZrNb.sub.24O.sub.(62-62 α) [0327] W.sub.7Nb.sub.4O.sub.(31-31 α) [0328] W.sub.6Nb.sub.8O.sub.(47-47 α) [0329] wherein a satisfies 0<a≤0.05. [0330] 6. The active electrode material according to any one of the preceding embodiments wherein at least some of the material has a Wadsley-Roth crystal structure and/or a tetragonal tungsten bronze crystal structure. [0331] 7. The active electrode material according to any one of the preceding embodiments wherein the active electrode material comprises a plurality of primary crystallites, some or all of the primary crystallites optionally being agglomerated into secondary particles. [0332] 8. The active electrode material according to embodiment 7, wherein the average diameter of the primary crystallites is from 10 nm to 10 μm. [0333] 9. The active electrode material according to embodiment 7 or embodiment 8, wherein some or all of the primary crystallites are agglomerated into secondary particles, and the average diameter of the secondary particles is from 1 μm to 30 μm. [0334] 10. The active electrode material according to any one of the preceding embodiments wherein the active electrode material comprises a carbon coating formed on the surface of the primary crystallites and/or secondary particles. [0335] 11. The active electrode material according to embodiment 10 wherein the carbon coating is present in an amount of up to 5 w/w%, based on the total weight of the active electrode material. [0336] 12. An active electrode material according to any one of the preceding embodiments wherein the crystal structure of the active electrode material, as determined by X-ray diffraction analysis, corresponds to the crystal structure of one or more of: [0337] MoNb.sub.12O.sub.33 [0338] WNb.sub.12O.sub.33 [0339] ZrNb.sub.24062 [0340] VNb.sub.9O.sub.25 [0341] W.sub.7Nb.sub.4O.sub.31 [0342] W.sub.9Nb.sub.8O.sub.47. [0343] 13. An active electrode material according to any one of the preceding embodiments, further comprising Li and/or Na. [0344] 14. An electrochemical device comprising an anode, a cathode and an electrolyte disposed between the anode and the cathode, wherein the anode comprises an electrode active material according to any one of embodiments 1 to 13. [0345] 15. A use of an electrode active material according to any one of embodiments 1 to 13 as an anode active material, or a component of an anode active material, in an anode in conjunction with a cathode and an electrolyte in: (i) a lithium ion battery for charging and discharging of the lithium ion battery; or (ii) a sodium ion battery for charging and discharging of the sodium ion battery. [0346] 16. A method for processing an electrode active material according to any one of embodiments 1 to [0347] 13 as or in an anode active material for: (i) a lithium ion battery, wherein the method includes diffusing lithium ions into the anode active material; or for (ii) a sodium ion battery, wherein the method includes diffusing sodium ions into the anode active material. [0348] 17. A method of making an active electrode material according to any one of embodiments 1 to 13, the method comprising steps of: [0349] providing one or more precursor materials; [0350] mixing said precursor materials to form a precursor material mixture; and heat treating the precursor material mixture in a temperature range from 400° C. — 1350° C. to form the active electrode material. [0351] 18. The method of making an active electrode material according to embodiment 17 wherein the one or more precursor materials includes a source of Mo, W, Zr, or V, and a source of Nb. [0352] 19. The method of making an active electrode material according to embodiment 17 or embodiment 18 wherein the one or more precursor materials includes an M1 ion source, an M2 ion source, and a source of Nb, and wherein the resulting active electrode material is a material as defined in any one of embodiments 1 to 4, or embodiments 6 to 13 as dependent from embodiment 1. 20. The method of making an active electrode material according to embodiment 17 wherein the precursor materials include one or more metal oxides, metal hydroxides, metal salts or oxalates. [0353] 21. The method according to any one of embodiments 17 to 20 wherein the one or more precursor materials are particulate materials, optionally having an average particle size of <20 μm in diameter. [0354] 22. The method according to any one of embodiments 17 to 21 wherein the step of mixing said precursor materials to form a precursor material mixture is performed by a process selected from dry or wet planetary ball milling, rolling ball milling, high shear milling, air jet milling, and/or impact milling. [0355] 23. The method according to any one of embodiments 17 to 22 wherein the step of heat treating the precursor material mixture is performed for a time of from 1 to 14 h. [0356] 24. The method according to any one of embodiments 17 to 23 wherein the step of heat treating the precursor material mixture is performed in a gaseous atmosphere, the gas being selected from air, N.sub.2, Ar, He, CO.sub.2, CO, O.sub.2, H.sub.2, and mixtures thereof. [0357] 25. The method according to any one of embodiments 17 to 24 wherein the method includes one or more post-processing steps selected from: [0358] (i) heat treating the active electrode material; [0359] (ii) mixing the active electrode material with a carbon source, and, optionally, further heating the mixture, thereby forming a carbon coating on the active electrode material; [0360] (iii) spray-drying the active electrode material; and/or [0361] (iv) milling the active electrode material to modify the active electrode material particle size.

REFERENCES

[0362] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0363] Goodenough and Park, “The Li-Ion Rechargeable Battery: A Perspective”, Journal of the American Chemical Society 2013 135 (4), 1167-1176, DOI: 10.1021/ja3091438

[0364] Griffith et al., High-Rate Intercalation without Nanostructuring in Metastable Nb.sub.2O.sub.5 Bronze Phases, Journal of the American Chemical Society 2016 138 (28), 8888-8899, DOI: 10.1021/jacs.6b04345

[0365] Griffith et al., “Structural Stability from Crystallographic Shear in TiO.sub.2Nb.sub.2O.sub.5 Phases: Cation Ordering and Lithiation Behavior of TiNb.sub.24O.sub.62” Inorganic Chemistry (2017), 56, 7, 4002-4010

[0366] Montemayor et al., “Lithium insertion in two tetragonal tungsten bronze type phases, M8W9047 (M=Nb and Ta)”, Journal of Material Chemistry (1998), 8, 2777-2781

[0367] Zhou et al., “Facile Spray Drying Route for the Three-Dimensional Graphene Encapsulated Fe2O.sub.3 Nanoparticles for Lithium Ion Battery Anodes”, Ind. Eng. Chem. Res. (2013), 52, 1197-1204

[0368] Zhu et al., “MoNb.sub.12O.sub.33 as a new anode material for high-capacity, safe, rapid and durable Li+ storage: structural characteristics, electrochemical properties and working mechanisms”, J. Mater. Chem. A. (2019),7, 6522-6532

[0369] Yang et al., “Porous ZrNb.sub.24O.sub.62 Nanowires with Pseudocapacitive Behavior Achieve High-Performance Lithium-Ion Storage”. J. Mater. Chem. A. (2017) 5. 10.1039/C7TA07347J.