Active electrode material

1. An active electrode material comprising a mixed niobium oxide, wherein the mixed niobium oxide has the composition M1 a M2 2-a M3 b Nb 34-b O 87-c-d Q d , wherein: M1 and M2 are different;

M1 is selected from Mg, Ca, Sr, Y, La, Ce, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, In, Si, Ge, Sn, Pb, P, Sb, Bi and mixtures thereof;

M2 is Zn or Cu;

M3 is selected from Mg, Ca, Sr, Y, La, Ce, Ti, Zr, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, In, Si, Ge, Sn, Pb, P, Sb, Bi, and mixtures thereof;

Q is selected from F, Cl, Br, I, N, S, Se, and mixtures thereof;

0≤a<1.0; ≤0b≤3.4; −0.5≤c≤4.35; 0≤d≤4.35;

one or more of a, b, c, and d does not equal 0; and

when a, b, and d equal zero, c is greater than zero;

wherein a crystal structure of the mixed niobium oxide as determined by X-ray diffraction corresponds to the crystal structure of one or more of Zn 2 Nb 34 O 87 and Cu 2 Nb 34 O 87 .

2. The active electrode material of claim 1 , wherein

(i) a>0; and/or

(ii) 0≤a≤0.6; and/or

(iii) 0≤a≤0.2.

3. The active electrode material of claim 1 , wherein

(i) b>0; and/or

(ii) 0≤b≤1.5; and/or

(iii) 0≤b≤0.3; or

(iv) b=0.

4. The active electrode material of claim 1 , wherein

(i) c≠0; or

(ii) 0≤c≤4.35; or

(iii) 0<c≤4.35.

5. The active electrode material of claim 1 , wherein

(i) d>0; and/or

(ii) 0≤d≤3.0; and/or

(iii) 0≤d≤2.17; or

(iv) d=0.

6. The active electrode material of claim 1 , wherein at least one of a and b is >0, or when both a and b are >0.

7. The active electrode material of claim 1 , wherein M1 is selected from

(i) Mg, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, Si, Ge, Sn, P, and mixtures thereof; or

(ii) Mg, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, B, Al, Si, Ge, P, and mixtures thereof; or

(iii) Mg, Zr, V, Cr, Mo, W, Fe, Cu, Zn, Al, Ge, P, and mixtures thereof.

8. The active electrode material of claim 1 , wherein M2 is Zn.

9. The active electrode material of claim 1 , wherein M3 is selected from

(i) Mg, Ti, Zr, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, Si, Sn, P, and mixtures thereof; or

(ii) Mg, Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Si, P, and mixtures thereof; or

(iii) Ti, Zr, V, Cr, Mo, W, Fe, Cu, Zn, Al, P, and mixtures thereof.

10. The active electrode material of claim 1 , wherein

(i) M1 has an equal or higher valency than 2; or

(ii) M3 has a lower valency than 5+; or

(iii) M1 has an equal or higher valency than 2+ and M3 has a lower valency than 5+.

11. The active electrode material of claim 1 , wherein M1 does not comprise Nb and wherein M3 does not comprise Zn and/or Cu.

12. The active electrode material of claim 1 , wherein

(i) Q is selected from F, Cl, N, S, and mixtures thereof; or

(ii) Q is selected from F, N, and mixtures thereof; or

(iii) wherein Q is F.

13. The active electrode material according to claim 1 , wherein:

M1 is selected from Cr, Al, Ge, and mixtures thereof;

M3 is selected from Ti, Zr, Fe, and mixtures thereof;

0<a<1.0;

0<b≤1.5;

−0.5≤c≤4.35; or

d=0.

14. The active electrode material according to claim 1 , wherein:

M1 is Cr;

M2 is Zn;

M3 is selected from Ti, Zr, and mixtures thereof;

0.01<a<1.0;

0.01<b<1.0;

−0.5≤c≤2; and/or

d=0.

15. The active electrode material according to claim 1 , wherein the mixed niobium oxide is oxygen deficient.

16. The active electrode material according to claim 1 , wherein the mixed niobium oxide is coated with carbon.

17. The active electrode material according to claim 1 , wherein the mixed niobium oxide is in particulate form, wherein the mixed niobium oxide has a D 50 particle diameter in the range of 0.1-100 μm.

18. The active electrode material according to claim 1 , wherein the mixed niobium oxide has a BET surface area in the range of 0.1-100 m 2 /g.

19. The active electrode material according to claim 1 , wherein the mixed niobium oxide further comprises Li and/or Na intercalated within the crystal structure of the mixed niobium oxide.

20. The active electrode material according to claim 1 comprising the mixed niobium oxide and at least one other component; wherein the at least one other component is selected from a binder, a solvent, a conductive additive, a different active electrode material, and mixtures thereof.

21. An electrochemical device comprising an anode, a cathode, and an electrolyte disposed between the anode and the cathode, wherein the anode comprises the active electrode material according to claim 1 .

22. An electrochemical device according to claim 21 , wherein the electrochemical device is a lithium-ion battery having a reversible anode active material specific capacity of greater than 190 mAh/g at 20 mA/g, wherein the battery can be charged and discharged at current densities relative to the anode active material of 200 mA/g or more whilst retaining greater than 70% of the initial cell capacity at 20 mA/g.

23. A method of making a mixed niobium oxide, 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., thereby providing the mixed niobium oxide;

wherein the mixed niobium oxide has the composition M1 a M2 2-a M3 b Nb 34-b O 87-c-d O d , wherein:

M1 and M2 are different;

M1 is selected from Mg, Ca, Sr, Y, La, Ce, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, In, Si, Ge, Sn, Pb, P, Sb, Bi and mixtures thereof;

M2 is Zn or Cu;

M3 is selected from Mg, Ca, Sr, Y, La, Ce, Ti, Zr, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, In, Si, Ge, Sn, Pb, P, Sb, Bi, and mixtures thereof;

Q is selected from F, Cl, Br, I, N, S, Se, and mixtures thereof;

0≤a<1.0;0≤b≤3.4;−0.5≤c≤4.35;0≤d≤4.35;

one or more of a, b, c, and d does not equal 0; and

when a, b, and d equal zero, c is greater than zero;

wherein a crystal structure of the mixed niobium oxide as determined by X-ray diffraction corresponds to the crystal structure of one or more of Zn 2 Nb 34 O 87 and Cu 2 Nb 34 O 87 .

24. An active electrode material of claim 1 , wherein the mixed niobium oxide is in particulate form and has a D10 particle diameter of at least 0.05 μm and a D90 particle diameter of no more than 200 μm.