Electrode materials for sodium batteries

1. An electrode suitable for use as a cathode in a sodium electrochemical cell or battery, the electrode comprising a layered material of formula Na c Li d Ni e Mn f M z O b , wherein M comprises one or more metal cation, 0.24≦c/b≦0.5, 0≦d/b<0.23, 0≦e/b≦0.45, 0≦f/b≦0.45, 0≦z/b≦0.45, the combined average oxidation state of the metallic components Na, Li, Ni, Mn, and M is in the range of about 3.9 to 5.2, and b is equal to (c+d+Ve+Xf+Yz)/2, wherein V is the average oxidation state of the Ni, X is the average oxidation state of the Mn, and Y is the average oxidation state of the M; and wherein a combined positive charge of the metallic components is balanced by a combined negative charge of the oxygen anions, the Na is predominately present in a sodium layer, and the Mn, Ni, and M are predominately present in a transition metal layer.

2. The electrode of claim 1 wherein c/b≦0.4, and (e+f+z)/(c/b) is about 2.5; and c/b is not less than 0.24.

3. The electrode of claim 1 wherein M comprises one or more monovalent, divalent, trivalent, or tetravalent cation.

4. The electrode of claim 1 wherein, z/b is 0, (c+d)/b is about 0.51, and (e+f)/b is about 0.42.

5. The electrode of claim 1 wherein f/b is 0.

6. The electrode of claim 1 wherein the Li is predominantly present in the transition metal layer.

7. The electrode of claim 1 wherein M comprises at least one cation selected from The group consisting of Mg 2+ , Co 2+ , Co 3+ , B 3+ , Fe 2+ , Fe 3+ , Ga 3+ , Al 3+ , and Ti 4+ .

8. The electrode of claim 1 wherein the Na c Li d Ni e Mn f M z O b has a structure in which Li clusters with Ni and/or Mn in the transition metal layer.

9. The electrode of claim 1 wherein the Na in the sodium layer has predominately trigonal prismatic coordination, and the Li predominantly is present in the transition metal layer.

10. The electrode of claim 1 wherein the ratio f/e is about 3, c/d is about 5 or about 3, and (c+d)/e+f) is about 1.2.

11. The electrode of claim 10 wherein the oxidation state of Mn in the Na c Li d Ni e Mn f M z O b , as determined by a X-ray absorption near-edge spectrum (XANES), is about (IV).

12. The electrode of claim 10 wherein the oxidation state of Mn in the Na c Li d Ni e Mn f M z O b , as determined by a X-ray absorption near-edge spectrum (XANES), is about (IV) after a charge to about 4.2 V vs. Na metal, followed by a discharge to 2.0 V vs. Na metal, in a sodium electrochemical cell.

13. The electrode of claim 10 wherein a charge-discharge profile of the electrode exhibits a plateau at about 4.5 V when used as the cathode in an electrochemical cell comprising a Li metal anode and an electrolyte comprising 1.2 M LiPF 6 in a mixture of ethylenecarbonate (EC) and ethylmethylcarbonate (EMC) in a weight ratio of about 3:7 EC:EMC.

14. The electrode of claim 1 wherein the Na c Li d Ni e Mn f M z O b exhibits a layering peak in the X-ray diffraction (XRD) pattern thereof.

15. The electrode of claim 1 wherein the Na c Li d Ni e Mn f M z O b has a repeating AABB layered, oxygen close-packed stacking structure.

16. The electrode of claim 1 wherein the Na c Li d Ni e Mn f M z O b is present within a layer or coating on a metallic substrate.

17. An electrochemical cell comprising an anode, an electrode of claim 1 as a cathode, and a sodium-containing electrolyte therebetween.

18. The electrochemical cell of claim 17 wherein the anode comprises sodium metal.

19. An electrochemical cell comprising an anode, an electrode of claim 11 as a cathode, and a sodium-containing electrolyte therebetween.

20. The electrochemical cell of claim 19 wherein the anode comprises sodium metal.

21. A battery comprising a plurality of electrochemical cells of claim 17 arranged in series, parallel, or both.

22. A battery comprising a plurality of electrochemical cells of claim 19 arranged in series, parallel, or both.