Electrode compositions and related energy storage devices

1. A positive electrode composition comprising granules that themselves comprise:

an electroactive metal that comprises nickel;

an alkali metal halide, and

a metal sulfide composition that is substantially free of oxygen, wherein a molar ratio of the nickel to an amount of sulfur in the metal sulfide composition in the granules is in a range of from 2:1 to 10:1,

wherein the positive electrode composition is substantially free of iron oxide, iron sulfate, cobalt oxide, and cobalt sulfate.

2. The positive electrode composition of claim 1 , wherein the alkali metal halide comprises at least one halide of sodium, potassium, or lithium.

3. The positive electrode composition of claim 1 , wherein the metal sulfide composition is M x S y , where M is selected from iron or cobalt; and the ratio of x to y is between about 0.5:1 and about 1.5:1.

4. The positive electrode composition of claim 3 , wherein the metal sulfide composition M x S y is selected from FeS, FeS 2 , CoS 2 , or Co 3 S 4 .

5. The positive electrode composition of claim 3 , wherein the metal sulfide composition M x S y is FeS.

6. The positive electrode composition of claim 1 , further comprising an electrolyte salt that comprises a complex metal halide, wherein the electrolyte salt has a melting temperature in a range from about 150 degrees Celsius to about 300 degrees Celsius.

7. The positive electrode composition of claim 6 , wherein the electrolyte salt is sodium tetrachloroaluminate (NaAlCl 4 ).

8. The positive electrode composition of claim 1 , wherein

the alkali metal halide comprises one or more of sodium chloride, sodium fluoride, sodium iodide, and sodium bromide; and

the metal sulfide composition comprises iron sulfide (FeS).

9. An energy storage device comprising a first compartment comprising an alkali metal, a second compartment comprising a positive electrode composition, and a solid separator capable of transporting alkali metal ions between the first compartment and the second compartment, wherein the positive electrode composition comprises:

(a) an electrolyte salt comprising a complex metal halide; and

(b) granules that themselves comprise:

(i) an electroactive metal that comprises nickel;

(ii) an alkali metal halide; and

(iii) a metal sulfide composition that is substantially free of oxygen, wherein a molar ratio of nickel to an amount of sulfur in the metal sulfide composition in the granules is in a range of from 2:1 to 10:1, and

wherein the positive electrode composition is substantially free of iron oxide, iron sulfate, cobalt oxide, and cobalt sulfate.

10. The energy storage device of claim 9 , wherein the alkali metal comprises sodium, potassium or lithium.

11. The energy storage device of claim 9 , wherein the first compartment comprises molten sodium.

12. The energy storage device of claim 9 , wherein the electrolyte salt is sodium tetrachloro aluminate (NaAlCl 4 ).

13. An energy storage system comprising a plurality of the energy storage devices of claim 9 .

14. The positive electrode composition of claim 1 , wherein a molar ratio of a total amount of an alkali metal in the alkali metal halide to the amount of sulfur in the metal sulfide composition is between about 1.75:1 and about 10:1.

15. The positive electrode composition of claim 1 , wherein the electroactive metal comprises iron, cobalt or combination thereof.