Sodium chalcogenide electrodes for sodium batteries
A sodium-ion electrochemical cell described herein comprises a cathode, an anode, and a non-aqueous sodium-containing electrolyte therebetween. The electrolyte comprises a sodium salt dissolved in a liquid organic carrier. The cathode comprises at least one transition metal chalcogenide compound in an initial discharged or partially discharged state and having the formula Na x MX 2 Cl n , wherein 0<x≦1; M is at least one transition metal having a +3, +4, or +5 fully discharged oxidation state, i.e., when x is 1. X is at least one chalcogen selected from the group consisting of S and Se, and n is 0 when the discharged oxidation state of M is +3, n is 1 when the discharged oxidation state of M is +4, and n is 2 when the discharged oxidation state of M is +5. In some embodiments, the cathode comprises Na x VS 2 , Na x TiS 2 , or a combination thereof.
1. A sodium-ion electrochemical cell capable of operating at an ambient temperature of 20 to 25° C. and comprising a cathode, an anode, and a non-aqueous sodium-containing electrolyte therebetween; wherein the electrolyte comprises a sodium salt dissolved in a liquid organic carrier; the cathode comprises at least one transition metal chalcogenide compound in an initial discharged or partially discharged state and having the formula Na x MX 2 Cl n prior to first discharge of the cell, wherein 0<x≦1; M is a transition metal having a +3, +4, or +5 fully discharged oxidation state, when x is 1; X is at least one chalcogen selected from the group consisting of S and Se; and n is 0 when the discharged oxidation state of M is +3, n is 1 when the discharged oxidation state of M is +4, and n is 2 when the discharged oxidation state of M is +5.
2. The electrochemical cell of claim 1 wherein each M independently is a transition metal selected from the group consisting of V, Ti, Ta, Zr, and Nb.
3. The electrochemical cell of claim 1 wherein each M independently is V or Ti.
4. The electrochemical cell of claim 1 wherein Xis S.
5. The electrochemical cell of claim 1 wherein each M independently is V or Ti, and X is S.
6. The electrochemical cell of claim 1 wherein the organic carrier comprises at least one solvent selected from the group consisting of an organic carbonate, an organic ether, an organic ester, and an organic nitrile.
7. The electrochemical cell of claim 1 wherein the sodium salt comprises NaPF 6 , NaBF 4 , NaF 2 BC 2 O 4 , NaB(C 2 O 4 ) 2 , NaClO 4 , NaAsF 6 , NaN(SO 2 CF 3 ) 2 , NaC(SO 2 CF 3 ) 3 , NaSO 3 CF 3 , NaPF 3 (CF 2 CF 3 ) 3 , or a combination of two or more of the foregoing salts.
8. The electrochemical cell of claim 1 wherein the at least one transition metal chalcogenide compound is a particulate material and the cathode is a composite comprising a layer of the particulate transition metal chalcogenide compound and, optionally, carbon particles, disposed on a metal current collector.
9. The electrochemical cell of claim 8 wherein the layer of the particulate transition metal chalcogenide compound and the carbon particles further comprises a binder.
10. The electrochemical cell of claim 9 wherein binder comprises poly(vinylidene difluoride).
11. The electrochemical cell of claim 8 wherein the carbon particles are selected from the group consisting of carbon nanotubes, carbon nanoparticles, and carbon microparticles.
12. The electrochemical cell of claim 8 wherein particles of the particulate transition metal chalcogenide compound are nanoparticles, microparticles, or a combination thereof.
13. The electrochemical cell of claim 8 wherein the metal current collector comprises a metal selected from the group consisting of aluminum, stainless steel, copper, nickel, and an alloy of two or more of the foregoing metals.
14. A sodium-ion electrochemical cell capable of operating at an ambient temperature of 20 to 25° C. and comprising a cathode, an anode, and a non-aqueous sodium-containing electrolyte therebetween; wherein the cathode comprises at least one transition metal chalcogenide compound in an initial discharged or partially discharged state and having the formula Na x MS 2 prior to first discharge of the cell, wherein M is selected from the group consisting of V and Ti; 0<x≦1; and the electrolyte comprises a sodium salt dissolved in a liquid organic carrier comprising at least one solvent selected from an organic carbonate, an organic ether, an organic ester, and an organic nitrile.
15. The electrochemical cell of claim 14 wherein the cathode comprises a transition metal chalcogenide compound of formula Na x VS 2 and a transition metal chalcogenide compound of formula Na x TiS 2 .
16. The electrochemical cell of claim 14 wherein the sodium salt comprises NaPF 6 , NaBF 4 , NaF 2 BC 2 O 4 , NaB(C 2 O 4 ) 2 , NaClO 4 , NaAsF 6 , NaN(SO 2 CF 3 ) 2 , NaC(SO 2 CF 3 ) 3 , NaSO 3 CF 3 , NaPF 3 (CF 2 CF 3 ) 3 , or a combination of two or more of the foregoing salts.
17. The electrochemical cell of claim 14 wherein the Na x MS 2 is a particulate material, and the cathode is a composite comprising a layer of the particulate Na x MS 2 and carbon particles disposed on a metal current collector.
18. The electrochemical cell of claim 17 wherein the layer of particulate Na x MS 2 and the carbon particles further comprises a binder.
19. The electrochemical cell of claim 18 wherein binder comprises poly(vinylidene difluoride).
20. The electrochemical cell of claim 17 wherein the carbon particles are selected from the group consisting of carbon nanotubes, carbon nanoparticles, and carbon microparticles.
21. The electrochemical cell of claim 17 wherein the particles of the Na x VS 2 are nanoparticles, microparticles, or a combination thereof.
22. A sodium-ion battery comprising a plurality of electrochemical cells of claim 1 electrically connected together in series, in parallel, or a combination of series and parallel.
23. A sodium-ion battery comprising a plurality of electrochemical cells of claim 14 electrically connected together in series, in parallel, or a combination of series and parallel.