Vanadyl phosphates as high energy density cathode materials for rechargeable sodium battery

1. A sodium ion electrochemical cell having a positive electrode comprising

ε-VOPO 4 as an active ingredient.

2. The sodium ion electrochemical cell of claim 1 , wherein the positive electrode further comprises a material selected from the group consisting of NaFePO 4 , NaVPO 4 F, Na 3 V 2 (PO 4 ) 2 F 3 , Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3 , a compound of formula Na x CoO 2 wherein x is from 0.4 to 1, orthorhombic Na 0.44 MnO 2 , layered sodium iron oxide of formula NaFeO 2 , a sodium chromium oxide of formula NaCrO 2 , layered NaNi 0.5 Mn 0.5 O 2 , a NaV 6 O 15 nanorod; a layer sulfide of formula Na x TiS 2 , a perovskite transition metal fluoride and a Na + superionic conductor (NASICON) compound.

3. The sodium ion electrochemical cell of claim 1 , wherein the positive electrode further comprises a conductive additive.

4. The sodium ion electrochemical cell of claim 1 , wherein the positive electrode further comprises a binder selected from the group consisting of a polyvinylidenefluoride (PVDF), a polytetrafluoroethylene (PTFE), a styrene butadiene rubber (SBR), and a polyimide.

5. The sodium ion electrochemical cell of claim 1 , wherein the positive electrode further comprises a sodium insertion product of formula:

Na x (ε-VOPO 4 )

wherein x is a value from 0.1 to 2.0 and the Na is capable of reversible extraction and insertion with the ε-VOPO 4 .

6. The sodium ion electrochemical cell of claim 5 , wherein the positive electrode further comprises an auxiliary material selected from the group consisting of NaFePO 4 , NaVPO 4 F, Na 3 V 2 (PO 4 ) 2 F 3 , Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3 , a compound of formula Na x CoO 2 wherein x is from 0.4 to 1, orthorhombic Na 0.44 MnO 2 , layered sodium iron oxide of formula NaFeO 2 , a sodium chromium oxide of formula NaCrO 2 , layered NaNi 0.5 Mn 0.5 O 2 , a NaV 6 O 15 nanorod; a layer sulfide of formula Na x TiS 2 , a perovskite transition metal fluoride and a Na + superionic conductor (NASICON) compound.

7. The sodium ion electrochemical cell of claim 5 , wherein the positive electrode further comprises a conductive additive.

8. The sodium ion electrochemical cell of claim 5 , wherein the positive electrode further comprises a binder selected from the group consisting of a polyvinylidenefluoride (PVDF), a polytetrafluoroethylene (PTFE), a styrene butadiene rubber (SBR), and a polyimide.

9. A reversible sodium battery comprising:

an anode;

a cathode; and

an electrolyte comprising sodium ions;

wherein the cathode comprises a current collector and an active material of formula (I):

ε-VOPO 4   (I).

10. The reversible sodium battery of claim 9 , wherein the cathode further comprises an auxiliary material selected from the group consisting of NaFePO 4 , NaVPO 4 F, Na 3 V 2 (PO 4 ) 2 F 3 , Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3 , a compound of formula Na x CoO 2 wherein x is from 0.4 to 1, orthorhombic Na 0.44 MnO 2 , layered sodium iron oxide of formula NaFeO 2 , a sodium chromium oxide of formula NaCrO 2 , layered NaNi 0.5 Mn 0.5 O 2 , a NaV 6 O 15 nanorod; a layer sulfide of formula Na x TiS 2 , a perovskite transition metal fluoride and a Na + superionic conductor (NASICON) compound.

11. The reversible sodium battery of claim 9 , wherein the cathode further comprises a conductive additive.

12. The reversible sodium battery of claim 9 , wherein the cathode further comprises a binder selected from the group consisting of a polyvinylidenefluoride (PVDF), a polytetrafluoroethylene (PTFE), a styrene butadiene rubber (SBR), and a polyimide.

13. The reversible sodium battery of claim 9 , wherein the electrolyte comprises a salt selected from the group consisting of Na 2 SO 4 , NaNO 3 , NaClO 4 , Na 3 PO 4 , Na 2 CO 3 , NaOH, NaPF 6 , NaN(CF 3 SO 2 ) 2 , NaN(SO 2 F) 2 , and NaCF 3 SO 3 .

14. The reversible sodium battery of claim 9 , wherein the electrolyte comprises an organic nitrile and/or carbonate solvent.

15. The reversible sodium battery of claim 14 , wherein the electrolyte comprises at least one of acetonitrile, ethylene carbonate, diethyl carbonate, and propylene carbonate.

16. The reversible sodium battery of claim 9 , wherein the cathode further comprises a sodium insertion product of formula:

Na x (ε-VOPO 4 )

wherein x is a value from 0.1 to 1.0 and the Na is capable of reversible extraction and insertion with the ε-VOPO 4 .

17. The reversible sodium battery of claim 16 , wherein the cathode further comprises an auxiliary material selected from the group consisting of NaFePO 4 , NaVPO 4 F, Na 3 V 2 (PO 4 ) 2 F 3 , Na 2 FePO 4 F, Na 3 V 2 (PO 4 ) 3 , a compound of formula Na x CoO 2 wherein x is from 0.4 to 1, orthorhombic Na 0.44 MnO 2 , layered sodium iron oxide of formula NaFeO 2 , a sodium chromium oxide of formula NaCrO 2 , layered NaNi 0.5 Mn 0.5 O 2 , a NaV 6 O 15 nanorod; a layer sulfide of formula Na x TiS 2 , a perovskite transition metal fluoride and a Na + superionic conductor (NASICON) compound.

18. The reversible sodium battery of claim 16 , wherein the cathode further comprises a conductive additive.

19. The reversible sodium battery of claim 16 , wherein the cathode further comprises a binder selected from the group consisting of a polyvinylidenefluoride (PVDF), a polytetrafluoroethylene (PTFE), a styrene butadiene rubber (SBR), and a polyimide.

20. The reversible sodium battery of claim 16 , wherein the electrolyte comprises a salt selected from the group consisting of Na 2 SO 4 , NaNO 3 , NaClO 4 , Na 3 PO 4 , Na 2 CO 3 , NaOH, NaPF 6 , NaN(CF 3 SO 2 ) 2 , NaN(SO 2 F) 2 , and NaCF 3 SO 3 .

21. The reversible sodium battery of claim 16 , wherein the electrolyte comprises a carbonate solvent.

22. The reversible sodium battery of claim 16 , wherein the electrolyte comprises at least one of ethylene carbonate, diethyl carbonate, and propylene carbonate.