Electrolyte composition and a sodium ion battery comprising the same

1. A sodium ion battery which comprises a cathode, an anode and an electrolyte composition comprising at least one sodium compound selected from the group consisting of sodium monofluorophosphate (Na 2 PO 3 F), sodium difluorophosphate (NaPO 2 F 2 ) and mixture thereof, wherein the cations in the electrolyte composition enabling conduction of electricity consist essentially of sodium ions, and wherein the cathode comprises a cathode active material comprising NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1/2 Ti 1/2 O 2 , NaNi 1/2 Mn 1/2 O 2 , Na 2/3 Fe 1/3 Mn 2/3 O 2 , NaNi 1/3 Co 1/3 Mn 1/3 O 2 , NaMn 2 O 4 , NaNi 1/2 Mn 3/2 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Na 2 FePO 4 F, Na 2 MnPO 4 F, Na 2 CoPO 4 F, or any combination thereof; wherein the concentration of the sodium compound is 0.2 to 2.0 wt %, relative to the total weight of the electrolyte composition, and wherein the electrolyte composition further comprises, in addition to the sodium compound, a sodium salt.

2. The sodium ion battery according to claim 1 , wherein the cathode active material comprises manganese.

3. The sodium ion battery according to claim 1 , wherein the electrolyte composition comprises a non-aqueous solvent selected from the group consisting of cyclic carbonates, acyclic carbonates and any combination thereof.

4. The sodium ion battery according to claim 3 , wherein the non-aqueous solvent comprises acyclic dialkyl carbonates, cyclic alkylene carbonates, or a combination thereof.

5. The sodium ion battery according to claim 4 , wherein the non-aqueous solvent comprises ethylene carbonate, propylene carbonate, or diethyl carbonate.

6. The sodium ion battery according to claim 1 , wherein the concentration of the sodium compound is 0.5 to 1.5 wt %, relative to the total weight of the electrolyte composition.

7. The sodium ion battery according to claim 6 , wherein the concentration of the sodium compound is 0.8 to 1.2 wt %, relative to the total weight of the electrolyte composition.

8. The sodium ion battery according to claim 1 , wherein the sodium salt is selected from the group consisting of NaPF 6 , NaBF 4 , NaClO 4 , NaAsF 6 , NaTaF 6 , NaAlCl 4 , Na 2 B 10 Cl 10 , NaCF 3 SO 3 , Na(CF 3 SO 2 ) 2 N, Na(C 2 F 5 SO 2 ) 2 N, NaB(C 6 H 5 ) 4 , NaCH 3 SO 3 , Na(SO 2 CF 3 ) 3 C, Na(FSO 2 ) 2 N, and any combination thereof.

9. The sodium ion battery according to claim 8 , wherein the sodium salt is selected from the group consisting of NaPF 6 , NaBF 4 , NaAsF 6 , NaTaF 6 , NaCF 3 SO 3 , Na(CF 3 SO 2 ) 2 N, Na(C 2 F 5 SO 2 ) 2 N, Na(SO 2 CF 3 ) 3 C, and any combination thereof.

10. The sodium ion battery according to claim 9 , wherein the sodium salt is NaPF 6 or Na(CF 3 SO 2 ) 2 N.

11. The sodium ion battery according to claim 1 , further comprising a halogenated organic compound, wherein the halogenated organic compound is a fluorinated carbonate.

12. The sodium ion battery according to claim 11 , wherein the fluorinated carbonate is a fluorinated cyclic carbonate.

13. The sodium ion battery according to claim 12 , wherein the fluorinated cyclic carbonate is a monofluoroethylene carbonate.